SURVIVAL OF BEMISIA-TABACI ADULTS UNDER DIFFERENT CLIMATIC CONDITIONS

The ability of the sweet potato whitefly, Bemisia tabaci Gennad., to s urvive a range of environmental conditions was investigated in the lab oratory. The range of temperature and humidity investigated correspond s to the normal climatic range during B. tabaci's summer migration in Israel. Adult whiteflies confined to small test cages were exposed to combinations of temperature (25, 30, 35, and 41 degrees C) and relativ e humidity (20, 50, 80, and 100%) for periods of 2, 4, or 6 h. A logis tic regression model describing the four-dimensional surface defining percent survival as a function of time, temperature, and humidity was developed. Using stepwise regression to exclude non-significant terms, the linear predictor included temperature, and the products of temper ature and time, and humidity and time. The model accounted for 75% of the variance. A reparameterization of the fitted regression model sugg ests that survival potential is conditioned by temperature conditions prevailing during the previous 10 h. Whitefly survival after 2 h expos ure ranged from approximate to 90% survival at 25 degrees C and 100% R H, to <2% survival at 41 degrees C and 20% r.h.. No whiteflies survive d more than 2 h exposure at these latter extremes of temperature and h umidity. Survival rates decreased slightly after experimental whitefli es were kept in a cage with food a further 20 h at 25 +/- 2 degrees C, 55 +/- 5% r.h. Investigations of the effects of hunger and virus infe ction, showed that both increased mortality.