Dhr. Mohammad Javad Ardeh : Whitefly control potential of Eretmocerus parasitoids

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7 Feb 2005 16:00
Unit: Wageningen University
Location: Aula (gebouw 362), Gen. Foulkesweg 1, Wageningen
Promotor: prof.dr. J.C. van Lenteren (Entomology)
Co Promotor: dr. P.W. de Jong

 Whiteflies (Homoptera; Aleyrodidae) are amongst the key pests of vegetable, ornamental, and agronomic crops throughout the world. Failing and expensive chemical control of whiteflies has led to the development of a biological control program. The aim of my work was to compare the effectiveness of a sexual- versus an asexual population of the hymenopteran parasitoid Eretmocerus mundus to control the whitefly, Bemisia tabaci.
The results showed that, while the sexual population produced more progeny, the intrinsic rate of population increase (rm) did not differ a lot between the two populations.
Males reacted to volatile and non-volatile pheromones of conspecific virgin females. However, the sexual- and asexual population did not produce any hybrid female offspring. Therefore, I studied the extent of genetic divergence between them using divergences of two nuclear genomic regions (ITS1 and ITS2) and a mitochondrial region (COII), to investigate whether the sexual and asexual strains could actually represent different species. Constructed trees, by using different clustering methods, and based on the three different sequence regions, were congruent and sexual and asexual populations of E. mundus formed two different groups.
The influences of asexuality on three fundamental aspects of foraging behavior -host handling behavior, host discrimination, and the competition- between the two populations were studied.
No correlation was found between the durations of different phases of host handling, but some components showed significant differences. The actual oviposition had the longest duration of all host-handling behaviors, and was longer on third nymphal instars than on younger ones. I recorded a relatively long time for host feeding, especially for making wounds in the host. Host feeding eventually leads to the death of the host.
Experienced females avoided to oviposit under parasitized hosts, but naïve females did not. In the case of super-parasitism, the outcome shows that neither of the E. mundus populations is stronger.
All in all, I found (1) differences between the biology of the asexual and sexual strains of E. mundus; (2) a mate finding challenge in the sexual population (3); sequence divergences between the sexual and the asexual populations; (4) no impact on host-handling behavior, host discrimination, and competition between them.
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