Management Guide of Sucking Insect Pest

Abstract

Sap feeders have typically piercing sucking mouthparts through which they suck sap from the plant, and due to this feeding, the plant produces specific symptoms. Their role as transmitting plant viruses is well known and considered a very important factor in achieving a desirable yield. Their small size, ability to develop quick resistance and biotypes make them very difficult to manage. Insecticide is considered the most potent weapon to cope with the sap feeders because of its quick knockdown effect and ease of application. At the same time, its indiscriminate use makes the situation harsh, leading towards the disruption of several ecological phenomena. We have seen a significant increase in honey bee colony collapse disorder in recent years, owing to extensive crop coverage with neonicotinoids. Similarly, the emergence of whitefly and jassids in Bt cotton as the dreadest pests is a result of not following the conservation of refuge strategy. As the crop ecosystem is a centre of multiple interactions between several biotic organisms along with abiotic factors, holistic approaches need to be developed combining cultural, mechanical, physical, biological, biopesticidal, and chemical management incorporating the host plant resistance.

1. Introduction

Sucking pests, as the name hints, incorporate a wide range of arthropods (mostly members of classes Insecta and Arachnida) that do feed on the cell sap, though pierced with slender, sharp-pointed mouthparts. Among herbivorous insects, those considered as potential crop pests 75% of the known polypagous, oligophagous, and monophagous herbivores are considered sucking insects [1]. Among the different orders of class insecta associated with crop loss hemiptera accounts the largest apart from thysanoptera. The order hemiptera is divided in four sub order Auchenorrhyncha, Sternorrhyncha, Coleorrhyncha and heteroptera [2]; whose members are frequently referred to as “true bugs” (though restricted to the suborder Heteroptera) and are regarded as one of the largest and most important orders. They are tiny to medium-sized, ranging from 1 mm (0.04 in) to around 15 cm (6 in) of true hemimetabolous insects with piercing-sucking mouthparts. They share diverse habitats, while most are terrestrial and some share aquatic habitats (Gerromorpha and the Nepomorpha). Phytophagous hemipterans are found in large numbers in the leaves, stems, or bark of plants and roots also. Some genuses are gall producers; they generally live in galls. Classical examples of hemipteran sap-sucking pests include whiteflies (Aleyrodidae), leafhoppers (Cicadellidae), planthoppers (Delphacidae), aphids (Aphidoidea), mealy bugs (Pseudococcidae), mirid bugs (Miridae), stink or shield bugs (Pentatomidae), psyllids (Psyllidae), scale insects (Coccidae), cicadas (Cicadidae), and many more. Due to feeding from the xylem and phloem, it causes several external symptoms in crop phenology like curling and yellowing/browning of leaves, stunted growth, deformed fruit, wilting in severe cases. Some of the members are important virus vectors responsible for transmitting large numbers of plant viruses. Members of Hemiptera have a unique ability to produce honey dew due to the excretion of sticky sugar-rich residues. This honeydew contains various floras of microbes on leaf surfaces that can lead to a sooty mould appearance [3], The presence of sooty mould is one of the important features in identifying the severity of infestation. The global spread of sucking pests is a major concern for crop production because the development of insecticide resistance in hemiptera is a common phenomenon [4]; while biological control methods are less adopted. Apart from that, resurgence is very well known in hemiptera, associated with sub-lethal doses of insecticides [5]. Not only is insecticidal exposure causing selection pressure, but abiotic factors are also closely linked to sucking pest outbreaks. Thus, it is essential to develop a strategic plan to deal with the insects in a sustainable manner by associating all the management practices.

2. Management of sucking insect pests

Sucking pest management entails integrating several management tactics available to us to protect our crop, which include the following:

2.1 Scouting to know our pest

Monitoring and field scouting is the pre requisite to develop any management strategies in sustainable manner [6]. Unvarying surveys need to be conducted throughout the cropping or pest’s breeding season in order to predict future population and forewarn the farmers to initiate the control measures or not. As the pest are associated with have specific crop growth stage thus a clear knowledge about the pest biology, their appearance and breeding potentiality and to know this facts one must have to conduct field scouting or monitoring. Several tactics may be followed to conduct the study like setting yellow sticky trap, rouging survey, population count etc. Sometimes during the off season survival of the pests needs to be checked on wild relatives, alternate and collateral host to understand the bio-ecology of the pests and this will help to predict the level of infestation and sometimes helps to manage judiciously before crop establishment. Visual observation of bagrada bugs at night with a fluorescent lamp is effective [7].

