Host‐associated chemical cues mediating host‐finding behaviour in the larval ectoparasitoid <scp> <i>Cephalonomia tarsalis</i> </scp>

BACKGROUND: 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. RESULTS: 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. CONCLUSION: 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.