Behavioural and chemical ecology of Meligethes aeneus: effects of non-host plant volatiles

The research in this thesis aims to develop an understanding of the olfactory aspects of host-location behaviour in the pest beetle Meligethes aeneus Fab., and to investigate the use of non-host plant volatiles as ‘repellents’ within a push-pull system of pest control for oilseed rape, which is being developed at Rothamsted Research. Novel laboratory bioassays were developed and used to establish that essential oils from non-host plants reduce M. aeneus colonisation of oilseed rape flowers. Lavender essential oil had the greatest negative effect on beetle numbers on rapeseed flowers. This was further examined using a 4-arm olfactometer, and it was established that lavender oil alone elicits avoidance behaviours in M. aeneus, in addition to overriding their attraction to host-plant volatiles. The chemical basis of this effect was investigated using gas chromatography linked with electroantennography and mass spectrometry and the results are discussed in relation to the ecology of the insect. It was established with semi-field studies that lavender essential oil reduces landing of M. aeneus, but does not affect the post-alighting behavioural process of host acceptance. These results are discussed in terms of behavioural plasticity in the importance of olfactory cues for host location such that, on alighting on a plant, the beetle may switch behavioural modes or may require a different suite of olfactory cues during host-acceptance behaviour. Field studies showed that lavender oil is effective at reducing natural movements of M. aeneus into plots of oilseed rape. Critically, the main reduction in infestation occurred during the vulnerable green-bud stage and the implications for optimal timing of repellent application during immigration are discussed. Flight patterns were further investigated using a novel combination of vertical-looking radar, suction traps and field counts to identify important meteorological and ecological factors. The thesis presents an experimental progression in scale from the laboratory, to semi-field and field scale, for research into the effect of semiochemicals. The application and efficacy of using lavender or other non-host plant odours within a push-pull system of pest management for M. aeneus in oilseed rape are discussed.