Abstract
The mechanisms of host shift in phytophagous insects are poorly understood. Among the many proposed processes involved, sexual selection via semiochemicals has recently been suggested. This hypothesizes that sexual communication using pheromones is modified as a result of development on a new host, and such plant-induced phenotypic divergence in mate recognition cues can lead to reproductive isolation between host lines. We tested this hypothesis on Acanthoscelides obtectus, an oligophagous bruchid of Phaseolus vulgaris beans worldwide, which also develops in acceptable non-hosts, such as chickpea (Cicer arietinum L.). Male sex pheromone blends of the bean, chickpea and chickpea/bean host lines during artificially induced host shifts showed different composition. Bean-reared females did not distinguish between blends, whereas chickpea and chickpea/bean females preferred the chickpea male pheromone. However, electrophysiological (EAG) responses to male odour of antennae of the three female host lines were similar, all preferring bean-reared males. Egg-laying choice tests revealed a uniform preference for bean seeds across female host lines, even after multiple generations, whereas larvae did not distinguish between bean and chickpea seeds. We conclude that the development of divergent chemical signalling systems during host shifts does not facilitate the evolution of host races in A. obtectus, because oviposition preferences remain unaffected.
Highlights
Of the ca. 450,000 known phytophagous insect species, at least 70% are mono- and oligophagous, consuming a narrow range of species within one plant family [1,2]
gas chromatographic (GC) and GC-MS analysis showed significant differences (p
There was an almost complete lack of methyl (2E,4Z,7Z)-2,4,7-decatrienoate in the headspace extract of 1st generation males reared on chickpea when compared to males reared on bean
Summary
Of the ca. 450,000 known phytophagous insect species, at least 70% are mono- and oligophagous, consuming a narrow range of species within one plant family [1,2]. 450,000 known phytophagous insect species, at least 70% are mono- and oligophagous, consuming a narrow range of species within one plant family [1,2]. Due to their making up a large proportion of the Insecta class (45%), the evolution of herbivorous insects strongly influences theories on the evolution of insect diversity [3]. Mono- and oligophagy is a more frequent strategy than polyphagy Host shift changes chemical signalling funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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