Environmental factors controlling the induction of diapause in the pink bollworm, Pectinophora gossypiella (Saunders)

Abstract

Fourth instar larvae of the pink bollworm may undergo a facultative diapause at the end of the larval feeding period. Diapause larvae are heavier, have a slower rate of heart beat, and consume oxygen at about one-sixth the rate of non-diapause individuals. In addition, the diapause condition is accompanied by an atrophy of the male gonads and an increase in fat content of both sexes. Diapause in the pink bollworm is primarily under the control of the photoperiod. With the strain of moths used in this study, day lengths of 13 hr or less induced diapause whereas longer day lengths averted this condition. Diet and temperature may also exert an effect on the percentage of the population that enters diapause; however, these effects are not readily apparent except under short days. Under inductive photoperiods the greatest incidence of diapause in the pink bollworm occurred in populations reared under the coolest temperatures on diets having the greatest oil content. A possible thermoperiodic effect of lowered temperatures during the scotophase was demonstrated. The pink bollworm appears to respond to absolute rather than changing day lengths. Although the early larval instars appear to be most sensitive to diapause-inducing photoperiods, diapause may be induced in some individuals in any instar. Furthermore, the effects of short-day exposure in the early instars may be largely nullified by exposure of the subsequent instars to long days.