Historical soil management practices influence insect responses to conservation plantings

Farmers can earn income by converting land under agricultural production into perennial native habitat designed to promote ecosystem health and conservation. However, depending on historical management practices, differences in soil health can impact plant-insect interactions within the planting. Our goal is to investigate the effects of previous agricultural management strategies on insect communities associated with native swamp milkweed plants (Asclepias incarnata) in conservation plantings via changes in the soil and associated microbiome. We grew swamp milkweed in pots with soil collected from conventional (tillage, no cover crops), conservation (no till, cover crops) and natural (native prairie) management plots and put them in a common garden for natural colonization. Insect populations were visually sampled and milkweed growth measured on a weekly basis for two months. In conservation and natural management treatments, we saw taller plants and higher insect biodiversity in contrast to the conventional treatments. This result could be attributable to soil nutrient content and availability or a more diverse soil microbiome. We also observed lower herbivore abundance on these plants, which we believe is a result of higher levels of defensive cardenolides that negatively impact generalist herbivores with minimal impact on specialists. These results highlight the role of agricultural management in influencing soil health, plant performance, and insect biodiversity in conservation plantings.