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 whitefly hosts (Homoptera: Aleyrodidae), the silverleaf whitefly, Bemisia argentifolii Bellows & Perring, and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), as well as the parasitoid, Eretmocerus eremicus Rose & Zolnerowich (Hymenoptera: Aphelinidae) attacking both hosts. Mean egg numbers 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 declined after 6 d, although the model fit was poor. The model did not fit the oviposition data at 32 degrees C. Maximal oviposition rate occurred at 24 degrees C (12 eggs per 48-h period), and the model was almost linear. For T. vaporariorum, the model closely fit mean eggs laid, with highest rates of approximate to 12 eggs per 48 h at 21 and 24 degrees C. Numbers of whitefly eggs as a function of time and temperature were described by a three-dimensional surface model that was also used to estimate temperature thresholds for oviposition (12.5 degrees C for B. argentifolii and 10.9 degrees C for T. vaporariorum). Increasing temperatures produced decreased preoviposition periods in B. argentifolii, whereas temperature extremes resulted in longer periods for T. vaporariorum. Development times from egg to adult, percentage 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 reared on both hosts. Development rate was higher for B. argentifolii than T. vaporariorum at 24 and 28 degrees C. Development of E. eremicus was faster using B, argentifolii as hosts than T. vaporariorum at 24, 28, and 32 degrees C. By extrapolation of development rates, lower developmental thresholds (degrees C) were estimated as follows: T. vaporariorum, 2.92; B. argentifolii, 10.32; E. eremicus on T. vaporariorum, 5.44; and E. eremicus on B. argentifolii, 8.7. Mean degree-day requirements for egg to adult development were calculated for T. vaporariorum, 483.4; B. argentifolii, 319.7; E. eremicus on T. vaporariorum, 417.3; and, E. eremicus on B. argentifolii, 314.4. Percentage 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 occurred 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 decreasing on B. argentifolii. The life history of E. eremicus was profoundly affected by that of its host.