**3. Results and discussion**

The total catch was 1357 specimens which belong to six orders: Thysanoptera, Hemiptera, Coleoptera, Lepidoptera, Diptera and Prostigmata (Table 2).

Out of 1357 specimens, only 73 individuals (5.37%) belong to beneficial fauna (mostly preda‐ tors), while all other collected specimens are herbivorous and therefore potential pests on soybean. All found beneficials belonged to predators and majority of them (70 individuals) belong to Hemiptera what confirms the statement of Ketzschmar [44] that predaceous Hem‐ iptera are usually more abundant in soybean fields than all other insect predators combined. In earlier investigations [21] conducted in Serbia no predaceous Hemiptera have been found while more recent investigations in Serbia [6] and in Croatia [9] stated that they are present in soybean crops. All predaceous Hemiptera feed on a wide range of hosts and may extend this polyphagy to plant feeding to some extent [45]. Such plant feeding causes no damage to row crops but almost certainly has survival value for the predators by maintaining popula‐ tions where prey are scarce or absent. Some of the species which belong to family Pentato‐ midae are also recognized as predators [45]. Since some of the individuals collected in our investigation were classified as family Pentatomidae but, were not identified to the species, it is possible that some of them are predaceous as well.

**ORDER FAMILY GENUS SPECIES TOTAL NUMBER OF INDIVIDUALS CAPTURED**

Curculionidae \* 1

sp. 5

sp. 1

7

Linnaeus 1758

\* 16

1836

Using the entomological net, 759 individuals were collected, whereas 211 individuals were

Number of arthropod individuals collected by sweep net sampling was the highest among the three methods applied. Using these methods, species belonging to 20 different systemat‐ ic categories were collected. The collected individuals belonged to five insect orders, Thysa‐ noptera, Hemiptera, Coleoptera, Lepidoptera and Diptera. The abundance of insect orders

Order Hemiptera was present in the sweep net sampling in the highest abundance (82.48%). The same order was the most frequent. It was present in 87.5% of all samples obtained by sweep net sampling. Order Coleoptera was present in 57.5% of all samples and was desig‐ nated as constant. Other orders (Thysanoptera, Lepidoptera and Diptera) were less frequent; they were present in 30-37.5% of all samples. Investigations conducted in different agro-eco‐ systems showed that the sweep net sampling is the most effective method to collect different

TOTAL 759 211 387

**Table 2.** Arthropod species established during the soybean vegetation in 2010 by three different methods

gathered by whole plant counts and 387 individuals by leaf inspection.

*Phyllobius* Germar 1824

*Sitophillus* Schnherr, 1838

Lepidoptera \* 2

Noctuidae 15 Diptera Nematocera \* 1

Nymphalidae *Vanessa cardui*

Prostigmata Tetranychidae *Tetranychus urticae* Koch

\* Identification was not possible; Beneficial species are marked in grey;

established by sweep net sampling is shown in Figure 2.

**3.1. Sweep net sampling**

**BY**

Arthropod Fauna Associated to Soybean in Croatia

http://dx.doi.org/10.5772/54521

**LEAF INSPECTION**

121

387

**PLANT COUNTS**

**SWEEP NET WHOLE**



**Table 2.** Arthropod species established during the soybean vegetation in 2010 by three different methods

Using the entomological net, 759 individuals were collected, whereas 211 individuals were gathered by whole plant counts and 387 individuals by leaf inspection.

#### **3.1. Sweep net sampling**

investigation were classified as family Pentatomidae but, were not identified to the species,

**ORDER FAMILY GENUS SPECIES TOTAL NUMBER OF INDIVIDUALS CAPTURED**

sp. 4

55

28

2

3

4

7

sp. 2 1

sp. 21

Linnaeus 1758

Linnaeus 1758

1861

& Yonke 1977

Linnaeus 1758

Kutschera 1860

Linnaeus 1758

*Haltica oleracea*

*Longitarsus* Berthold 1827

Marsham 1802

Anthocoridae \* 3 8

Pentatomidae \* 12 *Nezara viridula*

Membracidae *Stictocephala bisonia* Kopp

Cicadellidae *Cicadella viridis*

Coleoptera Coccinelidae \* 3 Chrysomelidae *Phyllotreta undulat*a

Latridiidae *Corticaria*

*Piezodorus* sp. Fieber

Thysanoptera \* 52 12 Hemiptera Miridae *Halticus apterus* 44 3 *Lygus* Hahn 1833

Nabidae *Nabis ferus*

**BY**

**LEAF INSPECTION**

**PLANT COUNTS**

**SWEEP NET WHOLE**

472 181

it is possible that some of them are predaceous as well.

120 Soybean - Pest Resistance

Number of arthropod individuals collected by sweep net sampling was the highest among the three methods applied. Using these methods, species belonging to 20 different systemat‐ ic categories were collected. The collected individuals belonged to five insect orders, Thysa‐ noptera, Hemiptera, Coleoptera, Lepidoptera and Diptera. The abundance of insect orders established by sweep net sampling is shown in Figure 2.

Order Hemiptera was present in the sweep net sampling in the highest abundance (82.48%). The same order was the most frequent. It was present in 87.5% of all samples obtained by sweep net sampling. Order Coleoptera was present in 57.5% of all samples and was desig‐ nated as constant. Other orders (Thysanoptera, Lepidoptera and Diptera) were less frequent; they were present in 30-37.5% of all samples. Investigations conducted in different agro-eco‐ systems showed that the sweep net sampling is the most effective method to collect different

need to encompass all three methods is confirmed later by the fact that species identified by each particular method differ. By employed methods we were able to get all relevant data on above ground arthropod fauna that could be found on soybean canopy. We did not aim to collect information on underground soybean arthropods and ground predators in soy‐ bean fields. To collect this information we should use common methods for sampling soil arthropods, soil samples and extraction [51] or pitfall trapping [48]. Some of earlier research‐ es on soybean arthropod fauna in the region collected information on underground soybean arthropods but, no research did pay attention on ground predators in soybean field. No re‐ searches among all conducted [6-29] did pay attention to abundance and frequency of par‐ ticular orders, genus or species as well, so it is not possible to compare if there are some

