Crop Pests Research Articles

Unravelling genetic diversity of whitefly species on different host plants from New Delhi

Aim: This study investigates the genetic diversity and distribution of different species of whiteflies on 20 host plants vegetables (cucumber, summer squash, pumpkin, tomato, brinjal, okra), field crops (sunflower, lettuce, field bean, lobia), commercial crops (cotton, tobacco), ornamentals (chrysanthemum, bellflower, marigold), fruit crops (lemon), trees (mulberry, wild tamarind, ficus), and others (wild brinjal) in New Delhi. Methodology: Genetic diversity was assessed through mitochondrial cytochrome oxidase-I gene-based molecular markers. Results: Phylogenetic analysis revealed that whitefly Bemisia tabaci was the most prevalent pest species across the crops reported in this study. The other whitefly species, viz., Dialeurodes sp., Singhiella simplex, Aleuroclava sp., Tetraleurodes acaciae, Trialeurodes vapororium, and Aleurodicus floccissimus were reported as pests of different horticultural crops. Interpretation: Genetic diversity of B. tabaci revealed that the genetic groups Asia II-1 and Asia II-7 were most prevalent, while Asia I was the minor one. Understanding the species composition and genetic diversity of whiteflies will help in devising appropriate control strategies. Key words: Hosts, Molecular markers, mtCOI, New Delhi, Phylogenetic analysis, Whitefly diversity

Review and phylogeny of Cyrtomenus Amyot & Serville (Hemiptera: Cydnidae: Cydninae) based on morphological characters

Cyrtomenus includes seven species arranged in two subgenera and belongs to the most diverse subfamily of burrower bugs, Cydninae. The species present polyphagous habits, and at least two species are considered crop pests. We conduct a phylogenetic analysis based on morphological characters and two weighting schemes to test its monophyly and the validation of the included subgenera, providing for the first time a phylogenetic hypothesis for the genus. Based on the results, a taxonomic review is presented, including redescriptions of the species, identification key, and distribution maps. Monophyly of Cyrtomenus is supported under implied weighting methods (IW), in both analyses, a clade including species of Prolobodes Amyot & Serville is recognized. The species of these two genera share the posterior tibia strongly flattened, a unique feature among Neotropical Cydninae. The subgeneric classification within Cyrtomenus is not corroborated.

Distribution and survival of the predatory mite Blattisocius mali on cucumber leaves with the addition of bran, yeast and pollen

Biological control has a special position in sustainable agriculture that requires continuous exploration and diversification in bio-agents to cope with emerging crop pests. Blattisocius mali is a promising biological control agent against some acarid mites, nematodes and moth pests. This study aimed to examine factors that could increase survival and diminish dispersal of B. mali deprived of its prey, the mold mite Tyrophagus putrescentiae, from cucumber plants. The impact of the presence of males on starving females’ lifespans and the influence of different substrates, i.e., wheat bran, dry yeast pellets, and cattail pollen, on the distribution and survival of starving females in groups with males were examined. Experiments were performed on cucumber leaf platforms in Petri dishes filled with water. The results showed that females lived longer and a lower percentage drowned in water when accompanied by males. On the platforms with the addition of a substrate, the mites mainly stayed within the substrate, and eggs were only recorded in the substrate. They clearly preferred bran over pollen or pollen + yeast pellet aggregations. However, the quality of the substrate deteriorated within the first days, and some mites died of entrapment in the substrates. On the 3rd day, the lowest mean percentage of live individuals was observed on platforms with yeast + pollen (54.4%) followed by pollen (68.9%) alone. At that time, females also stopped laying eggs, and cannibalism towards hatched larvae and adults was observed. By the end of the experiment, 54.67% of the mites had been found dead on the leaf surface, and none of the substrates had significantly influenced their lifespan. The females lived on average 8.19 days and the males 5.06 days. The obtained results are discussed in the context of potential application of B. mali in biological control strategies.

