Shifts in dynamic regime of an invasive lady beetle are linked to the invasion and insecticidal management of its prey

Patterns of asexual reproduction of the soybean aphid, Aphis glycines (Matsumura), with and without the secondary symbionts Wolbachia and Arsenophonus, on susceptible and resistant soybean genotypes

Plant breeding is used to develop crops with host resistance to aphids, however, virulent biotypes often develop that overcome host resistance genes. We tested whether the symbionts, Arsenophonus (A) and Wolbachia (W), affect virulence and fecundity in soybean aphid biotypes Bt1 and Bt3 cultured on whole plants and detached leaves of three resistant, Rag1, Rag2 and Rag1 + 2, and one susceptible, W82, soybean genotypes. Whole plants and individual aphid experiments of A. glycines with and without Arsenophonus and Wolbachia did not show differences in overall fecundity. Differences were observed in peak fecundity, first day of deposition, and day of maximum nymph deposition of individual aphids on detached leaves. Bt3 had higher fecundity than Bt1 on detached leaves of all plant genotypes regardless of bacterial profile. Symbionts did not affect peak fecundity of Bt1 but increased it in Bt3 (A+W+) and all Bt3 strains began to deposit nymphs earlier than the Bt1 (A+W-). Arsenophonus in Bt1 delayed the first day of nymph deposition in comparison to aposymbiotic Bt1 except when reared on Rag1 + 2. For the Bt1 and Bt3 strains, symbionts did not result in a significant difference in the day they deposited the maximum number of nymphs nor was there a difference in survival or variability in number of nymphs deposited. Variability of number of aphids deposited was higher in aphids feeding on resistant plant genotypes. The impact of Arsenophonus on soybean aphid patterns of fecundity was dependent on the aphid biotype and plant genotype. Wolbachia alone had no detectable impact but may have contributed to the increased fecundity of Bt3 (A+W+). An individual based model, using data from the detached leaves experiment and with intraspecific competition removed, found patterns similar to those observed in the greenhouse and growth chamber experiments including a significant interaction between soybean genotype and aphid strain. Combining individual data with the individual based model of population growth isolated the impact of fecundity and host resistance from intraspecific competition and host health. Changes to patterns of fecundity, influenced by the composition and concentration of symbionts, may contribute to competitive interactions among aphid genotypes and influence selection on virulent aphid populations.

Coexistence between similar invaders: The case of two cosmopolitan exotic insects

Biological invasions are usually examined in the context of their impacts on native species. However, few studies have examined the dynamics between invaders when multiple exotic species successfully coexist in a novel environment. Yet, long-term coexistence of now established exotic species has been observed in North American lady beetle communities. Exotic lady beetles Harmonia axyridis and Coccinella septempunctata were introduced for biological control in agricultural systems and have since become dominant species within these communities. In this study, we investigated coexistence via spatial and temporal niche partitioning among H. axyridis and C. septempunctata using a 31-year data set from southwestern Michigan, USA. We found evidence of long-term coexistence through a combination of small-scale environmental, habitat, and seasonal mechanisms. Across years, H. axyridis and C. septempunctata experienced patterns of cyclical dominance likely related to yearly variation in temperature and precipitation. Within years, populations of C. septempunctata peaked early in the growing season at 550 degree days, while H. axyridis populations grew in the season until 1250 degree days and continued to have high activity after this point. C. septempunctata was generally most abundant in herbaceous crops, whereas H. axyridis did not display strong habitat preferences. These findings suggest that within this region H. axyridis has broader habitat and abiotic environmental preferences, whereas C. septempunctata thrives under more specific ecological conditions. These ecological differences have contributed to the continued coexistence of these two invaders. Understanding the mechanisms that allow for the coexistence of dominant exotic species contributes to native biodiversity conservation management of invaded ecosystems.

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.

