Functional response and host preference of Encarsia formosa Gahan (Hym., Aphelinidae), a parasitoid of greenhouse whitefly T. vaporariorum (Westwood) (Hom., Aleyrodidae)
1987
Fransen, J.J. (Wageningen Univ. (Netherlands). Dept. of Entomology) | Montfort, M.A.J. van
German. Some of the factors considering parasitoid efficiency were investigated. Attention was focused on the effect of host density on parasitism and the appearance of host selection in the Encarsia formosa-Trialeurodes vaporariorum relationship. Functional responses were determined by offering E. formosa different densities of either first, second, third of fourth whitefly larval instars during a fixed time period. The relationship equated to a type 2 functional response. No correlation was found between the numbers of ovipositor punctures on the larvae and the numbers of parasitoid eggs, therefore, the numbers of parasitized whitefly larvae were recorded by dissection for parasitoid eggs. A statistical model was developed to analyse the results from experiments in which mixtures of different instars were offered to E. formasa. Because parasitoid searches at random once landed on the leaf, host encounters are dependent on the numbers of hosts and their size. Host preference also plays an important role. A significant preference of E. formosa for 2nd instar larvae to 1st, 3rd to 1st and 4th to 1st, and for 3rd + 4th to 2nd could be concluded from a statistical analysis of the data
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