An aphid-dip bioassay to evaluate susceptibility of soybean aphid (Hemiptera: Aphididae) to pyrethroid, organophosphate, and neonicotinoid insecticides

Ethyl Formate Fumigation for Controlling Two Major Aphid Pests, Aphis spiraecola and Aphis gossypii, on Passion Fruit, from Cultivation to Post-Harvest Storage

Tropical and subtropical crops are being increasingly cultivated in South Korea, leading to an increase in damage by exotic insect pests. Consequently, ethyl formate (EF) is currently being considered for quarantine and pre-shipment fumigation. In this study, we evaluated the effectiveness of EF fumigation for controlling Aphis spiraecola Patch and Aphis gossypii Glover, two representative quarantine pests on passion fruit ("Pink Bourbon") during greenhouse cultivation and post-harvest storage. The efficacy of EF against both aphids in terms of the lethal concentration causing 50% mortality (LCt50%) and LCt99% was 1.36-2.61 g h/m3 and 3.73-7.55 g h/m3 under greenhouse conditions (23 °C), and 1.37-2.02 g h/m3 and 3.80-14.59 g h/m3 post-harvest (5 °C), respectively. EF at 4 g/m3 for 4 h resulted in 100% mortality of A. spiraecola, which was more resistant to EF, without causing phytotoxic damage to the trees in a 340 m3 greenhouse. Post-harvest fruit fumigation at 10 g/m3 for 4 h in a mid-size (0.8 m3) fumigation chamber resulted in complete disinfection. Moreover, the EF level decreased below the EF threshold within 10 min after natural ventilation in the greenhouse. Therefore, our results suggest EF fumigation as an effective method for controlling A. spiraecola and A. gossypii.

Design, Synthesis, and Synergistic Activities of Eight-Membered Carbon Bridged Neonicotinoid Derivatives

Insecticide synergists are an effective approach to increase the control efficacy and reduce active ingredient usage. In order to explore neonicotinoid-specific synergists with novel scaffolds and higher potency, a series of eight-membered carbon bridged neonicotinoid derivatives were designed and synthesized in accordance with our previous research. The synergistic effects of the target compounds on neonicotinoids in Aphis craccivora were evaluated, and the structure-activity relationships were summarized. The results indicated that most of the target compounds exhibited significant synergistic effects on imidacloprid in A. craccivora at low concentrations. In particular, compound 1 at a concentration of 1 mg/L reduced the LC50 value of imidacloprid from 0.856 mg/L to 0.170 mg/L. Meanwhile, compound 1 also increased the insecticidal activity of most neonicotinoid insecticides belonging to the Insecticide Resistance Action Committee (IRAC) 4 A subgroup against A. craccivora. The present study might be meaningful for directing the design of neonicotinoid-specific synergists.

Insights into the Effects of Insecticides on Aphids (Hemiptera: Aphididae): Resistance Mechanisms and Molecular Basis

With the passage of time and indiscreet usage of insecticides on crops, aphids are becoming resistant to their effect. The different classes of insecticides, including organophosphates, carbamates, pyrethroids and neonicotinoids, have varied effects on insects. Furthermore, the molecular effects of these insecticides in aphids, including effects on the enzymatic machinery and gene mutation, are resulting in aphid resistance to the insecticides. In this review, we will discuss how aphids are affected by the overuse of pesticides, how resistance appears, and which mechanisms participate in the resistance mechanisms in various aphid species as significant crop pests. Gene expression studies were analyzed using the RNA-Seq technique. The stress-responsive genes were analyzed, and their expression in response to insecticide administration was determined. Putative insecticide resistance-related genes, cytochrome P450, glutathione S-transferase, carboxylesterase CarEs, ABC transporters, cuticle protein genes, and trypsin-related genes were studied. The review concluded that if insecticide-susceptible aphids interact with ample dosages of insecticides with sublethal effects, this will result in the upregulation of genes whose primary role is to detoxify insecticides. In the past decade, certain advancements have been observed regarding insecticide resistance on a molecular basis. Even so, not much is known about how aphids detoxify the insecticides at molecular level. Thus, to attain equilibrium, it is important to observe the manipulation of pest and insect species with the aim of restoring susceptibility to insecticides. For this purpose, this review has included critical insights into insecticide resistance in aphids.

