More Virulent Offspring Result From Hybridization of Invasive Aphid Species, Diuraphis noxia (Hemiptera: Aphididae), With Diuraphis tritici Endemic to the United States.

The Russian wheat aphid, Diuraphis noxia (Kurdjumov), invaded the United States in 1986 and soon became a significant pest of wheat. Diuraphis tritici (Gillette) is native to the United States and was firmly established on wild grasses before the arrival of Russian wheat aphid. Both species are known to coinfest the same grass hosts, during the time they enter the sexual phase in the fall, mate, and produce overwintering eggs. Therefore, we induced males and females under greenhouse conditions in the fall and conducted studies in the laboratory to determine if these two species interbred and produced viable offspring. Fitness and virulence to Russian wheat aphid-resistant wheat and barley entries were also compared among the hybrid progeny and both parents. Diuraphis tritici produced males and females in October. Diuraphis noxia biotype RWA8 produced enough oviparae to conduct crossing experiments. No males occurred in the D. noxia colony making it only possible to crossbreed D. tritici males with RWA8 oviparae and to inbreed D. tritici. No difference in egg production per female (2.0-2.5) or percent egg hatch (23.1-27.0%) was found between crosses. However, progeny survival after hatch for D. tritici inbreds (33.3%) was much higher than the D. tritici × D. noxia crosses (0.25%). Only one hybrid survived to reproductive adult. Intrinsic rate of increase (rm) indicated the hybrid (0.18) was less fit than both parents (0.24-0.29). The hybrid line produced damage ratings to the 16 cereal entries similar to D. tritici but was more virulent to wheat and barley entries than both parents.