Host recognition by the tick parasitoid Ixodiphagus hookeri (Hymenoptera: Encyrtidae)

We conducted laboratory experiments to determine whether the tick parasitoid Ixodiphagus hookeri Howard uses chemicals of the host tick Amblyomma variegatum F. as host recognition cues. When given a piece of polyethylene sheet containing an air bubble (a dummy host) treated or untreated with hexane, I. hookeri females did not respond to the dummy. However, when females contacted the dummy host treated with hexane extracts from unfed nymphs, engorged nymphs, or unfed adults of the host ticks, they probed the dummy with their ovipositors. When given a choice of dummies treated with hexane extract of engorged nymphs, hexane, or nothing, they did not demonstrate any selective attraction for the dummy with hexane extract from engorged nymphs over the other dummies. A fraction (hexane 9: ether 1) of hexane extract from engorged nymphs strongly stimulated ovipositor probing by females. These results suggest that I. hookeri females use chemicals contacted on host ticks as host recognition cues.