Temperature-dependent life history of Eretmocerus eremicus (Hymenoptera : Aphelinidae) on two whitefly hosts (Homoptera : Aleyrodidae)

The effects of temperature on insect life history were studied for two whit efly hosts (Homoptera: Aleyrodidae), the silverleaf whitefly, Bemisia argen tifolii Bellows & Perring, and the greenhouse whitefly, Trialeurodes vapora riorum (Westwood), as well as the parasitoid, Eretmocerus eremicus Rose & Z olnerowich (Hymenoptera: Aphelinidae) attacking both hosts. Mean egg number s as a function of time were fitted to models for age-specific oviposition for each whitefly. For B. argentifolii, numbers of eggs laid increased with time at 15, 21, and 24 degrees C. At 28 and 32 degrees C, the curve declin ed after 6 d, although the model fit was poor. The model did not fit the ov iposition data at 32 degrees C. Maximal oviposition rate occurred at 24 deg rees C (12 eggs per 48-h period), and the model was almost linear. For T. v aporariorum, the model closely fit mean eggs laid, with highest rates of ap proximate to 12 eggs per 48 h at 21 and 24 degrees C. Numbers of whitefly e ggs as a function of time and temperature were described by a three-dimensi onal surface model that was also used to estimate temperature thresholds fo r oviposition (12.5 degrees C for B. argentifolii and 10.9 degrees C for T. vaporariorum). Increasing temperatures produced decreased preoviposition p eriods in B. argentifolii, whereas temperature extremes resulted in longer periods for T. vaporariorum. Development times from egg to adult, percentag e mortality, and estimated degree-days for development were measured at 15, 21, 24, 28, and 32 degrees C for both whiteflies, and for E. eremicus rear ed on both hosts. Development rate was higher for B. argentifolii than T. v aporariorum at 24 and 28 degrees C. Development of E. eremicus was faster u sing B, argentifolii as hosts than T. vaporariorum at 24, 28, and 32 degree s C. By extrapolation of development rates, lower developmental thresholds (degrees C) were estimated as follows: T. vaporariorum, 2.92; B. argentifol ii, 10.32; E. eremicus on T. vaporariorum, 5.44; and E. eremicus on B. arge ntifolii, 8.7. Mean degree-day requirements for egg to adult development we re calculated for T. vaporariorum, 483.4; B. argentifolii, 319.7; E. eremic us on T. vaporariorum, 417.3; and, E. eremicus on B. argentifolii, 314.4. P ercentage mortality also was significantly affected by temperature in both species of whitefly. For T. vaporariorum, higher temperatures caused higher levels of mortality, with almost 98% killed at 32 degrees C. The reverse o ccurred in B. argentifolii, where highest levels of mortality were found at the lowest temperatures. Mortality patterns in E. eremicus reflected those of the host: increasing with temperature on T. vaporariorum, while decreas ing on B. argentifolii. The life history of E. eremicus was profoundly affe cted by that of its host.