Sexual reproduction in the Russian wheat aphid (Diuraphis noxia) and its role in creating biotypes

From 2003 to 2005, seven new biotypes of the Russian wheat aphid, (Diuraphis noxia) have been reported. Since its introduction into the USA in 1986, there have been no reports of D. noxia having a functional holocycle where males and females develop, mate and produce overwintering eggs. It has been generally established that the aphid holocycle facilitates genetic recombination and can be responsible for creating the biotypic diversity found in other aphids. From 2004-2009, studies on the overwinter ecology of RWA in five distinct regions in the western Great Plains and Rocky Mountains was conducted to determine if the RWA could be holocyclic under the proper environmental conditions. We present evidence of sexual reproduction of RWA discovered in 2007 in western Colorado. Ninety-three colonies were produced from individual fundatricies that hatched from eggs. Screening these colonies against sixteen sources of resistance in barley and wheat determined that collection consisted of 47 unique phenotypes (biotypes). Although holocycly in RWA was rare, the genetic recombination that results from this cycle can produce the biotypic variation that currently threatens wheat production in the Great Plains.