2.2 Cultural management

Cultural management deploy crop management practices related to agronomic practices like adjustment of crop calendar, fertiliser scheduling, irrigation pattern, crop rotation, trap cropping etc. Several practices may be followed against different insect pest based on the bio-ecology factors. Deep summer ploughing is essential to destroy the eggs of several bugs and application of first irrigation at 3–4 weeks after sowing is effective to manage pest population. Immediately ploughed field after harvest is followed to prevent the spread of cabbage aphids to other crops [8] is an important cultural management strategy. Eradication of alternate host plants, like volunteer crucifer plants or other cruciferous weeds and destruction of plant debris at the end of the season can help to kill pest during non-host period [9].

Adjustment of date of sowing exerted potential impact on the population incidence mustard aphid. Early sown brassica crops (late September or early October) have been reported to escape aphid attack from India and Pakistan [10]; while delaying in sowing beyond mid-October or sometimes in November and December results in progressive increase in aphid population on succeeding late sown crops at reproductive stage [11]. But also it is very intricate always to manage the pest without having its bio-ecology knowledge of the target pest as population abundance is highly associated with the abiotic factors [12]. Maintenance of good field sanitation by wiping out and removing the crop residues and weeds in vicinity is an effective practice against the sucking pests like whiteflies and leaf hopper. Cultivation of non-host crops in a crop calendar reduces the population load of aphids and plant hopper. Application of recommended fertiliser dose based on soil testing is always effective to reduce the sap feeders [13] as high dose of N makes the plant succulent and thus succumb to infestation by sap feeders [14]. Increased sulphur fertiliser application exerted negative correlation with aphid population in mustard [15]; while increasing dose of K triggered hostile effects on the reproduction and excretion of the mustard aphid as reported by Bhat and Sidhu [16]. Organic manure like farm yard manure, neem cake, vermicompost reduced the pest population compared to straight fertilised treatments as manures induced the production of phenols and tannins in groundnut [17]. Water stressed condition reduced the fecundity of several sap feeder including aphids when soil water regimes decreased from 8 to 2% [18], tiny sap feeders face difficulties to get concentrated cell sap with low cell turgidity. Afrin et al. [19] reported that intercropping mustard with garlic, onion and coriander significantly reduced aphid population trough acted as repellents. Boarder crop like maize and sorghum may be utilised to reduce the dispersal of the sucking pest like jassid, whitefly, shoot fly etc. Ghosal et al. [20] reported that raising seedlings covered with insect proof net reduces the early infestation of chilli leaf curl viruses vectored by whitefly; he also concluded that border netting with insect proof net at a height of 6 feet help to reduce the dispersal of mite, whitefly and thrips. Planting a nectar plant to attract beneficial insects could also be helpful to build and conserve bio-control agents.

3. Mechanical and physical control

It is a very useful method to check the infestation of pests in any crop; it is an age-old traditional practise now combined with physical management strategies. Removal or clipping of infested parts after field scouting is the quickest and easiest way to reduce the infestation of different insect pests [21]. Most of the sap feeders are attracted to yellow, so it is a well-established fact that the installation of yellow sticky traps at 12 traps/ha for monitoring and 25 traps/ha for mass trapping may be utilised to catch the alate adults [20, 22]. The yellow-coloured water pan trap also exerted a great impact on the reduction of sap-feeding insects. The Nozzle is an important device to check the sucking pest as reported by Nawaz et al. [23]. The hollow cone nozzle with a single orifice (modified) showed the highest percentage of reduction in aphid population by dislodging (90.8%) immediately after spraying of water. Predator or non-target-friendly light traps may be utilised for mass trapping of several sap feeders of cereal crops, pulse crops, vegetable crops, as well as horticultural crops. Light traps of 380–400 lux from energy-saving lamps showed the maximum effect in reducing the pest brown plant hopper [24].

