Cannibalism in mosquito larvae during microbial larvicide potency tests

We observed instances of cannibalism (intraspecific predation) among intra-instar larvae of Culex pipiens Linnaeus, 1758 while performing a bioassay of Lysinibacillus sphaericus (formerly named Bacillus sphaericus) larvicide, when the larvae were exposed to the larvicide for 48 h in the absence of food. Larvae without symptoms of poisoning attacked and devoured those visibly affected. Cannibalism was more prevalent in 1^st-2^nd instar larvae than in 3^rd-4^th instar. This phenomenon should be taken into account when interpreting the results of larvicide bioassays, especially when the exposure lasts over 24 h. The necessity of creating optimal conditions for organisms tested is emphasised.