Impact of different Bacillus thuringiensis variety israelensis treatments on a chironomid (Diptera Chironomidae) community in a temporary marsh

Bacillus thuringiensis variety israelensis is a selective biological insect icide for control of mosquito and black fly larvae and has little or no eff ect on nontarget organisms. Its impact on the structure of lentic communiti es, however, has rarely been tested in the field. Chironomid larvae were sa mpled in a control zone (0 mg B. thuringiensis/liter) and in a treated encl osure (1.6 mg/liter) on 5 sampling dates. The emergence of adults also was studied at 4 treatments-0, 1.6, 3.3, and 6.7 mg/liter. One week after treat ment with 1.6 mg B. thuringiensis/liter, chironomid larval density decrease d by 38%. Treatment with B. thuringiensis affected the emergence of sampled chironomids. Ten days after treatment, Polypedilum nubifer (Skuse) was the only sampled organism which increased in relative abundance. P. nubifer re presented >75% of the emerging adults.