Egg diapause in Psorophora columbiae (Dyar and Knab) : development of a predictive diapause induction model

Abstract

Diapause induction responses for Psorophora columbiae were investigated in photoperiod- and temperatue-controlled growth chambers. The results of these studies demonstrated that egg diapause was induced by photoperiods perceived by the larvae, pupae, and adult stages of development. Diapause induction was also temperature dependent. In response to temperature changes during the photophase and scotophase, the critical photoperiod required to induce diapause was modified identically. At 32(DEGREES)C, diapause induction was inhibited, persumably due to the inactivation of the physiological processes involved in diapause determination. Preconditioning nondiapause eggs to 15(DEGREES)C for greater than 17 days suppressed the hatching response. The percent of suppressed egg hatch was dependent upon the exposure time to both chilling and warming temperatures prior to hatching trials. Based on physiological concepts and the statistical analysis of diapause responses, a phenomenological model was developed to predict the incidence of diapause induced by photoperiods and temperatures. Conceptually, diapause was assumed to be induced in relation to the amount of photoproduct produced by the photoperiodic clock in response to the environmental cues perceived. A rate approach was used to describe photoproduct production during photophase and scotophase. Mean rates for the reactions were linearly related to photophase and scotophase temperatures. For 5 of the 6 observed diapause response curves, the variability in diapause induction responses was described by a cumulative quadratic distribution. Field evaluation of the model was conducted in Texas, Louisiana, and Mississippi. Model simulations with hourly temperatures indicated that P. columbiae perceived the initial 23 min of twilight as part of the photophase. Though maximum-minimum daily temperatures did not accurately describe environmental temperatures perceived by field populations of mosquitoes, the model compensated for the lack of accurate temperature data and predicted by 10% or less the incidence of diapause in 6 of the 7 field samples collected. Simulation of the model for Louisiana and Mississippi indicated that the change in photoperiodic responses for P. columbiae populations originating at different latitudes was 0.7 h for each 5(DEGREES) change in latitude.