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

Abstract

Abstract. 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 À2.3 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 ¼ 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.

Flexible Use of Patch-Leaving Mechanisms in a Parasitoid Wasp

“…Whitefly nymphs aggregated at several spatial scales in the field (Burger et al, 2004), which suggests that E. formosa should decrease its tendency to leave after a host encounter. However, a leaflet with only one host was still the second most common type of leaflet after empty leaflets (Burger et al, 2004). In such an environment, a single host encounter is not enough to decide whether to stay or to leave.…”

“…This density corresponds to the average field density and the average density in the treatment with an aggregated host distribution. In the treatment with an aggregated host distribution, the number of nymphs on the lower side of a leaflet was drawn from a Poisson distribution with mean and variance equal to a spatially dependent λ based on field sampling of plants within spots along transects (Burger et al, 2004). The average over 2500 leaflets was about 1.0 host per leaflet.…”

“…In the field, the number of hosts on a leaflet was highly variable and the spatial dependence provides parasitoids with some degree of predictability on presence of hosts (Burger et al, 2004). Greenhouse data showed that the whitefly distribution gradually changed from clustered towards regular in the course of time as a result of whitefly dispersal (Eggenkamp-Rotteveel Mansveld et al, 1982).…”

“…E. formosa is famous for its successful use as biological control agent against whitefly (Homoptera: Aleyrodidae) (van Lenteren et al, 1996;van Lenteren, 2000). Whitefly nymphs aggregated at several spatial scales in the field (Burger et al, 2004), which suggests that E. formosa should decrease its tendency to leave after a host encounter. However, a leaflet with only one host was still the second most common type of leaflet after empty leaflets (Burger et al, 2004).…”

“…We have quantified natural host densities and distributions in the presumed area of origin of our model species, the whitefly parasitoid Encarsia formosa Gahan (Hymenoptera, Aphelinidae) (Burger et al, 2004). E. formosa is famous for its successful use as biological control agent against whitefly (Homoptera: Aleyrodidae) (van Lenteren et al, 1996;van Lenteren, 2000).…”