4. Biological control

In nature, there are several insects and pathogens that are associated with the ecosystem as predators, parasitoids, or parasites. Utilisation of this biota as pest management is the main action threshold of natural farming. They may be conserved in the field or may be released to achieve inoculative or inundative control. A clear knowledge of these bio-control agents is the basic pre-requisite to achieving pest management in a judicious way. Ladybird beetles (Menochilus sexmaculata, Coccinella septempunctata, Hippodamia variegate, Coccinella transversalis, and Cheilomones sexmaculata) are widespread predators that actively predate on soft-bodied sap feeders such as whitefly, aphid, and jassid. Adult ladybird beetles are known to consume an average of 10–15 adult aphids per day. Conservation of natural enemies which predate upon aphids, like ladybird beetles [25], green lacewing (Chrysoperla zastrowi sillemi), several species of syrphid/hoverfly (Syrphus torvus, Episyrphus balteatus, Sphaerophoria spp., Sphaerophoria scripta, Xanthogramma spp., etc.) is the base for in situ management of mustard aphid. The beetles, Hippodamia convergens Guerin-Meneville and Collops vittatus (Say) fed mostly on whitefly (Bemisia tabaci) eggs, but readily and rapidly preyed on all of the whitefly life stages. The true bugs, Geocoris punctipes (Say) and Orius tristicolor (Say) preyed almost exclusively on adult whiteflies, while Lygus hesperus Knight preyed almost exclusively on nymphs. Cryptolaemus montrouzieri, often called as mealybug ladybird or mealybug destroyer is well known to check mealybug. Vennila et al. [26] reported that when the population of the green lace wing (Chrysoperla carnea) is more (at predatory to prey ratio of greater than or equal to 0.2) the decision to take up insecticidal spray should be abandoned. The braconids are the most dominant bio control agents of an array of hemiptera. Diaetriella rapae (Braconidae, Hymenoptera) is copiously present in the mustard ecosystem and naturally parasitize up to 60.0% aphid population. Acerophagus papayae Noyes and Schauff (Encyrtidae: Hymenoptera) is one of the efficient parasitoids for the management of papaya mealybug in its native range. In India this parasitoid was introduced from Puerto Rico in 2010 through USDA–APHIS for use against the papaya mealybug as inoculative release [27]. The parasitoids in the genera of Encarsia and Eretmocerus (Hymenoptera: Aphelinidae) are important biological control agents of whiteflies, and some of them not only parasitize hosts but also kill them with strong host feeding capacity [27]. Serangium parcesetosum Sicard (Coleoptera: Coccinellidae) can utilised effectively in biological control of B. tabaci [28]. There are known predators and parasitoids that attack Bagrada hilaris [29]. 79 species of natural enemies were identified by Chiu [30], comprising 34 species of insect parasites, 1 nematode, 7 pathogens, 21 species of insect predators and 16 species of spider predator. Some show considerable potential for biological control. The predator wolf spider, Lycosa pseudoannulata is a promising options in reducing brown plant hopper population successfully in 3 days exposure period indicating its high predation potentiality. Ladybird beetle, Micraspis discolour, Ophionea indica is also associated with predation of brown plant hopper [24]. The mirid bug, Cyrtorhinus lividipennis, is a plant-feeding and predatory insect, preferring plant and leafhopper eggs and young nymphs [31].

Entomopathogenic fungi are becoming increasingly important in pest management in a sustainable manner. Different workers have been studied on different bio-pesticides to evaluate their efficacy against different sucking pests. A number of entomogenous fungi, Beauveria bassiana, Metarhizium anisopliae, Verticillium lecanii (renamed Lecanicillium), Cephalosporium spp. and Nomuraea rileyi are also to infect aphids, whiteflies, jassid, mealy bugs etc. [32, 33]. Avoiding spray of chemical pesticides during heavy natural parasitism is quite beneficial to maintain sufficient number of biocontrol agents to suppress this pest. Wild mustard (Sinapis arvensis) and white mustard (Sinapis alba), Cowpea are very good border crop to conserve biological control agents like lady bird, lace wing etc. Predatory bird Motacilla cospica actively feeds on aphids in February–March. Therefore, provision bird perches @ 8–10/acre will boost natural control.

