Development and reproduction of the egg parasitoid, Gonatocerus ashmeadi Girault (Hymenoptera : Mymaridae), as a function of temperature
The development, fecundity, and life table parameters of Gonatocerus ashmeadi Girault, an egg parasitoid of the glassy-winged sharpshooter, Homalodisca coagulata (Say), were studied in the laboratory at six constant temperatures between 12 and 32 degrees C. At 12 degrees C, the parasitoid failed to develop beyond the third instar, and durations of the egg stage and the first and second instars were prolonged. Development from the egg stage to adult emergence varied from 27.1 d at 16 degrees C to 9.5 d at 28 degrees C. Temperature thresholds for development ranged from 3.8 degrees C for first-instar larvae to 12.8 degrees C for the pupal stage. The thermal constants were lowest for the second-instar larvae (26.7 DD) and highest for the pupae (75.4 DD). Nearly 207 DD were required above the lower temperature threshold of 8.5 degrees C to complete development from egg to adult. The optimum temperature for egg to adult development was 29.2 degrees C. Survival from egg to adult was 67.4% at 16 degrees C and ranged from 83.4 to 86.7% between 20 and 32 degrees C. At 16-32 degrees C, the population had a type I survivorship pattern. At 16 degrees C, longevity of adult females and males averaged 27.1 and 19.0 d, respectively, but declined to 6.4 and 6.9 d at 32 degrees C. At 20-32 degrees C, peak adult emergence occurred on the first day of emergence, but at 16 degrees C, it was greatest on the second day. When exposed to temperatures ranging from 16 to 32 degrees C, the female:male sex ratio was similar, ranging from 3.4 to 5.6. Lifetime fecundity was greatest at 24 degrees C and lowest at 32 degrees C, with the maximum net reproduction also occurring at 24 degrees C. Greatest intrinsic and finite rates of increase, shortest population doubling time, and mean generation time occurred when G. ashmeadi was held at 28 degrees C. The parameters defined in this study can influence geographical distribution and are important for the mass-rearing this wasp as biological control agent for the glassy-winged sharpshooter.