Effect of Bt toxin on net-spinning caddisfly Stenopsyche marmorata (Trichoptera, Stenopsychidae)

The Bacillus thuringiensis (Bt) toxin targets lepidopteran, dipteran and coleopteran pests. Despite their close taxonomic relationship to Lepidoptera, few studies have examined the hazard of Bt toxins on Trichoptera. We performed laboratory exposure tests to examine the effects of Bt var. aizawai on filter-feeding caddisflies, particularly Stenopsyche marmorata. In the continuous exposure test, the mortalities ranged from 0% at 1 mg/l to 100% at 20 mg/l 24 hours after exposure to Bta. The mortality at each concentration increased from 24 to 48 hours. In limited contact, mortality increased with contact time. Acclimatisation and water quality also affected larval mortality. Our results suggest that higher concentration and longer exposure to Bta affect or affect the increase of larval mortality.