Abnormal eyes and spine development in zebrafish (Danio rerio) embryos and larvae induced by triphenyltin

Triphenyltin (TPT) is widely used in crop pest control and ship antifouling coatings, which leads to its entry into aquatic environment and poses a threat to aquatic organisms. However, the effects of TPT on the early life stages of wild fish in natural water environments remains unclear. The aim of this study was to assess the toxic effects of TPT on the early life stages of fish under two different environments: field investigation and laboratory experiment. The occurrence of deformities in wild fish embryos and larvae in the Three Gorges Reservoir (TGR) and the developmental toxicity of TPT at different concentrations (0, 0.15, 1.5 and 15 μg Sn/L) to zebrafish embryos and larvae were observed. The results showed that TPT content was higher in wild larvae, reaching 27.21 ng Sn/g w, and the malformation of wild fish larvae mainly occurred in the eyes and spine under natural water environment. Controlled experiment exposure of zebrafish larvae to TPT also resulted in eye and spinal deformities. Gene expression analysis showed that compared with the control group, the expression levels of genes related to eye development (sox2, otx2, stra6 and rx1) and spine development (sox9a and bmp2b) were significantly up-regulated in the 15 μg Sn/L exposure group, which may be the main cause of eye and spine deformity in the early development stage of fish. In addition, the molecular docking results further elucidate that the strong hydrophobic and electrostatic interactions between TPT and protein residues are the main mechanism of TPT induced abnormal gene expression. Based on these results, it can be inferred that TPT is one of the teratogenic factors of abnormal eye and spine development in the early life stage of fish in the TGR. These findings have important implications for understanding the toxicity of TPT on fish.

Climate-smart Pest Management Strategies: Under Changing Climatic Scenarios

In the face of changing climatic conditions, it's crucial to acknowledge their far-reaching impacts on humans, animals, and agricultural systems worldwide, where negative consequences often overshadow any positive outcomes. With global warming and climate change, previously minor insect pests are now poised to wreak havoc, leading to widespread pest outbreaks. As a result, the effectiveness of various pest control measures, including host-plant resistance, natural enemies, transgenics, bio-pesticides, and synthetic chemicals, may undergo significant shifts. Growers and researchers are actively devising Integrated Pest Management (IPM) strategies to minimize environmental harm while maximizing crop yields and economic benefits. Numerous studies highlight the necessity of reevaluating pest management practices and IPM strategies to adapt to novel environmental conditions and enhance the resilience of diverse agroecosystems to weather variability. This involves initiatives such as breeding climate-resilient crops, adjusting crop calendars, employing GIS-based risk mapping for crop pests, and exploring novel pesticides with alternative modes of action, informed by predictive modeling data. Thus, this chapter explores the potential of these techniques for climate-smart insect pest management.

Development of biopellet formulation of Lecanicillium saksenae for the management of pepper root mealybug (Formicoccus polysperes)

Present study was carried out during 2020–23 in the Biocontrol Laboratory for Crop Pest Management, College of Agriculture, Vellayani, Thiruvananthapuram, Kerala. An indigenous isolate of Lecanicillium saksenae (Kushwaha) Kurihara and Sukarno, ITCC 7714 was assessed for its effectiveness against the pepper root mealybug (Formicoccus polysperes Williams). Peculiar symptoms like sudden dissolution of mealy coating subsequent to the application of conidial suspension and paralysis occurring 12 h post-treatment was observed in mealybugs upon infection. Its high potency to mealybug was established with its low LC50 value of 2.2 × 105 conidia/ml and its quick killing ability was proved with a lethal time of 23.13 h. Of the various carriers tested for pelleting, talc + chitin (95:5) was found to be the best as it exhibited highest conidial viability of 78.54%, 5-weeks after storage. Other carriers such as talc, chitin, chitosan and talc + chitosan (90:10) exhibited conidial viability of 33.96–74.58%. Among the different binding agents examined, the combination of talc + chitin (95:5) + carboxymethyl cellulose 6% was the superior one to maintain conidial viability to the tune of 80.63% when compared to microcrystalline cellulose 6% and acacia gum, Arabic 5% which exhibited 30.67–51.50% viability. The investigation therefore concluded that L. saksenae is a promising bioagent for the management of root mealybugs with high speed of action unlike the other microbes. Biopellets formulated at 109 conidia/ml using talc + chitin + 6% CMC at 15% moisture content were found to retain its viability and virulence during a storage period of three months, under ambient conditions.

