Spatial distribution of Aphis glycines (Hemiptera: Aphididae): a summary of the suction trap network

Tracking flight activity of potato leafhopper (Hemiptera: Cicadellidae) with the Midwest Suction Trap Network

Potato leafhopper (PLH), Empoasca fabae Harris (Hemiptera: Cicadellidae), is an economic pest of a variety of crops that migrates between overwintering sites in the southern United States and northern breeding grounds. Since 2005, the Midwest Suction Trap Network (STN) has monitored the magnitude and timing of aerially dispersing aphids' activity, but the potential of the network to monitor other taxa is only beginning to be explored. Here, we use the Midwest STN to examine how the magnitude and timing of PLH activity vary with weather, cropland cover, and time of year. We found that weekly PLH activity increased early in the season (May-June) with increasing degree day accumulation and decreased mid-season (July-August) with increasing occurrence of rain. The first detections occurred earlier in southern latitudes, while the last detections occurred sooner, when there was more surrounding potato land cover, and later over time between 2018 and 2021 and in southern latitudes. PLH activity was thus longer in duration in southern latitudes and has continued to extend later into the year overall. Resolving uncertainty about how well the Midwest STN captures migratory activity and how closely suction trap detections reflect local population densities in crop fields remain important research priorities before the potential of the Midwest STN for PLH monitoring can be realized. Still, observed patterns suggest that PLH could increase in economic importance as insects disperse over larger portions of the growing season in the warming, agriculturally productive US Midwest and that the STN can become a useful tool to monitor these changes.

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.

Comparing the cost-benefit probability of management based on early-stage and late-stage economic thresholds with that of seed treatment of Aphis glycines

BACKGROUND

The current integrated pest management (IPM) curative strategy for soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), relies on responsive spraying foliar insecticides during the R1-R5 soybean stage when aphid abundance reaches the economic threshold (ET) of 250 aphids plant-1 (traditional IPM). By analyzing the relationship between aphid abundance and yield loss before the R1 stage, we developed an early-stage ET. We propose to spray foliar insecticides on plants colonized with aphids using the early-stage ET as a trigger (improved IPM), together with seed treatment to manage A. glycines and delay them exceeding the ET of 250 aphids plant-1 in the late stage for whole-field spraying (traditional IPM). Finally, we compared the cost-benefit probabilities of the three management approaches.

RESULTS

The early-stage ET over all potential yields, market prices, and control costs was 64 aphids plant-1 , providing growers 7 days of preparation time to spray foliar insecticides before the economic injury level of 187 aphids plant-1 was reached. Improved IPM achieved the highest cost-benefit probabilities followed by traditional IPM, and the seed treatment achieved the lowest. However, in fields where the pressure from white grubs was high, the probability of achieving a positive net return with seed treatment was higher than that in other locations.

CONCLUSION

Improved IPM based on early-stage ET of 64 aphids plant-1 was the most cost-effective of all the three approaches. Neonicotinoid seed treatment can be applied as an insurance strategy to supplement A. glycines IPM in Liaoning, China. © 2022 Society of Chemical Industry.

Complex life histories predispose aphids to recent abundance declines

Many animals change feeding habits as they progress through life stages, exploiting resources that vary in space and time. However, complex life histories may bring new risks if rapid environmental change disrupts the timing of these switches. Here, we use abundance times series for a diverse group of herbivorous insects, aphids, to search for trait and environmental characteristics associated with declines. Our meta dataset spanned three world regions and >300 aphid species, tracked at 75 individual sites for 10-50 years. Abundances were generally falling, with median changes of -8.3%, -5.6%, and -0.1% per year in the central USA, northwestern USA, and United Kingdom, respectively. Aphids that obligately alternated between host plants annually and those that were agricultural pests exhibited the steepest declines, relative to species able to persist on the same host plant year-round or those in natural areas. This suggests that host alternation might expose aphids to climate-induced phenology mismatches with one or more of their host plant species, with additional risks from exposure to insecticides and other management efforts. Warming temperatures through time were associated with milder aphid declines or even abundance increases, particularly at higher latitudes. Altogether, while a warming world appeared to benefit some aphid species in some places, most aphid species that had time-sensitive movements among multiple host plants seemed to face greater risk of decline. More generally, this suggests that recent human-induced rapid environmental change is rebalancing the risks and rewards associated with complex life histories.

