*2.1.3 Damage*

*Diaphorina citri* is one of the devastating sucking insect pests of citrus plantations and losses due to attack of this pest ranges from 82 to 95% [42]. Both the nymphal and adult stages of this pest feed on juvenile plant shoots and leaves and floral buds and deprive the plant from essential nutrients by sucking phloem sap. Its infestation results in leaf curling, distortion, and shedding of flower and leaves [43, 44]. They also inject toxic saliva in the citrus plants during feeding [43]. The host range of *D. citri* has been known to be *Citrus* spp. and near relatives, spanning over 23 genera within the Rutaceae [45]. During its feeding, *D. citri* (4th and 5th instars and adults) transmits gram negative and phloem-limited bacterial pathogens (*Candidatus* Liberibacter *asiaticus, Candidatus* Liberibacter *americanus,* and *Candidatus* Liberibacter *africanus*) to citrus plants. These pathogens are the causal agents of devastating disease in the citrus plantations, which is known as citrus greening or Huanglongbing (HLB) or yellow dragon disease [46, 47]. The citrus greening is one of world's most serious diseases of all citrus cultivars. This disease is a threat for citrus industry throughout the world as it has perished millions of hectare of citrus in about 40 countries [48]. This disease results in poor quality fruit production, severe yield

#### **Figure 1.**

*Scaly eggs of* Diaphorina citri *laid singly in a row below the leaf surface (A), nymphal instars of* D. citri *congregated for feeding at soft branch (B), adult* D. citri *with elaborated body features and sitting in upright position with rear raised (C), and adults of* D. citri *infesting the underside of leaf surface and secreting honeydew and wax (D). Photographs by Douglas L. Caldwell, University of Florida, USA (A and C), https://www.koppert. com/challenges/pest-control/psyllids/asian-citrus-psyllid/ (B) and the citrus pest and disease prevention program, California Department of Food and Agriculture, USA (D).*

*Ecology, Biology, Damage, and Management of Sucking and Chewing Insect Pests of Citrus DOI: http://dx.doi.org/10.5772/intechopen.109846*

reduction (30–100%), and ultimately death of whole plant within 5–8 years of attack [49–51]. Other symptoms of HLB infection are progressive blotchy mottling of leaves, plant stunting, off-season bloom, deformed, small-sized, and off-flavor fruit with high acid contents and bitter taste and premature fruit drop thus inducing market losses in fresh and processed fruits [52–54]. Asymmetrical patterns with yellow veins on leaves are also clear indication of citrus greening. In addition to these, several other symptoms such as stunted plant growth, shoot dieback, fruit drop, and overall yellow appearance of citrus plants are visible signs of HLB infection [55]. Before the appearance of visible symptoms, the initiation of root dieback and decrease in root-shoot ratio have also been observed in HLB-infected plants [56].

#### *2.1.4 Management*

#### *2.1.4.1 Biological control*

Biological control is the control of insect pests using predators and parasitoids and should be adapted at large scale to avoid the unnecessary use of insecticides. There are various predators and parasitoids of *D. citri* in the citrus crop. The primarily source of generalist predators are syrphid flies, ladybird beetles, lacewings, predatory mites, and ants [57]. The immature of *D. citri* are attacked by ants [58]. Husain and Nath [35] and Batra et al. [59] also reported that different species of coccinellid attack the *D. citri* such as the seven-spot ladybird beetle *Coccinella septempunctata* Linnaeus, transverse ladybird beetle *C. repanda* Thunberg, Malaysian ladybird beetle *Chilocorus nigrita* (Fabricius), zigzag ladybird beetle *Cheilomenes sexmaculata* (Fabricius), and threestriped lady-beetle *Brumus suturalis* Fabricius. The larvae of syrphid fly *Allograpta* spp. have been reported to attack *D. citri* nymphs in the regions of Nepal and Reunion [60]. The primary effective parasitoids of *D. citri* are *Tamarixia radiata* (Waterston) (Hymenoptera: Eulophidae) [61] and *Diaphorencyrtus aligarhensis* (Shafee, Alam and Argarwal) (Hymenoptera: Encyrtidae) [62], which are native to India and provide better control than predators. Female of *T. radiata* prefers the 3rd, 4th, and 5th nymphal instars of *D. citri* [63, 64].

