Natural history of whitefly in Costa Rica: an evolutionary starting point

1. To understand evolution of foraging behaviour in the whitefly parasitoid Encarsia formosa (Hymenoptera, Aphelinidae), natural densities and distributions of whitefly (Homoptera, Aleyrodidae) were quantified in E. formosa's presumed area of origin, the Neotropics. 2. Leaves were collected in Costa Rican nature areas along long transects (2-4 km), short transects (100 m), within 3-D plots (50 dm(3)-2.3 m(3)) and along suspension bridges within the canopy, and checked for presence of whitefly nymphs. 3. Generalised linear mixed modelling revealed that the number of hosts on the lower side of a leaflet of an average plant within an average spot of an average transect could be described by a Poisson distribution with mean and variance equal to 0.241, in a ratio of I1:I2:I3:I4 = 0.14:0.23:0.26:0.37. The Poisson mean was affected largely by the plant and less by the spot or transect. Variation in leaf area explained little of the variation between plants. Based on the shape of the opening in vacated puparia, the probability that a whitefly became parasitised eventually was 12% on an average leaflet. Whitefly density was much lower in the canopy than at the forest floor in the same area. 4. Semivariance analyses showed that in one of the three short transects, the numbers of whiteflies on leaves were spatially dependent. In four of seven 3-D plots at least one level of spatial dependence could be detected. 5. Results are discussed in the context of understanding evolution of foraging behaviour by E. formosa.