Diapause in the Boll Weevil (Coleoptera: Curculionidae): Life-Stage Sensitivity to Environmental Cues

This study examines the diapause response in naturally occurring boll weevils under field and simulated field environments of north Mississippi. Squares containing early-stage weevils were collected in July, August, and September and subsamples from each group were installed into similar dynamic environments in the laboratory. In this manner, some weevils experienced uninterrupted photoperiods and temperatures between the field and laboratory (controls), and others experienced a shift forward in time or backward in time between the field and laboratory (treated). Results indicate selective sensitivity among individuals to diapause-inducing or averting daylengths and temperatures during early life stages independent of later stages and during late stages (including adults) independent of earlier stages. For example, it appears that some individuals are sensitive primarily during the early or late life stages, and depending on the environmental cues received at these times, they may or may not develop the diapause phenotype as adults. However, the rates of gain or loss in the acquisition of diapause depend on the intensity and duration of the token stimuli during part or all of the life cycle. If the proper cues are sustained throughout the life cycle, then the expression of diapause in the population will be maximized. Alteration in cues at any time will increase or decrease the percentage of weevils in diapause, with the relative effect related to the intensity and duration of the original stimuli. Once they receive a threshold to diapause-inducing stimuli, populations appear to be more responsive to environmental change. These results may explain some of the variability observed in diapause among studies.