Temperate insect species often enter diapause in preparation for overwintering. One such species is the invasive vinegar fly, Drosophila suzukii (Matsumura), which has seasonal polymorphisms, considered winter and summer morphs. To date, the morphs have been differentiated by color and size with winter morphs typically being darker and larger compared to summer morphs. 'Dark' and 'large' are subjective, however, and standardizing an identification process can ensure that the morph of interest is being accurately characterized. The goal of our research was to investigate a quantitative method to distinguish between D. suzukii morphs based on body and wing size. We reared winter and summer morph D. suzukii in the laboratory using standard procedures, and measured wing length, wing width, and hind tibia length. Additionally, we collected field D. suzukii to document the seasonal phenology of the morphs in Minnesota based on our model's cutoff criteria. A classification and regression tree analysis were used to determine which metrics would be best for predicting field-caught D. suzukii morphs. Using laboratory-reared flies as our known morphs for the training data in the classification model we developed classification trees based on wing length and the ratio of wing length to hind tibia length. The frequency of winter and summer morphs present in the field varied based on which classification tree was used. Nevertheless, we suggest ratio of wing length to hind tibia length as the most robust criteria for differentiating D. suzukii morphs because the ratio accounts for the size variability between laboratory-reared and field-caught flies and the error rate of misclassification is reduced to 0.01 for males. The results from this work can aid in future D. suzukii research by allowing scientists to objectively differentiate the morphs, and thereby improve our understanding of the biology and phenology of seasonal morph dynamics. OPEN ACCESSCitation: Tran AK, Hutchison WD, Asplen MK (2020) Morphometric criteria to differentiate Drosophila suzukii (Diptera: Drosophilidae) seasonal morphs. PLoS ONE 15(2): e0228780. ) through the Minnesota Environment and Natural Resource Trust Fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. in cooler temperatures by entering a diapause state [1]. Within the diapause state, reduced metabolism and biochemical alterations affect the insect's biology, behavior, and morphogenesis [1].One such diapausing species that exhibits this phenomenon is the vinegar fly, Drosophila suzukii (Matsumura), commonly known as spotted-wing drosophila. Native to east and southeast Asia, D. suzukii is an important economic pest of soft-skinned fruits (e.g., strawberries, raspberries, blueberries) and stone fruits (e.g. cherries, peach) [2][3][4][5][6]. Drosophila suzukii invaded the continental United States in 2008 and rapidly spread throughout the country [7], and has quickly become a global pest [2,8]. Given its recent global s...

Soybean aphid, Aphis glycines Matsumura, is one of the most important insect pests of soybean in the north central United States. Management of A. glycines currently relies on applications of broad-spectrum insecticides. However, broad-spectrum insecticides can negatively impact the natural enemies associated with aphids. Selective insecticides, on the other hand, are promising control tactics for reducing the negative impact of insecticide applications. Here, we compared the effects of sulfoxaflor (a new selective insecticide) and broad-spectrum insecticides on A. glycines and predators in a two-year field experiment. We sampled A. glycines and aphid predator populations using visual whole-plant inspection. In addition, sweep-net sampling was performed to monitor predator populations. To evaluate the toxicity of the insecticides on predator populations, laboratory bioassays were performed on Hippodamia convergens Guérin-Méneville, Orius insidiosus (Say), and Chrysoperla rufilabris (Burmeister). Field results showed that sulfoxaflor was as effective as the broad-spectrum insecticide in suppressing soybean aphid populations and was less impactful on predator populations. The laboratory bioassays showed that sulfoxaflor was moderately harmful to O. insidiosus, harmless to slightly harmful to H. convergens, and harmless to C. rufilabris These studies suggest that sulfoxaflor holds promise for improving integration of chemical and biological controls for A. glycines management.

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The soybean aphid, Aphis glycines Matsumura, is an economically important soybean pest. Many studies have demonstrated that predatory insects are important in suppressing A. glycines population growth. However, to improve the utilization of predators in A. glycines management, sampling plans need to be developed and validated for predators. Aphid predators were sampled in soybean fields near Rosemount, Minnesota, from 2006-2007 and 2013-2015 with sample sizes of 20-80 plants. Sampling plans were developed for Orius insidiosus (Say), Harmonia axyridis (Pallas), and all aphidophagous Coccinellidae species combined. Taylor's power law parameters from the regression of log variance versus log mean suggested aggregated spatial patterns for immature and adult stages combined for O. insidiosus, H. axyridis, and Coccinellidae in soybean fields. Using the parameters from Taylor's power law and Green's method, sequential fixed-precision sampling plans were developed to estimate the density for each predator taxon at desired precision levels of 0.10 and 0.25. To achieve a desired precision of 0.10 and 0.25, the average sample number (ASN) ranged from 398-713 and 64-108 soybean plants, respectively, for all species. Resulting ASNs were relatively large and assumed impractical for most purposes; therefore, the desired precision levels were adjusted to determine the level of precision associated with a more practical ASN. Final analysis indicated an ASN of 38 soybean plants provided precision of 0.32-0.40 for the predators. Development of sampling plans should provide guidance for improved estimation of predator densities for A. glycines pest management programs and for research purposes.

Tethered flight mills and free‐flight studies are two common approaches for examining insect flight behavior in the laboratory. Flight behavior studies are significant because they provide information with understanding dispersal and range expansion. Each approach has advantages and drawbacks and can influence the flight behavior of the study organism. However, tethered and untethered flight studies are rarely performed simultaneously to determine whether one technique is better suited for a particular species. Here, we conducted a tethered and untethered flight study to determine the limitations, benefits, and effects the two methods could have on assessing an insect's flight capacity. We focused the study on the global invasive pest, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). Propensity of flight and flight duration, distance, and velocity were examined for (1) females and males, and (2) summer and winter morphs, as the two morphs differ significantly in body and wing size. The study showed that summer morphs were more likely to fly when untethered than when tethered to a flight mill. Additionally, when comparing the length of time of flight for first take‐off, D. suzukii flew longer when untethered. Outcomes from this study provide information on D. suzukii flight behavior, which could assist with future research on this economically important fruit pest that is rapidly expanding its range. The results also suggest that the flight apparatus can affect D. suzukii flight behaviors, such that future laboratory flight research should be considerate of the flight technique utilized.