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123

Individuals that belonged to the order Thysanoptera have been found by sweep net sam‐ pling in highest abundance than by whole plan counts, and they haven't been found by leaf inspection at all. In Serbia one phytophagous thrips species (*Frankliniella intonsa* Trybom) on soybean has been identified [21]. Since in our investigation thrips were not established by leaf sampling and inspection, it could be concluded that they did not feed and develop on soybean. It might be that those species are predaceous because it is reported [52] that thrips are natural enemies of different pests. Important predaceous genera of thrips are *Aelothrips* Haliday, *Franklinothrips* Back, *Scolothrips* Hinds, *Leptothrips* Hood, *Karnyothrips* Watson and *Podothrips* Hood. Within the genus *Aeolothrips*, the species *Aeolothrips intermedius* Bagnall is distributed throughout western and eastern Europe [53], the middle East and India but now it can be considered cosmopolitan [54]. Comparative tests by many authors [53, 55, 56] using different types of prey (including various species of Thysanoptera), suggested that both the larvae and the adult females are generic predators, even though they present marked diet‐ ary preferences. In Italy [57] *A. intermedius* was detected in association with various different phytophagous Thysanoptera, which included *T. tabaci* but also frequently *F. occidentalis* on many different plant species including legume species *Medicago sativa* L. Predaceous thyrips belonging to the genus *Aelothips* are reported as important predators of *T. urticae* in soyben crops in north-eastern Italy [58]. *Franklinothrips* sp. adults and larvae are generalist predators and attack a wide variety of arthropod pests including two spotted spider mite (*T. urticae*) [59]. Genus *Scolothrips* is counting six species in Europe [60], and one of them, *Scolothrips longicornis* Priesner is a predator of *T. urticae* [61] and *T. turkestani* [62]. Both pest species are registered as soybean pests in Croatia. Genus *Leptothrips* is not present in Europe [60]. Genus *Karnyothrips* is counting three species in Europe [60]. Some species are reported as predators of scale insects [63]. Genus *Podothrips* is known as grass-living genus. It counts only two spe‐ cies in Europe present only in Italy and Cyprus [60]. Since identification to the species was

not possible, we cannot state which species of Thysanoptera were present.

belong to the **suborder Homoptera.**

Individuals belonging to six families of the **order Hemiptera** were identified in our research. Four families belong to the **suborder Heteroptera** (so called typical bugs) and two families

**Family Miridae** was presented by genus *Lygus* sp. Four individuals were captured. Identifi‐ cation to species was not possible. Species belonged to the genus *Lygus* were reported by

discrepancies with the results of previous researches.

**Figure 2.** Abundance of insect orders collected by sweep net sampling of soybean crop, Zagreb, 2010

leaf feeding pests as are leafhoppers [46], lepidopterous larvae [46, 47], leaf feeding Coleop‐ tera [48] and phytophagous Pentatomidae [49] as well as predaceous Hemiptera [45].

#### **3.2. Whole plant count**

The lowest number of individuals was established by whole plant count method. The major‐ ity of established individuals belonged to order Hemiptera. Only few Thysanoptera and Lepidoptera were established by this method. Some authors stated that this method is suita‐ ble for larvae of Lepidoptera [46, 47] and for phytophagous thryps [50]. There are no data on any damage caused by any phytophagous thrips in Croatia while *Vanessa cardui* L. was re‐ corded in previous investigations as important pest.

#### **3.3. Leaf sampling and inspection**

The only species established by leaf inspection was *T. urticae*. It was proved that this method is good for establishing population of phytophagous thrips [48], whiteflies [49] and mites [35]. It is obviously that out of these three groups, only phytophagus mites were present in experimental field.

#### **3.4. Collected species: abundance and importance**

Sampling arthropod populations is a cornerstone of basic research on agricultural ecosys‐ tems and the principal tool for building and implementing pest management programs. The purpose of sampling is dual, it is a research method for defining the nature and dynamics of communities in agricultural ecosystems and it is also a mean for providing pest manage‐ ment decision. The purpose of sampling in our investigation was to get deep knowledge on pest and beneficial species present in soybean crop. Conducted investigation encompassed three most common sampling methods for investigations of soybean arthropod fauna. The need to encompass all three methods is confirmed later by the fact that species identified by each particular method differ. By employed methods we were able to get all relevant data on above ground arthropod fauna that could be found on soybean canopy. We did not aim to collect information on underground soybean arthropods and ground predators in soy‐ bean fields. To collect this information we should use common methods for sampling soil arthropods, soil samples and extraction [51] or pitfall trapping [48]. Some of earlier research‐ es on soybean arthropod fauna in the region collected information on underground soybean arthropods but, no research did pay attention on ground predators in soybean field. No re‐ searches among all conducted [6-29] did pay attention to abundance and frequency of par‐ ticular orders, genus or species as well, so it is not possible to compare if there are some discrepancies with the results of previous researches.

Individuals that belonged to the order Thysanoptera have been found by sweep net sam‐ pling in highest abundance than by whole plan counts, and they haven't been found by leaf inspection at all. In Serbia one phytophagous thrips species (*Frankliniella intonsa* Trybom) on soybean has been identified [21]. Since in our investigation thrips were not established by leaf sampling and inspection, it could be concluded that they did not feed and develop on soybean. It might be that those species are predaceous because it is reported [52] that thrips are natural enemies of different pests. Important predaceous genera of thrips are *Aelothrips* Haliday, *Franklinothrips* Back, *Scolothrips* Hinds, *Leptothrips* Hood, *Karnyothrips* Watson and *Podothrips* Hood. Within the genus *Aeolothrips*, the species *Aeolothrips intermedius* Bagnall is distributed throughout western and eastern Europe [53], the middle East and India but now it can be considered cosmopolitan [54]. Comparative tests by many authors [53, 55, 56] using different types of prey (including various species of Thysanoptera), suggested that both the larvae and the adult females are generic predators, even though they present marked diet‐ ary preferences. In Italy [57] *A. intermedius* was detected in association with various different phytophagous Thysanoptera, which included *T. tabaci* but also frequently *F. occidentalis* on many different plant species including legume species *Medicago sativa* L. Predaceous thyrips belonging to the genus *Aelothips* are reported as important predators of *T. urticae* in soyben crops in north-eastern Italy [58]. *Franklinothrips* sp. adults and larvae are generalist predators and attack a wide variety of arthropod pests including two spotted spider mite (*T. urticae*) [59]. Genus *Scolothrips* is counting six species in Europe [60], and one of them, *Scolothrips longicornis* Priesner is a predator of *T. urticae* [61] and *T. turkestani* [62]. Both pest species are registered as soybean pests in Croatia. Genus *Leptothrips* is not present in Europe [60]. Genus *Karnyothrips* is counting three species in Europe [60]. Some species are reported as predators of scale insects [63]. Genus *Podothrips* is known as grass-living genus. It counts only two spe‐ cies in Europe present only in Italy and Cyprus [60]. Since identification to the species was not possible, we cannot state which species of Thysanoptera were present.

leaf feeding pests as are leafhoppers [46], lepidopterous larvae [46, 47], leaf feeding Coleop‐

