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Title: INTRASPECIFIC VARIATION IN THE ABILITY OF MICROCTONUS AETHIOPOIDES LOAN (HYM.: BRACONIDAE) TO PARASITIZE SITONA LEPIDUS GYL. (COLEOP.: CURCULIONIDAE)

Author
item PHILLIPS, CRAIG - AG RESEARCH NEW ZEALAND
item CANE, RACHEL - AG RESEARCH NEW ZEALAND
item MEE, J - AG RESEARCH NEW ZEALAND
item CHAPMAN, H - AG RESEARCH NEW ZEALAND
item Hoelmer, Kim
item COUTINOT, DOMINIQUE - USDA-ARS-EBCL

Submitted to: New Zealand Journal of Agricultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Sitona discoideus, a weevil pest of alfalfa, was controlled in New Zealand by the introduction of the parasitoid Microctonus aethiopoides. However, a second Sitona species, S. lepidus, which recently invaded New Zealand and has become a pest of white clover, is not attacked by this parasitoid. It was known that while the New Zealand strain of M. aethiopoides will attack S. lepidus, its eggs are killed by the weevils immune response. In contrast, M. aethiopoides successfully parasitises S. lepidus in Europe. An experiment was conducted to compare the suitability of French and New Zealand S. lepidus as hosts for French M. aethiopoides. No evidence was found of population variation in weevil susceptibility to parasitism. Furthermore, studies of M. aethiopoides DNA detected definite genetic differences between French and New Zealand M. aethiopoides. It was concluded that population variation in the ability of the parasitoid to evade the immune response of S. lepidus is the reason for the low levels of parasitism observed in New Zealand compared to Europe.

Technical Abstract: Sitona discoideus, a pest of alfalfa, was controlled in New Zealand by the introduction of the parasitoid Microctonus aethiopoides. A second Sitona species, S. lepidus, which has recently invaded New Zealand and has become a pest of white clover, Trifolium repens, is not parasitized by M. aethiopoides. Previous experiments have shown that New Zealand M. aethiopoides will attack S. lepidus, but its eggs are killed by the host immune response. In contrast, M. aethiopoides has been observed to successfully parasitise S. lepidus in Europe. It was possible either that New Zealand S. lepidus has a more effective immune response to M. aethiopoides than European S. lepidus, or that New Zealand M. aethiopoides is less able to evade the S. lepidus imune system than European M. aethiopoides. An experiment was conducted to compare the suitability of French and New Zealand S. lepidus as hosts for French M. aethiopoides. This provided no evidence of S. lepidus intraspecific variation in host suitability for parasitism. Furthermore, amplification of ISSR regions of M. aethiopoides DNA demonstrated clear genetic differences between French and New Zealand M. aethiopoides. It was concluded that intraspecific variation in the ability of M. aethiopoides to evade the immune response of S. lepidus is the reason for the low levels of parasitism observed in New Zealand compared to Europe.