Threshold temperatures and relative humidities, growth rates, and physiological development times were calculated for egg laying, larval development, progeny production, and sex ratio of the endoparasitoid Pediobius furvus (Gahan) (Hymenoptera: Eulophidae), a key pupal parasitoid of several graminaceos stem borers, among which is Chilo partellus Swinhoe (Lepidoptera: Pyralidae). These studies were conducted within a temperature range of 15–35°C, with a relative humidity of 30–80% at each temperature, and have shown that neither oviposition nor development is possible under extremes of temperature conditions such as 15 and 35°C. Optimum conditions for oviposition and development lie between 25 and 30°C and 60–80% RH. Low temperatures resulted in longer developmental period(s) and a preponderance of male progeny. However, parasitization activity increased with temperatures up to 30 ± 1.5°C under relative humidity levels of 60–80%. Thus, the criteria for optimum parasitoid production may not only be associated with unfavorable temperatures and relative humidity regimens during oviposition, but more importantly, with temperatures at which parasitoid development takes place.