Impact of direct and indirect ingestion of six systemic pesticides on the parasitoid Anagyrus vladimiri

Anagyrus vladimiri (Hymenoptera: Encyrtidae) is the main parasitoid of Planococcus citri (Hemiptera: Pseudococcidae), which is one of the most important pests of citrus crops in the Mediterranean Basin. Pesticide residue on trees and in the nectar of wildflowers growing in citrus orchards might cause side effects in beneficial insects. In the present study, we assessed the effects of six systemic pesticides (acetamiprid, dimethoate, cyantraniliprole, flupyradifurone, spirotetramat and sulfoxaflor) on the survival and progeny of A. vladimiri. Anagyrus vladimiri fed on the pesticide solutions and on the nectar of Fagopyrum esculentum Moench plants that had been watered with a solution containing these pesticides. Acetamiprid, dimethoate, flupyradifurone and sulfoxaflor increased female mortality more than the control (water) after 6h; after A. vladimiri consumed these pesticides, female mortality ranged from 62% to 73%. Cyantraniliprole had no immediate toxic effect on parasitoid survival but caused mortality after 15 days. All tested pesticides except flupyradifurone and spirotetramat reduced parasitoid progeny. After six days of feeding on F. esculentum nectar of plants watered with a pesticide solution, significantly increased female mortality was observed with dimethoate (96%), spirotetramat (80%), acetamiprid (62%), cyantraniliprole (62%) and sulfoxaflor (50%). Progeny was reduced in females that fed on plants treated with spirotetramat and dimethoate. These results demonstrate that some of these insecticides can have lethal or sublethal effects on A. vladimiri by both routes of exposure, via direct or indirect pesticide consumption through the nectar of treated plants.

Using eDNA to play whack-a-mole with invasive species in green yard waste.

As large cities begin to overrun their landfill capacities, they begin to look for alternative locations to handle the waste stream. Seeing an opportunity to bring in revenue, rural communities offer to handle municipal waste in their landfills. However, many rural communities are also places of agricultural production, which are vulnerable to attacks by invasive insect species, which could be present in green yard waste, the component of municipal waste most likely to contain agriculturally harmful insect species. We used environmental DNA (eDNA) to determine whether green yard waste could be a pathway for invasive insect species to enter and establish in the landfill-receiving agricultural community. We identified several target species that could be in green yard waste coming from Vancouver, BC, Canada, to Central Washington State, USA. We sampled green yard waste from 3 sites every 2 weeks from June to October in 2019 and 2020. DNA was extracted from the nearly 400 samples and subjected to amplification with COI barcoding primers followed by sequencing to identify target insects in the samples. Sequence analyses identified 3 species from the target list: 2 species that are pests of deciduous tree fruits and a generalist root-feeding crop pest. This eDNA technique was useful in identifying potential invasive species in green yard waste and may prove to be an important tool informing policy on the movement of biological material across borders and stemming the spread of invasive species.

Breeding for Resistance against Pest and Diseases in Tomatoes: A Review

Diseases and pests have a substantial effect on tomato production, greatly affecting both the quantity and quality of this crucial vegetable crop. Although fungicides and insecticides have been important in controlling plant diseases and pests, their excessive usage raises significant environmental issues. Vegetable breeders are increasingly concentrating on developing cultivars with natural tolerance to biotic stresses to promote sustainability and environmental friendliness. The change in focus is intended to cultivate tomato cultivars with inherent resistance to diseases and pests, hence decreasing the need for chemical treatments. Advancements in creating high-yielding genetically resistant tomato cultivars are a result of detailed study on the genetic basis of pest and disease resistance in tomato crops, as well as the complex interactions between the host plant and pathogens. For effective breeding programs and pre-breeding activities, scientists and breeders must have access to sources of resistance and a thorough grasp of the genetic complexities involved. This requires examining the genetic composition of both the tomato plants and the different infections that are impacting them. Breeders may generate tomato cultivars with strong resistance to common diseases and pests by using the inherent defensive mechanisms found in certain tomato types via selective crossing. Continuing to study how hosts and pathogens interact and the molecular processes involved in resistance is crucial. This information offers vital insights on how to improve and expand resistance, leading to the creation of cultivars with long-lasting and wide-ranging resistance. Currently, the emphasis on breeding is a proactive and sustainable strategy for transfer of resistances in high yielding tomato cultivars. Researchers aim to develop tomato cultivars that provide high yield and demonstrate tolerance to changing disease and pest stresses by integrating genetic knowledge with sophisticated breeding methods. This comprehensive method protects tomato crops and encourages environmental sustainability by decreasing the need on chemical inputs in agriculture.

Acute toxicity effects of pesticides on predatory snout mites (Trombidiformes: Bdellidae).

