The edaphic phase in the ontogenesis of Frankliniella occidentalis and comparison of Hypoaspis miles and Hypoaspis aculeifer as predators of soil-dwelling thrips stages
2004
Berndt, O. | Meyhofer, R. | Poehling, H.M.
The life cycle of the western flower thrips (WFT), Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), comprises an edaphic phase, which offers the opportunity to control this serious pest by the exploitation of soil-dwelling natural enemies. In the present study, the effect of the two soil-dwelling predatory mites, Hypoaspis miles (Berlese) and H. aculeifer (Canestrini) (Acari: Laelapidae), on the population development of the WFT feeding on French beans (Phaseolus vulgaris) was examined. The experiments were carried out in acrylglass tubes, which served as microcosms. The extent of the edaphic phase within a given population of synchronized WFT was investigated by the use of photo-eclectors (emergence traps). This method ensured (1) an easy determination of the proportion of a thrips population entering the soil for pupation and (2) the quantification of the efficiency of predatory mites on the thrips developmental stages in the soil. The results showed that 98% of the thrips population left the bean plant for pupation in the soil. The introduction of five predatory mites caused thrips mortality of at least 44.9%. Doubling the predator density to 10 H. miles increased thrips mortality to 61%. A maximum thrips mortality of 80.5% was attained by the introduction of 20 H. aculeifer. As a result, H. aculeifer showed a greater efficiency as a natural enemy against soil-dwelling developmental stages of the WFT. Both species can be important antagonists of the WFT in protected crops. Opportunities to enhance biocontrol efforts are discussed.
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