Towards Predictions of Interaction Dynamics between Cereal Aphids and Their Natural Enemies: A Review

(1) Although most past studies are based on static analyses of the pest regulation drivers, evidence shows that a greater focus on the temporal dynamics of these interactions is urgently required to develop more efficient strategies. (2) Focusing on aphids, we systematically reviewed (i) empirical knowledge on the drivers influencing the dynamics of aphid-natural enemy interactions and (ii) models developed to simulate temporal or spatio-temporal aphid dynamics. (3) Reviewed studies mainly focus on the abundance dynamics of aphids and their natural enemies, and on aphid population growth rates. The dynamics of parasitism and predation are rarely measured empirically, although it is often represented in models. Temperature is mostly positively correlated with aphid population growth rates. Plant phenology and landscape effects are poorly represented in models. (4) We propose a research agenda to progress towards models and empirical knowledge usable to design effective CBC strategies. We claim that crossover works between empirical and modeling community will help design new empirical settings based on simulation results and build more accurate and robust models integrating more key drivers of aphid dynamics. Such models, turned into decision support systems, are urgently needed by farmers and advisors in order to design effective integrated pest management.

Declining Abundance of Coccinellidae (Coleoptera) Among Crop and Prairie Habitats of Eastern South Dakota, USA

Lady (= ladybird) beetles (Coleoptera: Coccinellidae) provide agroecosystem services as major predators of aphids and other pests of field crops. Several native coccinellids in North America have declined in association with the introduction of invasive species of lady beetles. In particular, populations of three native species declined drastically (Coccinella transversoguttata richardsoni) or effectively disappeared (Coccinella novemnotata, Adalia bipunctata) from agricultural landscapes in eastern South Dakota, U.S.A., following establishment of an invasive coccinellid (Coccinella septempunctata) in the 1980s. Since then, two other non-native coccinellids (Harmonia axyridis and Hippodamia variegata) have established in eastern South Dakota, but long-term analysis of their impact on the aphidophagous coccinellid guild is lacking. This paper summarizes long-term results from 14 years (2007–2020) of sampling coccinellids by sweepnet and timed searches in five field crops and restored prairie in eastern South Dakota. In all, 17,338 aphidophagous coccinellids comprising 10 species were sampled. Two invasive species (Coc. septempunctata, Har. axyridis) were the third- and fourth-most abundant species, respectively. The seven most abundant species constituted 99% of all coccinellids sampled and were recorded from all six habitats. However, coccinellid species ranged considerably in their evenness of habitat use, resulting in differences in rank abundance among habitats. Coccinellid assemblages were similar for alfalfa and winter wheat, but not for other habitats, which possessed distinct coccinellid assemblages based on rank abundance. Annual abundance of coccinellids varied considerably within habitats, but declining trends were evident from significant negative regressions in annual abundance for adult and immature coccinellids in corn and adults in soybean. As a group, native adult coccinellids showed a significant declining trend in corn but not in other habitats, whereas trends for non-native adult coccinellids were non-significant in all habitats. Sample rates of coccinellids in alfalfa, spring grains, and corn in this study were 74, 26, and 6%, respectively, compared to that of a previous study from the region, further indicating substantial decreases in coccinellid abundance. Possible explanations and implications for observed patterns in coccinellid diversity and individual species abundances in field crops and restored prairie of eastern South Dakota are discussed with respect to prey, agronomic trends, and landscape factors.

Challenges for Adoption of Integrated Pest Management (IPM): the Soybean Example

Soybean is considered one of today's most important crops. Planted on millions of hectares worldwide, the management of soybean pests usually requires large amounts of chemicals. However, a key component to meet the increasing demand for food due to the rapidly growing global population is protecting crops from pests while maintaining environmental quality through ecologically and economically sound integrated pest management (IPM) practices. Not only can IPM result in more profitable agriculture due to the reduction of pest control costs but also assures equitable, secure, sufficient, and stable flows of both food and ecosystem services. Despite those ecological and economic benefits, the vast areas of cultivated soybean as well as the convenience of spraying insecticides are encouraging the adoption of prophylactic pest control as a relatively inexpensive safeguard compared to IPM practices. Thus, in this forum, we discuss the reasons for soybean IPM not reaching its potential. We give examples of how we can revive this once successful pest management program with a focus on experiences in Brazil and the USA. We analyze IPM case studies to illustrate the need for growers to have easy and fast access to IPM information on its medium- and long-term benefits. Overall, this forum highlights the importance of IPM for agricultural sustainability including ecological and financial benefits.