#### *2.1.4.2 Chemical control*

There is significant increase in insecticide use per year to control *D. citri* and citrus greening and annual cost for managing this pest could range from \$US 240 to>\$US 1000 depending upon application frequency, type of insecticide sprayed, and method of application [65]. Among various types of insecticides, the foliar applied broadspectrum insecticides are recommended to control the *D. citri* prior to flushing (to kill the overwintering adults) and during growing season. Foliar sprays with broadspectrum insecticides such as chlorpyrifos, dimethoate, fenpropathrin, bifenthrin, and zeta-cypermethrin along with foliar and soil applications with systemic neonicotinoid insecticides such as imidacloprid, thiamethoxam, and clothianidin are indicated to control *D. citri* [66–68]. Imidacloprid offers 50–90% control of adult psyllid population in the field (reviewed by Boina and Bloomquist, [48]). Spray of imidacloprid in rotation with chlorpyrifos or cypermethrin at two-week interval also reduces the psyllid population and incidence and spread of HLB during new flush stage of citrus plants [69]. In the world, all citrus-growing areas are not free from attack of citrus greening and its vector. There is no permanent cure for controlling this pest except chemical control, which keeps the pest population at low level and is one

of most effective management options for controlling the pest incidence and spread of citrus greening disease.

#### *2.1.4.3 Miscellaneous tactics*

Chemical and biological control should be combined with other control measures such as promoting a clean cultivation, which includes using a disease free and transgenic plants that are resistant to *D. citri* and removal of infected plants from the field; and use of antibiotics (e.g., tetracycline hydrochloride) for suppression of citrus greening symptoms is viable and sustainable tool to control the incidence of HLB [70]. To reduce the insecticides resistance in the *D. citri*, there is an immediate need for development of IRM (insecticide resistance management) strategies. Regular monitoring of *D. citri* in field to determine the rate of development of insecticide resistance is one of the major components of IRM. In addition, resistant colony should be developed in the laboratory for determining the genetic nature, mode of inheritance, stability of resistance, fitness costs, and pattern of cross resistance in order to manage insecticide resistance.

#### **2.2 Citrus whitefly**

Citrus whitefly (CWF) belonging to order Hemiptera and family Aleyrodidae is technically known as *Dialeurodes citri* (Ashmead).

#### *2.2.1 Distribution*

*Dialeurodes citri* has a wide range of distribution in different regions around the world [71]. With its origin in Southeast Asia, CWF occurrence was reported from southeastern United States mainly in Florida in the 1880s [72] from where in 1900 it spread to California, a region in the western United States [73]. Later its occurrence was recorded in the Mediterranean countries such as Western Galilee region of Israel in 1975 [74, 75] and in the Turkey's Eastern Mediterranean citrus groves in 1976 [76, 77]. In 1977, invasion of this species in citrus orchards was reported from South Adriatic, near Dubrovnik [78]. This species has also been detected from Oceania, New Zealand, in 2000 [79]. In Asia, this species is infesting citrus orchards in several parts of Pakistan [80], Taiwan, Japan, and China [81, 82], Uzbekistan, and Turkmenistan [83], and India [84, 85].

#### *2.2.2 Eco-biology*

The eggs of CWF are yellow and have smooth surface. Female adults lay their eggs on leaves and 8–24 days are required for hatching according to climate [86]. The CWF is an arrhenotokous species [87] in which unfertilized eggs always develop into males. The nymphs are elliptical, flat, and scale like. After first molt, the instars become fixed (legs and antennae are lacking) at the underside of the leaf surface until the adult stage. About 23–30 days are required to complete the nymphal period. The pupa of CWF is opaque and eye spots of developing adult are clearly visible from pupal integument and pupa completes its development in about 13–30 days. The total life cycle from egg to adult formation is completed in 41–333 days according to the ecological conditions such as temperature, humidity, and rainfall. The CWF overwinters as nymph (fourth instar) at the underside of the leaves. The pupae appear

*Ecology, Biology, Damage, and Management of Sucking and Chewing Insect Pests of Citrus DOI: http://dx.doi.org/10.5772/intechopen.109846*

early in spring and in March-April (late spring) the adult emergence occurs [86]. The number of generations varies according to the region with 2–5 per year [75, 88].

