|Eastern swallowtail (male?) resting on oak.|
|Along the causeway. River on the right, marsh on the left.|
I wasn't the only person out enjoying the brief reprieve from the heat of Texas summer. One couple had undertaken the marital trial-by-fire of paddling a two-person canoe (much to the amusement of the fisherman and anyone else within earshot). For my own part, I was hot-footing to dodge fire ants and ant lion pits. Trumpet creeper, button bush, and liatris were all still blooming along the river despite being deep in the late summer dormant season.
|Gulf fritillary (Agraulis vanillae) on liatris|
|Grasshopper on button bush. What is he doing?|
It's amazing to me how most butterflies are quite specific in their larval host plants. As first glance, it seems like a high-risk strategy. Why specialize at all when specialization means fewer food options? There must be some benefit, or host plant specialization wouldn't be the dominant strategy.
After doing a little digging in the literature, it appears that host plant chemistry and avoidance of parasitoids are proposed drivers for female butterflies to lay their eggs on one type of plant [3, 4]. Most of us are familiar with Monarch butterflies and how they use toxic alkaloids from the milkweed they eat as caterpillars to discourage predation. The gulf fritillary uses Passiflora spp. alkaloids towards similar ends. Unsurprisingly, tropical lepidoptera are more likely to be specialized than their temperate kin . Dyer et al. hypothesized increased competition as the driver of increased host plant specialization at lower latitudes , so perhaps it is the opposing pulls of predation and resource availability that drive this selectivity. Who knows, but it's certainly fun to ponder!
|Sulphur (little yellow?) butterfly next to leaf|
- Graves, Sherri D., and Arthur M. Shapiro. "Exotics as host plants of the California butterfly fauna." Biological Conservation 110.3 (2003): 413-433.
- Thompson, John N., and Olle Pellmyr. "Evolution of oviposition behavior and host preference in Lepidoptera." Annual review of entomology 36.1 (1991): 65-89.
- Dyer, Lee A., et al. "Host specificity of Lepidoptera in tropical and temperate forests." Nature 448.7154 (2007): 696-699.