6.85%

82.48%

The lowest number of individuals was established by whole plant count method. The major‐ ity of established individuals belonged to order Hemiptera. Only few Thysanoptera and Lepidoptera were established by this method. Some authors stated that this method is suita‐ ble for larvae of Lepidoptera [46, 47] and for phytophagous thryps [50]. There are no data on any damage caused by any phytophagous thrips in Croatia while *Vanessa cardui* L. was re‐

The only species established by leaf inspection was *T. urticae*. It was proved that this method is good for establishing population of phytophagous thrips [48], whiteflies [49] and mites [35]. It is obviously that out of these three groups, only phytophagus mites were present in

Sampling arthropod populations is a cornerstone of basic research on agricultural ecosys‐ tems and the principal tool for building and implementing pest management programs. The purpose of sampling is dual, it is a research method for defining the nature and dynamics of communities in agricultural ecosystems and it is also a mean for providing pest manage‐ ment decision. The purpose of sampling in our investigation was to get deep knowledge on pest and beneficial species present in soybean crop. Conducted investigation encompassed three most common sampling methods for investigations of soybean arthropod fauna. The

tera [48] and phytophagous Pentatomidae [49] as well as predaceous Hemiptera [45].

**Figure 2.** Abundance of insect orders collected by sweep net sampling of soybean crop, Zagreb, 2010

5.67%

2.90%2.11%

Thysanoptera Hemiptera Coleoptera Lepidoptera Diptera

**3.2. Whole plant count**

122 Soybean - Pest Resistance

experimental field.

corded in previous investigations as important pest.

**3.4. Collected species: abundance and importance**

**3.3. Leaf sampling and inspection**

Individuals belonging to six families of the **order Hemiptera** were identified in our research. Four families belong to the **suborder Heteroptera** (so called typical bugs) and two families belong to the **suborder Homoptera.**

**Family Miridae** was presented by genus *Lygus* sp. Four individuals were captured. Identifi‐ cation to species was not possible. Species belonged to the genus *Lygus* were reported by different authors [6, 8, 21, 24] to feed on soybean crops in Bosnia and Herzegovina and Ser‐ bia as well as in Croatia [9] without causing serious damages. More numerous were individ‐ uals of *Halticus apterus.* This species is distributed through Mediterranean region [64]. It was reported to feed on soybean only in Croatia [9]. Other research showed that it feeds on some legume plants such as *Medicago sativa* L., *Lotus corniculatus* L. and *Trifolium repens* L. in Italy, and also to be able to cause damages on onions and Gallium [64]. Since it was not reported as serious pest of soybean anywhere, it should be monitored in the future but the probabili‐ ty for this species to become important pest of soybean is low.

in Brazilian soybean [68]. Genus *Piezodorus* is counting three species in Europe [60]. Twelve individuals, members of family Pentatomidae remained unidentified. It is possible that some of them are phytophagous. Also it is possible that some of them are predators because

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125

Two families each represented with one species from the **suborder Homoptera** have been collected in low numbers. *Stictocephala bisonia* was reported to feed on soybean in Croatia [9], Serbia [21] and Bosnia and Herzegovina [24]. The second identified species was *Cicadella viridis*. This species was registered to feed on soybean in Croatia [9] but without significant damage. Within the USA, potato leafhopper (*Empoasca fabae* Harris) is the most important leafhopper species [69]. Even though aphids are recognized as a regular part of entomofau‐ na of soybean, we did not record them. Several species of aphids are known to attack soy‐ bean crops. The most important species in North America is *Aphis gyicines* Matsumura [70, 71]. This species is not registered in Europe [60]. Some other species of aphids that are mem‐ bers of the fauna of Europe [60] and Croatia [72, 73] successfully colonize and reproduce parthenogenetically on soybean [71]: *A. craccivora* Koch, *Aulacorthum solani* (Kaltenbach) and

Out of four families of the order Coleoptera that were identified, one represents mainly pre‐ daceous species (family Coccinelidae). Some species of the family Coccinelidae are reported as the members of arthropod fauna on soybean in Croatia and Serbia [9, 21]. Species *Epilach‐ na varivestris* Mulsant is known as a soybean pest in USA [48]. Three species of the phytoph‐ agous genus *Epilachna* are present in Europe, including Croatia [60] but only in Dalmatia where soybean cultivation is not common. Individuals from the genus *Corticaria*, family La‐ tridiidae were the most numerous. Adults and larvae of this family feed on the conidia of fungi and *Myxomycetes* [74]. All found species from the order Coleoptera were previously listed as potential members of soybean fauna in Croatia [9] but, due to the low populations, their potential to be significant pests or predators is not very high. We did not employ any method for sampling soil dwelling insects or underground fauna. Therefore we did not col‐ lect the species which belong to families Elateridae and Scarabaeidae that are known as pol‐

Only 22 individuals from **order Lepidoptera** were collected. Painted Lady (*Vanessa cardui*) was the only identified species. Other specimens were classified into the family Noctuidae. *V. cardui* was previously recorded to significantly damage soybean in Croatia [9, 25, 27, 29] and in neighboring countries [20, 23]. The outbreak of this pest is periodical. Higher popula‐ tion could be expected in weedy soybean fields because females are attracted by pollen sources and heavy plant density [25]. There are many of species from the family of Noctui‐ dae and from the other families, members of the order Lepidoptera which could cause the damage but, until now, serious damage in Croatia was reported only by *V. cardui*. In USA, the most important lepidopterous species are *Anticarsia gemmatalis* (Hubner), *Pseudoplusia in‐ cludens* (Walker), *Trichoplusia ni* (Hubner), *Platypena scabra* F., *Heliothis zea* Boddie, *Heliothis virescens* (Fabricius) and *Heliothis* (=*Helicoverpa*) *armigera* (Hubner) [46, 47, 75]. Except *T. ni* and *H. armigera,* other species are not distributed in Europe [60]. *H. armigera* is often men‐ tioned as one of the potentially very dangerous species. Because of its invasive nature this

yphagous soil pests that could cause damage on soybean crops [15, 21].

species which belong to family Pentatomidae are also recognized as predators [45].

*Aphys gossypii* Glover.

**Family Nabidae** was represented with one species, *N. ferus.* The same species was previ‐ ously reported in Croatia [9] and in Serbia [6]. Additionally two other species of this ge‐ nus, *N. feroides* and *N. pseudoferus,* were reported in Serbia [6]. The density of *N. ferus* was moderate, total of 55 individuals were captured. This species was reported as common predator species in Ukraine [65]. Aphids are the principal prey insects for this species, but numerous other families are acceptable, including other bugs [65]. Because of its possible importance in soybean agro-ecosystems, the dynamic of the appearance of this species will be further analyzed.

