Effect of PGPR on population growth parameters of cotton aphid

Plant-growth-promoting rhizobacteria (PGPR) help plants by increasing plant growth and defending them against pathogens and pests. There is considerable research supporting the use of these bacteria in plant pathogens management, but the number of research papers that have focused on their effect on insect pests control is quite few. In this research, we examined the ability of four native strains of Pseudomonas fluorescens to manage the cotton aphid, Aphis gossypii, on greenhouse-grown cucumbers in Iran. The strains UTPF (University of Tehran Pseudomonas fluorescens) 68, UTPF1, UTPF6 and PF169 of P. fluorescens were used as seed treatment to evaluate their impact on both cucumber growth and cotton aphid population growth parameters. The strains UTPF68 and PF169 of this bacterium influenced phenology of cucumber by decreasing the Growing Degree Days of flowering period. Also, the plants treated with these bacterial strains had a significant increase in yield weight of approximately 58%. In the other part of the study, various effects on developmental parameters of aphid were recorded among bacterial strains, but only PF169 caused significant decreasing effect on r_m value of aphid, which is the most important factor in aphid’s life table. We conclude that the PF169 treatment had significant negative effects on population growth rate of A. gossypii. The PF169 could be reliable in a control programme for A. gossypii on cucumber plants in greenhouses.     

Vertical distribution of some piercing sucking insects on some roselle varieties in Egypt and the role of amino acids concentration in infestation

Abstract

The cotton aphid, Aphis gossypii Glover was found to be the only aphid species infesting the tested roselle varieties (Sudani, Masri and White), Hibiscus sabdariffa L. which were cultivated in El-Kanater El-khayria (about 30 km north Cairo) as ex situ old land. The vertical distribution of the whitefly, Bemisia tabaci (Genn.); the leafhopper, Empoasca spp. and the pink hibiscus mealy bug, Maconellicoccus hirsutus Green, as insect pests attacking this crop had been studied. Moreover, certain morphological characters and amino acids concentrations in the three varieties of roselle, were obtained. The obtained results indicated that the experimental insect pests severely attacked leaves of the stem nodes from the 8th to the 11th (counting from the top of the plant), whereas whitefly were more abundant on these nodes. All tested insect species were less abundant on the 4th stem node. This may be due to the extensive existence of gland hairs, that excrete some compound especially phenols that might prevent the insects from reproducing on the leaves. The opposite was, however, true for M. hirsutus as it did not attack Sudani and Masri varieties but the infestation occurred at the highest level on the White variety.     

Assessment of cotton aphids, Aphis gossypii, and their natural enemies on aphid-resistant and aphid-susceptible wheat varieties in a wheat–cotton relay intercropping system

The cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae), is an important cotton pest in northern China, especially in the seedling stage of cotton. After large scale commercial use of transgenic Bt cotton, cotton aphids became one of the most important cotton pests. A 2‐year study was conducted to evaluate the role of four winter wheat varieties that were resistant or susceptible to wheat aphid, Sitobion avenae Fabricius (Homoptera: Aphididae), in conserving arthropod natural enemies and suppressing cotton aphids in a wheat–cotton relay intercropping system in northern China. The results indicated that wheat–cotton intercropping preserved and augmented natural enemies more than a monoculture of cotton. The density of natural enemies in cotton was significantly different among relay‐intercropping fields with different wheat varieties. The highest density of natural enemies and low cotton aphid populations were found in the treatment of cotton in relay intercropped with the wheat variety Lovrin10, which is susceptible to wheat aphid. The lowest density of predators and parasitoids associated with high cotton aphid populations were found with the wheat variety KOK1679, which is resistant to wheat aphid. The results showed that wheat varieties that are susceptible or moderately resistant to wheat aphid might reduce cotton aphids more effectively than an aphid‐resistant variety in the intercropping system by enhancing predators to suppress cotton aphids during the cotton seedling stage.     