5. Host plant resistance

Host plant resistance is generally based on the principle of antibiosis, antixenosis and tolerance, which has been achieved through hybridization process. Complete resistance to a specific group of insect pest only be achieved through genetic engineering only; but commercial hybridization only can add few resistance trait to the desired cultivar. Breeding programme for resistant variety targets to tap the best source of resistance in this genetically diverse species [34]. For management of several viral diseases vectored by sap feeders modern days hybridization have evolved very successfully. So many resistant varieties are now available in market for commercial cultivation for different cereal, pulse, oilseeds and vegetable crops. But it is difficult to have high degree resistant source which can be exploited in development of aphid resistant varieties in mustard as reported by Kumar and Sangha [35]. Cotton varieties with glabrous leaves are very much susceptible to jassids if compared to the hairy (hirsute) varieties. The vulnerability is correlated with both density & length of hairs on the below surface of the leaf mainly on veins where the jassid feeds & lays eggs. High hair thickness without length is ineffective. Strong positive correlation of jassid population with plant height suggested that improvement in plant height will result increase in jassid population significantly. There was a strong negative correlation of leaf N content, indicated that increasing leaf nitrogen (N) will result negative impact on jassid population. Total sugars, reducing sugars, nitrogen and protein content had a positive correlation with the whitefly population and OYVMV incidence. High resource availability can reduce anti-herbivore resistance in rice, but may also increase tolerance [36]. Development of biotypes in hemiptera is a serious matter of concern to development of resistant varieties. Resistant rice varieties have proved to be highly effective against the brown plant hopper Nilaparvata lugens, but their long-term stability is threatened because of the evolution of prolific biotypes [37]. They also reported that Biotype 1 can survive on and damage only those varieties that do not carry any genes for resistance. Biotype 2 can thrive on varieties carrying Bph 1 resistance gene and on those susceptible to biotype 1. Biotype 3 can infest and destroy varieties having bph 2 resistance gene and those susceptible to biotype 1. However, none of these biotypes is capable of damaging varieties with Bph 3 and bph 4 genes for resistance. Several varieties which are resistant in the Philippines are susceptible in India and Sri Lanka because the South Asian biotypes of N. lugens are more virulent than the Southeast Asian biotypes. Improved lines of okra have potential to broaden the genetic variability may improve resistance to these pests. Tolerance of BCO-1 genotype to whitefly and that of Arka Anamika to jassid is based on both antixenotic properties of the genotypes as reported by Acharya et al. [38]. In relation host plant, B. tabaci is affected mainly by the following features: (i) the external, physical characteristics of the leaf surface, e.g., hairiness vs. glabrousness, sticky glandular trichomes, leaf shape (okra/super okra) and probably the microclimate as a result of foliage density; and (ii) the internal, chemical characteristics of the leaf, e.g., pH of leaf sap [39]. Three different types of host plant resistance mechanisms against Silverleaf whitefly, B. tabaci (Gennadius) B Biotype was reported by Miyazaki et al. [40]; (i) okra leaf traits which reduced adult preference, (ii) glabrous leaf traits which reduced oviposition preference and (iii) possible biochemical traits in Gossypium arboreum which reduced immature development and/or survival. Although any potential negative effects of these traits on yield need to be carefully evaluated. Incidence of sap feeders are positively correlated with nitrogen content and negatively correlated with phenols and tannins. The organic manures induced the production of phenols and tannins in groundnut plant and thus, the induced resistance played an important role in management of jassid Empoasca kerri, aphid Aphis craccivora in groundnut [17].

6. Botanicals

The integrated pest management approach strongly encourages the use of botanicals as a component of pest management tools, which are less harmful to the ecosystem, biodegradable, and have a positive effect on a wide range of sap-feeding insects due to their antifeedant and repellent action. The anti-pest philosophy of neem and tobacco is well documented in agricultural history [41]. Apart from that several botanicals may be utilised effectively to reduce the population of sap feeders below ETL. Neem oil (2–5%) and neem seed kernel extract (NSKE-5%) is very effective to manage the several sap suckers like aphid, rice bug, coreid bug, jassid, whiteflies etc. [42]. Concerning susceptibility of different developmental stages, young larvae were the most sensitive. Foliar treatment was the most efficient. The mortality among immature increased in relation to azadirachtin concentrations. Ali et al. [43] reported that Mexican marigold extract @ 1:2.5 g/ml effectively reduced Lipaphis erysimi population by 96.4%. Chandel et al. [44] reported varied botanicals like NSKE, leaf extract of Vitex negundo, Parthenium hysterophorus, Adhatoda vasica, Lantana camara effective against aphid. Pavela and Herda [45] studied on repellent effects of pongam oil on settlement and oviposition of the common greenhouse whitefly, Trialeurodes vaporariorum. Akbar et al. [46] opined that Calotropis procera extract can reduce aphid population up to 54.9%. Chattree et al. [47] recorded maximum mortality (92.85%) with 20% neem leaf extract in case of first instar larvae of L. erysimi when treated for 18 hours. Castor leaf extract is very effective against aphid [48].