Predatory mites biologically control a range of arthropod crop pests and are often central to agricultural IPM strategies globally. Conflict between chemical and biological pest control has prompted increasing interest in selective pesticides with fewer off-target impacts on beneficial invertebrates, including predatory mites. However, the range of predatory mite species included in standardized pesticide toxicity assessments does not match the diversity of naturally occurring species contributing to biocontrol, with most testing carried out on species from the family Phytoseiidae (Mesostigmata). Here, we aim to bridge this knowledge gap by investigating the impacts of 22 agricultural pesticides on the predatory snout mite, Odontoscirus lapidaria (Kramer) (Trombidiformes: Bdellidae). Using internationally standardized testing methodologies, we identified several active ingredients with minimal impact on O. lapidaria mortality, including Bacillus thuringiensis,nuclear polyhedrosis virus, flonicamid, afidopyropen, chlorantraniliprole, and cyantraniliprole, which may therefore be good candidates for IPM strategies utilizing both chemical and biological control. Comparison of our findings with previous studies on Phytoseiid mites reveals important differences in responses to a number of chemicals between predatory mite families, including the miticides diafenthiuron and abamectin, highlighting the risk of making family-level generalizations from acute toxicity assessments. We also tested the impacts of several pesticides on a second Bdellidae species (Trombidiformes: Bdellidae)and found differences in the response to chlorpyrifos compared with O. lapidaria, further highlighting the taxon-specific nature of nontarget toxicity effects.

Discovering allatostatin type-C receptor specific agonists

Currently, there is no pesticide available for the selective control of the pine processionary moth (Thaumetopoea pityocampa-specific), and conventional methods typically rely on mechanical techniques such as pheromone traps or broad-spectrum larvicidal chemicals. As climate change increases the range and dispersion capacity of crop and forest pests, outbreaks of the pine processionary occur with greater frequency and significantly impact forestry and public health. Our study is carried out to provide a T. pityocampa-specific pesticide targeting the Allatostatin Type-C Receptor (AlstR-C). We use a combination of computational biology methods, a cell-based screening assay, and in vivo toxicity and side effect assays to identify, for the first time, a series of AlstR-C ligands suitable for use as T. pityocampa-specific insecticides. We further demonstrate that the novel AlstR-C targeted agonists are specific to lepidopteran larvae, with no harmful effects on coleopteran larvae or adults. Overall, our study represents an important initial advance toward an insect GPCR-targeted next-generation pesticide design. Our approach may apply to other invertebrate GPCRs involved in vital metabolic pathways.

Immature Stages and Chaetotaxy of <i>Spodoptera Litura</i> (F)

This study explores the chaetotaxy, and biology of immature stages of the tobacco cutworm, Spodoptera litura (F) which is a major pest of crops. From Himachal Pradesh, apricot (Prunus armeniaca), curly dock weed (Rumex crispus), apple (Malus domestica) and plum (Prunus salicina) are reported as its new hosts. It takes 29-39.32 days to complete its lifecycle with six larval instars. The chaetotaxy of final instar and pupal morphology are described and illustrated.

Tritrophic Interactions Mediated by Zoophytophagous Predator-Induced Host Plant Volatiles

The zoophytophagous mirid predator Nesidiocoris tenuis and the ectoparasitoid Stenomesius japonicus are important biological control agents for several agricultural pests including the invasive leafminer, Phthorimaea absoluta, a destructive pest of Solanaceous crops especially tomato in sub-Saharan Africa. However, little is known about how feeding by N. tenuis can influence the tritrophic interactions in the tomato plant. Here, we tested the hypothesis that N. tenuis phytophagy would influence the tritrophic olfactory interactions between the host plant tomato and pest, predator, and parasitoid. In olfactometer assays, P. absoluta females and N. tenuis adults were both attracted to constitutive volatiles released by the tomato plant. Whereas females of P. absoluta avoided volatiles released by N. tenuis-infested plants, S. japonicus females and N. tenuis adults were attracted to the induced volatiles. In coupled gas chromatography-electroantennographic detection (GC-EAD) recordings of intact and N. tenuis-infested plant volatiles, antennae of P. absoluta and S. japonicus females both detected eight components, whereas N. tenuis adults detected seven components which were identified by GC-mass spectrometry (GC-MS) as terpenes and green leaf volatiles (GLVs). Dose-response olfactometer bioassays revealed that the responses of P. absoluta, N. tenuis, and S. japonicus varied with the composition and concentration of blends and individual compounds tested from N tenuis-induced volatiles. Females of P. absoluta showed no preference for an eight-component blend formulated from the individual repellents including hexanal, (Z)-3-hexenyl butanoate, and δ-elemene identified in the volatiles. On the other hand, S. japonicus females were attracted to an eight-component blend including the attractants (E)-2-hexenal, (Z)-3-hexenol, methyl salicylate, β-phellandrene, and (E)-caryophyllene. Likewise, N. tenuis adults were attracted to a seven-component blend including the attractants β-phellandrene, δ-elemene, and (E)-caryophyllene identified in the volatiles. Our findings suggest that there is potential for the use of terpenes and GLVs to manage the insects in the tritrophic interaction.

