Observations of parasitoid behaviour in both no-choice and choice tests are consistent with proposed ecological host range

Abstract

The solitary larval endoparasitoid Eadya daenerys Ridenbaugh (Hymenoptera: Braconidae) is a proposed biocontrol agent of Paropsis charybdis Stål (Coleoptera: Chrysomelidae, Chrysomelinae), a pest of eucalypts in New Zealand. Eadya daenerys oviposition behaviour was examined in two assay types during host range testing, with the aim of improving ecological host range prediction. No-choice sequential and two-choice behavioural observations were undertaken against nine closely related species of New Zealand non-target beetle larvae, including a native beetle, introduced weed biocontrol agents, and invasive paropsine beetles. No behavioural measure was significantly different between no-choice and two-choice tests. In sequential no-choice assays the order of first presentation (target–non-target) had no significant effect on the median number of attacks or the attack rate while on the plant. Beetle species was the most important factor. Parasitoids expressed significantly lower on-plant attack rates against non-targets compared to target P. charybdis larvae. The median number of attacks was always higher towards target larvae than towards non-target larvae, except for the phylogenetically closest related non-target Trachymela sloanei (Blackburn) (Coleoptera: Chrysomelidae, Chrysomelinae). Most non-target larvae were disregarded upon contact, which suggests that the infrequent attack behaviour observed by two individual E. daenerys against Allocharis nr. tarsalis larvae in two-choice tests and the frass of Chrysolina abchasica (Weise) was probably abnormal host selection behaviour. Results indicate that E. daenerys is unlikely to attack non-target species apart from Eucalyptus-feeding invasive paropsines (Chrysomelinae). Non-lethal negative impacts upon less preferred non-target larvae are possible if E. daenerys does attack them in the field; however, this is likely to be rare.