Biology of Telenomus pachycoris (Hymenoptera: Scelionidae), a parasitoid of eggs of Pachycoris torridus (Hemiptera: Scutelleridae): the effects of egg age, exposure time, and temperature

Abstract

Telenomus pachycoris (Johnson) (Hymenoptera: Scelionidae) is a parasitoid of eggs of Pachycoris torridus (Scopoli) (Hemiptera: Scutelleridae), a main pest of physic nut (Jatropha curcas L.; Euphorbiaceae). The objective of this work was to know the biology of T. pachycoris in P. torridus eggs under various conditions in order to develop a rearing technique for this parasitoid in the laboratory. We offered eggs of P. torridus to T. pachycoris during 4 exposition periods (6, 12, 18, and 24 h), as well as eggs of different ages (1 to 11 d), to evaluate, in both experiments, the number of parasitized eggs, duration of the egg-to-adult period, percentage of emergence, and sex ratio. We also evaluated the effect of constant temperatures (18, 20, 22, 25, 28, and 30 degrees C) and determined the duration of the egg-to-adult period, percentage of emergence, and sex ratio and estimated the thermal requirements and the number of generations per yr of T. pachycoris at each temperature. Parasitism of eggs was the highest at 12 h of exposure. Eggs up to 3 d old were the most parasitized, and the parasitism was zero on day 11. The duration of the egg-to-adult period was inversely proportional to temperature, ranging from 33.6 d at 18 degrees C to 9.8 d at 30 degrees C. The threshold temperature estimated for T. pachycoris was 12.9 degrees C, and the estimated thermal constant was 163.9 degree-days. The number of generations of T. pachycoris ranged from 11.3 to 38.1 per yr at 18 and 30 degrees C, respectively. The results may contribute to developing techniques for rearing T. pachycoris in the laboratory.