Abstract/Summary

The cabbage stem flea beetle (CSFB, Psylliodes chrysocephala L.) is the most abundant and widely distributed autumn pest of winter oilseed rape (OSR, Brassica napus L.). A combination of the neonicotinoid seed treatment restrictions and resistance to pyrethroid insecticides - the only other remaining control option, has made control of this pest challeging and IPM methods are required. This Thesis has contributed to the ecological knowledge of CSFB and its hymenopteran parasitoids to facilitate the development and maximise the potential of IPM strategies for CSFB control. Migration activity of CSFB and their diurnal activity were studied. This study has revealed mean temperature and windspeed as important factors influencing CSFB migration; and, for the first time, has experimentally shown that they are more active in the field at dusk and night. The management and environmental factors affecting CSFB larval populations were analysed using a combination of statistical methods. Sowing date, field area and the interaction between temperature and rain in September, October and November and mean temperature in December and January had a significant effect on the number of CSFB larvae. This study has also updated the distribution and parasitism rates of CSFB larval parasitoids in the UK and optimized DNA metabarcoding methods to identify larval parasitoids and estimate parasitism levels. For the first time, this research has studied the spatiotemporal distribution and biocontrol potential of Microctonus brassicae, the main parasitoid attacking adult CSFB. It has shown that M. brassicae is widespread across the UK with parasitism rates ranging from 0 to 36%. Experiments on the sublethal effects of M. brassicae on CSFB showed that beetles exposed to M. brassicae feed less than non-exposed beetles (immediately after exposure). Also, parasitised CSFB female laid no eggs during the experiment. The implications of these results for integrated pest management strategies and the opportunities deriving from the new EU and UK policy strategies for the upcoming years are discussed.