Evaluating the role of insecticidal seed treatment and refuge for managing soybean aphid virulence

BACKGROUND

Managing insect virulence can extend the durability of host-plant resistant crops. Genetically modified resistant crops continue to be successful because of insect-resistant management strategies that delay resistance such as multiple toxins and a susceptible refuge. These strategies may also be useful for host-plant resistant crops, but more research is needed on their applicability. We investigated the interaction between a susceptible refuge and an insecticidal seed treatment to manage virulence in the soybean aphid. We tested four scenarios of an insecticidal seed treatment (plus an untreated control) in a microcosm containing 25% aphid-susceptible (refuge) and 75% aphid-resistant soybeans. Independent cohorts of plants were infested every week with avirulent and virulent aphids at equal frequencies. We used a molecular marker to estimate the change in virulence frequency across different plant maturities (from 7 to 42 days after planting).

RESULTS

The presence of an insecticidal seed treatment on either the susceptible or resistant soybean decreased the overall population size of the soybean aphid. However, the insecticidal seed treatment impacted both virulent and avirulent aphids similarly, and only altered frequencies in favor of virulence when the sole susceptible plant (i.e., refuge) was treated.

CONCLUSION

Under our experimental conditions, the frequency of avirulent aphids persisted with the use of a refuge. Although an insecticidal seed treatment decreased the overall aphid population size, it did not appear to benefit virulence management. © 2021 Society of Chemical Industry.

Genome scan detection of selective sweeps among biotypes of the soybean aphid, Aphis glycines, with differing virulence to resistance to A. glycines (Rag) traits in soybean, Glycine max

Multiple biotypes of soybean aphid, Aphis glycines, occur in North America adapted for survival (virulence) on soybean, Glycine max, with one or more different resistance to A. glycines (Rag) traits. The degree of genome-wide variance between biotypes and the basis of virulence remains unknown, but the latter is hypothesized to involve secreted effector proteins. Between 167,249 and 217,750 single nucleotide polymorphisms (SNPs) were predicted from whole genome re-sequencing of A. glycines avirulent biotype 1 (B1) and virulent B2, B3 and B4 colony-derived iso-female lines when compared to the draft B1 genome assembly, Ag_bt1_v6.0. Differences in nucleotide diversity indices (π) estimated within 1000 bp sliding windows demonstrated that 226 of 353 (64.0%) regions most differentiated between B1 and ≥ 2 virulent biotypes, representing < 0.1% of the 308 Mb assembled genome size, are located on 15 unordered scaffolds. Furthermore, these 226 intervals were coincident and show a significant association with 326 of 508 SNPs with significant locus-by-locus FST estimates between biotype populations (r = 0.6271; F1,70 = 45.36, P < 0.001) and genes showing evidence of directions selection (πN/πS > 2.0; r = 0.6233; F1,70 = 50.20, P < 0.001). A putative secreted effector glycoprotein is encoded in proximity to genome intervals of low estimated π (putative selective sweep) within avirulent B1 compared to all three virulent biotypes. Additionally, SNPs are clustered in or in proximity to genes putatively involved in intracellular protein cargo transport and the regulation of secretion. Results of this study indicate that factors on a small number of scaffolds of the A. glycines genome may contribute to variance in virulence towards Rag traits in G. max.

