Abstract
Thrips are serious pests throughout the world causing damage by both direct feeding and their ability to transmit viruses. Following crop colonisation their thigmotactic caustral behaviour can make them difficult to detect; short generation times result in rapid population increases and development of insecticide resistance can result in control failures. In recent years several species of thrips have been dispersed globally as a result of their association with the international trade in growing plants or plant products. For example Thrips palmi Karny was known to be widely distributed in limited geographical areas before spreading rapidly throughout the world. A similar pattern of spread is occurring for Scirtothrips dorsalis, a polyphagous pest that can cause significant economic losses in countries where it establishes. Several outbreaks have occurred in the UK on both edible crops, and large ornamentals in particular accessible Palm Houses (ongoing outbreak at a large public glasshouse). Pest Risk Assessments indicate the species represents a serious threat to UK industry, and the large publ;ic glasshouse outbreak incorporates the issue of public access as well as dealing with larger plants, requiring research into the development of effective integrated pest management (IPM) methods. Developing eradication, containment and management approaches for outbreaks of quarantine species remains a high priority for Plant Health and these thrips species represent a key gap in contingency planning. The limited range of chemical insecticides that are available for the control of S. dorsalis in the UK, the potential for development of insecticide resistance, and increased public concern about the effects of such pesticides on the environment, underline the need for reduced- or non-chemical approaches to thrips control to be developed. In addition, the trend in several sectors of the horticultural industry towards reduced or no-chemical production systems reinforces this requirement. The polyphagous nature of S. dorsalis often makes it difficult to predict, with accuracy, which UK crops or plants are most at risk of infestation. Thus any control strategy devised must be adaptable for use on a range of plants. This presents difficulties when using Biological Control Agents (BCAs), as most such agents are known to be effective on a limited range of host plants or growing conditions. The solution reached under an earlier project developing an IPM strategy for T. palmi (project PH0404) was to develop a modular IPM system in which each module addressed a particular crop horizon or the life stages of the pest living in that horizon, and to ensure that the control agents selected for use on the experimental plants used to develop each module had equivalents that were appropriate for use on other plant species. The modules could then be utilised to build a control system for a range of crops or plants at risk from the target pest. The quarantine status of the species restricted testing of the protocols produced to whole plant laboratory tests, which yielded very positive results. The methods developed under PH0404 now require field testing using outbreaks or a model thrips species and the IPM approach can also be built upon by investigation and where appropriate, incorporation of additional methods (e.g. use of UVC, steam, etc.). An additional element of Project PH0404 involved the investigation of an aggregation pheromone which identified a male produced monoterpene pentenoate that appeared to be analogous to the situation in Frankliniella occidentalis where males produce the aggregation pheromone neryl (S)-2-methylbutanoate. Further work is required to characterise the compound and investigate its effect (if any) on thrips behaviour before it can be considered as a component of the IPM protocols. The proposed work builds upon the advances recorded under project PH0404 to: Independently field-test the modular approach and SOPs for control of T. palmi using a model thrips species and experimental glasshouses. If a suitable outbreak site for T. palmi can be identified and selected by the PHSI, field-test the T. palmi protocol under quarantine outbreak management conditions. Investigate potential new methods for T. palmi control that could be incorporated into the modular strategy, and utilise output from other research (including pheromones; UVC; soil sterilisation) Evaluate in the laboratory the potential for adapting the IPM protocols to support the management of S. dorsalis in publicly accessible glasshouses with large plants, by establishing compatibility of selected BCAs for S. dorsalis control with each other and with chemical insecticides. Design, evaluate and refine preliminary modular-based control strategies for the control of S. dorsalis under quarantine cage conditions or alternatively, if a suitable outbreak site can be identified and selected by the PHSI (in a publicly-accessible glasshouse with large ornamentals or a crop outbreak), field-test the Scirtothrips protocols.
United Kingdom