DEVELOPMENTAL RATES FOR CHROMATOMYIA-FUSCULA (ZETT) (DIPT, AGROMYZIDAE) AT 5 CONSTANT TEMPERATURES

The median developmental rates for all immature stages of Chromatomyia fuscula (Zett.) increased linearly between 9 and 21 degrees C. An exp onential and a Cobb-Douglas model was tested, but gave only as good as or slightly better fits than the linear regression model. The lower t hermal developmental thresholds for all stages were 3.0 +/- 0.5 degree s C. Both sexes required 400 degree-days above 3.0 degrees C for the t otal development from egg to adult emergence. At the relatively low te mperatures investigated, C. fuscula had a fast developmental rate, esp ecially in the pupal stage, and low thermal thresholds compared to oth er agromyzids. The possible reasons for this are discussed. Introducti on of a dichotomous variable for sex in the regression model for egg t o adult emergence indicated an elevated mortality below 15 degrees C. Also, the introduction of a dichotomous variable proved the sex ratio 1 male:1.3 females to be significantly different from 1:1. The thermal sums calculated indicated that C. fuscula theoretically could have tw o generations per year in a large part of its range. The reasons why i t is still univoltine must be sought elsewhere.