Soil mediated conservation bio-control of Kelly’s citrus thripsPezothrips kellyanus pupae

Abstract: Kelly’s citrus thrips (KCT), Pezothrips kellyanus (Bagnall), emerged as a pest ofcitrus in the Riverland and Sunraysia districts in the early 1990’s and later became aneconomic pest in the Riverina and Western Australia. In earlier research soil-dwellingpredatory mites were identified as potential biological control agents of KCT. Populations ofpredatory mites in Riverland soils were positively correlated to soil organic carbon levels.Emergence traps were used to assess the emergence of KCT adults from soils in citrusorchards where composted soil amendments had been applied. Additionally, laboratory trialswere conducted to elucidate the potential cause(s) for any differences in KCT pupalmortality and resultant adult emergence. In field and laboratory trials increased mortality ofKCT pupae was demonstrated where the population density of predatory mites was increasedthrough application of composted green waste to increase soil carbon levels. While thisresearch does not definitively prove that populations of soil-borne predatory mites areresponsible for the increased mortality of KCT pupae, it shows that there is a closecorrelation between predatory mite population densities and KCT mortality. At the least, thedensity and diversity of soil borne predatory mites is a good indicator group for increasedmortality of KCT larvae.