Abstract:
Amblydromalus limonicus (Garman & McGregor) is a predatory mite of important insect pests for a range of agricultural crops around the world. Although it is commercially available and largely effective, limitations surrounding the use of A. limonicus are the sensitivity of its eggs to low air humidity, its cannibalistic behaviour, and limited predation ability on certain crops. Increasing the habitat structural complexity of a system is a possible solution to these limitations. In the present study, five different substrates were utilised to assess its impact on reducing cannibalism across two relative humidity treatments (70% and 85%) at 25oC. The substrates tested were buckwheat husks, gorse husks, rice husks, vermiculite, and wheat bran which were compared against a control treatment with no rearing media. The substrates had a strong significant effect on the populations of A. limonicus, while humidity did not. Rice husk was identified as the most suitable rearing media due to its capacity to reduce encounter rates, provide shelter and oviposition sites, and limit mould growth, resulting in the highest population density of A. limonicus. The second component of this study aimed to enhance the establishment success and persistence of A. limonicus on two host plants and also assess if this produced more effective control of greenhouse whitefly (Trialeurodes vaporariorum, Westwood). The effects of different combinations of pollen, thread, and substrate supplementation were examined on capsicums and eggplants over a 10 week period. For eggplants, no control was obtained as A. limonicus was not able to establish on the dense trichome covered leaves. Whitefly populations increased exponentially due to the combination of a high preference for eggplant, suitable climatic conditions, and the absence of a predator. On capsicums, the highest predator populations were on the pollen-thread and pollen-thread-substrate treatment. Overall, for capsicums all life stages of greenhouse whitefly were controlled in treatments that included some form of supplementation. These results suggest that A. limonicus has the potential to be an effective biological control agent when paired with supplemental food and oviposition sites, and should therefore be incorporated into an integrated pest management system for selected crops.