Effect of biosal®, deltamethrin and lambda-cyhalothrin on the activity of GOT, GPT and total protein contents in two fodder pests Hermolaus modestus and Hermolaus ocimumi

The assessment of the comparative effect of biosal (phytopesticide), deltamethrin, and lambda-cyhalothrin (pyrethroids) were made against two fodder pests, Hermolaus modestus and Hermolaus ocimumi by filter paper impregnation method. The activity of total protein contents, GPT (glutamic-pyruvic transaminase) and GOT (glutamic oxaloacetate transaminase) were affected in Hermolaus modestus and Hermolaus ocimumi against biosal, deltamethrin, and lambda cyhalothrin. The activity of total protein contents in H. modestus was 31.053%, 4.607%, and 24.575%, against biosal, deltamethrin, and lambda-cyhalothrin, respectively. The activity of total protein contents was observed as 24.202%, 15.25%, and 56.036% against deltamethrin, lambda-cyhalothrin, and biosal, respectively in H. ocimumi. The activity of GOT was observed as 98.675% for biosal 33.95% for deltamethrin and 83.619% for lambda-cyhalothrin in H. modestus. The GOT activity was estimated in H. ocimumi as 78.831%, 47.645%, and 71.287% against biosal, deltamethrin, and lambda-cyhalothrin, respectively. The efficacy of GPT enzyme against biosal, deltamethrin, and lambda-cyhalothrin was calculated as 89.26%, 73.07%, and 47.58%, respectively in H. modestus. The H. ocimumi showed GPT activity as 77.58% for biosal, 68.84% for deltamethrin, and 52.67% for lambda-cyhalothrin, respectively.

Transcriptional responses of soybean aphids to sublethal insecticide exposure

Insecticides are a key tool in the management of many insect pests of agriculture, including soybean aphids. The selection imposed by insecticide use has often lead to the evolution of resistance by the target pest through enhanced detoxification mechanisms. We hypothesised that exposure of insecticide-susceptible aphids to sublethal doses of insecticides would result in the up-regulation of genes involved in detoxification of insecticides, revealing the genes upon which selection might act in the field. We used the soybean aphid biotype 1 reference genome, version 6.0 as a reference to analyze RNA-Seq data. We identified multiple genes with potential detoxification roles that were up-regulated 12 h after sublethal exposure to esfenvalerate or thiamethoxam. However, these genes were part of a dramatic burst of differential gene expression in which thousands of genes were up- or down-regulated, rather than a defined response to insecticides. Interestingly, the transcriptional burst observed at 12 h s declined dramatically by 24-hrs post-exposure, suggesting a general stress response that may become fine-tuned over time.

Chlamyphilone, a Novel Pochonia chlamydosporia Metabolite with Insecticidal Activity

Metabolites from a collection of selected fungal isolates have been screened for insecticidal activity against the aphid Acyrthosiphon pisum. Crude organic extracts of culture filtrates from six fungal isolates (Paecilomyces lilacinus, Pochonia chlamydosporia, Penicillium griseofulvum, Beauveria bassiana, Metarhizium anisopliae and Talaromyces pinophilus) caused mortality of aphids within 72 h after treatment. In this work, bioassay-guided fractionation has been used to characterize the main bioactive metabolites accumulated in fungal extracts. Leucinostatins A, B and D represent the bioactive compounds produced by P. lilacinus. From P. griseofulvum and B. bassiana extracts, griseofulvin and beauvericin have been isolated, respectively; 3-O-Methylfunicone and a mixture of destruxins have been found in the active fractions of T. pinophilum and M. anisopliae, respectively. A novel azaphilone compound, we named chlamyphilone, with significant insecticidal activity, has been isolated from the culture filtrate of P. chlamydosporia. Its structure has been determined using extensive spectroscopic methods and chemical derivatization.

Acute-Contact and Chronic-Systemic In Vivo Bioassays: Regional Monitoring of Susceptibility to Thiamethoxam in Soybean Aphid (Hemiptera: Aphididae) Populations From the North Central United States

The risks associated with soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in the North Central soybean systems has fostered the adoption of prophylactic chemical control practices, such as planting seeds treated with neonicotinoid insecticides, especially thiamethoxam. Consequently, there is a concern that increased selection pressure imposed on the arthropod-pest complex by this insecticide may lead to resistance. Therefore, in vivo bioassays were conducted to determine the susceptibility of soybean aphid to thiamethoxam among North Central U.S.

POPULATIONS

Concentration-mortality data were collected using contact glass-vial and detached-leaf systemic bioassays. The results of these experiments indicate that both bioassays were reliable to detect shifts in susceptibility between different soybean aphid clones. The LC50s of field populations of soybean aphid were significantly different when mortality was recorded in contact and systemic exposure assays. Nevertheless, the magnitude of the resistance ratios was consistent in both methods. In addition, a significant increase in the LC50 and EC50 values was observed among field populations tested in detached-leaf systemic bioassays. These results represent the first extensive efforts to identify the variability in susceptibility of soybean aphid to thiamethoxam in the North Central United States Therefore, our results provide a baseline for future assessment and contribute to a better understanding of the applicability of in vivo bioassays for susceptibility monitoring and resistance detection of soybean aphid to thiamethoxam.

