Complex landscapes, complex diets: DNA metabarcoding reveals lady beetle prey richness increase with landcover diversity

Understanding the capacity of mobile organisms such as insects to utilize
resources across different patches in a landscape can reveal strategies
for their conservation. Past research suggests that higher levels of
non-crop habitat or landcover diversity in agricultural regions typically
benefits generalist predators who can fortify their diets with prey from
multiple adjacent habitats. For some taxa such as lady beetles
(Coccinellidae), dietary diversity is associated with improved fitness,
but foraging patterns in real landscapes are hard to measure. We used a
DNA metabarcoding approach to explore how the presence and taxonomic
richness of arthropod prey in lady beetle diets varied by local habitat
(crop vs. non-crop) and landscape complexity (non-crop habitat and
landcover diversity in a 250 m radius). We collected over 500 individual
lady beetles from a range of landscapes in 2019 and 2021 in southern
Wisconsin (USA), performed whole-body DNA extractions, amplified arthropod
DNA using primers optimized for insectivore diets, and used Illumina
sequencing to characterize the taxonomic composition and diversity of
prey. We found 50 unique prey taxa in lady beetle guts from eight
arthropod orders (mostly flies, true bugs, and thrips). Lady beetles in
landscapes with a greater proportion of crops were slightly more likely to
have prey in their gut, and community-level prey richness was strongly
positively correlated with surrounding landcover diversity. This effect
was dampened slightly in high-crop landscapes, likely due to smaller prey
species pool available to predators. Our results enhance knowledge of lady
beetle trophic ecology and demonstrate that supplementation of diets
through increased habitat diversity may be an important mechanism for the
success of mobile generalists in complex landscapes.