Volatile chemistry, not phylogeny, predicts host range of a biological control agent of old-world climbing fern.
The safety of weed biological control depends upon the selection and utilization of the target weed by the agent while causing minimal harm to non-target species. Selection of weed species by biological control agents is determined by the presence of behavioral cues, namely host secondary plant compounds that elicit oviposition and feeding responses. Non-target species that elicit the same behavioral cues as found in the target weed may be at risk of damage by classical biological control agents. Here we determined volatile secondary plant constituents of the invasive weed Old World climbing fern, Lygodium microphyllum and five Lygodium non-target species. Nonmetric multidimensional scaling and permutational analysis of variance indicated that the volatile profiles for each Lygodium species were significantly distinct from one another. Qualitative and quantitative comparisons of 32 volatile constituents indicated that several, including 1-octen-3-ol, 3-octanone, sativene, δ-cadinene, and ethyl hexanoate, distinguish the non-target Lygodium species from the target L. microphyllum. We retrospectively compared the ovipositional responses of the established classical biocontrol agent Neomusotima conspurcatalis, previously tested and released for biological control of L. microphyllum to these species and found similarity of volatile profile to L. microphyllum was a strong predictor of oviposition (R2 = 0.86), while phylogenetic distance predicted neither volatile profile nor oviposition for the Lygodium species tested. These results suggest that distinct volatile profiles among Lygodium species facilitated the selection of the target weed L. microphyllum and the invasive congener L. japonicum while avoiding other, non-target species native to the introduced range for oviposition. These volatile profiles could serve as behavioral cues used by this biological control agent N. conspurcatalis to select a narrow host range.