Assessing Field-Scale Risks of Foliar Insecticide Applications to Monarch Butterfly (Danaus plexippus) Larvae

Establishment and maintenance of milkweed plants (Asclepias spp.) in agricultural landscapes of the north central United States are needed to reverse the decline of North America's eastern monarch butterfly (Danaus plexippus) population. Because of a lack of toxicity data, it is unclear how insecticide use may reduce monarch productivity when milkweed habitat is placed near maize and soybean fields. To assess the potential effects of foliar insecticides, acute cuticular and dietary toxicity of 5 representative active ingredients were determined: beta-cyfluthrin (pyrethroid), chlorantraniliprole (anthranilic diamide), chlorpyrifos (organophosphate), and imidacloprid and thiamethoxam (neonicotinoids). Cuticular median lethal dose values for first instars ranged from 9.2 × 10-3 to 79 μg/g larvae for beta-cyfluthrin and chlorpyrifos, respectively. Dietary median lethal concentration values for second instars ranged from 8.3 × 10-3 to 8.4 μg/g milkweed leaf for chlorantraniliprole and chlorpyrifos, respectively. To estimate larval mortality rates downwind from treated fields, modeled insecticide exposures to larvae and milkweed leaves were compared to dose-response curves obtained from bioassays with first-, second-, third-, and fifth-instar larvae. For aerial applications to manage soybean aphids, mortality rates at 60 m downwind were highest for beta-cyfluthrin and chlorantraniliprole following cuticular and dietary exposure, respectively, and lowest for thiamethoxam. To estimate landscape-scale risks, field-scale mortality rates must be considered in the context of spatial and temporal patterns of insecticide use. Environ Toxicol Chem 2020;39:923-941. © 2020 SETAC.

The Dynamic Shift Detector: An algorithm to identify changes in parameter values governing populations

Environmental factors interact with internal rules of population regulation, sometimes perturbing systems to alternate dynamics though changes in parameter values. Yet, pinpointing when such changes occur in naturally fluctuating populations is difficult. An algorithmic approach that can identify the timing and magnitude of parameter shifts would facilitate understanding of abrupt ecological transitions with potential to inform conservation and management of species. The “Dynamic Shift Detector” is an algorithm to identify changes in parameter values governing temporal fluctuations in populations with nonlinear dynamics. The algorithm examines population time series data for the presence, location, and magnitude of parameter shifts. It uses an iterative approach to fitting subsets of time series data, then ranks the fit of break point combinations using model selection, assigning a relative weight to each break. We examined the performance of the Dynamic Shift Detector with simulations and two case studies. Under low environmental/sampling noise, the break point sets selected by the Dynamic Shift Detector contained the true simulated breaks with 70–100% accuracy. The weighting tool generally assigned breaks intentionally placed in simulated data (i.e., true breaks) with weights averaging >0.8 and those due to sampling error (i.e., erroneous breaks) with weights averaging <0.2. In our case study examining an invasion process, the algorithm identified shifts in population cycling associated with variations in resource availability. The shifts identified for the conservation case study highlight a decline process that generally coincided with changing management practices affecting the availability of hostplant resources. When interpreted in the context of species biology, the Dynamic Shift Detector algorithm can aid management decisions and identify critical time periods related to species’ dynamics. In an era of rapid global change, such tools can provide key insights into the conditions under which population parameters, and their corresponding dynamics, can shift.

Populations naturally fluctuate in abundance, and the rules governing these fluctuations are a result of both internal (density dependent) and external (environmental) processes. For these reasons, pinpointing when changes in populations occur is difficult. In this study, we develop a novel break-point analysis tool for population time series data. Using a density dependent model to describe a population’s underlying dynamic process, our tool iterates through all possible break point combinations (i.e., abrupt changes in parameter values) and applies information-theoretic decision tools (i.e. Akaike's Information Criterion corrected for small sample sizes) to determine best fits. Here, we develop the approach, simulate data under a variety of conditions to demonstrate its utility, and apply the tool to two case studies: an invasion of multicolored Asian ladybeetle and declining monarch butterflies. The Dynamic Shift Detector algorithm identified parameter changes that correspond to known environmental change events in both case studies.