Title

Abstract

Development and Validation of a Resistance Management Model for the Soybean Cyst Nematode, Heterodera glycines.

Plant-parasitic nematodes are a key yield-limiting pest of crops around the world. Deployment of plant resistance genes are an important management tactic for many economically important plant-parasitic nematodes. The selection for virulence in nematode populations is a major threat to the effectiveness of resistance gene-based management. Little research has gone into resistance management modelling despite the importance of both plant-parasitic nematodes and resistance genes for their management. In this paper, we report on a cyst nematode resistance management model created to explore the factors which are most important for determining the durability of resistance genes to this important family of plant-parasitic nematodes. The relative dominance of virulence expression, the level of inbreeding, and the number of generations per cropping season were the most important factors in predicting resistance gene durability. Aspects of cyst nematode biology that reduce the number of generations per season for a portion of the population had a much smaller effect on the durability of resistance genes. These factors included delayed hatching within a season and early dormancy. The accuracy and utility of the model was tested using the soybean cyst nematode (SCN) rhg1-mediated resistance system. The model accurately predicted the rate at which virulence to the rhg1b resistance gene developed in Iowa over a two-decade period. The model suggested resistance gene pyramids as the most durable management solution for SCN with multiple possible avenues to obtain acceptable efficacy and durability.

Genomic analyses of a new baculovirus isolated from the wheat armyworm, Mythimna sequax (Franclemont) (Lepidoptera: Noctuidae)

We report the genomic analysis of a novel alphabaculovirus, Mythimna sequax nucleopolyhedrovirus isolate CNPSo-98 (MyseNPV-CNPSo-98), obtained from cadavers of the winter crop pest, Mythimna sequax Franclemont (Lepidoptera: Noctuidae). The insects were collected from rice fields in Southern Brazil in the 1980′s and belongs to the ‘EMBRAPA-Soja’ Virus Collection. High-throughput sequencing reads of DNA from MyseNPV occlusion bodies and assembly of the data yielded an AT-rich circular genome contig of 148,403 bp in length with 163 annotated opening reading frames (ORFs) and four homologous regions (hrs). Phylogenetic inference based on baculovirus core protein sequence alignments indicated that MyseNPV-CNPSo-98 is a member of Alphabaculovirus genus that clustered with other group II noctuid-infecting baculoviruses, including viruses isolated from Helicoverpa armigera and Mamestra spp. The genomes of the clade share strict collinearity and high pairwise nucleotide identity, with a common set of 149 genes, evolving under negative selection, except a bro gene. Branch lengths and Kimura-2-parameter pairwise nucleotide distances indicated that MyseNPV-CNPSo-98 represents a distinct lineage that may not be classified in any of the currently listed species in the genus.

Identification, synthesis, and field evaluation of components of the female-produced sex pheromone of Helopeltis cinchonae (Hemiptera: Miridae), an emerging pest of tea.

Helopeltis cinchonae (Hemiptera: Miridae) is a major pest of tea plantations in Asia. Conventional control of pests with pesticides is unsustainable. Therefore, safe and eco-friendly alternatives, such as pheromones, are required to manage the pest. In gas chromatography-electroantennographic detection (GC-EAD) analysis of whole-body extracts of virgin female H. cinchonae, two compounds elicited electroantennogram (EAG) responses from male antennae. These were identified as hexyl (R)-3-acetoxybutyrate and (R)-1-acetoxy-5-butyroxyhexane using gas chromatography-mass spectrometry (GC-MS) analysis compared to synthetic compounds. This is the first study to report 1-acetoxy-5-butyroxyhexane as an insect pheromone component. The synthetic compounds elicited dose-dependent EAG responses from the antennae of male H. cinchonae. In two field trapping experiments, the individual compounds were highly attractive to male H. cinchonae when dispensed from polyethylene vials. However, higher catches were obtained with blends of the two compounds in a 1:10 ratio. The blend of racemic compounds was as attractive as the blend of (R)-enantiomers. We reported that 1-acetoxy-5-butyroxyhexane and hexyl 3-acetoxybutyrate are components of the female-produced sex pheromone of H. cinchonae, but further work is required on the blend and loading of pheromone and on trap design to provide an optimized system for monitoring and control of this pest. The results may also facilitate the identification of the pheromones of other Helopeltis species, which are major pests in many crops. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Agromet Advisories to Mitigate the Effects of Aberrant Weather in Himachal Pradesh

