**5. Insecticide and insectistatic activity of plant lectins**

There are several evidences for the defensive role of vegetal lectins in protecting plants against insect pests [108–110], and lectins are currently receiving a significant interest as insecticidal agents against sap-sucking insects including aphids and leaf and plant hoppers, with no effect on human metabolism [111, 112]. Lectins act on insects by binding to glycoproteins present in insect gut epithelium, eventually causing death of insect by inhibiting absorption of nutrients. It was believed that N-linked glycans in insects were exclusively of the high mannose type; therefore, there are great interests, especially in mannose-specific plant lectins, as possible insecticidal or insect-deterring molecules for the new pest management strategies [113, 114]. Nevertheless, the lectins possess different sugar specificities and, considering the variety of glycan structures in the bodies of insects, have many different possible targets. Advances have been made in the knowledge related to glycan diversity and function(s) of protein glycosylation in insects, N-glycosylation, and O-glycosylation, and it postulated that the interference in insect glycosylation appears to be a promising strategy for pest insect control [115]. Therefore, it is difficult to predict the exact mode of action of each lectin and even more difficult to understand the variability in insect toxicity upon exposure to different plant lectins. The use of initial bioassays employing artificial diets has led to the most recent advances, such as plant breeding and the construction of fusion proteins, using lectins for targeting the delivery of toxins and to potentiate expected insecticide effects [116–118].

of lectin ingestion is variable, and the binding of a lectin to the gut does not necessarily imply toxicity. Other studies signal that lectins affect various insect hydrolytic enzymes such as glucosidases, phosphatases, and proteases which are involved in digestion, development, growth, and detoxification. To date a great number of studies have shown lectin toxicity in insects belonging to different orders, including Lepidoptera, Coleoptera, and Hemiptera. However, the exact mode of action of lectins in providing resistance against insects remains unclear. The most relevant property of lectin's anti-insect activity can be related to its interactions with different glycoproteins or glycan structures in insects, which may interfere with a number of physiological processes in these organisms. Lectins possess at least one carbohydrate-binding domain and different sugar specificities, possible targets for lectin binding

Plant Lectins with Insecticidal and Insectistatic Activities http://dx.doi.org/10.5772/intechopen.74962 29

Preliminary evidence of Gleheda's insecticidal activity against Colorado potato beetle larvae (*Leptinotarsa decemlineata*) has been obtained using a single dose of lectin [130]; it would have been very interesting to carry out dose-response experiments and to assay several insect pests to elucidate whether the lectin was insect specific. Nevertheless, Gleheda's insecticidal activity stresses the importance of this unusual lectin, begging the question of whether such activity is shared by other Lamiaceae lectins. To date Lamiaceae lectin is unique with known insecticidal activity. The importance of lectins due to their insecticidal properties, isolation of native lectins, and lectin genes could be agronomically important tools for crop plants for developing resistance against insect pests mainly for sap-sucking

**Lectin Insect pests Activity References** PSA *Meligethes aeneus* Insecticidal, insectistatic [140] ConA *Tarophagous proserpina* Insectistatic [141] Gleheda *Leptinotarsa decemlineata* Insectistatic [130] ConA *Callosobruchus maculatus* Insectistatic **[**142**]** ConA *Helicoverpa armigera* Insectistastic [143] GS-II *Callosobruchus maculatus* Insectistastic [144] PHA *Callosobruchus maculatus* Insecticidal [145] PHA-E *Empoasca fabae* Insecticidal [146]

DGL *C. maculatus* [108]

*rostrata* (DRL), *Cratylia floribunda* (CFL). Taking from Calvacante et al. [60] and modified.

**Table 4.** Legume lectins domain with insectistatic and insecticidal activity.

*Pisum sativum* (PSA), *Canavalia ensiformis* (concanavalin A (ConA)), *Glechoma hederacea* (Gleheda), GS-II: *Griffonia simplicifolia* aglutinina, *Phaseolus vulgaris* (PHA), *Bauhinia monandra* leaf lectin (bmoll), *Dioclea grandiflora* (DGL), *D.* 

Insecticidal [147]

are numerous, and several mechanisms can be associated (**Figure 2**).

