Pre‐ and post‐landing response of the parasitoid Encarsia formosa to whitefly hosts on Gerbera jamesonii

Abstract

One of the factors that may complicate biological control of the greenhouse whitefly on Gerbera jamesonii by Encarsia formosa is the rosette shape of this ornamental, which differs from the vertical shape of most vegetable plants (cucumber, egg plant, tomato, etc.). Therefore, host-habitat location and the behaviour prior to landing on uninfested and infested leaves was studied. Attraction of E. formosa from a short distance by infested leaves could not be detected: the parasitoid females landed at random on uninfested and infested leaves. After the first landing, a redistribution of the wasps occurred on the leaves. After 24 h three times as many wasps were found on the infested leaves than on uninfested ones. In a dispersal experiment with four plants, E. formosa appeared to have no preference for landing on leaves of the medium age class, which is the age class on which most of the whiteflies in a suitable stage for parasitism occur. Twenty percent of the parasitoids were found on the plants 20 min after releasing them. These results were independent of the plant cultivar and the host density on the plants. In the course of 8 h, the number of E. formosa females recovered from plants increased linearly, and this increase was greater on plants where hosts were present and also greater on the plant cultivar with the lowest trichome density. After 24 h, the percentage of females was highest (56%) on plants with the highest host density. E. formosa females were arrested on leaves where hosts were present. Contrary to our expectation, the results from the two G. jamesonii cultivars that differed strongly in leaf hairiness were not significantly different in most experiments. Only at the high host density was parasitism found to be lower on the cultivar with the higher hair density. Parasitoids may walk on top of the 'hair coverlet' of cultivars with high trichome density and, therefore, be hampered less than expected.

Flexible Use of Patch-Leaving Mechanisms in a Parasitoid Wasp

“…It is well established that parasitoids and predators use herbivore-induced plant volatiles to locate their herbivorous hosts or prey (Vet and Dicke, 1992;Steidle and van Loon, 2003). However, several studies showed that E. formosa does not (Noldus and van Lenteren, 1990;Sütterlin and van Lenteren, 2000;Romeis and Zebitz, 1997;van Roermund and van Lenteren, 1995;van Lenteren et al, 1976; but see Birkett et al, 2003). Rodriguez-Saona et al (2003) found that plants infested by the silverleaf whitefly emitted plant volatiles similar to undamaged plants.…”

“…Nymphs were carefully transferred from their original feeding site onto the leaflets. Previous experiments revealed that parasitoids still accept transferred nymphs for both oviposition and host feeding, and that E. formosa does not exploit herbivore-induced plant volatiles to locate hosts from a distance (Noldus and van Lenteren, 1990;Romeis and Zebitz, 1997;Sütterlin and van Lenteren, 2000). Only fourth nymphal stages were used because younger stages are easily damaged during transfer.…”

“…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). 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.…”

Leaf Trichome Formation and Plant Resistance to Herbivory

“…In some studies, an effect of trichomes on natural enemies was detectable only at high prey/host densities (e.g., Sutterlin and van Lenteren 2000) while in other studies such an effect was observed only at low densities (Krips et al 1999). …”

Among-tree variation in leaf traits and herbivore attacks in a deciduous oak, Quercus dentata

“…In this study, it is not known whether trichomes increase the survival and performance of leafminer larvae. However, Sü tterlin and van Lenteren (2000) reported that trichomes hinder host-searching behaviours of parasitoids and lower the parasitism rate of leafminers. In addition, trichomes could indirectly raise survival of leafminer larvae by reducing leaf damage by ectophagous herbivores.…”