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.

Demographic histories of three predatory lady beetles reveal complex patterns of diversity and population size change in the United States

Predatory lady beetles (Coccinellidae) contribute to biological control of agricultural pests, however, multiple species frequently compete for similar resources in the same environment. Numerous studies have examined ecological interactions among the native North American convergent lady beetle (Hippodamia convergens) and two introduced species, the seven-spotted lady beetle (Coccinella septempunctata) and the Asian lady beetle (Harmonia axyridis), in agricultural fields and described multiyear population dynamics. However, the evolutionary dynamics of these interacting species of predatory beetles are uncharacterized. We utilize publicly available multilocus genotype data from geographically disjunct populations of these three species to estimate demography across North American populations. Coalescent analyses reveal (1) a recent (∼4-5 years) decline (>12 fold) in microsatellite effective population size of H. convergens, while expanding (mutation scaled growth rate in 1/u generations = 2910, SD = 362) over evolutionary time scales, (2) a massive (>150 fold), and very recent, effective population size decline in Ha. axyridis, and (3) population size growth (mutation scaled growth rate = 997, SD = 60) over recent and evolutionary time scales in C. septempunctata. Although these estimates are based on genetic data with different mutation rates and patterns of inheritance (mitochondrial versus nuclear), these dynamic and differing population size histories are striking. Further studies of the interactions of these predatory lady beetles in the field are thus warranted to explore the consequences of population size change and biological control activities for evolutionary trajectories in North America.

Response of the European Ladybird Adalia bipunctata and the Invasive Harmonia axyridis to a Neonicotinoid and a Reduced-Risk Insecticide

The spread of the multicolored Asian lady beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in Europe coincided with the decline of the native Adalia bipunctata (L.) (Coleoptera: Coccinellidae). Both species are predators of aphids in orchards, and differential susceptibility to insecticides used to control fruit pests may contribute to explain the competitive advantage of the invasive over the native species. In this study, the insecticidal activity of imidacloprid and spinetoram was tested on third instars and adults of both ladybird species under laboratory conditions. Insects were exposed to insecticide residues on potted peach plants that were sprayed with the maximum recommended field doses (100 mg/liter for imidacloprid and 66.67 mg/liter for spinetoram). Mortality was scored after short (2 d for both stages) and long (7 and 10 d for adults and larvae, respectively) exposure periods. The susceptibility to the insecticides was very similar for H. axyridis and A. bipunctata. Imidacloprid caused a significant increase in the mortality of both stages of the two species for every exposure period. On the other hand, when exposed to spinetoram residues, larvae and adults of both ladybirds did not show higher mortality than controls after short and long exposure periods. The pest suppression provided by ladybirds, which could be severely hampered by the applications of nonselective pesticides, might be enhanced by the adoption of reduced-risk insecticides, selective for these beneficial insects.

A Meta-analysis and Economic Evaluation of Neonicotinoid Seed Treatments and Other Prophylactic Insecticides in Indiana Maize From 2000-2015 With IPM Recommendations

Corn rootworm remains the key pest of maize in the United States. It is managed largely by Bt corn hybrids, along with soil insecticides and neonicotinoid seed treatments (NSTs), the latter of which are applied to virtually all conventionally (non-Bt) produced maize. Frequently, more than one of these pest-management approaches is employed at the same time. To determine the utility and relative contributions of these various approaches, a meta-analysis was conducted on plant health and pest damage metrics from 15 yr of insecticide efficacy trials conducted on Indiana maize to compare the pest-protection potential of NSTs to that of other insecticides and Bt hybrids. The probability of recovering the insecticide cost associated with each treatment was also calculated when possible. With the exception of early-season plant health (stand counts), in which the NSTs performed better than all other insecticides, the vast majority of insecticides performed similarly in all plant health metrics, including yield. Furthermore, all tested insecticides (including NSTs) reported a high probability (>80%) of recovering treatment costs. Given the similarity in performance and probability of recovering treatment costs, we suggest NSTs be optional for producers, so that they can be incorporated into an insecticide rotation when managing for corn rootworm, the primary Indiana corn pest. This approach could simultaneously reduce costs to growers, lower the likelihood of nontarget effects, and reduce the risk of pests evolving resistance to the neonicotinoid insecticides.

