Thermal Requirements and Performance of the Parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) on Helicoverpa armigera (Lepidoptera: Noctuidae) Eggs Under Variable Temperatures.

ABSTRACT

Temperature causes physiological and behavioral changes in egg parasitism. Egg parasitoids are a possible alternative for the control of Lepidoptera pests. The cotton bollworm Helicoverpa armigera (Hübner) is a generalist pest that has recently been introduced into Brazil. We evaluated the suitability of H. armigera eggs as hosts for Trichogramma pretiosum Riley and the effects of temperature (18-33°C) on its survival and development. We assessed the developmental time (egg adult), thermal requirements, age-specific fertility, and parasitism rate upon eggs of H. armigera at six different temperatures. Linear and nonlinear (Brière2) models were fitted to our data in order to describe the relationship between developmental rate and temperature for the immature stages of T. pretiosum and estimate the thermal constant (K), lower developmental temperature threshold (LT), optimum temperature for development (Topt), and upper developmental temperature threshold (Tmax). The estimated K and LT estimated by linear model were 130.38 degree days and 10.3°C, respectively. The T0, Topt, and Tmax by Brière model were 11.52, 32.89, and 41.1°C, respectively. Females of T. pretiosum developed at each temperature were assessed, and parasitism rate was above 75% on the first day, except at 30°C where it took 2 d to reach 75%. At 33°C, the highest rate of parasitism was 38%. The life table parameters predict population increases across the temperature range evaluated. The results demonstrated that T. pretiosum are suitable for the control of H. armigera, and the best performance will be achieved when used in regions with temperatures up to 30°C.