Weekly Survivorship Curves of Soybean Aphid Biotypes 1 and 4 on Insecticidal Seed-Treated Soybean

Thiamethoxam, an insecticide used in soybean seed treatments, effectively suppresses soybean aphids (Aphis glycines) Matsumura (Hemiptera: Aphididae) for a short time after planting. However, exactly when and how quickly soybean aphid populations could increase is unknown. Likewise, we lack data on virulent soybean aphid biotypes (that can overcome soybean resistance) when fed on seed-treated soybean. Determining the survival of soybean aphids over time on insecticidal seed-treated soybean is critical for improving soybean aphid management and may provide insights to manage aphid virulence to aphid resistant-soybean. In greenhouse and field experiments, aphid-susceptible soybean plants (with and without an insecticidal seed treatment) were infested at 7, 14, 21, 28, 35, and 42 days after planting (DAP). We compared aphid survival among biotypes 1 (avirulent) and 4 (virulent) and insecticide treatment 72 h after infestation. We also measured thiamethoxam concentrations in plant tissue using liquid chromatography-tandem mass spectrometry. As expected, soybean aphid survival was significantly lower on seed-treated soybean up to 35 DAP for both biotypes, which correlates with the decrease of thiamethoxam in the plant over time. Moreover, we found no significant difference between avirulent and virulent biotype survivorship on insecticidal seed-treated soybean plants, although we did find significantly greater survival for the virulent biotype compared with the avirulent biotype on untreated soybean in the field. In conclusion, our study further characterized the relative short duration of seed treatment effectiveness on soybean aphid and showed that survivorship of virulent aphids on seed-treated soybean is similar to avirulent aphids.

Rapid evolution to host plant resistance by an invasive herbivore: soybean aphid (Aphis glycines) virulence in North America to aphid resistant cultivars

Preventing rapid evolution of herbivores to plant traits that confer resistance is an area of active research for applied entomologists. The subfield of insect resistance management (IRM) uses elements of population genetics and ecology to prevent increases in the frequency of virulent (i.e. resistant) sub-populations of an insect pest. Efforts to delay such an increase include using highly lethal toxins (i.e., a high dose), combining multiple resistance traits in one cultivar (i.e., pyramids), and using susceptible plants (i.e. a refuge) within or near plantings of the resistant crop. Even if fully implemented, theoretical models suggest that IRM plans for asexually-reproducing insects (e.g. aphids) cannot limit the frequency of resistance to provide sustainable use of a pest-resistant cultivar. We discuss how feeding by conspecifics aphids induces susceptibility such that a "within plant" refuge is created, allowing both virulent and avirulent (i.e. susceptible) populations to persist. We use the soybean aphid (Aphis glycines Matsumura), and the rapid occurrence of virulence in the US to resistant cultivars of soybean (Glycine max). We describe how feeding by A. glycines on soybeans alters the quality of the plant as a host. These systemic changes to the plants' physiology allow avirulent A. glycines to thrive on resistant cultivars. We explore how the induction of susceptibility by a herbivore can slow an increase in the frequency of virulent populations to resistant host plants. We suggest that a within plant refuge, combined with standard IRM practices, can allow for sustainable use of plant resistance to asexually-reproducing insect pests.

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.

Ecoinformatics (Big Data) for Agricultural Entomology: Pitfalls, Progress, and Promise

Ecoinformatics, as defined in this review, is the use of preexisting data sets to address questions in ecology. We provide the first review of ecoinformatics methods in agricultural entomology. Ecoinformatics methods have been used to address the full range of questions studied by agricultural entomologists, enabled by the special opportunities associated with data sets, nearly all of which have been observational, that are larger and more diverse and that embrace larger spatial and temporal scales than most experimental studies do. We argue that ecoinformatics research methods and traditional, experimental research methods have strengths and weaknesses that are largely complementary. We address the important interpretational challenges associated with observational data sets, highlight common pitfalls, and propose some best practices for researchers using these methods. Ecoinformatics methods hold great promise as a vehicle for capitalizing on the explosion of data emanating from farmers, researchers, and the public, as novel sampling and sensing techniques are developed and digital data sharing becomes more widespread.

