Bionomics and ecology of Bemisia tabaci (Sternorrhyncha: Aleyrodidae) in Italy.

The development of a B-biotype Bemisia tabaci Italian colony was studied on bean at 9 constant temperatures (15, 16, 17, 20, 23, 26, 29, 32, 35°C). The developmental time from egg-to-adult varied from 70 days at 16°C to 22 at 26°C and higher temperatures. A thermal requirement for egg-to-adult development of 307 day-degrees was calculated, based on a lower developmental threshold of 11.53° C. The survival of egg, nymph and adult whiteflies was investigated at 0, 2, 4, and 6°C on broad bean for periods of 1-8 days. The adult was the most cold-sensitive stage, while the egg and nymph showed a similar level of cold resistance. The effect of sub-lethal cold stress of 4-8 days at 4°C on eggs and nymphs was studied. After exposure to low temperatures, whiteflies needed longer developmental times, from 5 to 8 days more. The presence of B. tabaci under outdoor conditions in Italy was investigated with field surveys and correlated with climatic data; the whitefly species was found in open field conditions only south of the 41° parallel, in areas characterised by less than 5 frost days per winter and by annual mean temperatures > 16°C.