DIAPAUSE INDUCTION IN THE HORN FLY (DIPTERA, MUSCIDAE)

Laboratory studies of diapause induction in the horn fly Haematobia ir ritans irritans (L.) indicated that the incidence of diapause was unre lated to daylength or the number of day-night cycles. Transfer experim ents were conducted to estimate the beginning and end of diapause sens itivity and the required number of days for diapause induction. On ave rage, sensitivity was between the ages 0.10 and 0.82 on a physiologica l age scale of immature development. The number of days required for 5 0% diapause was estimated as 19.1 days. A model was developed relating the proportion of insects in diapause to the number of days spent in the interval 0.10-0.82. Additional experiments revealed that diapause in the puparia was related to the mean temperatures experienced by imm atures during the interval of sensitivity. An equation relating the pr oportion in diapause to temperature was also developed and compared wi th the required day number model. Both models provided similar estimat es of the proportion of horn flies entering diapause.