Abstract
The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is a major pest of semi-protected strawberry crops in the UK. These crops are grown outdoors but sheltered by clear polythene tunnels during the growing season from about April to October. The aims of the study were (1) to test whether F. occidentalis overwinters in strawberry crops in central England, where overwintering in outdoor crops has not previously been demonstrated and (2) to test whether overwintering affects the thrips population during the following season. F. occidentalis was found breeding on several crop weeds that often flower throughout the year, including common chickweed (Stellaria media), groundsel (Senecio vulgaris) and dandelion (Taraxacum officinale). F. occidentalis female adults were found throughout the winter in flowers of these weeds and caught every month on blue sticky traps. Transparent emergence traps placed over various locations in a second-year crop in March caught adult thrips over the following month, showing that thrips survived within the crop. Second-year strawberry crops had earlier infestations and significantly more F. occidentalis adults per flower than nearby first-year crops at the start of the season, indicating that thrips that overwinter in and around retained crops contribute to pest build-up in the following season. Control of overwintering F. occidentalis after the end of first-year cropping before second-year cropping, or growing crops for only 1 year, is a potential strategy to improve thrips management in strawberry. The survival of F. occidentalis over winter on outdoor crops raises concerns that the species could in time become established on other outdoor crops.
Highlights
The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), has become a major pest of semi-protected strawberry crops (Fragaria × ananassa Duchesne) in the UK
Strawberry crops are sometimes grown for 2 years in the UK, everbearer crops are more commonly grown for only 1 year to avoid the greater risk of F. occidentalis damage
The annual loss of UK strawberry crops to F. occidentalis has been as high as 10–20%, with some growers experiencing complete crop loss, but this has improved in recent years with better understanding of integrated pest management practices (Sampson 2014, 2018)
Summary
The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), has become a major pest of semi-protected strawberry crops (Fragaria × ananassa Duchesne) in the UK. These crops are grown outdoors but are protected by open-sided ‘Spanish’ polythene tunnels through the growing season from about April to October. Everbearer strawberry crops, which have a long flowering and fruiting season, are commonly grown in this way, and their long season favours the build-up of thrips numbers. The annual loss of UK strawberry crops to F. occidentalis has been as high as 10–20%, with some growers experiencing complete crop loss, but this has improved in recent years with better understanding of integrated pest management practices (Sampson 2014, 2018). Observations that thrips are more of a problem in fields with a history of the pest or where plants are retained from 1 year to the suggest that overwintering can contribute to outbreaks (Bennison and Fitzgerald 2008; Sampson 2014, 2018)
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