#### *2.2.3 Damage*

The CWF has sucking mouth parts and both nymphs and adults injure the plants by sucking sap. The further injury is caused by honeydew release, which results in the development of sooty mold fungus over fruits and foliage [86]. The sooty mold may cover the leaves and cause indirect damage by interfering with respiration and photosynthetic activity of plants, which leads to leaf drop and yield reduction [75]. The infested citrus trees become weak and tasteless. Easy peeler citrus varieties such as mandarins and sweet orange cultivars are preferred citrus hosts of CWF [87]. Besides this, CWF has also been reported as a vector of disease known as Citrus Yellow Vein Clearing Virus (CYVCV) [89]. This viral disease was reported for the first time from Pakistan in 1988 in sour orange (*Citrus aurantium* L.) and lemon (*C. limon* Burm.f.) [90]. Now this disease is widely distributed in major Chinese province of citrusgrowing areas and considered to be most serious disease, which affects the lemon production [91]. The major symptoms of CYVCV that appear in sour orange and lemon are severe vein clearing, vein necrosis, and leaf distortion [91–93]. Usually, this virus does not cause tree death but it can reduce the yield for example in Anyue, Sichuan Province of China up to 80% lemon production is affected by CYVCV and yield is reduced by 50–80% [89].

#### *2.2.4 Management*

#### *2.2.4.1 Biological control*

The biological control of CWF is poorly studied but it includes mainly the use of potential predatory insects. The main natural enemies of CWF include representatives of predatory coccinellid with highlight to *Serangium japonicum* Chapin (Coleoptera: Coccinellidae)*.* This natural enemy has been reported in pesticide-free crops with many CWF, in the Japan with peaks in May and July reducing the CWF number in the second peak [94]. Release of another ladybird beetle *S. parcesotum* Sicard (Coleoptera: Coccinellidae) in the East Mediterranean region reveals that the predator has success in the colonization of orchards with potential to control CWF [77, 95]. Some parasitoids also have potential to control CWF, including *Encarsia lahorensis* (Howard) (Hymenoptera: Aphelinidae), and *Eretmocerus debachi* Rose and Rosen (Hymenoptera: Aphelinidae) [96–98] but further studies to optimize the control are necessary. Likely parasitoids, pathogenic agents are also poorly evaluated. The fungus *Aschersonia placenta* Berkeley and Broom (Hypocreales: Clavicipitaceae) isolates were evaluated in China and three of them have potential to control CWF [82]. In addition, *A. aleyrodis* Webber (Hypocreales: Clavicipitaceae) was reported causing high mortality in *D. citri* at Southern Alabama and China [99]. *Lecanicillium attenuatum* Zare and Gams from order Hypocreales have also been reported to kill the nymphs of CWF, thus considered a potential biological control agent of this pest [100, 101].

#### *2.2.4.2 Physical control*

Physical control involving the use of ultraviolet (UV) light to control insects mainly CWF is gaining importance as one of the components of IPM because this technique is environmentally benign and non-hazardous to non-target organisms [102–105]. Traps designed with UV releasing tubes can be installed in the field to monitor and reduce the population of CWF as adults of this pest exhibit positive phototactic behavior to UV source [102, 106, 107]. UV light kills the captured insects by inducing oxidative stress and altering some life traits such as behavior, developmental patterns, and biochemistry [108–110]. Exposure of CWF for longer period, for example, about seven hours per day, can decrease the fecundity, and oviposition rate. Moreover, pupal formation, longevity of adult females, and adult emergence have also been reported to decrease significantly in CWF upon exposure to UV light [107]. Apart from UV light, colored sticky cards and yellow sticky traps should also be used during the active season of CWF in orchards to detect, monitor, and control the insect population as a part of IPM [111, 112].

#### *2.2.4.3 Cultural control*

All the practices in citrus orchard that enhance the passage of air flow through the canopy of citrus trees come under the cultural control, these practices include the following: maintaining a proper plant to plant and row to row distance, weed eradication, light to moderate pruning, and optimum application of irrigation and fertilizer. These cultural practices do not allow humidity among the trees to increase significantly and thus keep the population under check [113, 114].

#### *2.2.4.4 Chemical control*

Chemical control using inorganic compounds, botanicals, and synthetic insecticides is an integral part of IPM for the control of CWF; however, it should be used judiciously and only when required. Two applications of summer oil or white oil (petroleum) emulsion are recommended during peak activity of CWF; however, in case of very high populations density spray can be done 3–4 times, Refs. [113–115] suggested that use of pyriproxyfen or buprofezin @0.05% twice with the span of 45 days can give good control of CWF in citrus orchards. The joint application of an organophosphate insecticide triazophos and neem formulation can suppress the nymphs and adults of CWF if sprayed twice at 15-day interval in the citrus orchards [116]. Use of tree spray oil (0.5 and 1%) along with lime sulfur diluted with water can provide satisfactory control of CWF eggs mainly in the orchards of sweet oranges. Moreover, significant nymphal control of CWF can be achieved by spraying 0.03% dimethoate and formothion [117]. Sole reliance upon conventional chemical control of CWF should be avoided as this pest can develop resistance quickly to different pesticides render them ineffective [118, 119].

