COMPARATIVE SUSCEPTIBILITY OF CHIRONOMID LARVAE (DIPT, CHIRONOMIDAE) TO BACILLUS-THURINGIENSIS SEROVAR ISRAELENSIS WITH SPECIAL REFERENCE TO ALTERED SUSCEPTIBILITY DUE TO FOOD DIFFERENCE

Bacillus thuringiensis serovar israelensis exhibited larvicidal activities, with varying degrees, against detritus-feeding larvae of the six species belonging to the subfamily Chironominae (Dipt., Chironomidae): Chironomus kiiensis, Chironomus yoshimatsui, Dicrotendipes pelochloris, Glyptotendipes tokunagai, Paratanytarsus sus sp., and Stictochironomus akizukii. Of these, the most susceptible were C. kiiensis, C. yoshimatsui, and Paratanytarsus sp.; in these species a high/rapid mortality (70-100%) occurred within 2 days at a bacterial concentration of 17 mu g/ml. The least susceptible was S. akizukii. The degree of difference in susceptibility ranged from 10 to 1000 times among the six species. There was a marked difference in susceptibility between two larval populations of a euryphagous species, Pentapedilum tigrinum, when reared on different foods prior to treatment; the larvae reared on aquatic plant tissue were 100 times more susceptible than the larvae fed on detritus.