Impact of Plant Suitability, Biogeography, and Ecological Factors on Associations between the Specialist Herbivore Heliothis subflexa G. (Lepidoptera: Noctuidae) and the Species in its Host Genus, Physalis L. (Solanaceae), in West-Central Mexico

Abstract

Caterpillars of the moth species Heliothis subflexa G. (Lepidoptera: Noctuidae) are known to feed exclusively on fruits of plants in the genus Physalis L. (Solanaceae). However, data were lacking on whether H. subflexa is constrained to feeding on a subset of the approximately 90 species in this plant genus. The purpose of this research has been to determine which Physalis species are utilized by H. subflexa and to assess the relative importance of plant nutritional suitability, biogeography, and ecological factors in shaping the realized host range of H. subflexa. This was accomplished through a combination of field observations of plants of 17 Physalis species occurring at 76 field sites in West-Central Mexico, a common garden study, and laboratory bioassays. Variation among Physalis species in their biogeography, life history, fruit traits, and concentrations of essential fatty acids were characterized to determine if these factors impact H. subflexa host use.

The realized host range of this specialized herbivore proved to be constrained to thirteen of the seventeen Physalis species examined in this study. Heliothis subflexa varied with respect to the frequency and the intensity with which it infested these thirteen host species. Although H. subflexa's potential host range included species that it did not infest in the field, some of the potential hosts were suboptimal for larval development, and survivorship on these Physalis species did not differ from survivorship on fruits of a non-Physalis species, Nicandra physalodes, which is not infested by H. subflexa. Positive correlations found between patterns of host use in the field, the common garden, and the laboratory bioassays indicates that plant suitability to larvae and attractiveness to ovipositing females are important determinants of H. subflexa's realized host range. Heliothis subflexa associations with Physalis species are also influenced by biogeographical factors. Differences in host associations at low versus high elevations may be associated with contemporary population isolation and differentiation.