Eleven individuals belonging to **family Anthocoridae** were captured in our investigation. Family Anthocoridae was previously reported in soybean in Croatia [9] and in Serbia [6]. This family is mentioned as one of the most important predaceous family of Heteroptera in soybean crops [45]. Within the family Anthocoridae, members of the genus *Orius* occur as predators in soybean fields all around the world [45]. The species *Orius niger* Woolf has been found in soybean fields in Serbia [6]. In some areas, species of the genus *Anthocoris* Fallen are probably also important predators in soybean [45]. Captured individuals were not iden‐ tified to the species so it is not possible to discuss which genus was the most abundant in our investigations.

Among the established Hemiptera, **family Pentatomidae** was the most abundant. Altogeth‐ er 512 individuals were found in sweep-net samples and 181 individuals by whole plant counts. The most abundant species was the southern green stink bug, *Nezara viridula* L. This species was reported as present in Croatia [9]. Recently the serious damages caused by this species were reported in Croatia [26]. It is not mentioned as serious pest in neighboring countries, while it was mentioned as serious threat to soybeans in Italy [58, 66]. It was re‐ ported [49] as one of the most abundant phytophagous stink bugs on soybean worldwide among of almost 40 species of stink bugs that have been found on soybean. Due to high number of captured individuals and registered damages caused by this species, it might be identified as one of the potential pests on soybean in Croatia. Therefore the dynamic of the appearance will be further analyzed. Species belonging to phytophagous genus *Piezodorus* were captured in lower number. Genus *Piezodorus* was reported as possible pest genus in Croatia [9] and in Italy [58]. The importance of the species *P. guildinii* Westwood is increas‐ ing in USA as well as in Brazil. This species was observed for the first time in southern Loui‐ siana in 2000 and since 2002, it has been a significant pest of soybean [67]. At present, *Eustichus heros* (F.) and *P. guildinii* are more widespread and occur in greater numbers than *N. viridula,* and *P. guildinii* is principally responsible for the green bean syndrome observed in Brazilian soybean [68]. Genus *Piezodorus* is counting three species in Europe [60]. Twelve individuals, members of family Pentatomidae remained unidentified. It is possible that some of them are phytophagous. Also it is possible that some of them are predators because species which belong to family Pentatomidae are also recognized as predators [45].

different authors [6, 8, 21, 24] to feed on soybean crops in Bosnia and Herzegovina and Ser‐ bia as well as in Croatia [9] without causing serious damages. More numerous were individ‐ uals of *Halticus apterus.* This species is distributed through Mediterranean region [64]. It was reported to feed on soybean only in Croatia [9]. Other research showed that it feeds on some legume plants such as *Medicago sativa* L., *Lotus corniculatus* L. and *Trifolium repens* L. in Italy, and also to be able to cause damages on onions and Gallium [64]. Since it was not reported as serious pest of soybean anywhere, it should be monitored in the future but the probabili‐

**Family Nabidae** was represented with one species, *N. ferus.* The same species was previ‐ ously reported in Croatia [9] and in Serbia [6]. Additionally two other species of this ge‐ nus, *N. feroides* and *N. pseudoferus,* were reported in Serbia [6]. The density of *N. ferus* was moderate, total of 55 individuals were captured. This species was reported as common predator species in Ukraine [65]. Aphids are the principal prey insects for this species, but numerous other families are acceptable, including other bugs [65]. Because of its possible importance in soybean agro-ecosystems, the dynamic of the appearance of this species will

Eleven individuals belonging to **family Anthocoridae** were captured in our investigation. Family Anthocoridae was previously reported in soybean in Croatia [9] and in Serbia [6]. This family is mentioned as one of the most important predaceous family of Heteroptera in soybean crops [45]. Within the family Anthocoridae, members of the genus *Orius* occur as predators in soybean fields all around the world [45]. The species *Orius niger* Woolf has been found in soybean fields in Serbia [6]. In some areas, species of the genus *Anthocoris* Fallen are probably also important predators in soybean [45]. Captured individuals were not iden‐ tified to the species so it is not possible to discuss which genus was the most abundant in

Among the established Hemiptera, **family Pentatomidae** was the most abundant. Altogeth‐ er 512 individuals were found in sweep-net samples and 181 individuals by whole plant counts. The most abundant species was the southern green stink bug, *Nezara viridula* L. This species was reported as present in Croatia [9]. Recently the serious damages caused by this species were reported in Croatia [26]. It is not mentioned as serious pest in neighboring countries, while it was mentioned as serious threat to soybeans in Italy [58, 66]. It was re‐ ported [49] as one of the most abundant phytophagous stink bugs on soybean worldwide among of almost 40 species of stink bugs that have been found on soybean. Due to high number of captured individuals and registered damages caused by this species, it might be identified as one of the potential pests on soybean in Croatia. Therefore the dynamic of the appearance will be further analyzed. Species belonging to phytophagous genus *Piezodorus* were captured in lower number. Genus *Piezodorus* was reported as possible pest genus in Croatia [9] and in Italy [58]. The importance of the species *P. guildinii* Westwood is increas‐ ing in USA as well as in Brazil. This species was observed for the first time in southern Loui‐ siana in 2000 and since 2002, it has been a significant pest of soybean [67]. At present, *Eustichus heros* (F.) and *P. guildinii* are more widespread and occur in greater numbers than *N. viridula,* and *P. guildinii* is principally responsible for the green bean syndrome observed

ty for this species to become important pest of soybean is low.

be further analyzed.

124 Soybean - Pest Resistance

our investigations.

Two families each represented with one species from the **suborder Homoptera** have been collected in low numbers. *Stictocephala bisonia* was reported to feed on soybean in Croatia [9], Serbia [21] and Bosnia and Herzegovina [24]. The second identified species was *Cicadella viridis*. This species was registered to feed on soybean in Croatia [9] but without significant damage. Within the USA, potato leafhopper (*Empoasca fabae* Harris) is the most important leafhopper species [69]. Even though aphids are recognized as a regular part of entomofau‐ na of soybean, we did not record them. Several species of aphids are known to attack soy‐ bean crops. The most important species in North America is *Aphis gyicines* Matsumura [70, 71]. This species is not registered in Europe [60]. Some other species of aphids that are mem‐ bers of the fauna of Europe [60] and Croatia [72, 73] successfully colonize and reproduce parthenogenetically on soybean [71]: *A. craccivora* Koch, *Aulacorthum solani* (Kaltenbach) and *Aphys gossypii* Glover.

