Host-associated chemical cues mediating host-finding behaviour in the larval ectoparasitoid Cephalonomia tarsalis

Understanding how parasitoids locate their hosts is essential for improving the effectiveness of these insects as biological control agents. The bethylid ectoparasitoid Cephalonomia tarsalis is a key natural enemy of the sawtoothed grain beetle Oryzaephilus surinamensis, an important stored product pest. While some aspects of its host-finding behaviour are understood, the significance of larval host-associated volatile cues remains largely unclear. This study investigated the influence of host-specific odours on host location by C. tarsalis females.

Volatile compounds released from fourth-instar larval faeces were identified by gas chromatography-mass spectrometry and their behavioural relevance was evaluated using Y-tube olfactometer bioassays alongside odours from different host stages (live larvae and adults) and from host-associated food substrates. Females responded positively to most of the tested odours, including those from host adults, larval faeces, and host-associated food substrates. Among the compounds identified in the faecal volatiles of host larvae, 1-pentadecene was found to be significantly attractive. In flight-cage experiments, 1-pentadecene induced behavioural responses in test parasitoids that were similar to those elicited by larval faeces.

Host-associated volatile cues, particularly those derived from larval faeces, play a key role in mediating the host-searching behaviour of C. tarsalis females. These findings provide a basis for the development of semiochemical-based approaches to enhance the efficiency of this biological control agent for stored-product pests. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.