Fenoxycarb-induced caste differentiation and mortality in Coptotermes formosanus (Isoptera: Rhinotermitidae)

Abstract

In no-choice feeding bioassays, Formosan subterranean termites, Coptotermes formosanus Shiraki, exposed to the insect growth regulator (IGR) fenoxycarb underwent dosage- and time-dependent caste differentiation and mortality. Survival curves for 2 colonies indicated a decline in the number of workers over time at fenoxycarb concentrations ranging from 10 to 3.162 ppm, with a steeper decline generally at higher concentrations and after 2 wk exposure. Termite workers in the 2 colonies differed significantly in their response to the IGR. The worker population of colony A was reduced because of differentiation into intercastes, presoldiers, and soldiers. Reduction in the worker population of colony B resulted primarily from death of undifferentiated individuals. Termites accepted the treated blocks as a food source as evidenced by consumption data. Protozoan populations were reduced significantly in both colonies, but generally not eliminated in workers exposed to fenoxycarb for 4 wk. This study provides further evidence that responses of different termite colonies to IGRs can be extremely variable.