Behavioral Ecology of Brachycentrus Occidentalis Banks during the Pupation Period

The behavioral ecology of four populations of Brachycentrus occidentalis, maintained on different rations in four separate simulated stream channels, was followed daily from February to May as the larvae pupated and eclosed. Before pupation, the behavior of the population changed markedly as filtering decreased and larvae became unattached and laboratory drift increased. Cases of males were about 3 mm shorter than females. Median time within the pupal case of males and females was 34.5 and 31.0 days, respectively at 10°C. As pupation proceeded, larvae cannibalized pupae. Generally as feeding rate decreased, behavioral changes and pupation were delayed, cannibalism increased and percentage of females eclosing decreased. Females attempted cannibalism more often than males, and showed a higher percentage of successes. Of 160 pupal cases collected from Lawrence Creek, Wisconsin, approximately 9% showed evidence of cannibalism. An additional 32% were infested with Eukieffefriella sp., a small chironomid. Cannibals, predators, and parasites are considered as agents of selection pressure in connection with case construction and pupal distribution among the Trichoptera.