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New Zealand Plant Protection 63 (2010): 272

Detection of young Microctonus hyperodae eggs in the Argentine stem weevil (Listronotus bonariensis)

J. Vereijssen, K.F. Armstrong, L.M. Winder and S.L. Goldson

ABSTRACT

The braconid endoparasitoid Microctonus hyperodae was successfully introduced into New Zealand in 1991 to control the exotic pastoral pest Argentine stem weevil (ASW). The wasp parasitises adult ASW and the weevil normally dies only when the fifth-instar parasitoid larva emerges. However, during biocontrol research over the last 20 years, premature mortality of ASW has been observed under conditions of high parasitoid pressure in the field and laboratory. It was hypothesised that this occurs because of injection of venom without an egg. To conclude absence of a parasitoid egg in a prematurely dead weevil, a sensitive method is needed to detect a newly oviposited parasitoid egg. However, this cannot be confirmed by visual observation or by dissection, because fresh tissue is subsequently needed to detect venom. A molecular method was therefore developed. Firstly, to model oviposition, eggs were dissected from the ovaries of an adult parasitoid and one ovarian parasitoid egg was used to spike ASWs that had been dissected to confirm absence of parasitism. Secondly, multiplex-PCR was successful in detecting a single ovarian egg in ASW. This result greatly benefits research into the observed premature mortality of ASW after being exposed to M. hyperodae.

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