Evidence for Soybean Aphid (Hemiptera: Aphididae) Resistance to Pyrethroid Insecticides in the Upper Midwestern United States

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a damaging invasive pest of soybean in the upper Midwest. Threshold-based insecticide applications are the primary control method for soybean aphid, but few insecticide groups are available (i.e., pyrethroids, organophosphates, and neonicotinoids). To quantify current levels of soybean aphid susceptibility to pyrethroids in the upper Midwest and monitor for insecticide resistance, leaf-dip bioassays were performed with λ-cyhalothrin in 2013-2015, and glass-vial bioassays were performed with λ-cyhalothrin and bifenthrin in 2015 and 2016. Soybean aphids were collected from 27 population-years in Minnesota and northern Iowa, and were compared with a susceptible laboratory colony with no known insecticide exposure since discovery of soybean aphid in North America in 2000. Field-collected aphids from some locations in leaf-dip and glass-vial bioassays had significantly lower rates of insecticide-induced mortality compared with the laboratory population, although field population susceptibility varied by year. In response to sublethal concentrations of λ-cyhalothrin, adult aphids from some locations required higher concentrations of insecticide to reduce nymph production compared with the laboratory population. The most resistant field population demonstrated 39-fold decreased mortality compared with the laboratory population. The resistance documented in this study, although relatively low for most field populations, indicates that there has been repeated selection pressure for pyrethroid resistance in some soybean aphid populations. Integrated pest management and insecticide resistance management should be practiced to slow further development of soybean aphid resistance to pyrethroids.

Comparative proteomic analysis in Aphis glycines Mutsumura under lambda-cyhalothrin insecticide stress

Lambda-cyhalothrin is now widely used in China to control the soybean aphid Aphis glycines. To dissect the resistance mechanism, a laboratory-selected resistant soybean aphid strain (CRR) was established with a 43.42-fold resistance ratio to λ-cyhalothrin than the susceptible strain (CSS) in adult aphids. In this study, a comparative proteomic analysis between the CRR and CSS strains revealed important differences between the susceptible and resistant strains of soybean aphids for λ-cyhalothrin. Approximately 493 protein spots were detected in two-dimensional polyacrylamide gel electrophoresis (2-DE). Thirty-six protein spots displayed differential expression of >2-fold in the CRR strain compared to the CSS strain. Out of these 36 protein spots, 21 had elevated and 15 had decreased expression. Twenty-four differentially expressed proteins were identified by MALDI TOF MS/MS and categorized into the functional groups cytoskeleton-related protein, carbohydrate and energy metabolism, protein folding, antioxidant system, and nucleotide and amino acid metabolism. Function analysis showed that cytoskeleton-related proteins and energy metabolism proteins have been associated with the λ-cyhalothrin resistance of A. glycines. The differential expression of λ-cyhalothrin responsive proteins reflected the overall change in cellular structure and metabolism after insecticide treatment in aphids. In summary, our studies improve understanding of the molecular mechanism resistance of soybean aphid to lambda-cyhalothrin, which will facilitate the development of rational approaches to improve the management of this pest and to improve the yield of soybean.

Specific Synergist for Neonicotinoid Insecticides: IPPA08, a cis-Neonicotinoid Compound with a Unique Oxabridged Substructure

Insecticide synergists are key components to increase the control efficacy and reduce active ingredient use. Here, we describe a novel insecticide synergist with activity specific for insecticidal neonicotinoids. The synergist IPPA08, a cis configuration neonicotinoid compound with a unique oxabridged substructure, could increase the toxicity of most neonicotinoid insecticides belonging to the Insecticide Resistance Action Committee (IRAC) 4A subgroup against a range of insect species, although IPPA08 itself was almost inactive to insects at synergistic concentrations. Unfortunately, similar effects were observed on the honey bee (Apis mellifera) and the brown planthopper (Nilaparvata lugens), resistant to imidacloprid. IPPA08 did not show any effects on toxicity of insecticides with different targets, which made us define it as a neonicotinoid-specific synergist. Unlike most insecticide synergists, by inhibition of activities of detoxification enzymes, IPPA08 showed no effects on enzyme activities. The results revealed that IPPA08 worked as a synergist through a distinct way. Although the modulating insect nicotinic acetylcholine receptors (nAChRs, targets of neonicotinoid insecticides) were supposed as a possible mode of action for IPPA08 as a neonicotinoid-specific synergist, direct evidence is needed in further studies. In insect pest control, IPPA08 acts as a target synergist to increase neonicotinoid toxicity and reduce the amount of neonicotinoid used. Combinations of IPPA08 and insecticidal neonicotinoids may be developed into new insecticide formulations. In summary, combining an active ingredient with a "custom" synergist appears to be a very promising approach for the development of effective new insecticide products.

