Specialist insects have been widely studied, while comparatively little is known about the evolutionary ecology of generalists. We study the evolution of diet breadth for generalist species, focusing specifically on polyphagous slug caterpillars and fall webworms.
Slug CaterpillarsI am collaborating with Dr. John Lill (the George Washington University) to investigate the evolution of diet breadth for generalist species, specifically focusing on polyphagous slug caterpillars (Lepidoptera: Limacodidae). Specialist insects have been widely studied, while comparatively little is known about the evolutionary ecology of generalists. We study the evolution of diet breadth for generalist species, focusing specifically on polyphagous slug caterpillars (Lepidoptera: Limacodidae).
Ours is one of the first studies to investigate how polyphagy is maintained in generalist insect species. A tri-trophic view that encompasses both host plant characteristics and predation is often evoked when explaining why so many insect species are specialists. We are attempting to understand how tri-trophic interactions may also function to maintain polyphagous habits for generalist species (Lill and Murphy, in preparation). Slug caterpillars are known for their unusual morphologies, including various types of protuberances and stinging spines on their dorsal surfaces, which suggest that their evolution has been strongly shaped by their interactions with predators (Murphy et al. 2010). We have studied multiple aspects of their life history (Murphy et al. 2011, Stoepler et al 2014, Fiorentino et al. 2014) and although predators are a major source of mortality (Murphy and Lill 2010), limacodid parasitoids (Gates et al. 2012) play an extremely important role in this system and appear to partition the limacodid community based on host body size (Stoepler et al. 2011, Murphy et al. 2014a, Murphy et al. 2014b). We are also studying how global change may be changing the number of generations per year for a prominent limacodid species (Murphy and Lill, in preparation). Relevant Publications Murphy, S. M., J. T. Lill, M. D. Bowers and M. S. Singer. 2014. Enemy-free space for parasitoids. Environmental Entomology 43(6): 1465-1474. Stoepler, T. M., J. T. Lill and S. M. Murphy. 2014. Intraplant movement of generalist slug caterpillars (Limacodidae: Lepidoptera): Effects of host plant and light environment. Environmental Entomology 43(6): 1561-1573. Murphy, S. M., T. M. Stoepler, K. Grenis*, and J. T. Lill. 2014. Host ontogeny determines parasitoid use of a forest caterpillar. Entomologia Experimentalis et Applicata 150: 217-225. Fiorentino, V. L.**, S. M. Murphy, T. M. Stoepler and J. T. Lill. 2014. Facilitative effects of group feeding on performance of the saddleback caterpillar, Acharia stimulea (Lepidoptera: Limacodidae). Environmental Entomology 43:131-138. Gates, M. W., J. T. Lill, R. R. Kula, J. E. O’Hara, D. B. Wahl, D. R. Smith, J. B. Whitfield, S. M. Murphy and T. M. Stoepler*. 2012. Review of parasitiod wasps and flies (Hymenoptera, Diptera) associated with Limacodidae (Lepidoptera) in North America, with a key to genera. Proceedings of the Entomological Society of Washington 114(1): 24-110. Stoepler, T. M.*, J. T. Lill and S. M. Murphy. 2011. Cascading effects of host size and host plant species on parasitoid resource allocation. Ecological Entomology 36: 724-735. Murphy, S. M., J. T. Lill. and M. E. Epstein. 2011. Natural history of limacodid moths (Zygaenoidea) in the environs of Washington, DC. Journal of the Lepidopterists’ Society 64(3): 137-152. Murphy, S. M. and J. T. Lill. 2010. Winter predation of diapausing cocoons of slug caterpillars (Lepidoptera: Limacodidae). Environmental Entomology 39(6): 1893-1902. Kula, R. R., J. T. Lill, S. M. Murphy and T. Stoepler*. 2010. The first host records for the nearctic species Triraphis discoideus (Hymenoptera: Braconidae: Rogadinae). Entomological News 120(4): 380-386. Murphy, S. M., S. M. Leahy**, L. S. Williams** and J. T. Lill. 2010. Stinging spines protect slug caterpillars (Limacodidae) from multiple generalist predators. Behavioral Ecology 21(1): 153-160. Murphy, S. M., J. T. Lill and D. R. Smith. 2009. A scattershot approach to host location: Uncovering the unique life history of the Trigonalyid hyperparasitoid Orthogonalys pulchella Cresson. American Entomologist 55(2): 82-87. |
Fall WebwormSince my arrival at DU, we have studied fall webworms (Lepidoptera: Erebidae), which are one of the most polyphagous herbivore species, feeding on hundreds of plant species worldwide. Herbivore diet breadth is predicted to evolve in response to both bottom-up and top-down selective pressures, including host plant abundance, quality and natural enemy pressure. As the relative importance and strength of interactions change over an herbivore’s geographic range, local patterns of host plant use should change in response, altering local diet breadths. Populations of fall webworm in Colorado remain polyphagous (Loewy et al. 2013), but their diet breadth is restricted compared to other populations and thus local populations present an ideal opportunity to test the ecological drivers of host use by a polyphagous herbivore (Murphy and Loewy, 2015). In collaboration with my graduate student Mayra Vidal, we are studying how a geographic mosaic of selection pressures may cause populations of a generalist herbivore like fall webworm to narrow its diet breadth (Vidal and Murphy 2018a) and how bottom-up and top-down forces drive selection (Vidal and Murphy 2018b).
We have NSF funding to continue this project for a few more years!! I'm excited to continue working with Dr. Dhaval Vyas as co-PI and Mayra Vidal and Gina Wimp as PI's at U Mass Boston and Georgetown University, respectively. Relevant Publications Vyas, D. K.¶ and S. M. Murphy. 2022. Diet mediated immune response to parasitoid attacks on a caterpillar with a broad diet breadth. Ecological Entomology 47: 636-644. Vidal, M. C.*, J. T. Lill, R. J. Marquis, and S. M. Murphy. 2020. Geographic variation in performance of a widespread generalist herbivore. Ecological Entomology 45:617-625. Vidal, M. C.*, T. Quinn, J. Stireman, R. Tinghitella, and S. M. Murphy. 2019. Geography is more important than host plant use for the population genetic structure of a generalist insect herbivore. Molecular Ecology 28: 4317-4334. Vidal, M. C.* and S. M. Murphy. 2018a. Quantitative measure of fitness in tri-trophic interactions and its influence on diet breadth of insect herbivores. Ecology 99(12): 2681-2691. Vidal, M. C.* and S. M. Murphy. 2018b. Bottom-up vs. top-down effects on terrestrial insect herbivores: a meta-analysis. Ecology Letters 21:138-150. Murphy, S. M. and K. J. Loewy*. 2015. Trade-offs in host choice of an herbivorous insect based on parasitism and larval performance. Oecologia 179: 741-751. Loewy, K. J.*, A. Flansburg**, K. Grenis*, M. Kjeldgaard**, J. McCarty**, L. Montesano**, J. Vernick** and S. M. Murphy. 2013. Life history traits and rearing techniques for fall webworm (Hyphantria cunea Drury) in Colorado. Journal of the Lepdiopterists’ Society 67(3): 196-205. |