Out of four families of the order Coleoptera that were identified, one represents mainly pre‐ daceous species (family Coccinelidae). Some species of the family Coccinelidae are reported as the members of arthropod fauna on soybean in Croatia and Serbia [9, 21]. Species *Epilach‐ na varivestris* Mulsant is known as a soybean pest in USA [48]. Three species of the phytoph‐ agous genus *Epilachna* are present in Europe, including Croatia [60] but only in Dalmatia where soybean cultivation is not common. Individuals from the genus *Corticaria*, family La‐ tridiidae were the most numerous. Adults and larvae of this family feed on the conidia of fungi and *Myxomycetes* [74]. All found species from the order Coleoptera were previously listed as potential members of soybean fauna in Croatia [9] but, due to the low populations, their potential to be significant pests or predators is not very high. We did not employ any method for sampling soil dwelling insects or underground fauna. Therefore we did not col‐ lect the species which belong to families Elateridae and Scarabaeidae that are known as pol‐ yphagous soil pests that could cause damage on soybean crops [15, 21].

Only 22 individuals from **order Lepidoptera** were collected. Painted Lady (*Vanessa cardui*) was the only identified species. Other specimens were classified into the family Noctuidae. *V. cardui* was previously recorded to significantly damage soybean in Croatia [9, 25, 27, 29] and in neighboring countries [20, 23]. The outbreak of this pest is periodical. Higher popula‐ tion could be expected in weedy soybean fields because females are attracted by pollen sources and heavy plant density [25]. There are many of species from the family of Noctui‐ dae and from the other families, members of the order Lepidoptera which could cause the damage but, until now, serious damage in Croatia was reported only by *V. cardui*. In USA, the most important lepidopterous species are *Anticarsia gemmatalis* (Hubner), *Pseudoplusia in‐ cludens* (Walker), *Trichoplusia ni* (Hubner), *Platypena scabra* F., *Heliothis zea* Boddie, *Heliothis virescens* (Fabricius) and *Heliothis* (=*Helicoverpa*) *armigera* (Hubner) [46, 47, 75]. Except *T. ni* and *H. armigera,* other species are not distributed in Europe [60]. *H. armigera* is often men‐ tioned as one of the potentially very dangerous species. Because of its invasive nature this pest is currently placed on Annex I A II of Council Directive 2000/29/EC, indicating that it is considered to be relevant for the entire EU and that phytosanitary measures are required when it is found on any plants or plant products. Some countries made pest risk analyses [76]. Damages caused by this species were reported on soybeans in Vojvodina Province of Serbia and in Montenegro in the very warm summer of 2003 [77] when 85.3% of the soybean pods were injured in August. *H. armigera* is a serious pest on outdoor crops in Portugal and Spain, predominantly on tomato crops as well as on cottom and maize. It developed resist‐ ance to many groups of insecticides [78]. We did not find caterpillars of limabean pod borer (*Etiella zinckenella* Treitschke) even though this species was reported as soybean pest in Cro‐ atia [9] and in neighboring countries [6, 14, 21]. In Southern Europe and in Central and South America *E. zinckenella* is only damaging pod borer species in soybean.

**Order Diptera** was represented by 17 individuals that were not indentified to the species. The pest species from the order Diptera reported in the literature are *Delia platura* Meigen [6, 58], *Liriomyza congesta* Becker and *Clinodiplosis trotteri* Kief. [21]. Larvae of *D. platura* could cause damage on soybean seed during the emergence. Larvae of *L. congesta* are damaging leaves [21] and larvae of *C. trotteri* are damaging plant stem [21]. Some of Diptera species in soybean could be natural enemies, for example predaceous species *Acarolestes tetranychorum* feed on mites [21].

We established one species from **order Prostigmata** (infraclass Acari). This was the species *T. urticae* which was established only by leaf inspection. This species is the most important pest of soybean in the whole region [6, 8-10, 13, 17, 19, 29]. The pest outbreaks are occurring in dry and warm years in which farmers must apply control measures. Besides *T. urticae*, soybean in Croatia [9] and neighboring countries [16, 17, 19] is often attacked by *T. atlanticus* (= *turkestani*). Both species have similar thermal requirements but, *T. atlanticus* prefers ex‐ tremely dry conditions [9]. Some differences were established in their response to host plant nutrient status [79]. The development of *T. urticae* is positively influenced by potassium con‐ tent in the plant host, while *T. atlanticus* is positively influenced by content of phosphorus. According to the data obtained from Meteorological and Hydrological Service of Republic of Croatia, somewhat lower temperatures and higher amount of rainfalls in July and August in 2010, comparing to the average were recorded. That could cause the absence of *T. atlanticus* in experimental field and relatively low population of *T. urticae.*

**Total number of individuals**

in Croatia in 2010

sampling methods

24-Jun

1-Jul

**3.33% 1.63% 1.26%**

**28.60%**

8-Jul

15-Jul

22-Jul

29-Jul

Thysanoptera Hemiptera Coleoptera Lepidoptera Diptera Prostigmata

**Figure 3.** The dominance indices of arthropod orders established in the total capture of arthropod species on soybean

**4.73%**

**60.46%**

Arthropod Fauna Associated to Soybean in Croatia

http://dx.doi.org/10.5772/54521

127

sweep net whole plant inspection

phenophase: R1, R2 R3, R4, R6 R7, R8

**Figure 4.** The dynamic of the appearance of *Nezara viridula* (L.) on soybeans in Croatia in 2010 established by two

The southern green stink bug, *N. viridula*, is one of the most economically important soy‐ bean pests [80]. It has a worldwide distribution, occurring throughout the tropical and sub‐ tropical regions of Europa, Asia, Africa and America [49]. This pest is in constant expansion as a consequence of the increased acreage for soybean production, particularly in South America [80]. This pentatomid is highly polyphagous, attacking more than 145 species of plants (including cultivated and uncultivated species) within 32 families [49]. Life cycle of the southern green stink bug has been studied by number of authors in different parts of the world [81-85]. The biology of this pest has not been studied in Croatia jet but, some data were presented by different authors [26, 29]. From literature it is known [49] that southern green stink bug, like most pentatomids, overwinters in the adult stage under different ob‐ jects that offer protection (litter, bark etc.). In the northern hemisphere [49] overwintering

4-Aug

11-Aug

18-Aug

26-Aug

2-Sep

9-Sep-12

The dominance indices of the insect orders established in total capture are shown in Figure 3.

In total catch the eudominant orders were Hemiptera (60.46%) and Acarina (28.6%), while subdominant were orders Thysanoptera (4.73%), Coleoptera (3.33%), Lepidoptera (1.63%) and Diptera (1.26%).

#### **3.5. Most important phytophagous species**

The significant feeding on soybean was established by two species, *N. viridula* and *T. urticae.* Therefore we will further analyze their appearance with the respect of their life cycle and possible damages that they can cause.

