Rate of consumption of Western flower thrips pupae by the soil-dwelling mite Hypoaspis sclerotarsa (Acari: Laelapidae)

Western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), are one of the most serious pests of horticultural crops worldwide. Despite one third of its lifecycle being in the soil, the potential for biological control of WFT in the soil is poorly understood and requires further elucidation. A number of studies report that polyphagous predatory mites prey on pupal stages of WFT in the soil, but little has been done on consumption rates. Therefore, we designed a laboratory study to examine the rate of consumption of WFT pupae in potting media, by the soil-dwelling mite Hypoaspis sclerotarsa (Costa). Five predator densities were evaluated (0, 2, 4, 6 and 8) against four densities of WFT prey (5, 10, 15 and 20 pupae). Pupal consumption was assessed at 2 hourly intervals over a six-hour period. The study confirmed that H. sclerotarsa did consume WFT pupae and that the rate of consumption increased with increasing density of H. sclerotarsa. The rate of consumption also increased with the density of WFT pupae. However, this was not consistent because, as the numbers of WFT pupae increased, so did the ratio of WFT pupae remaining to those consumed, increase. This paper is the first report of H. sclerotarsa in Kenya, and of its potential as a biocontrol agent of WFT. Further studies are now needed to understand interaction of foliar and soil dwelling predatory mites (H. sclerotarsa) for control of WFT under field conditions.