Winter Mortality of the Russian Wheat Aphid (Homoptera: Aphididae) on Range Grasses in Northern Utah

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Great Basin Naturalist



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The Russian wheat aphid, Diuraphis noxia (Mordvilko), is a newly established pest of small grains in western North America (Stoetzel 1987). This aphid also feeds on several native and introduced grasses, including grasses that are widely planted for forage improvement or erosion prevention in rangelands (Kindler and Springer 1989, Kindler et al. 1991). Recent attention has focused on the potential importance of these grasses as "oversummering" hosts for D. noxia, Le., as sources of aphid populations between the summer harvest and fall sowing of winter wheat, Triticum aestivum L. (Clement et al. 1990, Armstrong et al. 1991). Comparatively little information is available on the role of grasses as overwintering sites, even though migrants from noncrop hosts could cause extensive damage to cereals in the spring. In this study I investigated the overwintering success of the Russian wheat aphid on cool-season grasses in northern Utah. The ability of D, noxia to survive winter conditions varies regionally in North America. Winter mortality may reach 100% at higher latitudes (Butts 1992), so that aphid populations must be reestablished by migrants each season. Such high mortality may stem from a lack of sexual reproduction (anholocycly) in North American populations (Kiriac et al. 1990, Stoetzel and Hammon 1992), since a sexual generation in the fall is needed to produce the cold-hardy egg stage. Parthenogenetic females of D. noxia are quite coldhardy (Harvey and Martin 1988), however, and occasionally survive winter conditions in northern regions, including Colorado, Idaho, and Alberta (Butts 1992, Feng et al. 1992, Hammon and Peairs 1992). IDepartment of Biology. Utah Stale University, Logan, Utah 84322-5305. The overwintering success of D. noxia in northern Utah has not been investigated, but the typical absence of aphids in early spring suggests that fall populations are eliminated during most winters. In October 1991 I detected a population of D. noxia on cool-season grasses in an experimental garden near Utah State University. I surveyed this population throughout the winter and compared the pattern of mortality with local temperature data.

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