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In experiments conducted in semi-field and field environments, the scientists showed that a change in the petal colour of oilseed rape from yellow to red can result in a significant reduction in pollen beetle infestation. They said their findings open up possibilities for a new sustainable pest management strategy. 

Scientists systemically dyed the flowers of a white-petalled oilseed rape variety using food colouring, which was taken up by the roots of the plant. They then assessed the attractiveness of the plants to pollen beetles by measuring the number of beetles found on plants of the different colours – white (control), yellow, red and blue. Yellow and white were most attractive while red was least attractive. 

Having tested the plants' odours, the researchers found there was no significant change between the differently treated OSR plants, and deduced that the beetles' preferences must be related to petal colour.

Dr Sam Cook, a Rothamsted agroecologist and lead scientist of the study said, "This is an exciting and intriguing finding. Significantly more beetles were found in the white plants and plants dyed yellow than on the plants dyed blue or red. This was the case both in controlled environmental conditions and in experiments conducted in the field over two consecutive years."

Further insight was also shed into the mechanism that drives the beetles' behavioural response. The light wavelengths at which the beetles show more sensitivity were analysed and correlated with their attraction to the plants. Pollen beetles are attracted to objects that reflect more ultraviolet light, such as the white and yellow colours tested in the study.

Dr Cook commented on this, "These findings are important as they can be used to help us develop highly attractive traps or less attractive crop varieties for improved pollen beetle control."

Also commenting on the study, fellow Rothamsted scientist Professor John Pickett added, "It is essential that we look for sustainable pest control strategies to maximise crop yield. Understanding how pests use visual cues to identify and select hosts can provide us with more evidence-based sustainable pest management solutions for farmers."

Oilseed rape is currently the most important source of plant-derived oil grown in Europe. As well as cooking oil, the plant is increasingly finding favour amongst biodiesel manufacturers, although EU parliament rapporteurs and the influential UK government International Development Committee have criticised the use of food crops in biofuel production and questioned EU support for the growing industry.

The pollen beetle is a major insect pest, most common at the flowering stage of the plant. Populations of the bug that are resistant to insecticides used for their control have spread in many OSR-growing regions.

The Rothamsted scientists involved in the colour experiment said this growing resistance highlights the need for effective-low impact strategies to combat pollen beetle infestations.