Limited genetic evidence for host plant-related differentiation in the Western cherry fruit fly, Rhagoletis indifferens
Citation
Saint Jean, G., Hood, G.R., Egan, S.P., Powell, T.H.Q., Schuler, H., Doellman, M.M., Glover, M.M., Smith, J.J., Yee, W.L., Goughnour, R.B., Thistlewood, H.M.A., Maxwell, S.A., Keyghobadi, N., Rull, J., Aluja, M., Feder, J.L. (2018). Limited genetic evidence for host plant-related differentiation in the Western cherry fruit fly, Rhagoletis indifferens. Entomologia Experimentalis et Applicata, [online] 166(9), 739-751. http://dx.doi.org/10.1111/eea.12712
Plain language summary
Some insects are able to lay eggs inside fruits, and in Canada this group includes three species of cherry fruit flies, apple maggot, and blueberry maggot. The infested fruit can be spread long distances if harvested and shipped, which causes important problems for trade within Canada and for high-value export crops. Research into the ability to infest different fruits is important for easing trade barriers and for ecological understanding. The apple maggot evolved onto apple by shifting over from its native host plant, hawthorn, in the eastern USA in the 1800s. Genetically distinct races of apple maggot flies now prefer different hosts. This study examined western cherry fruit fly, Rhagoletis indifferens, from locations across the northwestern USA and in British Columbia. This fly shifted from infesting a native plant, bitter cherry, and became an economic pest of sweet cherry as it introduced by growers. The team found little evidence for genetic differences between western cherry fruit flies in different host plants, nor any difference in an important measure of population development. The results support earlier studies of cherry fruit flies in British Columbia, Canada, and Michigan, USA, which suggested no differences between cherry fruit flies infesting different host plants. However, they are not the same as those for apple maggot flies on various host plants. Possible reasons as to why host races are detected for apple maggot, but not cherry fruit flies, are discussed. The results help to clarify ecological processes and to improve monitoring for export purposes.
Abstract
The shift of the fruit fly Rhagoletis pomonella (Walsh) in the mid-1800s from downy hawthorn, Crataegus mollis (Torrey & Asa Gray) Scheele, to introduced domesticated apple, Malus domestica (Borkhausen), in the eastern USA is a model for ecological divergence with gene flow. A similar system may exist in the northwestern USA and British Columbia, Canada, where Rhagoletis indifferens Curran (Diptera: Tephritidae) attacks the native bitter cherry Prunus emarginata (Douglas ex Hooker) Eaton (Rosaceae). Populations of R. indifferens have shifted and became economic pests on domesticated sweet cherry, Prunus avium (L.) L., shortly after sweet cherries were introduced to the region in the mid-1800s. The fruiting phenologies of the two cherries differ in a similar manner as apples and hawthorns, with domesticated sweet cherries typically ripening in June and July, and bitter cherries in July and August. Here we report, however, little evidence for genetic differentiation between bitter vs. sweet cherry populations of R. indifferens or for pronounced genetic associations between allele frequencies and adult eclosion time, as has been documented for apple and downy hawthorn flies. The current findings support a previous more geographically limited survey of R. indifferens in the province of British Columbia, Canada, and an analysis of its sister species, R. cingulata, in the state of Michigan, USA, implying a lack of host-related differentiation for flies infesting different cherry host plants. Possible causes for why host races are readily genetically detected for R. pomonella but not for R. indifferens are discussed.