Abstract
We studied the degree of overlap of spatial distribution and life history parameters of two sympatric whiteflies, Trialeurodes vaporariorum Westwood and Bemisia argentifolii Bellows & Perring, on tomatoes under greenhouse and laboratory conditions. The association of the micro-spatial distributions of the two species was investigated using interspecies mean crowding analysis. This association was neutral in the immature stages (nymph and pupa), whereas no consistent tendencies were seen in the adult stage in the greenhouse. In 2 out of 4 cases in the immature stages and 3 out of 4 cases in the adult stage, the mean relative leaf height of the distributions of the two species were significantly different, showing that T. vaporariorum has a tendency to occupy a higher leaf position than B. argentlfolii. For both species, the mean numbers of eggs laid per female per leaflet under two thermal conditions (20°C and 30°C) were not significantly different between two rearing situations, but the total developmental period in the isolated situation was longer for both species under both thermal conditions. At 30°C, the survival rate of T. vaporariorum was significantly lower in the isolated situation than in the mixed one, while that of B. argentifolii showed the reverse tendency. These differences in the survival rate in response to rearing treatments could be caused by l) a specific difference in the optimum density, or, 2) an asymmetric interspecific interaction during an early developmental stage.
