The grounds for burrowing: The impact of substrate on Heterocampa pulverea (Notodontidae) wandering behavior

Current landscape designs may help explain declines in Lepidopteran diversity and abundance within managed landscapes, particularly regarding ground covers under host trees, as this is frequently the site of pupation. We used modified choice test methods to elucidate the influence of substrate type and soil compaction on the subsurface pupation and wandering behavior using Heterocampa pulverea (Notodontidae) as a model organism to compare turf, mulch, leaves, and bare soil. At the start of the wandering phase, a caterpillar was placed at the center of the mesocosm, and a video recording was started. Up to 2-5 caterpillars entered a single mesocosm at separate times. Caterpillars pupated at different depths across the substrates, with a greater average depth within mulch and leaves compared to turfgrass. Caterpillars also preferred mulch and avoided bare soil. Mulch had the highest rate of immediate pupation, 70%, and it was selected most often by 40% of caterpillars. Bare soil was selected by only 4.8% of caterpillars and the time spent digging was nearly five times that in mulch.  Pupation occurred equally often in turf and leaves and these substrates had comparable rates of pupation success for each dig attempt. Landscapers should prioritize protecting the soil beneath trees with organic substrates and reducing disturbances to promote efficient pupation of H. pulverea, and by inference, many other macro-moth species that are disappearing from urban and suburban spaces.