Aphid Honeydew Quality as a Food Source for Parasitoids Is Maintained in Bt Cotton

Bt-transgenic cotton has proven to be highly efficient in controlling key lepidopteran pests. One concern with the deployment of Bt cotton varieties is the potential proliferation of non-target pests. We previously showed that Bt cotton contained lower concentrations of insecticidal terpenoids as a result of reduced caterpillar damage, which benefited the aphid Aphis gossypii. It is thus important that non-target herbivores are under biological control in Bt cotton fields. The induction or lack of induction of terpenoids could also influence the quality of aphid honeydew, an important food source for beneficial insects. We therefore screened A. gossypii honeydew for cotton terpenoids, that are induced by caterpillars but not the aphids. We then tested the influence of induced insect-resistance of cotton on honeydew nutritional quality for the aphid parasitoid Lysiphlebus testaceipes and the whitefly parasitoid Eretmocerus eremicus. We detected the cotton terpenoids gossypol and hemigossypolone in A. gossypii honeydew. Although a feeding assay demonstrated that gossypol reduced the longevity of both parasitoid species in a non-linear, dose-dependent manner, the honeydew was capable of sustaining parasitoid longevity and reproduction. The level of caterpillar damage to Bt and non-Bt cotton had no impact on the quality of honeydew for the parasitoids.These results indicate that the nutritional quality of honeydew is maintained in Bt cotton and is not influenced by induced insect resistance.     

Seasonal Phenology and Species Composition of the Aphid Fauna in a Northern Crop Production Area

Background

The species diversity of aphids and seasonal timing of their flight activity can have significant impacts on crop production, as aphid species differ in their ability to transmit plant viruses and flight timing affects virus epidemiology. The aim of the study was to characterise the species composition and phenology of aphid fauna in Finland in one of the northernmost intensive crop production areas of the world (latitude 64°).

Methodology/Principal Findings

Flight activity was monitored in four growing seasons (2007–010) using yellow pan traps (YPTs) placed in 4–8 seed potato fields and a Rothamsted suction trap. A total of 58,528 winged aphids were obtained, identified to 83 taxa based on morphology, and 34 species were additionally characterised by DNA barcoding. Seasonal flight activity patterns analysed based on YPT catch fell into three main phenology clusters. Monoecious taxa showed early or middle-season flight activity and belonged to species living on shrubs/trees or herbaceous plants, respectively. Heteroecious taxa occurred over the entire potato growing season (ca. 90 days). Abundance of aphids followed a clear 3-year cycle based on suction trap data covering a decade. Rhopalosiphum padi occurring at the end of the potato growing season was the most abundant species. The flight activity of Aphis fabae, the main vector of Potato virus Y in the region, and Aphis gossypii peaked in the beginning of potato growing season.

Conclusions/Significance

Detailed information was obtained on phenology of a large number aphid species, of which many are agriculturally important pests acting as vectors of plant viruses. Aphis gossypii is known as a pest in greenhouses, but our study shows that it occurs also in the field, even far in the north. The novel information on aphid phenology and ecology has wide implications for prospective pest management, particularly in light of climate change.     

Influence of vermicompost and cucumber cultivar on population growth of Aphis gossypii Glover

The melon aphid, Aphis gossypii Glover (Hem., Aphididae), is one of the most important pests of cucumber throughout the world. This aphid has a short generation time and high fecundity that result in an enormous reproductive potential, especially in cucumber‐growing greenhouses. Vermicomposts, which are produced by exploiting interactions between earthworms and microorganisms, may enhance plant growth and plant resistance against some pests and disease. In this study, the effects of vermicompost and cucumber cultivar (Cucumis sativus L.) on infestation levels with A. gossypii were evaluated. We conducted a factorial experiment with two cucumber cultivars (Royal and Storm) and five concentrations of vermicompost in the soil, including 0% (control), 10%, 20%, 30% and 50%, employing a randomized complete block design with four replicates. The experiment was conducted in a growth chamber at 25 ± 2°C, 65 ± 10% RH and a photoperiod of 14 L: 10 D h. The number of aphids was counted 3, 5, 7, 9, 12, 15, 18 and 21 days after infestation of cucumber seedlings by aphids. We found that in all vermicompost‐amended treatments, aphid numbers were lower than when plants were grown in soil without any vermicompost. The highest and lowest aphid counts occurred in the control treatment on cucumbers of the Royal cultivar and in the 30% and 50% vermicompost treatments on the storm cultivar, respectively. Overall, our study showed that the application of vermicompost has a high potential for reducing A. gossypii populations in cucumber cultures.     

Alatae production and population increase of aphid vectors on virus-infected host plants

Summary Zucchini yellow mosaic virus (ZYMV) and Aphis gossypii Glover are two components of a recently identified plant-parasite system that provides an excellent opportunity to study interrelations between a virus and a vector that share the same host, but have no direct physiological interaction. In a field experiment we documented numbers of alate and apterous A. gossypii on healthy Cucurbita pepo and on plants inoculated with virus 0, 7, 14, and 21 days before aphid infestation. When plants were inoculated and infested simultaneously, more than twice as many alatae were produced after 20 days of colony growth than on any other treatment. This indicates that properties unique to the early stages of viral infection somehow stimulated wing formation. Because it is spread by the activities of alatae, virus dispersal would be greater as a result of these properties. Developmental rate, total numbers of aphids, and numbers of alatae and apterae decreased as the time between virus inoculation and aphid colonization increased.     

