Adult host-plant preference and larval performance in an oligophagous insect (Chnootriba elaterii)

The present research investigates host preferences and larval development of the melon ladybird Chnootriba elaterii (Rossi) (Coleoptera: Coccinellidae), considering seven Cucurbitaceae plant species (Citrullus lanatus, Cucumis melo, Cucumis sativus, Cucurbita pepo, Cucurbita moschata, Lagenaria siceraria and Luffa aegyptiaca), to determine whether mother host preference is related with larval performance. The damaged area on plant leaves due to insect feeding in dual-choice experiments was used to evaluate food preferences. Behavioural experiments in a Y-tube olfactometer tested the role of olfaction in host-plant selection. Parameters such as development duration and morphometric characters of emerged adults were evaluated to estimate larval performance. Adult females selected watermelon and melon as their favourite food while firmly refusing loofah and calabash. Insects preferred melon over watermelon, but the larval development on melon was slower; moreover, watermelon allowed larvae to develop faster than other tested plants, while loofah did not allow larval development. Larvae fed and developed on melon, pumpkin, zucchini, cucumber and calabash, without strong differences. These results only partially supported the preference-performance hypothesis suggesting that it could be context dependent. Contrary to expectation, volatile organic compounds (VOCs) belonging to the host, only partially could guide adult females in the olfactometer. This result suggests that long-distance olfactory stimuli alone cannot provide sufficient information for host-plant selection in melon ladybirds. Considering the economic relevance of C. elaterii, the results of the present paper answer some basic questions about host-plant selection for this pest insect, potentially useful to improve control strategies in crops.