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

Abstract

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.

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

“…These results were not expected given previous EAG investigations, demonstrating that antennae of C. elaterii can perceive a wide range of volatiles emitted by cucurbits (E2-exenal, heptanal, nonanal, decanal, methyl salicylate, (-) -linalool, Z3-hexen-1-ol, pentanol, hexanol, nonanol and octanol), and plant extracts from watermelon, melon, pumpkin, calabash, cucumber and zucchini but not loofah (Piersanti et al, 2022). We cannot exclude that olfactory cues may be important in host searching by melon ladybug, but probably in combination with other stimuli, as reported in many insects orders (Fernandez & Hilker, 2007;Harris & Miller, 1988;Prokopy & Owens, 1978;Saxena & Goyal, 1978;Vaishampayan et al, 1975).…”

“…This plant is widely distributed in Africa and Asia, and fruits, traditionally used as sponges (Chomicki et al, 2019), are recently considered a promising sustainable and renewable biomass for new materials development (Hlel et al, 2021;Paglicawan et al, 2005;Su et al, 2018). The unpalatability of loofah could be due to some chemical defence, as suggested by the absence of EAG responses to loofah extract (Piersanti et al, 2022), which aligns with previous preliminary observations (El-Abdin & Siragelnour, 1991); otherwise, C. elaterii does not have any problem of adhesion to the loofah leaves (Saitta et al, 2022). For this reason, loofah could be used as an intercrop in cucurbit cultivations, developing interesting biocontrol strategies against the melon ladybug, similar to the protection of cabbage crops from Pieris rapae (L.) (Lepidoptera:…”

“…inodorus and cantalupensis ), cucumber ( C. sativus ) and calabash ( Lagenaria siceraria ) are reported as possible hosts of the ladybird (Liotta, 1964), few or no data are available about the damages on these crops, as well as on zucchini ( Cucurbita pepo ) and loofah ( Luffa aegyptiaca = L. cylindrica ), all species economically relevant in Europe. In addition, a recent paper investigates the sensitivity of the antennae (electroantennographic EAG responses) of C. elaterii to VOCs emitted by Cucurbitaceae crops ( C. lanatus , C. melo , C. pepo , Cucurbita moschata , L. siceraria , L. aegyptiaca , C. sativus ), such as E2‐exenal, heptanal, nonanal, decanal, methyl salicylate, linalool, Z3‐hexen‐1‐ol, pentanol, hexanol, nonanol and octanol (Piersanti et al, 2022). Antennae of C. elaterii clearly respond to many of these chemicals, still data need to be available on the role of this sensory ability in host‐plant selection (Piersanti et al, 2022).…”

“…In addition, a recent paper investigates the sensitivity of the antennae (electroantennographic EAG responses) of C. elaterii to VOCs emitted by Cucurbitaceae crops ( C. lanatus , C. melo , C. pepo , Cucurbita moschata , L. siceraria , L. aegyptiaca , C. sativus ), such as E2‐exenal, heptanal, nonanal, decanal, methyl salicylate, linalool, Z3‐hexen‐1‐ol, pentanol, hexanol, nonanol and octanol (Piersanti et al, 2022). Antennae of C. elaterii clearly respond to many of these chemicals, still data need to be available on the role of this sensory ability in host‐plant selection (Piersanti et al, 2022).…”

“…Cucurbits selected for the experiments belong to major (watermelon, melon, cucumber, zucchini, pumpkin and calabash) and minor (loofah) crops economically relevant in Europe. These species are representative of five genera widespread in the phylogenetic cladogram of Cucurbitaceae (Chomicki et al, 2019) and have been previously tested in C. elaterii EAG recordings (Piersanti et al, 2022).…”