The dynamic of the appearance of *N. viridula* is shown in Figure 4.

pest is currently placed on Annex I A II of Council Directive 2000/29/EC, indicating that it is considered to be relevant for the entire EU and that phytosanitary measures are required when it is found on any plants or plant products. Some countries made pest risk analyses [76]. Damages caused by this species were reported on soybeans in Vojvodina Province of Serbia and in Montenegro in the very warm summer of 2003 [77] when 85.3% of the soybean pods were injured in August. *H. armigera* is a serious pest on outdoor crops in Portugal and Spain, predominantly on tomato crops as well as on cottom and maize. It developed resist‐ ance to many groups of insecticides [78]. We did not find caterpillars of limabean pod borer (*Etiella zinckenella* Treitschke) even though this species was reported as soybean pest in Cro‐ atia [9] and in neighboring countries [6, 14, 21]. In Southern Europe and in Central and

**Order Diptera** was represented by 17 individuals that were not indentified to the species. The pest species from the order Diptera reported in the literature are *Delia platura* Meigen [6, 58], *Liriomyza congesta* Becker and *Clinodiplosis trotteri* Kief. [21]. Larvae of *D. platura* could cause damage on soybean seed during the emergence. Larvae of *L. congesta* are damaging leaves [21] and larvae of *C. trotteri* are damaging plant stem [21]. Some of Diptera species in soybean could be natural enemies, for example predaceous species *Acarolestes tetranychorum*

We established one species from **order Prostigmata** (infraclass Acari). This was the species *T. urticae* which was established only by leaf inspection. This species is the most important pest of soybean in the whole region [6, 8-10, 13, 17, 19, 29]. The pest outbreaks are occurring in dry and warm years in which farmers must apply control measures. Besides *T. urticae*, soybean in Croatia [9] and neighboring countries [16, 17, 19] is often attacked by *T. atlanticus* (= *turkestani*). Both species have similar thermal requirements but, *T. atlanticus* prefers ex‐ tremely dry conditions [9]. Some differences were established in their response to host plant nutrient status [79]. The development of *T. urticae* is positively influenced by potassium con‐ tent in the plant host, while *T. atlanticus* is positively influenced by content of phosphorus. According to the data obtained from Meteorological and Hydrological Service of Republic of Croatia, somewhat lower temperatures and higher amount of rainfalls in July and August in 2010, comparing to the average were recorded. That could cause the absence of *T. atlanticus*

The dominance indices of the insect orders established in total capture are shown in Figure 3. In total catch the eudominant orders were Hemiptera (60.46%) and Acarina (28.6%), while subdominant were orders Thysanoptera (4.73%), Coleoptera (3.33%), Lepidoptera (1.63%)

The significant feeding on soybean was established by two species, *N. viridula* and *T. urticae.* Therefore we will further analyze their appearance with the respect of their life cycle and

South America *E. zinckenella* is only damaging pod borer species in soybean.

in experimental field and relatively low population of *T. urticae.*

The dynamic of the appearance of *N. viridula* is shown in Figure 4.

feed on mites [21].

126 Soybean - Pest Resistance

and Diptera (1.26%).

**3.5. Most important phytophagous species**

possible damages that they can cause.

**Figure 3.** The dominance indices of arthropod orders established in the total capture of arthropod species on soybean in Croatia in 2010

**Figure 4.** The dynamic of the appearance of *Nezara viridula* (L.) on soybeans in Croatia in 2010 established by two sampling methods

The southern green stink bug, *N. viridula*, is one of the most economically important soy‐ bean pests [80]. It has a worldwide distribution, occurring throughout the tropical and sub‐ tropical regions of Europa, Asia, Africa and America [49]. This pest is in constant expansion as a consequence of the increased acreage for soybean production, particularly in South America [80]. This pentatomid is highly polyphagous, attacking more than 145 species of plants (including cultivated and uncultivated species) within 32 families [49]. Life cycle of the southern green stink bug has been studied by number of authors in different parts of the world [81-85]. The biology of this pest has not been studied in Croatia jet but, some data were presented by different authors [26, 29]. From literature it is known [49] that southern green stink bug, like most pentatomids, overwinters in the adult stage under different ob‐ jects that offer protection (litter, bark etc.). In the northern hemisphere [49] overwintering adults emerge in March and first generation develops on clover. The total developmental time from eggs to adults lasts between 23 days [82] and 49 days [81]. In USA, it develops 3-5 generations per year, depending on the climate. The 3rd, 4th and 5th generations attack soy‐ bean. We found it on soybean when soybeans began to mature, in August and onward what corresponds with the data presented by Todd and Herzog [49]. Probably the first two gener‐ ations developed on some other plants. Stink bugs feed primarily on the seeds of soybean. Feeding results with puncture marks on the seed coat, deformation of the seed coats and re‐ duced seed weight and size. Adults live longer, approximately 30 to 50 days [81, 82] and they cause more damage than nymphs [86]. Croatian authors [26] proposed economic threshold of 1 bug/30 m of soybean row or 8-10 bugs/10 sweep nets what seems to be too low. It is important to point out that the threshold depends on the period when insects oc‐ cur. Early infestation causes more damage than late infestation [86]. Late in the season high infestation level of 2 bugs/m2 will not result with the damage [86]. In our investigation we established infestation of 2 bugs/plant by whole plant count method and 4-5 bugs/10 sweep nets without seeing any damage on the yield. The appearance of *N. viridula* was in literature [26] connected with higher temperatures and drought, what was not the case in our investi‐ gation. Generally, in other countries the southern green stink bug is controlled with non-se‐ lective insecticides, which belong to carbamates, the organophosphate group, or the cyclodiene group, such as endosulfan or to pyrethroids [80]. Some of the mentioned insecti‐ cides are banned in Croatia and others are not allowed for that purpose. In the case of pest outbreak farmers do not have any available option to control this pest.

The maximal infestation of *T. urticae* was recorded on August 11th and it was 2.25 mites/leaf. This infestation is considered as very weak to weak infestation [87]. After that date, the number of mites significantly decreased without the use of acaricides. The reason of the de‐ crease of the population is the period in August in which strong rain occurred. Strong rain probably caused washing up the spider mites from the leaves as it was mentioned by some authors [29, 87]. *T. urticae* injure soybean by feeding on the green foliage and pods. By their needle-like chelicerate mouthparts that are used to puncture individual plant tissue cells and consume the entire cytoplasmic contents, they are leaving and empty irreversible dam‐ aged cell. The presence of numerous empty cells results in the yellow or brown spots on mite-injured leaves. Extensive feeding by large numbers of mites causes the leaves to appear yellow or brown [37]. Complete defoliation due to mite feeding can reduce pod set and seed yield. Under the favorable conditions mites have very short developmental time, between 8-20 days [9]. That enables them to develop several generations in a very short time and to increase population up to the economic threshold very fast. Therefore permanent monitor‐ ing of the pest population is needed. No acaricides are allowed for the control of *T. urticae* in soybean crops at the moment in Croatia. Even though there are some mite resistant cultivars