Population Dynamics of the Soybean Aphid (Hemiptera: Aphididae) in Quebec (Canada)

The population dynamics of the soybean aphid ( Aphis glycines Matsumura) was studied over a 12-yr period (2004-2015) from archive and field data collected in the Montérégie area of Quebec (Canada). As observed in the United States, a 2-yr oscillation cycle was observed from 2005 to 2011 in Quebec, with high infestations during odd years, while the opposite was found in 2014 and 2015. A broader pattern could also be observed, with high infestation in two consecutive years every 10 yr. In addition, the infestation intensity observed in high infestation years decreases throughout the years, which questions the evolution of the oscillation cycle in the future.

Trophic cascades in agricultural landscapes: indirect effects of landscape composition on crop yield

The strength and prevalence of trophic cascades, defined as positive, indirect effects of natural enemies (predatory and parasitic arthropods) on plants, is highly variable in agroecosystems. This variation may in part be due to the spatial or landscape context in which hese trophic cascades occur. In 2011 and 2012, we conducted a natural enemy exclusion experiment in soybean fields along a gradient of landscape composition across southern Wisconsin and Michigan, USA. We used structural equation modeling to ask (1) whether natural enemies influence biocontrol of soybean aphids (SBA) and soybean yield and (2) whether landscape effects on natural enemies influence the strength of the trophic cascades. We found that natural enemies (NE) suppressed aphid populations in both years of our study, and, in 2011, the yield of soybean plants exposed to natural enemies was 37% higher than the yield of plants with aphid populations protected from natural enemies. The strength of the :rophic cascade was also influenced by landscape context. We found that landscapes with a higher proportion of soybean and higher diversity habitats resulted in more NE, fewer aphids, and, in some cases, a trend toward greater soybean yield. These results indicate that landscape context is important for understanding spatial variability in biocontrol and yield, but other factors, such as environmental variability and compensatory growth, might overwhelm the beneficial effects of biocontrol on crop yield.

Seasonal occurrence of Aphis glycines and physiological responses of soybean plants to its feeding

The soybean aphid Aphis glycines Matsumura (Hemiptera: Aphididae) is an important pest of soybean in China. To monitor and manage this pest effectively it is necessary to understand its population dynamics and demographics, as well as the physiological responses of soybean plants to its feeding. In this study, using field surveying and suction-trap monitoring, we investigated the population dynamics of the soybean aphid in Xiuyan County, Liaoning Province in northeastern China during 2009-2012. The results indicated that the population dynamics of the soybean aphid followed a unimodal curve distribution, with the insect generally colonizing soybean fields from the middle of June to early July and the population reaching a peak between early July and early August. On the whole, soybean aphids occurred in suction-traps at least 2 weeks earlier than they were found in field surveys. A total of 72 alates were collected by suction-trapping over the 4 years, with the earliest alate captures occurring on 28 May in 2009, 2011, 2012 and 4 June in 2010. The life table parameters clearly showed that this aphid had a short doubling time (4.73 ± 0.21 days), and 7.36 ± 0.98 nymphs were produced by a soybean aphid adult during its lifetime (13.57 ± 0.30 days). Finally, biochemical assays indicated that the amount of malondialdehyde and the activities of four defense-related enzymes in soybean leaves significantly changed between 0 day and 7 days of aphid infestation. Polyphenol oxidase (PPO) and catalase (CAT) activities increased more dramatically after 1 day of aphid feeding. In addition, significantly higher levels of superoxide dismutase and CAT were found after aphid feeding for 7 days, whereas there was no significant change in the activities of peroxidase and PPO. Consequently, this study will be beneficial in determining the seasonal occurrence of the soybean aphid and selecting insect-resistant soybean varieties, and thus in developing a theoretical framework for appropriate management strategies.