Origin and phylogeography of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera : Cephidae): implications for pest management

Authors: LESIEUR, VINCENT - MONTPELLIER SUPAGRO – INTERNATIONAL CENTER FOR HIGH EDUCATION IN AGRICULTURAL SCIENCES; MARTIN, JEAN-FRANCOIS - MONTPELLIER SUPAGRO – INTERNATIONAL CENTER FOR HIGH EDUCATION IN AGRICULTURAL SCIENCES; WEAVER, DAVID - MONTANA STATE UNIVERSITY; HOELMER, KIM; Shanower, Thomas; SMITH, DAVID - RETIRED ARS EMPLOYEE; MORILL, WENDELL - RETIRED NON ARS EMPLOYEE; KADIRI, NASSERA - UNIVERSITY OF MONTPELLIER; COCKRELL, DARREN - COLORADO STATE UNIVERSITY; RANDOLF, TERRI - COLORADO STATE UNIVERSITY; WATERS, DEBRA; BON, MARIE-CLAUDE - EUROPEAN BIOLOGICAL CONTROL LABORATORY (EBCL)

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2016
Publication Date: 12/13/2016
Citation: Lesieur, V., Martin, J., Weaver, D.K., Hoelmer, K.A., Shanower, T.G., Smith, D.R., Morill, W.L., Kadiri, N., Cockrell, D., Randolf, T.L., Waters, D.K., Bon, M. 2016. Origin and phylogeography of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera : Cephidae): implications for pest management. PLoS One. 11(12):e0168370. doi:10.1371/journal.pone.0168370.

Interpretive Summary: The wheat stem sawfly is a key pest of wheat in the northern Great Plains of of North America, but damage caused by this species has been expanding southwards. Current pest management practices are not very effective, and uncertainties regarding the sawfly’s origin and its population structure and dynamics across North America have hindered the development of improved management and biological control strategies. We investigated the origin of the American wheat stem sawfly populations using two mitochondrial markers from samples collected in North America and Northeastern Asia, the assumed native range of the sawfly. We then examined the genetic diversity of the sawfly in the major wheat producing areas in North America using samples collected both on wheat and wild grasses using mitochondrial and nuclear markers. The level of genetic diversity of North American sawflies is high and North American and Asian sawflies clearly differ genetically, two clues in favor of an American origin for this sawfly. The genetic diversity of the North American populations is structured into three distinct groups that are correlated with geography. Our results suggest that the increasing problems with sawfly in the southern Great Plains are due to adaptation to wheat by the local populations, and not to an expansion of the northern sawfly populations. Management strategies, including conservation biological control to enhance activity of the sawfly’s native natural enemies, will need to account for biological differences among these three population groups.

Technical Abstract: he wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a key pest of wheat in the northern Great Plains of North America, and damage by this species has recently expanded southward. Current pest management practices are not very effective and uncertainties regarding its origin and its population structure and dynamics across North America preclude the design of more effective management and biological control strategies. We investigated the origin of the American wheat stem sawfly populations using two mitochondrial regions (COI and 16S) for samples collected in North America and Northeastern Asia, the assumed native range of C. cintus. Subsequently, we characterized the structure of genetic diversity in the main wheat producing areas in North America using a combination of one mtDNA marker and microsatellites on populations collected both on wheat and wild grasses. The divergence observed between North American samples and Asian congeners reinforced the hypothesis of an American origin of C. cintus. Furthermore, the relatively high genetic diversity both with mtDNA and microsatellite markers offered another clue in favor of the native American origin of this pest. The genetic diversity of the North American populations is structured into three genetic clusters and is highly correlated with geography. Regarding the recent southern outbreaks, the results presented in this study tend to exclude the hypothesis of a recent introduction of the wheat stem sawfly from the northern part of the wheat production area. Adaptation by local populations to wheat appears to be the most likely scenario. Pest management strategies will need to account for biological differences among the three geographic clusters. Given its American origin, conservation biological control to enhance the activity of native parasitoids should be considered as a strategy.