Blockage of stylet tips as the mechanism of resistance to virus transmission by Aphis gossypii in melon lines bearing the Vat gene

Aphis gossypii is the main virus vector in muskmelon crops. The melon gene Vat confers resistance to non‐persistent virus transmission by this aphid. The mechanism of this resistance is not well understood, but no relationship has been detected between resistance and the probing behaviour of aphids on resistant plants. Results presented here suggest that temporary blockage of aphid stylet tips preventing virus particle release may explain the resistance conferred by Vat gene. We performed experiments in which viruliferous aphids were allowed to probe different sequences of resistant (Vat‐bearing) and/or susceptible melon plants. The results demonstrated that A. gossypii inoculates Cucumber mosaic virus (CMV) efficiently in susceptible plants having previously probed resistant plants, showing that the resistance mechanism is reversible. Furthermore, the infection rate obtained for susceptible plants was the same (25%) regardless of whether the transmitting aphid had come directly from the CMV source or had subsequently probed on resistant plants. This result suggests that virus is not lost from stylet to plant during probing of resistant plants, supporting the temporary blockage hypothesis. We also found that the ability of Myzus persicae to transmit CMV is noticeably reduced after probing on resistant plants, providing evidence that this aphid species also responds to the presence of the Vat gene. Finally, we also found that in probes immediately after virus acquisition M. persicae inoculates resistant plants with CMV more efficiently than susceptible plants, perhaps because the Vat gene product induces increased salivation by this aphid.     

Foraging behaviour of the parasitoid Lysiphlebus testaceipes (Hymenoptera: Braconidae) in response to plant volatiles,with reference to biocontrol of aphids in peri-urban vegetable production systems

Foraging behaviour of Lysiphlebus testaceipes was studied in a Y-tube olfactometer. Naïve females responded to the Aphis gossypii/eggplant complex on which they had been reared, but did not show a preference for this aphid/plant complex over an uninfested eggplant, an eggplant that had been damaged by the aphid or an A. gossypii/okra complex. Females that had been allowed to forage on the A. gossypii/eggplant complex before being tested in the olfactometer showed a strong preference for an uninfested eggplant over an uninfested okra plant and for the A. gossypii/eggplant complex over an A. gossypii/okra complex, indicating that they had learned to associate eggplant-derived volatiles with host availability. When females that had been reared on the A. gossypii/eggplant complex were tested after foraging experience on the A. gossypii/okra complex, they did not show a preference for either complex, suggesting that they still retained a memory of the cues associated with the complex on which they had been reared. The efficiency of L. testaceipes as a biological control agent in peri-urban vegetable production, such as the Cuban organoponics system, potentially could be improved by producing and releasing females behaviourally primed to prefer specific host/plant complexes.     

Forecasting virus disease in seed potatoes using flight activity data of aphid vectors

We compiled data from the Swiss seed certification programme for the country‐wide incidence of viruses in seed potato crops for the years 1989–2012. Model selection techniques were used to regress year‐to‐year variation in the incidence of potato viruses – largely dominated by Potato virus Y (PVY) – in three susceptible varieties against the abundance of virus vectors (winged aphids), obtained in a suction trap, to identify the most important vector species. The ultimate aim of this study was to develop a decision‐support system capable of forecasting virus spread during the current season using trap data of aphid flights. The average virus incidence in the varieties Bintje, Sirtema and Charlotte varied considerably among years, ranging from 1.0% in 2009 to 13.6% in 1989 (N = 150–611 seed lots per year). A linear regression model including the cumulative sums (until mid‐June) of two aphid species (Brachycaudus helichrysi and Phorodon humuli) as predictor variables for virus disease was remarkably well supported by the data (R² = 0.86). Similarly, using counts of B. helichrysi alone resulted in a good model fit (R² = 0.81). Cross‐validation revealed high predictive accuracy of the model. Although prediction root mean squared errors (RMSE) calculated for different timings of forecasts were high for extremely early forecasts, they rapidly declined for forecasts conducted by the end of May (i.e. 2–4 weeks after potato emergence). Winter temperature (January–February) was positively correlated with the abundance of B. helichrysi in early summer as well as with post‐harvest virus incidence. Remarkably, the abundance of Myzus persicae, often considered the main vector of PVY, was not correlated with virus incidence. Taken together, our analysis suggests that the early migrating aphid B. helichrysi, rather than M. persicae, is the main vector of PVY in Switzerland, and that suction trap data are useful for the design of decision‐support systems aimed to optimise virus control in seed potato production.     

