The cabbage whitefly, Aleyrodes proletella, has in recent years become a primary pest of several brassica crops in Europe. In the UK, its greatest impact has been on kale, where nymphs, wax deposits and sooty mould caused by honeydew excretion reduce the marketable portion of the crop, particularly later in the year. In order to test the contribution of insecticide resistance to these outbreaks, a leaf-dip bioassay method was developed. Resistance to several pyrethroids was found in multiple populations in Lincolnshire and Kent, with similar patterns between compounds but differing magnitudes of resistance. This resistance was expressed to a similar degree by both adults and nymphs. The host plant used in bioassays influenced lethal concentrations but not resistance factors. A diagnostic concentration of lambda-cyhalothrin was identified and used to screen further populations over successive years. No cross-resistance to neonicotinoid insecticides was evident in highly pyrethroid-resistant populations. Bioassays with the synergist piperonyl butoxide provided no evidence of mixed-function oxidase or associated nonspecific esterase involvement in pyrethroid resistance. Attempts to sequence the sodium channel gene of susceptible and resistant whiteflies to check for target-site resistance were unsuccessful. Field surveys of whitefly populations on wild cabbage were carried out to identify candidate native biological control agents for use in IPM strategies in field crops. These identified several parasitoid wasps and a coccinellid beetle, Clitostethus arcuatus. One of the parasitoids, Encarsia tricolor, and C. arcuatus were successfully cultured at NRI and tested in outdoor cage trials. In 2011, a multiple generation trial demonstrated the superiority of parasitoid release during the development of the first generation of whiteflies over later releases of E. tricolor or C. arcuatus. A Horticultural Development Company funded field trial in 2012 showed that insecticide application early in a whitefly infestation could provide prolonged control equivalent to regular spraying. This research will contribute to the development of future integrated pest IV management programmes for A. proletella through avoiding ineffective pyrethroid applications, facilitating insecticide resistance management and identifying non-chemical approaches.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:732851 |
| Date | January 2016 |
| Creators | Springate, Simon |
| Contributors | Colvin, John ; Seal, Susan ; Cooper, Jeremy |
| Publisher | University of Greenwich |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://gala.gre.ac.uk/18118/ |
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