Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/1999
Publication Date: 4/1/2000
Interpretive Summary: The Russian wheat aphid (RWA) is a serious pest of wheat and barley in the United States. In North America it reproduces asexually year-round and lacks the typical over-wintering egg stage exhibited by most temperate aphids. Consequently, it must survive on wild grasses during the intervening period between cereal crops. Noncultivated host species of RWA include a wide range of perennial and annual grasses, most of which appear to be poor hosts when compared with wheat and barley. We measured aphid population growth on 6 cool-season grasses that commonly occur within the range of RWA. To determine the suitability of these grasses for RWA host- switching, we tested the effect of the previous aphid host on aphid reproduction. We found that aphid populations, especially those from plants that had been exposed to winter conditions, increased more quickly when they were initiated with individuals taken from wheat plants. Aphid population increased on all of the grasses tested as the infestation time increased, and plant growth was largely unaffected by aphid feeding. However, when plants were pretreated by exposure to winter conditions, crested wheatgrass supported significantly more aphids than some of the other hosts. These results suggest that all of the cool-season grasses tested are capable of sustaining RWA during summer when small grains are not in cultivation. Consequently, when environmental conditions are favorable, these grasses will serve as the primary oversummering hosts for the RWA in North America.
Technical Abstract: The Russian wheat aphid reproduces parthenogenetically in North America and must survive year-round on host plants, including in late summer when small grains are not in cultivation. During this time, cool-season perennial wheatgrasses contribute substantially to aphid survival, crested wheatgrass particularly. In greenhouse studies, the number of aphids per plant was measured after 4 infestation periods on unvernalized and vernalized wheatgrasses. Before placement on these test plant species, aphids were reared either on winter wheat or on the grass host species on which aphid progeny were counted. On vernalized plants, aphids reared on wheat resulted in more aphids per test plant than when the aphids were reared on wheatgrasses, but on unvernalized plants the number of aphids per test plant did not differ significantly regardless of rearing host. Aphids on crested wheatgrass were similar in number to the other grasses when plants were unvernalized. However, when plants were vernalized crested wheatgrass supported significantly more aphids than some of the other hosts. Aphid numbers increased on all test species as infestation period lengthened, and plant growth was largely unaffected by aphid feeding. These results suggest that if sufficient moisture is available during summer when small grains are not in cultivation, all host species observed are capable of sustaining aphids. Crested wheatgrass is an abundant and important host of the Russian wheat aphid in its northern range of the western United States, but other less prevalent wheatgrasses also may contribute to aphid survival during late summer when small grains are not in cultivation.