Weather is a pivotal factor in agricultural production, influencing crop growth, disease and pest occurrences, water and fertilizer needs, and the effectiveness of cultural and preventive measures. Extreme weather events can cause physiological stress, physical damage, soil erosion, and crop quality degradation. In India, agriculture's vulnerability to adverse weather is a significant concern, with natural disasters like floods, droughts, and cyclones leading to crop failure, food insecurity, and economic impacts. To mitigate these challenges, Agrometeorological Advisory Services (AAS) play a crucial role in providing farmers with weather-based advisories to manage agricultural risks. The Integrated Agro-Meteorological Advisory Service (IAAS), run by the Indian Ministry of Earth Sciences and the India Meteorological Department (IMD), offers district-level weather forecasts and agromet advisories to support farmers in adapting to weather fluctuations. These advisories cover various weather-related risks, including cold injury and frost, high temperatures, wind damage, hailstorms, and floods. Sample advisories suggest measures like irrigation for frost protection, mulching to reduce heat stress, and shelter belts to mitigate wind damage. Effective dissemination of advisories involves communication through electronic media, Krishi Vigyan Kendras (Agriculture Science Centres), and Kisan (Farmer) Call Centres. Thrust areas for enhancing AAS include improved scientific understanding, advanced monitoring and prediction of severe weather events, satellite-based communication technologies, and real-time forecasting. By integrating these strategies, farmers can better prepare for extreme weather and mitigate its impact on agriculture.

Serine proteinase inhibitors from Nicotiana benthamiana, a nonpreferred host plant, inhibit the growth of Myzus persicae (green peach aphid).

The green peach aphid (Myzus persicae) is a severe agricultural crop pest that has developed resistance to most current control methods, requiring the urgent development of novel strategies. Plant proteinase inhibitors (PINs) are small proteins that protect plants against pathogens and/or herbivores, likely by preventing efficient protein digestion. We identified 67 protease genes in the transcriptomes of three M. persicae lineages (USDA-Red, G002 and G006). Comparison of gene expression levels in aphid guts and whole aphids showed that several proteases, including a highly expressed serine protease, are significantly overexpressed in the guts. Furthermore, we identified three genes encoding serine protease inhibitors (SerPIN-II1, 2 and 3) in Nicotiana benthamiana, which is a nonpreferred host for M. persicae. Using virus-induced gene silencing (VIGS) with a tobacco rattle virus (TRV) vector and overexpression with a turnip mosaic virus (TuMV) vector, we demonstrated that N. benthamiana SerPIN-II1 and SerPIN-II2 cause reduced survival and growth, but do not affect aphid protein content. Likewise, SerPIN-II3 overexpression reduced survival and growth, and serpin-II3 knockout mutations, which we generated using CRISPR/Cas9, increased survival and growth. Protein content was significantly increased in aphids fed on SerPIN-II3 overexpressing plants, yet it was decreased in aphids fed on serpin-II3 mutants. Our results show that three PIN-IIs from N. benthamiana, a nonpreferred host plant, effectively inhibit M. persicae survival and growth, thereby representing a new resource for the development of aphid-resistant crop plants. © 2024 Society of Chemical Industry.

Cellular dynamics of host − parasitoid interactions: Insights from the encapsulation process in a partially resistant host

Cotesia typhae is an eastern African endoparasitoid braconid wasp that targets the larval stage of the lepidopteran stem borer, Sesamia nonagrioides, a maize crop pest in Europe. The French host population is partially resistant to the Makindu strain of the wasp, allowing its development in only 40% of the cases. Resistant larvae can encapsulate the parasitoid and survive the infection. This interaction provides a very interesting frame for investigating the impact of parasitism on host cellular resistance. We characterized the parasitoid ovolarval development in a permissive host and studied the encapsulation process in a resistant host by dissection and histological sectioning compared to that of inert chromatography beads. We measured the total hemocyte count in parasitized and bead-injected larvae over time to monitor the magnitude of the immune reaction. Our results show that parasitism of resistant hosts delayed encapsulation but did not affect immune abilities towards inert beads. Moreover, while bead injection increased total hemocyte count, it remained constant in resistant and permissive larvae. We conclude that while Cotesia spp virulence factors are known to impair the host immune system, our results suggest that passive evasion could also occur.