The main effects and interactions between temperature and host instar on development and survival of Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae), a parasitoid of many pyralid (Lepidotera: Pyralidae) larvae, were studied under laboratory conditions. The duration of development in Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) larvae of second, third, fourth and fifth instar and at seven constant temperatures (15, 17.5, 20, 25, 30, 31, and 32°C) was measured. Development time decreased significantly with increasing temperature within the range 15–30°C. When parasitism took place on second instar hosts the parasitoid development took significantly longer compared with other instars. Differences among third, fourth and fifth instar proved to be insignificant. Thermal requirements of development (developmental thresholds, thermal constant, optimum temperature) of V. canescens in each host instar were estimated with application of a linear and one nonlinear model (Logan I). Upper and lower developmental thresholds ranged between 36.01–36.41 and 10.86–11.37°C, respectively. Optimum temperature for development was estimated at between 30.59–30.81°C. All above-mentioned parameters did not vary significantly with host instar. The thermal constant decreased with host instar at parasitism and ranged between 370.4 and 555.6 d-degrees. Immatures’ survival peaked at 30°C and was higher in older instars (third-fifth).
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