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Host recognition by the egg–larval parasitoid Chelonus inanitus: effects of physical and chemical cues

Parasitoid wasps are widely used as biocontrol agents. For successful deployment, it is important to know how they search for and recognize their hosts. They often use chemical cues in host searching and recognition. Little attention has been paid to the use of physical cues, particularly when combined with chemical cues, though a combination of cues may improve searching efficiency. Chelonus inanitus L. (Hymenoptera: Braconidae) is a solitary, egg–larval parasitoid wasp that parasitizes various lepidopteran species, including serious crop pests. In this study, effects of physical and/or chemical cues on host recognition were investigated in C. inanitus by observing its antennal searching, ovipositor probing, and the duration of arrestment. In a physical cue test, egg‐mass models with glass beads differing in size were used, and a single‐egg model with a specific size of bead. Egg‐mass models with beads of 0.4–1.0 mm in diameter arrested C. inanitus, in accordance with egg size and arrangement of the host. In a chemical cue test, extract from egg masses of the host Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), equivalent to half of a host egg mass and extract diluted 100‐fold were used, and the undiluted extract stimulated C. inanitus. Untreated egg‐mass models (0.2‐mm‐diameter glass beads) and diluted egg extract arrested C. inanitus less effectively; however, when glass beads were treated with the diluted extract, arrestment increased to the same degree as the undiluted extract. These results suggest that C. inanitus uses both physical and chemical cues to recognize eggs of its host, S. litura, and that these stimuli act synergistically.