#### **2.3 Citrus mealybug**

The scientific name of citrus mealybug (CMB) is *Planococcus citri* (Risso) and this species belongs to order Hemiptera and family Pseudococcidae.

#### *2.3.1 Distribution*

CMB is polyphagous and most destructive pest of citrus orchards and nurseries. It is distributed in different parts of the world such as in Egypt [120], Florida [121], California [122], Portugal [123], Turkey [124], South Africa [125], USA [126], South

#### *Ecology, Biology, Damage, and Management of Sucking and Chewing Insect Pests of Citrus DOI: http://dx.doi.org/10.5772/intechopen.109846*

pacific region [127], Australia [128, 129], India [130], Mediterranean region [131, 132], America [122, 133], and Pakistan [134].

#### *2.3.2 Eco-biology*

Sexual dimorphism occurs in CMB [135]. The female of CMB has oval, flat, and soft body, which is covered with wax and long waxy filaments [136]. The length of adult female insect is about 3 mm [135]. Similar to other scale insects, females of CMB are wingless [137]. Female lays yellow eggs within ovisacs in soil and each ovisac contains about 300–800 eggs. About 10–20 days are required to egg hatching. After hatching, the amber colored nymphs emerge and start feeding by inserting the mouthparts in the lower side of leaves epidermis. The female molts three time to become an adult and complete its nymphal duration in six to eight weeks. The male is gray, winged, and midge like and has long antennae but no mouthparts (**Figure 2**) [138]. Adult males are 1 mm in length and have two caudal filaments [135]. In its early stage, male resembles with female but as it grows, male secretes fibrous, cottony cocoon from which adult male emerges [139]. The male nymphal instars molt 4 times until adult [138]. During winter, they hide themselves in cracks and cavities in tree trunks in the adult female or egg stage. In late spring according to the temperature, especially at the end of April or beginning of May (early summer), they emerge from hibernating sites. CMB has about three to six overlapping generations per year but the Spring-Summer life cycle is major concern for citrus growers as peak infestation occurs in the month of June in Mediterranean region of the Turkey [140]. The males of CMB exhibit the phenomena of polygyny and can fertilize multiple females during their short life span [141, 142]. Generally, the sperm from younger males has more chances to fertilize the female eggs [143].

#### *2.3.3 Damage*

The CMB has potential to cause high loss in agriculture especially in citrus and grapevine industry. The CMB infestation causes direct and indirect type of damage to citrus orchards [144]. All parts of tree such as new leaves, stem, flowers, and fruits are damaged by CMB except underground portion of the plant. The CMB (nymphs and adult female) sucks the sap from different parts of plant, which results in defoliation (about 80%), wilting, dropping of fruits and flowers, deformed fruit appearance [132], and premature yellowing and causes approximately 95% loss in crop yield [145, 146]. In case of heavy infestation, stunting and death of plants occur [136]. According to Smith et al. [128], in South Africa, the early ripening cultivars are more susceptible to damage by CMB than the late maturing cultivars. In early ripening cultivars, the natural enemies have less opportunity to suppress the pest population of CMB in the field before harvesting stage. Generally, fruit damage is caused by CMB between petal fall and at that time when fruits are size of golf ball [147]. The indirect damage to plant by CMB is the production of copious amount of honeydew on foliage and fruits, which provides the growth medium for development of sooty mold fungus [145]. Sooty mold is dark superficial coating on different parts of plants, which decreases the photosynthetic capacity of plant by reducing the amount of light entering the leaf cells; the presence of this black mass upon harvested fruit ultimately reduces the market value [144]. Honeydew is also source of food for ants, which may protect the CMB from their natural enemies [148].

#### **Figure 2.**

Planococcus citri *adult male having membranous wings and tail filaments (A), cottony ovisac with egg mass deposited by adult female of* P. citri *(B), nymphs, pre-pupae and pupae of* P. citri *(C) and adult female of* P. citri *whose body is covered with white powdery mass (D). Photographs by lance S. Osborne, the University of Florida, USA (A), Lyle J. buss, University of Florida, USA (B) Paul J. Johnson, South Dakota State University, USA (C) and William Bodine in 1455 N Val vista Dr., Mesa, AZ 85213, USA captured on august 19 2022 (D).*

#### *2.3.4 Management*