Control of Aphis gossypii and Myzus persicae (Hemiptera: Aphididae) by a flightless strain of Harmonia axyridis (Coleoptera: Coccinellidae) on green pepper plants in open fields

The cotton aphid Aphis gossypii Glover and the green peach aphid Myzus persicae (Sulzer) are economically important pests with a worldwide distribution. We evaluated the efficacy of releasing a flightless adult strain of the multicolored Asian lady beetle Harmonia axyridis (Pallas) as a control measure against these aphids on green pepper plants in open fields. Flightless H. axyridis adults were observed on the green pepper plants in the releasing plots throughout the experimental period and were found to be effective biocontrol agents, markedly decreasing the numbers of aphids. These results suggest that adults of this flightless strain of H. axyridis are effective in controlling aphids on green pepper plants in open fields.     

Nematophagous fungus <Emphasis Type="Italic">Paecilomyces lilacinus</Emphasis> (Thom) Samson is also a biological agent for control of greenhouse insects and mite pests

Pathogenicity of nematophagous fungus Paecilomyces lilacinus (Thom) Samson in control of the most destructive greenhouse pests such as: greenhouse whitefly, Trialeurodes vaporariorum, glasshouse red spider mite, Tetranychus urticae, the cotton aphid, Aphis gossypii and western flower thrips, Frankliniella occidentalis was examined in laboratory and pot experiments. The fungus showed the greatest efficacy in controlling winged and wingless forms of the cotton aphid. The cotton aphid’s population was almost totally eliminated. In controlling the greenhouse whitefly, P. lilacinus was most successful when applied against nymphal growth stages (L₃-L₄). Control of the western flower thrips was most efficient against prepupal and pupal stages when the fungus was applied as a water spore suspension to the soil. When the fungus was applied at temperatures below 10 °C, it was able to reduce a glasshouse red spider mite population by 60%.     

Spatial and temporal spread of Citrus tristeza virus and its aphid vectors in the North western area of Morocco

First report of Citrus tristeza virus (CTV,Closterovirus) in Morocco datesback to 1961 in collections of citrus varieties. An exhaustive survey of citrus in the north of the country in 2009 revealed that CTV was spread all over the citrus production area. We attempted to evaluate the relative contribution of different aphid species in the spread of CTV disease in a Citrus reticulata orchard at the Loukkous region during 2 years (2012 and 2013). The overall CTV incidence estimated in the experimental site increased from 17.8% in 2012 to 31.15% in 2013. The most abundant aphid species colonising clementine trees was Aphis spiraecola and A. gossypii. Both aphid species reached their maximum peaks during the spring season. The rate of viruliferous aphids, estimated by real‐time RT‐PCR of single aphid, revealed that 35.4% of winged A. gossypii and 28.8% of winged A. spiraecola were viruliferous, confirming a high inoculum pressure in the area surrounding the experimental site. The aphid species Toxoptera citricida, which is able to transmit the aggressive isolates of CTV, was not found in the Loukkous region. The study of the spatial distribution of the CTV showed that in general, the disease was randomly distributed in the field. Overall, the results seem to indicate that A. spiraecola may be considered as the major aphid species contributing to CTV spread in our experimental conditions. The prevalence of mild strains in the region and the high level of aphid flight activity could explain the rapid evolution of CTV incidence in the experimental area.     

Dispersal strategies of phytophagous insects at a local scale: adaptive potential of aphids in an agricultural environment

Background  

The spread of agriculture greatly modified the selective pressures exerted by plants on phytophagous insects, by providing these insects with a high-level resource, structured in time and space. The life history, behavioural and physiological traits of some insect species may have evolved in response to these changes, allowing them to crowd on crops and to become agricultural pests. Dispersal, which is one of these traits, is a key concept in evolutionary biology but has been over-simplified in most theoretical studies. We evaluated the impact of the local-scale dispersal strategy of phytophagous insects on their fitness, using an individual-based model to simulate population dynamics and dispersal between leaves and plants, by walking and flying, of the aphid Aphis gossypii, a major agricultural pest, in a melon field. We compared the optimal values for dispersal parameters in the model with the corresponding observed values in experimental trials.     

