Interactions between the predatory mite Amblyseius Swirskii and it's factitious prey Suidasia Medanensis with implications for field release

Abstract

Predatory mites are important components in biological control of arthropod pests in protected crops. The whitefly and thrips predator Amblyseius swirskii (Acari: Phytoseiidae) is an efficient biocontrol agent used widely for pest control in protected vegetable and ornamental crops. Amblyseius swirskii can be mass-reared on at least three species of astigmatid mites but little is known about their predator-prey interactions and population dynamics. These factitious prey allow for large-scale efficient rearing systems and novel crop inoculation methods. The use of breeding sachets offer a predatory mite delivery method with prolonged and sustained crop inoculation. This study endeavoured to assess the suitability of the factitious prey Suidasia medanensis (Acari: Suidasidae) for mass-rearing and field deployment of A. swirskii by studying the life table parameters of the predator on a diet of the said prey. The underlying predator-prey interactions were examined through a series of laboratory experiments focusing on the response of A. swirskii to prey density, preference of prey life stage, capture success ratio and the defence volatiles of adult S. medanensis against predators. Furthermore, in order to understand the behaviour and performance of a breeding sachet the internal population dynamics were studied in relation to release rates from the sachet. These studies were extended to examine the effect of different simulated crop conditions on predator release, focusing on temperature and relative humidity at constant and alternating controlled conditions. In addition to different crop conditions, A. swirskii may be exposed to various other crop protection products in the field as part of an IPM programme. The compatibility of A. swirskii with one such product, the fungal entomopathogen Beauveria bassiana (Balsamo), for concomitant use in the field was investigated through pathogenicity studies and sublethal effects under controlled conditions. Suidasia medanensis was found to be of good nutritional value to A. swirskii resulting in population growth rates similar to target pests, as reported in literature. Specific predator-prey interactions were identified, such as Type II functional response, preference to egg stages of the prey and the defence volatile of S. medanensis, the significance of which are discussed in depth in the thesis. Underlying dispersal strategies and the association between breeding sachet productivity and predator output was established. Furthermore, climatic conditions were found to have significant effects on sachet performance with clear indications of what constitutes favourable and unfavourable conditions. Amblyseius swirskii was found to be a physiological host to B. bassiana. Due to low-to-moderate mortality rates under ideal laboratory conditions, little effect on juvenile mites and no effect on offspring of treated mites these two biocontrol agents were concluded to have good potential for concomitant use, but with further trials required.