A simultaneous extraction method for organophosphate, pyrethroid, and neonicotinoid insecticides in aqueous samples

A method was developed for the extraction and analysis of 2 organophosphate, 8 pyrethroid, and 5 neonicotinoid insecticides from the same water sample. A salted liquid-liquid extraction (LLE) was optimized with a solid-phase extraction (SPE) step that separated the organophosphates (OPs) and pyrethroids from the neonicotinoids. Factors that were optimized included volume of solvent and amount of salt used in the LLE, homogenization time for the LLE, and type and volume of eluting solvent used for the SPE. The OPs and pyrethroids were quantified using gas chromatography-mass spectrometry, and the neonicotinoids were quantified using liquid chromatography-diode array detector. Results showed that the optimized method was accurate, precise, reproducible, and robust; recoveries in river water spiked with 100 ng L(-1) of each of the insecticides were all between 86 and 114 % with RSDs between 2 and 8 %. The method was also sensitive with method detection limits ranging from 0.1 to 27.2 ng L(-1) depending on compounds and matrices. The optimized method was thus appropriate for the simultaneous extraction of 15 widely applied insecticides from three different classes and was shown to provide valuable information on their environmental fate from field-collected aqueous samples.

Microbiome diversity of Aphis glycines with extensive superinfection in native and invasive populations

Associations among insects and microbes can lead to beneficial or parasitic interactions. Using 454 sequencing of 16S RNA genes, we compared microbiome diversity and abundance among field-collected (F) and laboratory-reared (L) populations of the invasive soybean aphid (Aphis glycines), a pest of soybean. Additionally, we screened A. glycines populations from native (Japan, South Korea and China) and invasive regions (North America) to broadly determine the microbiome diversity. Our results suggested that Arsenophonus (relative abundance of 54.6%), Buchnera (38.7%) and Wolbachia (3.7%) were the major bacteria associated with A. glycines. Arsenophonus was the most abundant in F populations but was significantly reduced in L populations; additional bacteria species also had lower relative abundances in L populations. Native and invasive populations were largely similar in bacteria communities and revealed substantial superinfection of Arsenophonus and Wolbachia. The lone exception was a lack of Arsenophonus in A. glycines from Japan. Divergent selection pressures among natural and laboratory populations were inferred as factors driving the differential bacterial communities observed. Our results will allow for improved comparative aphid-symbiont research and broaden our understanding of the interactions among insects, endosymbionts and their environments.

Soybean aphid (Hemiptera: Aphididae) response to soybean plant defense: stress levels, tradeoffs, and cross-virulence

A variety of management methods to control the soybean aphid (Aphis glycines Matsumura) have been investigated since its invasion into North America in 2000, among them plant resistance has emerged as a viable option for reducing aphid damage to soybeans and preventing outbreaks. Plant resistance methods often use natural soybean plant defenses that impose stress on aphids by reducing fitness and altering behavior. Research efforts have heavily focused on identification and development of aphid resistant soybean varieties, leaving much unknown about soybean aphid response to stressful host plant defenses. In this study, we aimed to 1) evaluate lifetime fitness consequences and phenotypic variation in response to host plant-induced stress and 2) investigate whether trade-offs involving fitness costs and/or cross-virulence to multiple antibiotic soybean varieties exists. We compared aphid survival and reproduction during and after a short period of exposure to soybeans with the Rag2 resistance gene and measured aphid clonal variation in response to Rag2 soybeans. In addition, we measured the performance of Rag2 virulent and avirulent aphids on five soybean varieties with various forms of antibiotic resistance. Our results indicate that plant defenses impose high levels of stress and have long-term fitness consequences, even after aphids are removed from resistant plants. We identified one aphid clone that was able to colonize Rag2 among the seven clones tested, suggesting that virulent genotypes may be prevalent in natural populations. Finally, although we did not find evidence of cross-virulence to multiple antibiotic soybean varieties, our results suggest independent mechanisms of aphid virulence to Rag1 and Rag2 that may involve fitness costs.