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129

Total of 73 predaceous species are collected in the investigation. Family Nabidae was repre‐ sented by one specius, *N. ferus*. Members of the family Nabidae are confirmed predators of different kind of insects [89]. Most types of insect prey of nabids are plant-feeding species, but nabids sometimes attack predaceous insects, including members of their own species. The polyphagous feeding habits of the nabids make them less effective than species-specific predators against specific prey species [89]. Altogether 55 individuals of *N. ferus* were count‐

*Nabis ferus* is a common, widespread species in the Palearctic region [89]. It was reported as predatory species on *Trialeurodes vaporariorum* Westwood [90], *Oulema melanopus* L. [91], *Si‐ tobion avenae* F. [92] and other aphid species [65], *N. viridula* [93] and leafhoppers in all stages [89]. Species *N. ferus* overwinters in the adult stage [65]. Adults emerge from the soil and migrate to field of various crops in April and May according to the weather. They mate, lay eggs and the nymphs appear between late May and June and are present until July [65]. There is a second generation with nymphs in July-August and adults in August-October. The dynamic of the appearance of *N. ferus* in experimental field corresponds with the data on life cycle of this species [65]. In mid-late July we collected adults of the first generation and nymphs were collected in August. Kereši [94] stated that zoophagous *Nabis* species de‐ velop one generation per year in soybeans. She mentioned adult appearance at the end of July and maximal larval appearance at the end of August. It remains unknown in which crop species is developing the first generation. Due to its preference to prey aphids which are abundant in wheat fields, it could be that the first generation is developing in wheat fields. The experimental field in our investigation was surrounded by wheat fields what

in USA [88], they are not registered in Croatia.

ed. The dynamic of the appearance of *N. ferus* is shown in Figure 6.

**3.6. Most important zoophagus species**

could influence high population of *N. ferus*.

The second species which was recorded in high population density was *T. urticae*. The infes‐ tation with *T. urticae* started somewhat earlier that the attack of *N. viridula*. The dynamic of the appearance of *T. urticae* is shown in Figure 5.

**Figure 5.** The dynamic of the appearance of *Tetranychus urticae* on soybeans in Croatia in 2010

The maximal infestation of *T. urticae* was recorded on August 11th and it was 2.25 mites/leaf. This infestation is considered as very weak to weak infestation [87]. After that date, the number of mites significantly decreased without the use of acaricides. The reason of the de‐ crease of the population is the period in August in which strong rain occurred. Strong rain probably caused washing up the spider mites from the leaves as it was mentioned by some authors [29, 87]. *T. urticae* injure soybean by feeding on the green foliage and pods. By their needle-like chelicerate mouthparts that are used to puncture individual plant tissue cells and consume the entire cytoplasmic contents, they are leaving and empty irreversible dam‐ aged cell. The presence of numerous empty cells results in the yellow or brown spots on mite-injured leaves. Extensive feeding by large numbers of mites causes the leaves to appear yellow or brown [37]. Complete defoliation due to mite feeding can reduce pod set and seed yield. Under the favorable conditions mites have very short developmental time, between 8-20 days [9]. That enables them to develop several generations in a very short time and to increase population up to the economic threshold very fast. Therefore permanent monitor‐ ing of the pest population is needed. No acaricides are allowed for the control of *T. urticae* in soybean crops at the moment in Croatia. Even though there are some mite resistant cultivars in USA [88], they are not registered in Croatia.

#### **3.6. Most important zoophagus species**

adults emerge in March and first generation develops on clover. The total developmental time from eggs to adults lasts between 23 days [82] and 49 days [81]. In USA, it develops 3-5 generations per year, depending on the climate. The 3rd, 4th and 5th generations attack soy‐ bean. We found it on soybean when soybeans began to mature, in August and onward what corresponds with the data presented by Todd and Herzog [49]. Probably the first two gener‐ ations developed on some other plants. Stink bugs feed primarily on the seeds of soybean. Feeding results with puncture marks on the seed coat, deformation of the seed coats and re‐ duced seed weight and size. Adults live longer, approximately 30 to 50 days [81, 82] and they cause more damage than nymphs [86]. Croatian authors [26] proposed economic threshold of 1 bug/30 m of soybean row or 8-10 bugs/10 sweep nets what seems to be too low. It is important to point out that the threshold depends on the period when insects oc‐ cur. Early infestation causes more damage than late infestation [86]. Late in the season high

established infestation of 2 bugs/plant by whole plant count method and 4-5 bugs/10 sweep nets without seeing any damage on the yield. The appearance of *N. viridula* was in literature [26] connected with higher temperatures and drought, what was not the case in our investi‐ gation. Generally, in other countries the southern green stink bug is controlled with non-se‐ lective insecticides, which belong to carbamates, the organophosphate group, or the cyclodiene group, such as endosulfan or to pyrethroids [80]. Some of the mentioned insecti‐ cides are banned in Croatia and others are not allowed for that purpose. In the case of pest

The second species which was recorded in high population density was *T. urticae*. The infes‐ tation with *T. urticae* started somewhat earlier that the attack of *N. viridula*. The dynamic of

> 1-Jul 8-Jul 15-Jul 22-Jul 29-Jul 4-Aug 11-Aug 18-Aug 26-Aug 2-Sep 9-Sep R3, R4, R6 R7, R8

> > leaf inspection

**Figure 5.** The dynamic of the appearance of *Tetranychus urticae* on soybeans in Croatia in 2010

outbreak farmers do not have any available option to control this pest.

the appearance of *T. urticae* is shown in Figure 5.

**Total number of individuals**

will not result with the damage [86]. In our investigation we

infestation level of 2 bugs/m2

128 Soybean - Pest Resistance

Total of 73 predaceous species are collected in the investigation. Family Nabidae was repre‐ sented by one specius, *N. ferus*. Members of the family Nabidae are confirmed predators of different kind of insects [89]. Most types of insect prey of nabids are plant-feeding species, but nabids sometimes attack predaceous insects, including members of their own species. The polyphagous feeding habits of the nabids make them less effective than species-specific predators against specific prey species [89]. Altogether 55 individuals of *N. ferus* were count‐ ed. The dynamic of the appearance of *N. ferus* is shown in Figure 6.

