Olfaction in phytophagous ladybird beetles: antennal sensilla and sensitivity to volatiles from host plants in Chnootriba elaterii

Olfaction and chemical ecology in phytophagous ladybird beetles have been largely ignored so far. The present paper describes for the first time basiconic, grooved, and trichoid porous olfactory sensilla on the antennae of the phytophagous ladybird Chnootriba elaterii (Epilacnini) and demonstrates the sensitivity of the antennae to Volatile Organic Compounds (VOCs) from host plants, belonging to common and less common Cucurbitaceae crops and wild species (Citrullus lanatus, Cucumis melo, Cucumis sativus, Cucurbita pepo, Cucurbita moschata, Lagenaria siceraria, Luffa cylindrica, and Ecballium elaterium). Epilachnini ladybirds are phytophagous, with adult and larvae feeding on various Cucurbitaceae, Fabaceae, and Solanaceae. Notwithstanding some species are serious pests in crops, their chemical ecology has been largely disregarded so far. The present paper discusses the ultrastructure of antennal sensilla (scanning electron microscopy-SEM) and the electroantennographic recordings (EAG) from the olfactory sensilla responding to the proposed chemicals, also considering the literature on chemical ecology and olfaction of aphidophagous ladybugs. In particular, antennal sensilla are similar to those described in predatory species but in Epilachnini they are much more numerous on the apical flagellum, probably because involved in host plant location and selection. This research can be considered a first step in developing semiochemical-based and sustainable control strategies for melon ladybird in crops.