Abstract
Bemisia tabaci (the tobacco whitefly) is an important agricultural pest of global significance primarily because of its ability to transmit multiple damaging plant viruses. To date, UK outbreaks of the whitefly have been restricted to glasshouses and there are no records of the whitefly establishing outdoors during the summer. This is despite the fact that annual degree-day models (that estimate accumulated warmth over the year above the development threshold), indicate that B. tabaci has the thermal potential for multiple summer generations in the UK. A set of 49 climate indices calculated using the present day climate (1986–2015) were therefore compared between the UK and the south of France, where B. tabaci is able to establish outdoors, to identify the factors limiting its establishment. The number of cold days and nights in summer, as well as the time spent within the whitefly’s optimum temperature range, were most significantly different between the two areas. These indices may impact the development of B. tabaci and offer an explanation for the absence of the whitefly outdoors in the UK during the summer. Further analyses undertaken with climate projections suggest that in a 2–4°C warmer world this pest could pose a risk to outdoor UK crops in July and August. A clear south-north gradient can be demonstrated for these indices. Linking any possible northwards spread of B. tabaci populations outdoors in France with changes in these indices could therefore provide an important indicator of any change in the risks of outdoor populations of this species developing in the UK. The effectiveness of climate indices in pest risk analysis is compellingly demonstrated, and it is recommended that in-depth comparisons of climatic indices between areas of pest presence and absence are conducted in other situations where forecasting the risks of pest establishment are complex and challenging.
Highlights
Bemisia tabaci is an important agricultural pest with a worldwide distribution, but is currently non-native to the UK
The thresholds used for MED were the higher of the values reported. Mapping these means the UK was depicted as less favourable than the other set of thresholds would imply. Given these less favourable data still show that much of the UK is theoretically suitable for 1–2 generations per year, this increased our confidence that at least some parts of the UK would be suitable for outdoor establishment
When climate indices of East Anglia in the UK were compared with Mediterranean France, significant differences were shown that could impact on the establishment of the whitefly
Summary
Bemisia tabaci (tobacco whitefly) is an important agricultural pest with a worldwide distribution, but is currently non-native to the UK. The UK has a Protected Zone for European populations of the whitefly, and is subject to a heightened level of surveillance and management against B. tabaci. The Committee on Climate Change Adaptation Sub-Committee [2] has identified new and emerging animal and plant pests and diseases as one of the principal climate change risks and key research priorities for the UK. This is because future climate change may allow pests and pathogens to survive better over winter in the UK and extend their current range, and once a pest or pathogen has established, they become difficult to eradicate [2]. Risk management strategies rely on early warning systems and surveillance to identify these pests and pathogens as soon as possible
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