Impact of Environmental Factors on Trichogramma pretiosum Reared on Southwestern Corn Borer Eggs

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Abstract
We investigated the effect of constant temperature, fluctuating temperature, relative humidity, and photophase on Trichogramma pretiosum Riley developmental time, longevity, fecundity, and sex ratio. Equations describing developmental time were derived for all life stages using second-degree polynomials. The optimal developmental rate occurred at approximately 30°C for all life stages. Developmental thresholds for egg, larval, prepupal, and pupal stages, and for development from oviposition to adult, were 13.3, 10.3, 10.7, 13.7, and 13.1°C, respectively. Adult longevity was approximately 2 days under constant temperatures, with the exception of 17 and 35°C (7.67 and 0.60 days, respectively). Fecundity under constant temperature was 18.0 ova per female below 30°C and 9.0 ova per female above 30°C. Parasite sex ratios (male:female) were 1:1, 1:1, 1:2, 1:3, 1:4, and 1:5 for host eggs containing 1, 2, 3, 4, 5, and 6 parasites, respectively. Median developmental time was affected only when the temperature fluctuated between 22 and 38°C. Fecundity and longevity were not significantly affected by the fluctuating temperatures included in the study. Developmental time at 20% RH was approximately 2 days longer than at 60 and 80% RH. Adult female longevity was also significantly longer at 20% RH. However, fecundity was significantly greater at 80% RH. Developmental time was increased under a 12 and 16 h photophase. Female longevity was significantly shorter under a 12 h photophase. Fecundity was unaffected by photophase.