Will the accidental introduction of Neopolycystus insectifurax improve biological control of the eucalyptus tortoise beetle, Paropsis charybdis, in New Zealand?

Paropsis charybdis is a key pest of eucalypt plantations in New Zealand, where it is attacked by two primary egg parasitoids and one hyperparasitoid. One of the primary parasitoids, Enoggera nassaui, was a deliberate introduction for the purpose of biological control whereas the other species were self-introductions. The hyperparasitoid, Baeoanusia albifunicle, parasitises E. nassaui but not the other primary parasitoid, Neopolycystus insectifurax. It has been hypothesised that N. insectifurax may compensate for any reduction in parasitism of P. charybdis by E. nassaui due to the hyperparasitoid. The biology of the two primary parasitoids was compared under controlled conditions and field parasitism of P. charybdis measured to test this possibility of N. insectifurax compensating for reduced E. nassaui populations. The lifespan of the two primary parasitoids was similar with or without access to food but the species differed in their patterns of egg maturation and responses to temperature. Enoggera nassaui was less synovigenic and had a lower temperature threshold for development than N. insectifurax. In eucalypt plantations, P. charybdis is bivoltine with adults being active from August to March. Parasitism by E. nassaui appeared first, during the first generation of P. charybdis, followed by hyperparasitism by B. albifunicle. Neopolycystus insectifurax usually appeared later around the beginning of the second P. charybdis generation. Overall, parasitism was greatest during this late summer period (February–March). While N. insectifurax will contribute to the parasitism burden of P. charybdis, its comparatively poor synchrony with the first P. charybdis generation each season means that it is unlikely to have a substantial effect on control of P. charybdis populations in New Zealand.

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► Two apparently similar egg parasitoids have different biological control potential.
► Key differences are in timing of egg maturation and cold temperature thresholds.
► Accidental arrival of primary parasitoid may compensate for hyperparasitoid.
► First generation of target pest continues to escape biological control.