Bmoll *Anagasta kuehniella*

DRL CFL

*Zabrotes subfasciatus Callosobruchus maculatus Callosobruchus maculatus*

The first lectin known for insecticidal activity was *Galanthus nivalis* agglutinin, which belongs to a superfamily of alpha-D-mannose-specific plant bulb lectins [105, 119]. The mannose-binding lectins have shown strong insecticidal activity against chewing and sap-sucking insects and particularly in controlling aphids [120–124]. Lectin isolated from bulbs of *Phycella australis* presented a strong insecticidal activity against the pea aphid and green peach aphid, affecting the survival, feeding behavior, and fecundity of aphids, where *Acyrthosiphon pisum* proved to be particularly sensitive [125].

No considerable mortality effect of ASA lectins (native or recombinant lectins) was shown on larvae of potato moths (*Tecia solanivora*); however, recombinant ASAII lectin had an effect on the pupa mortality, which was bigger than the native lectin effect. The effect of lectins on the weight and fertility of adults showed that both lectins had a big effect on fertility when the lectin is used in a low concentration (lower than 0.003 mg/mL), and, in some cases, lectins produced malformations in female adults [126]. Fitches et al. found toxic effects on *Acyrthosiphon pisum* using both recombinant lectins; however, ASA II was more toxic than ASA I, at the same dose [127].

Lectins from legume family have shown insectistastic and insecticidal activity [52] (**Table 4**). The lectins from seeds of *Canavalia brasiliensis*, *Dioclea grandiflora*, *Dioclea rostrata*, *Cratylia floribunda*, and *Phaseolus vulgaris* have shown to protect seeds against the beetle *Callosobruchus maculatus*. In general, the plant lectins are the most potent agents against insect pests of a variety of crops including wheat, rice, tobacco, and potatoes [128]. *Canavalia* lectins exhibited a range of different toxicities toward *Artemia nauplii* and bound to a similar area in the digestive tract; differences in spatial arrangement and volume of CRD (carbohydrate recognition domain) may explain the variation of the toxicity showed by each lectin despite the high structural similarity [129]. The sensitivity of different insect species to the insecticidal effects of lectin ingestion is variable, and the binding of a lectin to the gut does not necessarily imply toxicity. Other studies signal that lectins affect various insect hydrolytic enzymes such as glucosidases, phosphatases, and proteases which are involved in digestion, development, growth, and detoxification. To date a great number of studies have shown lectin toxicity in insects belonging to different orders, including Lepidoptera, Coleoptera, and Hemiptera. However, the exact mode of action of lectins in providing resistance against insects remains unclear. The most relevant property of lectin's anti-insect activity can be related to its interactions with different glycoproteins or glycan structures in insects, which may interfere with a number of physiological processes in these organisms. Lectins possess at least one carbohydrate-binding domain and different sugar specificities, possible targets for lectin binding are numerous, and several mechanisms can be associated (**Figure 2**).

**5. Insecticide and insectistatic activity of plant lectins**

28 Insecticides - Agriculture and Toxicology

delivery of toxins and to potentiate expected insecticide effects [116–118].

*Acyrthosiphon pisum* proved to be particularly sensitive [125].

The first lectin known for insecticidal activity was *Galanthus nivalis* agglutinin, which belongs to a superfamily of alpha-D-mannose-specific plant bulb lectins [105, 119]. The mannose-binding lectins have shown strong insecticidal activity against chewing and sap-sucking insects and particularly in controlling aphids [120–124]. Lectin isolated from bulbs of *Phycella australis* presented a strong insecticidal activity against the pea aphid and green peach aphid, affecting the survival, feeding behavior, and fecundity of aphids, where

No considerable mortality effect of ASA lectins (native or recombinant lectins) was shown on larvae of potato moths (*Tecia solanivora*); however, recombinant ASAII lectin had an effect on the pupa mortality, which was bigger than the native lectin effect. The effect of lectins on the weight and fertility of adults showed that both lectins had a big effect on fertility when the lectin is used in a low concentration (lower than 0.003 mg/mL), and, in some cases, lectins produced malformations in female adults [126]. Fitches et al. found toxic effects on *Acyrthosiphon pisum* using both recombinant lectins; however, ASA II was more toxic than ASA I, at the same dose [127].