Insecticide Resistance Signals Negative Consequences of Widespread Neonicotinoid Use on Multiple Field Crops in the U.S. Cotton Belt

The intensification of industrial agriculture has been enabled by improved crop varieties, genetically engineered crops, fertilizers, and pesticides. Over the past 15 years, neonicotinoid seed treatments have been adopted worldwide and are used on a large proportion of U.S. field crops. Although neonicotinoids are used widely, little is known about how large-scale deployment affects pest populations over long periods. Here, we report a positive relationship between the deployment of neonicotinoid seed-dressings on multiple crops and the emergence of insecticide resistance in tobacco thrips (Frankliniella fusca), a polyphagous insect herbivore that is an important pest of seedling cotton but not soybean or maize. Using a geospatial approach, we studied the relationship between neonicotinoid resistance measured in 301 F. fusca populations to landscape-scale crop production patterns across nine states in the southeastern U.S. cotton production region, in which soybean, maize and cotton are the dominant crops. Our research linked the spatiotemporal abundance of cotton and soybean production to neonicotinoid resistance in F. fusca that is leading to a dramatic increase in insecticide use in cotton. Results demonstrate that cross-crop resistance selection has important effects on pests and, in turn, drives pesticide use and increases environmental impacts associated with their use.

Variable Isotopic Compositions of Host Plant Populations Preclude Assessment of Aphid Overwintering Sites

Soybean aphid (Aphis glycines Matsumura) is a pest of soybean in the northern Midwest whose migratory patterns have been difficult to quantify. Improved knowledge of soybean aphid overwintering sites could facilitate the development of control efforts with exponential impacts on aphid densities on a regional scale. In this preliminary study, we explored the utility of variation in stable isotopes of carbon and nitrogen to distinguish soybean aphid overwintering origins. We compared variation in bulk 13C and 15N content in buckthorn (Rhamnus cathartica L.) and soybean aphids in Wisconsin, among known overwintering locations in the northern Midwest. Specifically, we looked for associations between buckthorn and environmental variables that could aid in identifying overwintering habitats. We detected significant evidence of correlation between the bulk 13C and 15N signals of soybean aphids and buckthorn, despite high variability in stable isotope composition within and among buckthorn plants. Further, the 15N signal in buckthorn varied predictably with soil composition. However, lack of sufficient differentiation of geographic areas along axes of isotopic and environmental variation appears to preclude the use of carbon and nitrogen isotopic signals as effective predictors of likely aphid overwintering sites. These preliminary data suggest the need for future work that can further account for variability in 13C and 15N within/among buckthorn plants, and that explores the utility of other stable isotopes in assessing likely aphid overwintering sites.

Assessing the value and pest management window provided by neonicotinoid seed treatments for management of soybean aphid (Aphis glycines Matsumura) in the Upper Midwestern United States

BACKGROUND

A 2-year, multi-state study was conducted to assess the benefits of using soybean seed treated with the neonicotinoid thiamethoxam to manage soybean aphid in the upper Midwestern USA and compare this approach with an integrated pest management (IPM) approach that included monitoring soybean aphids and treating with foliar-applied insecticide only when the economic threshold was reached. Concentrations of thiamethoxam in soybean foliage were also quantified throughout the growing season to estimate the pest management window afforded by insecticidal seed treatments.

RESULTS

Both the IPM treatment and thiamethoxam-treated seed resulted in significant reductions in cumulative aphid days when soybean aphid populations reached threshold levels. However, only the IPM treatment resulted in significant yield increases. Analysis of soybean foliage from thiamethoxam-treated seeds indicated that tissue concentrations of thiamethoxam were statistically similar to plants grown from untreated seeds beginning at the V2 growth stage, indicating that the period of pest suppression for soybean aphid is likely to be relatively short.

