Comparison of plant preference hierarchies of male and female moths and the impact of larval rearing hosts

Abstract

Selection of a suitable host plant is essential for the fitness of herbivorous insects. For polyphagous insects the underlying proximate mechanisms for host plant selection, including phenotypic plasticity, remain only partially understood. We established an experimental protocol evaluating preferences to five plant species in males and females of the polyphagous moth Spodoptera littoralis. Female preference hierarchies were assessed by oviposition decisions; those of males were assessed by the attraction to female sex pheromones in background odors of different plant species. The experiments revealed clear preference hierarchies in both males and females, which were partly overlapping in spite of the different behavioral contexts of the respective assays. Furthermore, we demonstrated strong effects of the larval rearing host on adult plant preference, where the larval host plant species was generally elevated to the most preferred plant in both sexes, without otherwise affecting the overall preference hierarchy. Our results suggest that both sexes are involved in host plant choice and that experience-based convergent intersexual plant preferences may confer selective advantages. The host plant choice is guided by a stable plant preference hierarchy, which can be modified by the larval rearing host, permitting fast adaptation to variation in local conditions and to novel environments. It may also provide a mechanism for reducing costs associated with polyphagy by functional plasticity in plant choice.

Host Plant Species Differentiation in a Polyphagous Moth: Olfaction is Enough

“…The case of maize, however, seems to challenge this view. The results from Thöming et al (2013) show that S. littoralis adults are able to utilize experiences of maize perceptual appearance that they have formed during larval development (individuals grown on maize prefer it as adults), whereas we did not detect any conserved feature in the GC-EAD active odor profile of this plant. It is, however, possible that the picture of olfactory perception of maize by S. littoralis we have depicted is incomplete.…”

“…We chose our plant material in order to fit that used by Thöming et al (2013). The selected plants are cabbage (Brassica oleracea subsp.…”

“…Plant-naïve adults (individuals reared on artificial diet), show a well-defined innate preference hierarchy among those five plant species. However, experienced adults prefer the plant species on which they have been fed as larvae (Thöming et al 2013). This plasticity of host plant preference has been found to function in all model host plants, except cabbage, which is the least innately preferred species and is still avoided by individuals that have successfully completed their larval development on it.…”

“…While females had access to olfactory and contact cues (oviposition choice assay), males only had access to olfactory cues (wind tunnel choice assay). This suggests that olfaction plays a major role in host plant selection (Thöming et al 2013;Zakir et al 2013a).…”

“…We compare the GC-EAD active volatile profiles of five host plant species that S. littoralis adults are able to distinguish (Thöming et al 2013), and show that olfaction alone can explain their ability to differentiate them. We discuss our results is the light of already documented differences in behaviour.…”