Abstract
Bemisia tabaci is a serious threat to the UK horticultural industry, with the most serious biotype a vector of over 111 viruses. Its feeding activity causes physiological symptoms in the foliage and fruits of some plants, and nymphal stages of the pest produce a sticky honeydew that often becomes colonised by sooty moulds affecting marketability of the crop. Within the European Community the UK has “Protected Zone” status to prevent the spread of B. tabaci. The primary concern is that adult whitefly imported on ornamentals such as poinsettia can infect tomatoes with tomato yellow leaf curl virus (TYLCV), a virus not currently present in the protected area but which has been detected in B. tabaci intercepted in the UK. Since 1987 outbreaks have occurred annually, predominantly on poinsettia, but also on a range of other plant species (both ornamentals and herbs). Statutory action is taken to prevent the pest entering the UK, but where outbreaks do occur eradication measures must be taken. Where crops have a distinct growing season clean up measures can be used to prevent the pest transferring to subsequent plantings but this is difficult when commodities with a longer growing season such as vegetables and cut flowers are planted. Intensive cropping regimes offer a continuous supply of young plant material for the pest to infest with few opportunities for complete glasshouse sterilisation. Thus unless a targeted and synchronised treatment regime is implemented, long-term outbreaks can occur. Bemisia tabaci occurs as a number of morphologically indistinguishable biotypes (e.g. B, B(2), Q, S) that differ in a number of biological attributes that have important ramifications for control strategies. Of the B. tabaci biotypes considered to pose a risk in the UK, the B-type is by far the more damaging and aggressive colonizer. However, the Q-type appears to have the capacity to develop resistance much more rapidly to the modern chemistries used against whiteflies. The Q-type was introduced into the USA in around 2004 and was determined to be essentially unaffected by pyriproxyfen and also had noticeably reduced susceptibility to acetamiprid, buprofezin, mixtures of fenpropathirn and acephate, imidacloprid, and thiamethoxam. Outbreaks can occasionally be mixtures of both biotypes and B-types can out-compete Q-types when the latter is resistant. Selection pressure, however, will drive some populations to become Q-type dominated, even when the initial population was predominantly B-types. Where introductions of a single biotype occur, specifically the Q-type, control problems and resistance are very likely (i.e. there will be no competing B-types in the population to regenerate susceptibility once resistance starts eliciting a competitive drag in the Q-types). What is quite clear from the literature is that ascertaining biotype is extremely important and has been routinely undertaken wherever serious attempts to manage B. tabaci have been implemented. However the biotype status of the B. tabaci occuring at interceptions/outbreaks in the UK is unknown. The potential for insecticide resistance, coupled with the ongoing reduction of available insecticides, the increasing consumer drive for lower pesticide use and the utilisation of IPM approaches in a range of glasshouse production regimes provides the stimulus for the development of an IPM approach to the containment and eradication of B. tabaci. This IPM approach will need to utilise both traditional and novel chemical and biological approaches. For example, there are new pesticides, some with new modes of action (e.g. ryanodine receptor activators) and a range of ‘biorational’ pesticides that may well fit within a suitable IPM program. Also, the utilsation of temporal synergism (an approach where a synergist, which reduces the capacity of the insect’s metabolism to deal with the pesticide, is applied before the insecticide treatment) using an encapsulated formulation, has the potential to play a major role in the eradication of resistant biotypes. Biocontrol agents and biopesticides have shown the potential to play significant roles in IPM systems (PH0404, PH0157, PH0405 and emerging publications) and it is important to evaluate these with regards to B. tabaci (where this hasn`t previously occurred) and their compatability with the chemical approaches. This project has 3 important interlinked areas: 1. Determine the biotype status of current and new outbreaks of B. tabaci 2. Investigate the efficacy of a range of traditional, new or resistance breaking chemicals/approaches and their potential to be incorporated into an IPM approach for the eradication of B. tabaci 3. Investigate the efficacy of a range of commercially available biocontrol agents and their potential to be incorporated into an IPM approach for the eradication of B. tabaci The results of these 3 interlinked areas will be developed into a set of protocols for the key crops that outbreaks occur on and will feed into contingency plans to deal with potential future outbreaks in significant crops (e.g. tomato). It is likely that the protocols will differ between biotypes as well as between plants. The final stage of the project will utilise an outbreak site, if possible, to test the protocols developed (alternatively the tests will take place in smaller scale tests in the laboratory).
United Kingdom