Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/27/2011
Publication Date: 3/1/2012
Citation: Puterka, G.J., Hammon, R.M., Burd, J.D., Peairs, F., Randolph, T., Cooper, W.R. 2012. Cyclical partenogenetic reproduction in the Russian wheat aphid (Hemiptera: Aphididae) in the United States: Sexual reproduction and its outcome on biotypic diversity. Journal of Economic Entomology. 105(3):1057-1068. Interpretive Summary: The Russian wheat aphid (RWA) is an invasive species that was introduced into the United States in 1986 and soon became a significant wheat pest. Recently, new biotypes of this pest occurred which were capable of killing wheat varieties that were previously resistant to this pest. Aphid has two different life cycles. One main lifecycle is asexual reproduction where adults give live birth to nymphs without mating. Another lifecycle used in harsh winter environments involve a phase where males and females mate to produce overwintering eggs and in doing so create new biotypes and genetic diversity. The sexual life cycle has not been documented in RWA, therefore we conducted field studies from 2004-2009 to determine if this cycle occurs. RWA were found to be mainly asexual and no males or eggs were documented. In the spring of 2007, we did locate one RWA population that overwintered as eggs. We screened ninety-three offspring on resistant and susceptible cereal cultivars and found there was a high degree of biotypic diversity (41.4%). Although this cycle is rare in RWA populations, we demonstrated it can occur and can lead to the biotypes that are occurring in the US.
Technical Abstract: Russian wheat aphid (RWA) (Diuraphis noxia Kurd.) is an invasive species detected in the United States (US) in 1986. It soon became a serious threat to cereal production in the western US and more recently diversified into biotypes capable of killing resistant wheat varieties in the field. Aphids with cyclical parthenogenesis generate genetic and biotypic diversity during the sexual phase of their holocyclic lifecycle. The incidence of cyclical and strict (asexual) parthenogenesis in RWA populations was determined in the Central Great Plains and the Rocky Mountain Region of the US from during the fall, 2004-2009. Colonies from sites were held under unheated greenhouse conditions for further observation for the presence of sexual morphs and eggs during the fall and winter months. RWA populations were found to be mainly asexual and attempt to overwinter as adults, regardless of region sampled. Only few sites were found with ovipara which were not specific to any particular region. Observation of the RWA colonies under greenhouse conditions failed to produce males or eggs. In the spring of 2007, a small population that hatched from eggs (fundatricies) was discovered in the Colorado Plateau within a small area with wheat and mixed grasses. Ninety-three fundatricies from this site were collected and colonies were made to screen them against sixteen cereal plant entries to verify their biotypic classification. A high degree of biotypic diversity (41.4%) was found in this localized population of fundatricies. Our finding is the first report of cyclical parthenogenesis in RWA populations in the US but it is a rare event that is difficult to detect in the field. Further we demonstrated that genetic recombination during the sexual cycle leads to the proliferation of new biotypes that are being discovered in the US. This phenomenon, together with other genetic adaptations and new introductions of this pest, will make the development of new and durable resistance sources to this pest more challenging to wheat and barley plant breeders in the future.