Dicamba drift alters plant-herbivore interactions at the agro-ecological interface

Abstract

Natural populations evolve in response to biotic and abiotic changes in their environment, which shape species interactions and ecosystem dynamics. Agricultural systems can introduce novel conditions via herbicide exposure to non-crop habitats in surrounding fields. While herbicide drift is known to produce a variety of toxic effects in plants, little is known about its impact on non-target wildlife species interactions. In a two-year study, we investigated the impact of herbicide drift on plant-herbivore interactions with common weed velvetleaf (Abutlion theophrasti) as the focal species. The findings reveal a significant increase in the phloem feeding silverleaf whitefly (Bermisia tabaci) abundance on the plants exposed to herbicide at drift rates of 0.5% and 1% of the field dose. Additionally, we found evidence that drift imposes correlated selection on whitefly resistance and growth rate as well as positive linear selection on herbicide resistance. We also identified a significant phenotypic tradeoff between whitefly resistance and herbicide resistance in addition to whitefly resistance and relative growth rate in the presence of dicamba drift. These findings suggest herbicide exposure to non-target communities can significantly alter herbivore populations, potentially impacting biodiversity and community dynamics of weed populations found at the agro-ecological interface.

Dicamba drift alters patterns of chewing herbivory in three common agricultural weeds

“…Our results thus show heterogeneity in herbivory between species given dicamba exposure, and importantly, demonstrate that conclusions drawn from one weed cannot be used to generalize how dicamba drift may influence herbivory in other weeds. Further, a separate experiment using A. theophrasti found a nonsignificant increase in the proportion of chewing herbivory when plants were exposed to dicamba drift, again in a common garden field setting (Johnson and Baucom, 2022), potentially suggesting that results may be heterogeneous between experiments, whether due to changes in herbivore abundance or some other, unexamined environmental factor. While not chewing herbivory, this previous work also found that A. theophrasti exposed to dicamba drift exhibited higher abundance of whitefly larvae – a result that was replicated between two field seasons (Johnson and Baucom, 2022).…”

“…Further, a separate experiment using A. theophrasti found a nonsignificant increase in the proportion of chewing herbivory when plants were exposed to dicamba drift, again in a common garden field setting (Johnson and Baucom, 2022), potentially suggesting that results may be heterogeneous between experiments, whether due to changes in herbivore abundance or some other, unexamined environmental factor. While not chewing herbivory, this previous work also found that A. theophrasti exposed to dicamba drift exhibited higher abundance of whitefly larvae – a result that was replicated between two field seasons (Johnson and Baucom, 2022).…”

“…Our specific questions were: 1) Does dicamba drift alter the proportion or type of chewing herbivory experienced by plants, and 2) Do different weed species show different patterns of chewing herbivory when exposed to dicamba drift? Given that recent work in A. theophrasti showed a non-significant increase in chewing herbivory (Johnson and Baucom, 2022), we expected to find similar results for this species; however, we had no a priori expectation for how patterns of herbivory might be altered in the other species examined, especially since they are in separate families (Convolvulaceae, Solanaceae, and Malvaceae) and are thus each distantly related from one another.…”

“…For example, while there are a number of studies that assess how direct exposure to herbicides may impact the survival and growth of insects (Bohnenblust et al, 2013; Sharma et al, 2018; Fuchs et al, 2020), there are strikingly few reports of how herbicides impact insect herbivory (but see Gutiérrez et al, 2020), and few that examine plant herbivory in the context of herbicide drift (but see Johnson and Baucom 2022). This dearth of knowledge is especially relevant given the recent and widespread shift to the herbicide dicamba (3,6-dichloro-2-methoxybenzoic acid) in contemporary agriculture (Wechsler et al, 2019).…”

“…Exposure to synthetic auxins through an herbicide drift event may directly impact herbivory defense responses since natural auxins closely interact with other phytohormones involved in defense – jasmonic acid (JA), ethylene and abscisic acid (ABA) (Peña-Cortés et al, 1995; Liu and Wang, 2006; Muday et al, 2012; Xu et al, 2020). Despite the likely role of dicamba exposure on plant herbivory, our knowledge of how dicamba drift may affect patterns of herbivory in weed communities remains exceedingly limited: while one study shows an increased abundance of Bemisia tabaci (whitefly) larvae, and an (albeit nonsignificant) increase in chewing herbivory on plants exposed to dicamba drift (Johnson and Baucom, 2022), there are no other examples, to our knowledge, that examine the influence of dicamba drift on herbivory.…”