Efficacy of three plant essential oils,Azadirachta indica (Adr. Juss.), Eucalyptus camaldulensis (Dehn.) and Laurus nobilis (L.) on mortality cotton aphids,Aphis gossypii Glover (Hem: Aphididae)

The cotton aphid, Aphis gossypii Glover (Hem: Aphididae), is one of the most injurious pests of fruits, vegetables and ornamental plants worldwide, both outdoor and indoor. Currently, the main method of control of this pest is through application of pesticides which is mostly accompanied by the resistance of the pest against pesticide(s). The resurgence of resistant aphid populations brings about further contamination of foodstuff and environment. Essential oils obtained from the aerial parts of plants may have the potential to be an alternative to synthetic pesticides, since they have been demonstrated to possess a wide range of bioactivities against insects and mites. So, the aim of the current study was to investigate the effect of essential oils extracted from three different plants namely: Azadirachta indica Adr. Juss. (Meliaceae), Eucalyptus camaldulensis Dehn. (Myrtaceae) and Laurus nobilis L. (Lauraceae) against A. gossypii. The LC₅₀ values of essential oils of A. indica, E. camaldulensis and L. nobilis against A. gossypii were 1.96, 2.28 and 3.16?μl L^?1 air, respectively. This shows that A. indica possesses the highest lethal activity whereas L. nobilis the lowest. These data suggest that essential oils of all the three plants have the potential to be employed in the pest management programmes designed for a control of A. gossypii under greenhouse conditions.     

How does atmospheric elevated CO2 affect crop pests and their natural enemies? Case histories from China

Abstract Global atmospheric CO₂ concentrations have risen rapidly since the Industrial Revolution and are considered as a primary factor in climate change. The effects of elevated CO₂ on herbivore insects were found to be primarily through the CO₂‐induced changes occurring in their host plants, which then possibly affect the intensity and frequency of pest outbreaks on crops. This paper reviews several ongoing research models using primary pests of crops (cotton bollworm, whitefly, aphids) and their natural enemies (ladybeetles, parasitoids) in China to examine insect responses to elevated CO₂. It is generally indicated that elevated CO₂ prolonged the development of cotton bollworm, Helicoverpa armigera, a chewing insect, by decreasing the foliar nitrogen of host plants. In contrast, the phloem‐sucking aphid and whitefly insects had species‐specific responses to elevated CO₂ because of complex interactions that occur in the phloem sieve elements of plants. Some aphid species, such as cotton aphid, Aphis gossypii and wheat aphid, Sitobion avenae, were considered to represent the only feeding guild to respond positively to elevated CO₂ conditions. Although whitefly, Bemisia tabaci, a major vector of Tomato yellow leaf curl virus, had neutral response to elevated CO₂, the plants became less vulnerable to the virus infection under elevated CO₂. The predator and parasitoid response to elevated CO₂ were frequently idiosyncratic. These documents from Chinese scientists suggested that elevated CO₂ initially affects the crop plant and then cascades to a higher trophic level through the food chain to encompass herbivores (pests), their natural enemies, pathogens and underground nematodes, which disrupt the natural balance observed previously in agricultural ecosystems.     

Association between Aphis gossypii genotype and phenotype on melon accessions

Development of molecular markers has allowed the characterization of several host–aphid interactions. We investigated the usefulness of microsatellite markers to characterize the plant resistance interaction in the model Aphis gossypii/Cucumis melo. Six aphid clones, collected in different localities and years and belonging to two multilocus genotypes (MLGs) based on eight microsatellite markers, were phenotyped on a set of 33 melon accessions, some of them known to carry the Vat gene. Three parameters were used: acceptance of plant, ability to colonize the plant and resistance to virus when inoculated by aphids. Concordance and correlation analyses showed that aphid clones sharing a same MLG exhibited a very agreeable phenotype on the set of accessions for acceptance of plant and resistance to virus when inoculated by aphids. From host point of view, melon accessions were grouped into four clear categories, resistant to aphids of both MLGs, only resistant to the NM1 MLG, only resistant to the C9 MLG, susceptible to both MLGs and another group of unclear characteristics. The four categories revealed different patterns of virulence for NM1 and C9 MLGs that are likely controlled by a single avirulence gene in accordance with a gene for gene interaction. In contrast, the ability to colonize the plant appeared slightly variable among clones sharing a same MLG. We hypothesize it is due to the putative polygenic control of this aphid trait. Because the phenotypic variability of A. gossypii matched the genetic variability revealed by eight microsatellite markers, these markers could be used to infer the frequency of biotypes in field experiments and help to elucidate the allele diversity of melon resistance genes.     

