Abstract
Utilization of a novel plant host by herbivorous insects requires coordination of numerous physiological and behavioral adaptations in both larvae and adults. The recent host range expansion of the crucifer-specialist diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), to the sugar pea crop in Kenya provides an opportunity to study this process in action. Previous studies have shown that larval ability to grow and complete development on sugar pea is genetically based, but that females of the pea-adapted strain do not prefer to oviposit on pea. Here we examine larval preference for the novel host plant. Larvae of the newly evolved pea-adapted host strain were offered the choice of the novel host plant sugar pea and the original host cabbage. These larvae significantly preferred pea, while in contrast, all larvae of a cabbage-adapted DBM strain preferred cabbage. However, pea-adapted larvae, which were reared on cabbage, also preferred cabbage. Thus both genetic differences and previous exposure affect larval host choice, while adult choice for the novel host has not yet evolved.
Highlights
The present-day patterns of species diversity of flowering plants and herbivorous insects reflect the ongoing process of co-evolution in which insects and their plant hosts are in a constant arms race [1].Plants evolve novel substances to defend themselves and escape from the pressure of herbivory and the herbivore, in turn, evolves tolerance to these defenses to explore a novel host plant that provides reduced competition [1,2,3]
We showed that the ability of diamondback moth (DBM)-P larvae to complete development on pea has a polygenic genetic basis [22]. These results suggest that host range expansion in DBM-P is still in the early stages, and raises the question how larval preference is involved in the host choice behavior of this strain, which was the purpose of this study
Total amount of leaf area consumed by DBM-P larvae differed significantly from the amount consumed by DBM-Cj larvae (Padj = 0.01), but not from DBM-P larvae raised on cabbage (DBM-Pc) (Padj = 0.37) after 6 h
Summary
The present-day patterns of species diversity of flowering plants and herbivorous insects reflect the ongoing process of co-evolution in which insects and their plant hosts are in a constant arms race [1].Plants evolve novel substances to defend themselves and escape from the pressure of herbivory and the herbivore, in turn, evolves tolerance to these defenses to explore a novel host plant that provides reduced competition [1,2,3]. The successful use of a host plant depends on specific behavioral and physiological adaptations in the adult and larval stage. The acquisition of a novel plant as host, i.e., the establishment of a novel insect-plant interaction, is presumably governed by changes in behavior by adults or larvae or both. Feeding and/or oviposition behavior have to change from “not being attracted to” or “being repelled from” to “acceptance of” or even “preference for” the novel host. This was the case in the checkerspot butterfly Euphydryas editha, which incorporated the introduced plant Plantago lanceolata into its diet in the last 100 years [9]. Oviposition preference for the novel host, and rejection of the native host, has since evolved in populations that reside in regions where the introduced plant grows [9,10]
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