Soft landings for tough times: the influence of ground cover characteristics on the wandering behavior and subsurface pupation of overwintering Lepidoptera in urban ecosystems
Date
2025
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Publisher
University of Delaware
Abstract
North American caterpillars predominately feed on tree hosts, and subsurface pupation among arboreal Lepidoptera is widespread. Therefore, such species are vulnerable to conditions under host trees during the vulnerable wandering and pupation stages. Current landscaping practices may contribute to declines in Lepidopteran diversity and abundance, particularly in compacted soils of urban environments. Understory plant choice and detritus management following land development characterize soil structure. Therefore, dominant cover types, such as turfgrass, may form novel subsurface microhabitats. The goals of this study were threefold: (a) to determine the most frequently encountered substrates beneath trees in the urban and suburban Eastern U.S. by arboreal, wandering Lepidoptera, (b) to test pupation substrate preference and the influence of substrate type, heterogeneity, and compaction on wandering behavior and pupation depth in the lab, and (c) to test for evidence of ecological traps and characterize the most optimal “soft landing” environments for burrowing Lepidoptera by measuring the ecological and management influences of the aboveground-belowground interface on their burrowing success, overwintering survival, and moisture retention. The Google Earth survey showed that turfgrass is the most frequently encountered substrate beneath urban trees. I found strong evidence that Heterocampa pulverea (Notodontidae) pupated at significantly greater depths within mulch and leaves compared to turfgrass. Caterpillars of this species preferred shredded bark mulch the most, and it had the highest rate of immediate pupation. Burrowing time on bare soil increased nearly fivefold compared to mulch and it was the least preferred substrate. Tests of overwintering survival in Anisota stigma (Saturniidae) showed a positive correlation with tree canopy density. Substrate type also significantly influenced emergence rates, with A. stigma showing the highest success in forest remnants, followed by mulch then mature turf. This species’ emergence rate was lowest in layered urban understories, followed by recently established turf, then bare soil. When soil temperature parameters were included in emergence success models with a smaller sample size of this species, daily average temperature range showed a significant negative relationship. Overwinter water retention of A. stigma adults was weakly, positively correlated with the average daily maximum soil temperature and surface pupation, suggesting the use of discontinuous gas exchange for water conservation under stress. Finally, soil compaction, which was negatively correlated with organic matter, and the proportion of bare soil cover were two covariates negatively correlated with burrowing success in A. stigma and Manduca sexta (Sphingidae), respectively. These findings reveal that common landscaping practices likely contribute to urban declines in burrowing Lepidoptera. Evidence of an ecological trap substrate was highest for layered urban understories and recently established turf, which were surprisingly inhospitable compared to forest remnants. Specific strategies such as mulching or incorporating organic soil amendments may be required to restore habitat productivity exemplified by forests. These data emphasize the importance of “soft landing” management beneath moth host plants, which protect and remediate soil health following land development. Social acceptance of ecological landscaping must be cultivated, and the initiative can start beneath the canopy. Future research should include turfgrass-associated disturbances such as foot or mower traffic when examining this substrate’s potential as an ecological trap because of the propensity of turf thatch to promote shallow burrowing.
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Keywords
Landscaping, Lepidoptera, Pupation, Soil, Urban environments