Effects Of Low Temperatures On Development And Growth Of Bemisia Tabaci (Gennadius) B-biotype And Trialeurodes Vaporariorum (Westwood) (Homoptera: Aleyrodidae)

Greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and silverleaf whitefly, Bemisia tabaci (Gennadius) B-biotype are important insect pests in greenhouses and fields throughout the world. They are widespread agricultural pest with a comparatively broad geographic distribution covering temperate, tropical and subtropical zones. T. vaporariorum has been an important pest for many years in northern China. However, since 1990s, the T. vaporariorum population has been gradually decreased, and the B. tabaci B-biotype has become a predominant species in both fields and greenhouses.Cold tolerance and growth of the two whitefly species were studied by exposure experiments in laboratory, in order to explain the mechanism of competition and displacement. The results were as follows:1. The cold tolerances of laboratory populations of B. tabaci B-biotype and T. vaporariorum were compared. All developmental stages of the two species were exposed to 2℃ low temperature for a series durations from 1d to 12d. The results showed that T. vaporariorum was significantly more cold-telorant than B. tabaci B-biotype. When the eggs and pupae of both whitefly species were maintained at 2℃ for 12d, 49.2 and 45.0% of T. vaporariorum survived, whereas none of the eggs and pupae of B. tabaci B-biotype survived. Under the same temperature, 41.2% of T. vaporariorum adults survived for 7d, whereas only 4.6% of B. tabaci B-biotype survived for 3d. Adults mortality of the summer and fall populations of the two whitefly species were evaluated by storing them at -4℃, -8℃ and -12℃ for different time between 0.5h and 84h. As the temperature decreased, the low lethal time (LT₅₀, LT₉₀) also decreased. The fall population was cold hardier than the summer population, which coincided with the cold acclimation experiment, and the fall population of B. tabaci had rapid response to the cold stress. At -4℃, the LT₅₀ and LT₉₀ of the fall population of T. vaporariorum adults were 1.7 and 1.4 times than that of the summer population, respectively, while the LT₅₀ and LT₉₀ of the fall population of B. tabaci B-biotype were 4.4 and 3.8 times than that of the summer population, respectively. At -8℃, the LT₅₀ and LT₉₀ of the fall population of T. vaporariorum adults were 1.5 and 1.7 times than that of the summer population, respectively, while the LT₅₀ and LT₉₀ of the fall population of B. tabaci B-biotype were 3.4 and 2.9 times than that of the summer population, respectively. At -12℃, the LT₅₀ and LT₉₀ of the fall population of T.