Modeling seasonal development of the sorghum midge, Contarinia Sorghicola (Coquillett)

Abstract

Two separate temperature-dependent models were formulated which described spring emergence from overwintering and development of nondiapausing generations of the sorghum midge, Contarinia sorghicola (Coquillett) (Diptera: Cecidomyiidae). Adult emergence rates and distributions were determined for diapausing and nondiapausing midges reared at constant temperatures. These data were used to develop stochastic, two-component, temperature-based models which predicted the emergence of adult midges in the field. The first component of each model used a poikilotherm rate equation to predict emergence rates as a function of temperature. The second model component distributed emerging adults over normalized time using a temperature-independent cumulative Weibull distribution. When coupled, components formed temperature-dependent simulation models which distributed emerging adults over calendar time and were suitable for incorporation into a larger seasonal dynamics model for the sorghum midge. Development of the spring emergence model involved determining the influence of different constant temperatures on adult emergence from diapausing midges. Adults emerged when temperatures were between 15(DEGREES)C and 35(DEGREES)C. When temperatures were outside 20(DEGREES)C to 30(DEGREES)C, numbers of emerged adults declined sharply. As temperatures increased, fewer days were required for adult emergence. At 35(DEGREES)C, the thermal optimum was exceeded which resulted in longer emergence times. The poikilotherm rate equation and Weibull distribution accurately described the emergence data. Simulations of spring emergence tended to predict emergence before it actually occurred in the field. Incorporating a 1.27 cm precipitation threshold which modified emergence rates to reflect daily rainfall totals corrected the discrepancy.