Effect of light intensity on colour morph formation and performance of the grain aphid Sitobion avenae F. (Homoptera: Aphididae).

The grain aphid Sitobion avenae F., one of the major pest aphids of cereals in Central Europe, exhibits colour polymorphism, even within the same clones. Although there is evidence that green and brown morphs of S. avenae contain different carotenoids, the mechanisms determining the induction of colour morphs are unknown. The common understanding is that the formation of colour morphs is controlled by light and affected by genetic and environmental factors and by host plant species. So far, there is no unequivocal evidence that light intensity, photoperiod, or a mixture of several variables are involved in the induction of S. avenae colour formation, resulting in the induction of S. avenae colour formation and carotenoid synthesis. Here we determined the effect of light intensity on the colour formation and performance of ten clones of S. avenae with experiments that controlled for the effects of host plant and genetic factors. We found that some clones remained green under all test conditions. In other clones, colour morph formation was controlled by light. The synthesis of carotenoids correlated with changes in colour formation. Host plant did not affect colour formation in the ten clones studied. Although colour of the aphid clones did not affect their performance, high light intensity increased the fecundity and fresh weight of S. avenae clones, while low light intensity stimulated the production of alatae.