Robin Bagley Project Director: Testing the host-shift speciation hypothesis in the red-headed pine sawfly (Neodiprion lecontei)

Phytophagous insects make up over one quarter of described species on Earth and this incredible diversity seems directly linked to feeding on plants. Comparative studies of sister groups have shown shifts to herbivory are consistently associated with increased species diversity in insects, but the reasons for this diversification remain unclear. While other explanations, such as decreased extinction rates or influences on population structure, exist, one prominent hypothesis suggests shifts and subsequent adaptation to novel host plants directly promote herbivorous insect speciation. If host-shift speciation is prevalent, there will likely be evidence of host-driven divergence within insect species occurring on a wide range of host plants. Therefore, I propose to examine populations of the red-headed pine sawfly, Neodiprion lecontei, an abundant, well-studied pest species that occurs on multiple hosts, for evidence of incipient host-shift speciation. I have identified a field site that harbors sympatric populations of N. lecontei across three hosts. I propose to collect ecological, reproductive, and genomic data from these three populations to determine whether there is 1) ecological divergence in female preference and larval performance, 2) reproductive isolation between populations, and 3) genetic differentiation between populations. This project applies to the Primary Foundational Area "Plant health and production and plant products," as it explores several aspects of the biology of a major economic pest species. On a broader scale, understanding if host shifts predictably lead to insect speciation may also provide critical insight for the management pest species that utilize multiple hosts throughout their range.