CONCLUSION

These data demonstrate that an IPM approach, combining scouting and foliar-applied insecticide where necessary, remains the best option for treatment of soybean aphids, both in terms of protecting the yield potential of the crop and of break-even probability for producers. Furthermore, we found that thiamethoxam concentrations in foliage are unlikely to effectively manage soybean aphids for most of the pests' activity period across the region. © 2017 Society of Chemical Industry.

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.

Value of neonicotinoid seed treatments to US soybean farmers

BACKGROUND

The benefits of neonicotinoid seed treatment to soybean farmers have received increased scrutiny. Rather than use data from small-plot experiments, this research uses survey data from 500 US farmers to estimate the benefit of neonicotinoid seed treatments to them. As seed treatment users, farmers are familiar with their benefits in the field and have economic incentives to only use them if they provide value.

RESULTS

Of the surveyed farmers, 51% used insecticide seed treatments, averaging 87% of their soybean area. Farmers indicated that human and environmental safety is an important consideration affecting their pest management decisions and reported aphids as the most managed and important soybean pest. Asking farmers who used seed treatments to state how much value they provided gives an estimate of $US 28.04 ha-1 treated in 2013, net of seed treatment costs. Farmer-reported average yields provided an estimated average yield gain of 128.0 kg ha-1 treated in 2013, or about $US 42.20 ha-1 treated, net of seed treatment costs.

CONCLUSION

These estimates using different data and methods are consistent and suggest the value of insecticide seed treatments to the US soybean farmers who used them in 2013 was around $US 28-42 ha-1 treated, net of seed treatment costs. © 2016 Society of Chemical Industry.

Meta-analysis reveals that seed-applied neonicotinoids and pyrethroids have similar negative effects on abundance of arthropod natural enemies

Background

Seed-applied neonicotinoids are widely used in agriculture, yet their effects on non-target species remain incompletely understood. One important group of non-target species is arthropod natural enemies (predators and parasitoids), which contribute considerably to suppression of crop pests. We hypothesized that seed-applied neonicotinoids reduce natural-enemy abundance, but not as strongly as alternative insecticide options such as soil- and foliar-applied pyrethroids. Furthermore we hypothesized that seed-applied neonicotinoids affect natural enemies through a combination of toxin exposure and prey scarcity.

Methods

To test our hypotheses, we compiled datasets comprising observations from randomized field studies in North America and Europe that compared natural-enemy abundance in plots that were planted with seed-applied neonicotinoids to control plots that were either (1) managed without insecticides (20 studies, 56 site-years, 607 observations) or (2) managed with pyrethroid insecticides (eight studies, 15 site-years, 384 observations). Using the effect size Hedge’s d as the response variable, we used meta-regression to estimate the overall effect of seed-applied neonicotinoids on natural-enemy abundance and to test the influence of potential moderating factors.

Results

Seed-applied neonicotinoids reduced the abundance of arthropod natural enemies compared to untreated controls (d = −0.30 ± 0.10 [95% confidence interval]), and as predicted under toxin exposure this effect was stronger for insect than for non-insect taxa (Q_M = 8.70, df = 1, P = 0.003). Moreover, seed-applied neonicotinoids affected the abundance of arthropod natural enemies similarly to soil- or foliar-applied pyrethroids (d = 0.16 ± 0.42 or −0.02 ± 0.12; with or without one outlying study). Effect sizes were surprisingly consistent across both datasets (I₂ = 2.7% for no-insecticide controls; I₂ = 0% for pyrethroid controls), suggesting little moderating influence of crop species, neonicotinoid active ingredients, or methodological choices.

Discussion

Our meta-analysis of nearly 1,000 observations from North American and European field studies revealed that seed-applied neonicotinoids reduced the abundance of arthropod natural enemies similarly to broadcast applications of pyrethroid insecticides. These findings suggest that substituting pyrethroids for seed-applied neonicotinoids, or vice versa, will have little net affect on natural enemy abundance. Consistent with previous lab work, our results also suggest that seed-applied neonicotinoids are less toxic to spiders and mites, which can contribute substantially to biological control in many agricultural systems. Finally, our ability to interpret the negative effect of neonicotinoids on natural enemies is constrained by difficulty relating natural-enemy abundance to biological control function; this is an important area for future study.

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.