Lectins from legume family have shown insectistastic and insecticidal activity [52] (**Table 4**). The lectins from seeds of *Canavalia brasiliensis*, *Dioclea grandiflora*, *Dioclea rostrata*, *Cratylia floribunda*, and *Phaseolus vulgaris* have shown to protect seeds against the beetle *Callosobruchus maculatus*. In general, the plant lectins are the most potent agents against insect pests of a variety of crops including wheat, rice, tobacco, and potatoes [128]. *Canavalia* lectins exhibited a range of different toxicities toward *Artemia nauplii* and bound to a similar area in the digestive tract; differences in spatial arrangement and volume of CRD (carbohydrate recognition domain) may explain the variation of the toxicity showed by each lectin despite the high structural similarity [129]. The sensitivity of different insect species to the insecticidal effects

There are several evidences for the defensive role of vegetal lectins in protecting plants against insect pests [108–110], and lectins are currently receiving a significant interest as insecticidal agents against sap-sucking insects including aphids and leaf and plant hoppers, with no effect on human metabolism [111, 112]. Lectins act on insects by binding to glycoproteins present in insect gut epithelium, eventually causing death of insect by inhibiting absorption of nutrients. It was believed that N-linked glycans in insects were exclusively of the high mannose type; therefore, there are great interests, especially in mannose-specific plant lectins, as possible insecticidal or insect-deterring molecules for the new pest management strategies [113, 114]. Nevertheless, the lectins possess different sugar specificities and, considering the variety of glycan structures in the bodies of insects, have many different possible targets. Advances have been made in the knowledge related to glycan diversity and function(s) of protein glycosylation in insects, N-glycosylation, and O-glycosylation, and it postulated that the interference in insect glycosylation appears to be a promising strategy for pest insect control [115]. Therefore, it is difficult to predict the exact mode of action of each lectin and even more difficult to understand the variability in insect toxicity upon exposure to different plant lectins. The use of initial bioassays employing artificial diets has led to the most recent advances, such as plant breeding and the construction of fusion proteins, using lectins for targeting the

Preliminary evidence of Gleheda's insecticidal activity against Colorado potato beetle larvae (*Leptinotarsa decemlineata*) has been obtained using a single dose of lectin [130]; it would have been very interesting to carry out dose-response experiments and to assay several insect pests to elucidate whether the lectin was insect specific. Nevertheless, Gleheda's insecticidal activity stresses the importance of this unusual lectin, begging the question of whether such activity is shared by other Lamiaceae lectins. To date Lamiaceae lectin is unique with known insecticidal activity. The importance of lectins due to their insecticidal properties, isolation of native lectins, and lectin genes could be agronomically important tools for crop plants for developing resistance against insect pests mainly for sap-sucking


*Pisum sativum* (PSA), *Canavalia ensiformis* (concanavalin A (ConA)), *Glechoma hederacea* (Gleheda), GS-II: *Griffonia simplicifolia* aglutinina, *Phaseolus vulgaris* (PHA), *Bauhinia monandra* leaf lectin (bmoll), *Dioclea grandiflora* (DGL), *D. rostrata* (DRL), *Cratylia floribunda* (CFL). Taking from Calvacante et al. [60] and modified.

**Table 4.** Legume lectins domain with insectistatic and insecticidal activity.

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**Figure 2.** Possible targets and associated mechanisms of lectin anti-insect activity. Lectins have antinutritional properties by which they interact with several targets in digestive tract and other organs.

insect. These proteins are very interesting, and its molecular properties have been well described; however, there is still a long way to study and learn about the mechanisms of these molecules at a physiological and molecular level.
