Specialization of Colorado Fall Web Worm to Local Host Plants
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Variation in host use by herbivorous insects is driven by ecological factors, which drive the process of natural selection. If the relative importance and strength of such pressures change over an herbivores geographic distribution, local adaptation can occur. Studies of this type of local adaptation may provide insight into the evolutionary process of natural selection and selection pressures acting on populations of herbivorous insects. Fall webworm (Hyphantria cuena) are moth larva which have two distinct morphological types, one with red head capsules and one with black head capsules. Populations of H. cuena larvae have been noted to utilize different species of host plants based on both geographical location and color of the head capsule. We investigated the specialization of these larvae, looking for evidence of local adaptation between two distinct populations of fall webworm: Colorado red-headed larvae and East Coast black-headed larvae. This was done by measuring larval fitness of each population when reared on each of four host plants: Choke Cherry (Prunus virginiana) and Narrowleaf Cottonwood (Populus angustifolia), which are both commonly used by the Colorado population, as well as Box Elder (Acer negundo) and Green Ash (Frazinus pennsylvanica), which are common hosts to East Coast populations. It was hypothesized that Colorado red-headed larvae have adapted to use the host plants on which they are most commonly found on, having lost the physiological ability to utilize the host plants which the East Coast black-headed larvae commonly use. We found evidence of local adaptation in the Colorado red-headed larvae, and evidence that the East Coast black headed larvae are also best adapted to the host plants which they commonly use.