Effect of gypsum dust on lepidopterous larvae

Abstract

Airborne particulate matter is a significant concern to human health, but the effects of the deposition of dust on other species in the wild has not been well investigated. The vulnerability of insects to mineral dusts has been well known from agricultural management and the current co-occurrence of endangered species with dust-producing industry makes this knowledge more relevant and in need of expansion. To investigate the effects of fugitive gypsum dust on an endangered butterfly species, we exposed a surrogate lepidopterous species (Gloveria medusa; Lasiocampidae) to realistic quantities of gypsum dust either on its hostplant or externally applied to larvae. We then used surviving larvae in a choice experiment to ascertain if previous exposure to gypsum contaminated hostplant affected larval preferences. Consumption of gypsum-dusted foodplant increased risk of death for larvae significantly compared with both controls (hazard ratio = 4.80; 95% CI = 2.08–11.03; p = 0.0002) and the external treatment (HR = 2.85; 95% CI 1.41–5.76; p = 0.003). External treatment elevated death rate, but not significantly (HR = 1.68; 95% CI =0.65–4.33; p = 0.28). Elevated risk of death was greater for smaller larvae. Hostplant choice after previous exposure was not significant, but suggestive that larvae consume more of the hostplant in the condition that they previously experienced (either with or without gypsum). Based on these results and previous studies, we conclude that fugitive gypsum dust may affect populations through direct mortality, reduced developmental rates, lower weights, and extended development periods that disrupt natural phenology. Use of dust to reduce insect infestations is an ancient practice, and knowledge of these effects should be revived to address chronic harms of fugitive dust on insects as they face worldwide declines.