Effects of predation pressure and prey density on short-term indirect interactions between two prey species that share a common predator

1. Generalist predators are important contributors to reliable conservation biological control. Indirect interactions between prey species that share a common generalist predator can influence both community dynamics and the efficacy of biological control. 2. Laboratory cage experiments investigated the impact of the combined consumptive and non-consumptive effects of predation by adult Hippodamia convergens as a shared predator on the population growth and relative abundance of Acyrthosiphon pisum and Aphis gossypii as prey species. Predation pressure and prey density were varied. 3. At low predation pressure the indirect interaction between aphid species was asymmetrical with a proportionally greater negative impact of predation on A. gossypii than on A. pisum. At intermediate predation pressure, the indirect interaction became symmetrical. At high predation pressure and higher levels of prey density, it was asymmetrical with greater negative impact on A. pisum, often driven to local extinction while A. gossypii populations persisted. 4. A linear mixed-effects model including early population growth of both aphid species and predation pressure explained 96% and 92% of the variation in the population growth of A. pisum and A. gossypii, respectively, over an 8-day period. The overall effect of shared predation on the indirect interaction between the two aphid species is best described as apparent commensalism, where A. pisum benefited from early population growth of A. gossypii, while A. gossypii was unaffected by early population growth of A. pisum. Considering these indirect interactions is important for conservation biological control efforts to be successful.     

Recombinant and classically selected factors of potato plant resistance to the Colorado potato beetle, Leptinotarsa decemlineata, variously affect the potato aphid parasitoid Aphidius nigripes

Different forms of crop resistance developed against majorpotato pests such as the Colorado potato beetle (CPB), Leptinotarsadecemlineata, may be variously compatible with biological controlof secondary pests such as aphids. We compared the performance of theparasitoid Aphidius nigripes developing in the aphid hostMacrosiphum euphorbiae, on five potato lines, including atransgenic `Superior-BT' line expressing the CryIIIA toxin ofBacillus thuringiensis, which is specific to Coleoptera; andthe `NYL 235-4' line derived from Solanum berthaultii,characterized by relatively unspecific resistance to herbivores based onmoderately-high density of glandular trichomes. The other lines testedwere a `Kennebec-OCI' transgenic line expressing the protease inhibitorrice cystatin I (OCI), a potential resistance factor against coleopteranpests; and the commercial cultivars `Superior' and `Kennebec' used ascontrols. Parasitoid immature survival and adult size were reducedcompared to controls when the wasps developed on aphids fed the`Superior-BT' potato. In contrast, parasitoid size and fecundityincreased above control when the wasps developed on aphids fed the`Kennebec-OCI' potato. Parasitoids reached the adult stage faster andwere more fecund on `NYL 235-4' than control lines. The results indicatethat the different forms of potato resistance currently developed mainlyagainst the CPB had various unexpected effects on aphid parasitoidfitness. These effects on the parasitoid were complex but were generallyinterpretable in terms of host aphid quality variation among potatolines used as food by the aphids during parasitoiddevelopment.     

First report of voltage-gated sodium channel M918V and molecular diagnostics of nicotinic acetylcholine receptor R81T in the cotton aphid

The cotton aphid, Aphis gossypii Glover, is one of the most important agricultural insect pests. Pyrethroid and neonicotinoid insecticides have generally shown excellent control of A. gossypii, but many populations of this pest have developed resistance against these classes of insecticides. The success of insecticide resistance management strategies requires detailed knowledge of both phenotype and genotype of the target insect pest. In this study, we attempted to understand the molecular status of insecticide resistance in cotton aphid populations in Xinjiang Uygur Autonomous Region of China, the major cotton planting region of China. In addition to the previously reported M918L mutation, we discovered another substitution (M918V) in the voltage-gated sodium channel (VGSC). Moreover, we developed a molecular assay that could be used to detect precisely the R81T mutation in the nicotinic acetylcholine receptor (nAChR). This survey revealed that 918L was the predominant VGSC allele with a frequency ranging from 50.0% to 56.7%. Notably, appreciable frequencies (between 10% and 40%) of the resistance 81T allele of the nAChR gene were detected in three investigated populations. The prevalent co-occurrence of both VGSC 918L/V and nAchR 81T indicates a worrisome situation of multiple resistance to both pyrethroids and neonicotinoids.