The edaphic phase in the ontogenesis of Frankliniella occidentalis and comparison of Hypoaspis miles and Hypoaspis aculeifer as predators of soil-dwelling thrips stages

Abstract

Abstract 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.