Impacts of the herbicide Roundup® and biofertilizers on flower visitor and herbivore foraging in native plants
Date
2023
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Publisher
University of Delaware
Abstract
Interactions between plants and insects are complex and mediated by environmental factors, including land and plant management strategies. With many insects facing population declines in response to anthropogenic disturbances, there is an increasing need to provide high quality forage for beneficial insects that provide ecosystem services such as pollination. Insects may be impacted by agricultural products designed to improve crop yields or reduce pests not only through direct contact while foraging, but also indirectly through changes to the host plants themselves. A better understanding of how the management strategies we implement impact not just plant health but also the quality and attractiveness of plants to foraging insects is necessary to maintaining high quality habitat for beneficial insects in human dominated landscapes. In this study, we examine how application to plants of two biofertilizers and the glyphosate-based herbicide RoundUp® impact insect foraging behavior and nutritional quality of floral rewards. Specifically, we test 1) whether simulated glyphosate drift to sunflowers alters flower visiting insect visitation frequency or pollen nutritional content, 2) whether addition of biofertilizers containing plant growth promoting rhizobacteria (PGPR) of the genus Bacillus and/or mycorrhizae impact flower visiting insect visitation, pollen nutrition, or nectar concentration in sunflower and partridge pea, and 3) whether simulated glyphosate drift alters monarch caterpillar feeding behavior on milkweed leaves. We found that glyphosate at levels corresponding to glyphosate drift significantly reduce insect visitation to flowers but does not impact pollen nutrition. Furthermore, monarch caterpillars do not avoid feeding on leaves contaminated with drift levels of glyphosate. Results of the microbial inoculant experiments were less conclusive. We did not find any significant effects of biofertilizers on insect visitation or pollen and nectar nutritional quality, but our sample size in this exploratory experiment were not adequate to detect effects if they were present. While our findings do not explore every avenue through which these products may impact foraging insects, they indicate that effects of both herbicides and biofertilizers on plants may have implications for insect health, opening the door to further study.
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Keywords
Bees, Monarch butterfly, Pollinator, Environmental factors, Anthropogenic