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Aphids attacking lettuce fields in England are showing surprising regional patterns that could complicate efforts to protect one of the country's most important salad crops, new research has revealed.

The currant-lettuce aphid, Nasonovia ribisnigri, is a destructive aphid that feeds on outdoor lettuces. The new analysis found that populations in England are divided sharply between the east and west of the country. The finding, based on nearly two decades of genetic sampling, suggests that the pest's movements are strongly tied to lettuce-growing regions and may not spread as widely as previously thought.

The study, which analyzed insects collected from ten sites between 2003 and 2020, showed that while aphids migrate from the west into eastern lettuce fields, they rarely move in the opposite direction. Researchers say the pattern could be linked to the insect's relationship with its winter host, blackcurrant and related Ribes plants, and its summer host, lettuce. The work is in the Journal of Insect Science.

The findings come at a critical time for growers. Traditional defenses against the pest, such as resistant lettuce varieties, have started to fail in recent years, leaving few effective alternative options for control. Despite this, populations of N. ribisnigri appear to have remained relatively stable, even as warmer temperatures and shifting weather patterns create more favorable conditions for the aphid.

Dr. Dion Garrett, who led the study, also found that the insects are highly inbred and mostly reproduce in cycles tied to the seasons, a factor that may help explain their long-term persistence.

With the UK lettuce industry worth hundreds of millions of pounds annually, the work highlights the urgent need to rethink pest management strategies. "The clear geographic divide we see has major implications for how we monitor and control N. ribisnigri," said Dr. Garrett, warning that growers will need region-specific approaches to tackle the pest in future.