7. Chemical control

Insecticides are the most reliable weapons in pest management strategies. Because of their quick knock down effect and more persistency in the field, they are the most acceptable agents against different pest spectrums. Crop protection with chemicals is a desirable and unavoidable part of integrated pest management. Nowadays, insecticides with varied chemistry are well studied and available in the market. At the same time, development of resistance, resurgence, and residue are three common phenomena associated with chemical management of pests also. Thus, one must be very choosy and selective in the selection of the insecticide effective against the target pest without having hazardous issues. It is very essential to select pesticides for those crops actively visited by an array of pollinators like bees. ETL-based pest management is necessary, but it is awful to desire the insecticide application by the end user following an ETL-based recommendation. One must have sound knowledge of the incidence pattern of insects in relation to weather to protect crops through the adoption of prophylactic spraying [49].

Ghosal et al. [50, 51] reported that imidacloprid 17.8 SL@ 50 g ai/ha was found as a most effective neonicotinoid insecticide against aphid (Aphis gossypii) and jassid (Cestius phycitis). 84.54% reduction of population over control was achieved. Other two popular neonicotinoids viz., thiamethoxam 25WG@ 50 g ai/ ha and acetamiprid 20SP@ 40 g ai/ha were also found effective and showed better result than acephate 75WP and dimethoate 30EC, those are commonly used against aphid. Dotasara et al. [52] reported that imidacloprid 17.8% SL @ 0.2 g/l reduced the incidence of mustard aphid by 87.5% followed by fipronil 5 SC @ 1.0 ml/l (83.6%) at 7 days after spray. Roy et al. [53] revealed that flonicamid (94.7% mortality) and pyriproxyfen (93.0%) effectively managed L. erysimi pest up to 15–18 days. Chau [54] reported that imidacloprid at recommended rates of 28 and 20 g a.i/ha showed very good control of BPH in wet season. Though in India, plant hopper resistance by 35.13, 10.78 and 4.98 fold to imidacloprid, thiamethoxam and clothianidin respectively have been detected during 2006 by Krishnaiah et al. [55]; thus it very pertinent to select the best chemical for the control of plant hoppers. Plant hoppers showed allopatric speciation and showed varied level of resistance depending on exposure. Buprofezin 15% + acephate 35% WP @ 1500 ml/ha is best effective insecticide against brown plant hopper (BPH) and white backed plant hopper (WBPH) as reported by Ghosal et al. [56]. Cotton fields treated with quinalphos, chlorpyriphos induced build-up of jassid population. If Seeds treated with imidacloprid/thiomethoxam - 7 to 10 g/kg of seeds before sowing cotton provides good control against different sap feeders up to 45 days after planting. Ghosal and Chatterjee [5] opined that at sub lethal dose of imidacloprid induced resurgence of whitefly (+2.02% & +9.84%). While, clothianidin induced upsurge rend in whitefly in cotton and tomato. Diafenthiuron 50 WP @ 600 g/ha, imidacloprid 70 WG @ 75 g/ha and thiamethoxam 25 WG @ 100 g/ha reduced the incidence of yellow mosaic viruses in okra through management of its vector whitefly significantly [57, 58]. Spirotetramat could be a better alternative for management of mealy bug instead of chlorpyriphos or any organophosphates as chlorpyriphos shows 100% mortality to vine mealybug parasitoid Anagyrus sp. while spirotetramat do not [59]. Cotton mealybug (Phenacoccus solenopsis) developed resistance against so many insecticides like pyrethroids, carsulfan, endosulfan, chlorphos, etc. so, restriction of using this insecticides against cotton mealy bug is strictly advisable. Spray volume and nozzle is a very crucial for management of sap feeders as most of them settled down under the leaves. It is preferable to use hollow cone nozzle with spray volume of 500 l/ha for knapsack sprayer and must be greater than 250 l/ha using power sprayers. Proper coverage of the underside of leaves during the insecticidal sprays is very necessary for desired efficacy. Not to spray or avoid spraying during the blooming season for the nectar producing crop and preferably advised to spray the insecticide in the evening hours to avoid mortality of honey bees and other pollinators. Field near bee keeping is strictly instructed to not to use neonicotinoid insecticides during flowering and ethically need to restrict the bee foraging from that field for the following day.

8. Conclusion

Our crops are infested by several sap-feeding insects. They are responsible for a considerable loss in production. Recrudescence of sap-feeding insects due to selection pressure is a common phenomenon. Rapid development of resistance to insecticides is another matter of concern in successful crop production. Sole dependency on insecticides makes the situation more aggravating. A holistic approach involving cultural, mechanical, physical, biological, and botanical boosting of host plant resistance and chemical management is essential to protect the crop and ecosystem.