**2. Cereal aphids occurring on rainfed wheat in Kenya**

The six most important cereal aphid species reported as pests that attack wheat and bar‐ ley include: Greenbug *Schizaphis graminum* R*.*, English grain aphid *Sitobion avenae* F*.*, Oat bird cherry aphid *Rhopalosiphum padi* L, Cereal leaf aphid *R. maidis* F*.*, Rose grain aphid *Metopolophium dirhodum* W*.* and Russian wheat aphid *D. noxia* M*.* [31, 32, 42]. Of these species, the Russian wheat aphid which is a recent introduction in Kenya in 1995 is the most destruc‐ tive followed by Greenbug *S. graminum* [25]. The other species are less serious and usually cause no significant yield reduction. In reality, there are usually two or more aphid species present at one time.

The Russian wheat aphid was first officially detected in June 1995 [25] and affected areas experienced damaging infestations resulting in 90–100% crop loss. Since then most reports from major wheat and barley growing areas of Narok, Nakuru, Uasin Gishu, Trans Nzoia and Mt Kenya region indicate that *D. noxia* has become a serious pest causing estimated crop losses of 25–80% depending on the stage of infestation. The pest is now a major constraint to wheat production in eastern Africa region [54]. The appearance of these aphids resulted in a dramatic increase in use of insecticides in cultivated wheat crops. According to the eco‐ nomic losses attributable to Russian wheat aphid [25], it can be categorized as reduced grain yields, loss of kernel weight and quality and increased costs of production due to application of insecticides.

The Russian wheat aphid causes damage to host plants through direct feeding and by inject‐ ing toxins during feeding which cause leaf rolling and unfolding thus making it difficult to control by application of contact insecticides [21, 54, 56]. Visible damage to the susceptible host plants is manifested as chlorotic lesions, white streaking, purple discoloration and tightly curled leaves. The level of infestation, the growth stage of host plant and the duration of the infestation, all influence the severity of the damage caused by *D. noxia*.
