Host plant specialization in the generalist moth Heliothis virescens and the role of egg imprinting
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Even though generalist insects are able to feed on many different host plants, local specialization may occur, which could lead to genetic differentiation. In this paper we assessed the level and extent of host plant specialization in the generalist herbivore Heliothis virescens Fabricius (Lepidoptera, Noctuidae). This generalist can grow and survive on many different plant species, belonging to more than 37 families. Previously, two laboratory strains were described that differ in their performance on cotton and chickpea. In this study we explored this phenomenon further. Specifically, we asked the following questions: (1) Do the two strains still differ in their performance on cotton and chickpea? Since we found that the most pronounced difference between the two strains was in their growth on fresh chickpea leaves, we then asked: (2) Does this variation in performance have a genetic basis? In our genetic analysis, we found that growth rates changed over time and that two linkage groups significantly affected the ability to grow on chickpea. One QTL was homologous to Bombyx mori chromosome 15, onto which genes for insecticide resistance and detoxicative enzymes have previously been mapped. (3) Is there a difference in oviposition preference between the two strains? Oviposition experiments revealed no preference in either strain when females were reared on the same artificial diet. However, we did find a maternal inheritance of oviposition preference: daughters collected as eggs from cotton oviposited significantly more eggs on cotton, and daughters collected as eggs from chickpea likewise laid more eggs on chickpea. Thus, Hopkins’ host selection principle seems to holds in this species, although imprinting seems to happen not at the larval but at the egg stage, which is a new finding. This study shows how genetic and nongenetic factors can interact to shape the patterns of local specialization in a generalist herbivore.
KeywordsTobacco budworm Gossypium hirsutum Cicer arietinum Herbivore Oviposition Quantitative trait locus analysis Preference Performance Maternal imprinting
We thank Dr. Carlos Blanco from the USDA for providing us with individuals from the MON and ARS strains, Susanne Donnerhacke and Antje Schmaltz for their help with the creation of the AFLP markers and the chromosome mapping, and Regina Seibt for the rearing of the two strains. We also thank Domenica Schnabelrauch for sequencing the selected AFLP markers. This research was partly funded by the National Science Foundation (award IOS-1052238), the W. M. Keck Center for Behavioral Biology, and the Max-Planck-Gesellschaft.
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