Variable isotopic compositions of host plant populations preclude assessment of aphid overwintering sites

Authors: CROSSLEY, MICHAEL - University Of Wisconsin; Steffan, Shawn; VOEGTLIN, DAVID - Illinois Natural History Survey; HAMILTON, KRISTA - Wisconsin Department Of Agriculture; HOGG, DAVID - University Of Wisconsin

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2017
Publication Date: 12/5/2017
Citation: Crossley, M.S., Steffan, S.A., Voegtlin, D.J., Hamilton, K.L., Hogg, D.B. 2017. Variable isotopic compositions of host plant populations preclude assessment of aphid overwintering sites. Insects. 8(4):128. https://doi.org:10.3390/insects8040128.
DOI: https://doi.org/10.3390/insects8040128

Interpretive Summary: In Wisconsin, the soybean aphid is a major pest of a major crop (soybeans). Given the very specific use of alternate host plants (buckthorn) during the winter months, there is the possibility that overwintering sites could be targeted to drastically reduce soybean aphid numbers in the spring. It is hoped that the isotopic compositions of soybean aphids might reveal where in the landscape they had overwintered, permitting targeted sprays to buckthorn patches that are serving as aphid hosts. Findings and impact: The findings of our study suggest that while the soybean aphid’s isotopic composition can be positively linked to that of its host plant, the isotopic signals of the buckthorn patches across the landscape were not distinct enough from one another to reliably trace the overwintering locations of soybean aphids that had dispersed to soybean fields. That said, the data generated in our study are not definitive, and further sampling over more years would likely help to better address whether broad environmental factors (e.g., soil type, latitude/longitude, watershed) are affecting the isotopic composition of buckthorn enough to discern the aphids’ prior use of buckthorn.

Technical Abstract: 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 both soil composition and organic matter content. However, lack of sufficient differentiation of geographic areas along axes of isotopic and environmental variation appears to preclude the use of 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.