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U.S. Department of Agriculture (USDA) scientists in Illinois, USA, are investigating the role of anthocyanins in pest-control. They believe that the plant pigment can adversely affect crop pests such as the corn earworm caterpillar and the cabbage looper caterpillar that feed on it.

Cabbage looper caterpillar. Copyright A. Shelton.

Anthocyanins are a plant pigment which give blackcurrants and flowers, such as petunias, their blue and purple colour. They absorb blue-green and UV light, protecting plant cells from high-light stress.

In the experiments the scientists used corn earworm caterpillars (Helicoverpa zea). H.zea damage is usually serious and costly because of the larval feeding preference for the reproductive structures and growing points which are rich in nitrogen.

The caterpillars were forced to feed on blue areas of petunia petals which contained higher levels of anthocyanins than the white areas. It was found that these individuals gained less weight than other individuals which were fed on only the white leaf areas. Further experiments found that isolated anthocyanins slowed the caterpillar’s growth rate.

The researchers also investigated the effect of anthocyanins on the cabbage looper caterpillars (Trichoplusia ni). T.ni populations can cause both severe yield and quality losses with severe cabbage infestations resulting in whole yields being unsellable.  Cabbage looper larvae that ate the blue petal areas of the petunia died at higher rates than those that ate the white areas.

It’s unclear as to what petal compound(s) were involved in the cabbage looper larvae mortality but it is thought that the anthocyanins increased the effectiveness of the toxic compound.

To find out more, read the original article on the USDA website.

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