<i>Microctonus hyperodae</i> in Otago and Southland

Abstract

In 1990 Microctonus hyperodae was released in Otago and Southland as a biocontrol agent against Argentine stem weevil (ASW) (Listronotus bonariensis) At that time ASW was New Zealands major pasture pest but attained only sporadic importance in the southern South Island Since then possibly due to higher nutritional qualities of modern ryegrass cultivars and/or changes in annual thermal accumulation ASW has increased in significance Farmers once relied on endophytefree ryegrasses but now sow infected grasses While endophyte helps protect against ASW damage augmentation by M hyperodae parasitism is desirable Establishment and localised spread of M hyperodae was measured around the release sites but subsequent distribution over the wider southern South Island was not Between September and November 2011 52 pastures were sampled and ASW was found in all Microctonus hyperodae was reared from 18 of these pastures at levels of 133 parasitism but in 15 pastures parasitism was less than 7 The information gathered covers a limited period but suggests that M hyperodae is not as successful in the far south as in other parts of New Zealand The reasons for this and possible implications warrant further investigation both to understand the situation and to investigate if supplementary releases of M hyperodae can be usefully undertaken