*Nabis ferus* is a common, widespread species in the Palearctic region [89]. It was reported as predatory species on *Trialeurodes vaporariorum* Westwood [90], *Oulema melanopus* L. [91], *Si‐ tobion avenae* F. [92] and other aphid species [65], *N. viridula* [93] and leafhoppers in all stages [89]. Species *N. ferus* overwinters in the adult stage [65]. Adults emerge from the soil and migrate to field of various crops in April and May according to the weather. They mate, lay eggs and the nymphs appear between late May and June and are present until July [65]. There is a second generation with nymphs in July-August and adults in August-October. The dynamic of the appearance of *N. ferus* in experimental field corresponds with the data on life cycle of this species [65]. In mid-late July we collected adults of the first generation and nymphs were collected in August. Kereši [94] stated that zoophagous *Nabis* species de‐ velop one generation per year in soybeans. She mentioned adult appearance at the end of July and maximal larval appearance at the end of August. It remains unknown in which crop species is developing the first generation. Due to its preference to prey aphids which are abundant in wheat fields, it could be that the first generation is developing in wheat fields. The experimental field in our investigation was surrounded by wheat fields what could influence high population of *N. ferus*.

one existing species became significant pest of soybean. The life cycle of this pest as well as other issues related to sampling procedure, economic threshold and control possibilities have not been studied jet in Croatian agro-ecological conditions. In the future, investigations should be carried out with the aim to collect more data on this pest and to be able to imple‐

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131

*V. cardui* is causing defoliation of the soybean plants. As periodical pest it appears from time to time in certain areas causing significant damage. Sampling procedure for this pest is establish‐ ed but, research should be conducted in order to determine economic threshold and the effica‐ cy of environmentally acceptable insecticides (*B.t.k.*, spinosad, neem, IGRs, avermectins).

Phytophagous mites, *T. urticae* and *T. turkestani* as soybean pests are well known to Croatian farmers. Due to their feeding on soybean leaves they are causing defoliation. Their infestation is related to the climatic condition. In warm and dry years these pests cause more severe dam‐ age than in "normal" years. Sampling procedure for these pests is established but, due to the lack of registered acaricides, their control is not possible. The future research should be fo‐ cused on finding appropriate ecologically acceptable acaricide for the control of this pest.

The critical period for the infestation by all four species is from flowering through maturity in which period all four pests should be monitored and sampled on a regularly basis in or‐

Some other pests that were found in our investigation are capable of becoming key pests if environmental conditions and population of their natural control agents are disrupted by unnecessary application of insecticides. One of these species belongs to *Piezodorus* sp. which is world widely recognized as very important soybean pest. Thus the future systematic and intensive study of the arthropod fauna associated with soybean in Croatia has to be contin‐ ued. It will allow us to monitor the changes in the pest population and to prepare strategies

The main zoophagous species found on soybeans was *Nabis ferus*. The role of this species in soybean ecosystems, including its varying feeding strategies, needs much additional attention.

We thank Prof. Hrvoje Šarčević for providing us adequate experimental field conditions.

der to ensure the proper information about the need for control measure.

for the control of the new pests that could arise over the time.

Renata Bažok, Maja Čačija, Ana Gajger and Tomislav Kos

University of Zagreb, Faculty of Agriculture, Zagreb, Croatia

\*Address all correspondence to: rbazok@agr.hr

ment IPM principles in its control.

**Acknowledgements**

**Author details**

**Figure 6.** The dynamic of the appearance of *Nabis ferus* on soybeans in Croatia in 2010

### **4. Conclusions**

Literature reports that soybean crops in the region where Croatia belongs (Croatia, Hun‐ gary, Serbia, Romania, Bulgaria and Bosnia and Herzegovina) are attacked by over 180 pests (150 insects and 30 species from other animal classes). However, by literature review from Croatia, Serbia and Bosnia and Herzegovina we established that 52 species (or genus) of ar‐ thropods are reported to be associated with soybean crops. Out of these 52 species, seven species are zoophagous, 44 species are phytophagous and one species is myceliophagous. Additionally, we have found data on 43 species of phytoparasitic nematodes that can be find in soybean fields but without causing significant damages and literature also reports on three species of rodents that could cause significant damage on soybean fields.

In our investigations the number of established species was lower than the number obtained by literature review. Total of 1357 individuals were collected and classified into the five or‐ ders from the class of Insects and one order from the class of Arachnida (infraclass Acari). 1232 individuals were classified in 15 species or genus, 58 individuals were classified into the six families while 67 individuals were classified into the orders. Phytophagous arthro‐ pods were more abundant than zoophagous. The ratio between phytophagous and zoopha‐ gous specimens was 94.63% : 5.37%.

Based on the results of the literature review and of the research conducted, it could be con‐ cluded that significance of the arthropod pest fauna connected with soybean has changed over the time. Nowadays, soybean production in Croatia could be endangered by four phy‐ tophagous arthropod species: *N. viridula* L., *V. cardui* L., *T. urticae* and *T. turkestani*.

*N. viridula* is attacking soybean pods and seed causing the loss in yield quantity and quality. The early infestation is very dangerous. The population of this pest has been increasing in the past few years. This could be connected with the increase of soybean cultivation area. Obtained results indicate that the increase in pest population has occurred recently and that

one existing species became significant pest of soybean. The life cycle of this pest as well as other issues related to sampling procedure, economic threshold and control possibilities have not been studied jet in Croatian agro-ecological conditions. In the future, investigations should be carried out with the aim to collect more data on this pest and to be able to imple‐ ment IPM principles in its control.

*V. cardui* is causing defoliation of the soybean plants. As periodical pest it appears from time to time in certain areas causing significant damage. Sampling procedure for this pest is establish‐ ed but, research should be conducted in order to determine economic threshold and the effica‐ cy of environmentally acceptable insecticides (*B.t.k.*, spinosad, neem, IGRs, avermectins).

Phytophagous mites, *T. urticae* and *T. turkestani* as soybean pests are well known to Croatian farmers. Due to their feeding on soybean leaves they are causing defoliation. Their infestation is related to the climatic condition. In warm and dry years these pests cause more severe dam‐ age than in "normal" years. Sampling procedure for these pests is established but, due to the lack of registered acaricides, their control is not possible. The future research should be fo‐ cused on finding appropriate ecologically acceptable acaricide for the control of this pest.

The critical period for the infestation by all four species is from flowering through maturity in which period all four pests should be monitored and sampled on a regularly basis in or‐ der to ensure the proper information about the need for control measure.

Some other pests that were found in our investigation are capable of becoming key pests if environmental conditions and population of their natural control agents are disrupted by unnecessary application of insecticides. One of these species belongs to *Piezodorus* sp. which is world widely recognized as very important soybean pest. Thus the future systematic and intensive study of the arthropod fauna associated with soybean in Croatia has to be contin‐ ued. It will allow us to monitor the changes in the pest population and to prepare strategies for the control of the new pests that could arise over the time.

The main zoophagous species found on soybeans was *Nabis ferus*. The role of this species in soybean ecosystems, including its varying feeding strategies, needs much additional attention.
