Linear patterns of dispersal and build up of the introduced parasitoidMicroctonus hyperodae(Hymenoptera: Braconidae) in Canterbury, New Zealand

Abstract

The dispersal of Microctonus hyperodae Loan, an introduced parasitoid of the South American grassland pest Listronotus bonariensis Kuschel, was measured in Canterbury, New Zealand. Considering all directions, the mean annual dispersive increment was 1.9 ± 0.9 km year -1 as measured in the winters of 1993, 1994 and 1995. The parasitoid's ground distribution suggested that its movement was biased towards the south-west indicating probable wind-borne dispersal. The overall relatively low rate of dispersal was thought to be related to the inhibitory effects of M. hyperodae parasitism on L. bonariensis flight. A generalized linear model fitted to percentage of L. bonariensis parasitized took a simple form, with a quadratic increase in weevil infection, that with time, gradually decreased. The build-up of parasitism at the release site was significantly greater than the rates at the other sites measured in this study (P < 0.001) with a ratio of release site: dispersal site rates of 1.33: 1. The simplicity of the fitted generalized linear model indicated remarkable uniformity in both parasitism build-up and dispersal from one year to the next; this finding indicated that all dispersal was 'natural' and unassisted by human activity. Despite such modest dispersal rates, by the winter of 1996, five years after its release, the parasitoid had spread geometrically over an area of c. 140 km 2 .

Field release, establishment and initial dispersal of Irish Microctonus aethiopoides in Sitona lepidus populations in northern New Zealand pastures

“…The dispersal rate of Irish M. aethiopoides appears to be more similar to Moroccan M. aethiopoides than M. hyperodae. Initial rates of spread of around 10 km year -1 were reported for M. aethiopoides in Australia (Aeschlimann 1983) while mean rate of M. hyperodae dispersal in the South Island (Goldson et al 1999) and the North Island (McNeill et al 2002b) was found to be under 2 km year -1 . Sitona spp.…”

Unexpected Listronotus bonariensis (Coleoptera: Curculionidae) mortality in the presence of parasitoids

“…This experiment was established in September 1992, using weevils swept from a ryegrass/white clover paddock known to be parasitoid-free (Goldson et al, 1998a(Goldson et al, , 1999a and parasitoids reared from culture. The parasitoids used were all р 3 days old and had been provided with honeywater to increase their longevity as demonstrated by Hodgson et al (1993).…”

“…Population dynamics data were collected between 1992 and 1997 at the original 1991 M. hyperodae release site on the AgResearch farm at Lincoln (43°39ЈS, 172°28ЈE), 19 km south of Christchurch (Goldson et al, 1999a). The pasture consisted of a ryegrass (cv.…”

“…In 1991, the South American parasitoid Microctonus hyperodae Loan (Hymenoptera: Braconidae) was released in New Zealand as a control agent for the grassland pest Argentine stem weevil, Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae) (Goldson et al, 1993a(Goldson et al, , 1998a(Goldson et al, , 1999a. By 1995, this endoparasitoid of adult weevils had reached parasitism levels of > 90% (Goldson et al, 1998a).…”

Biology of the Introduced Biocontrol AgentMicroctonus hyperodae(Hymenoptera: Braconidae) and Its HostListronotus bonariensis(Coleoptera: Curculionidae) in Northern New Zealand

“…In addition, avoidance behavioral adaptations by adult L. bonariensis to presence of the parasitoid (Barratt et al 1996, Barker and Addison 1997, Gerard 2000 can lead to short eruptive phases of oviposition effort during periods when M. hyperodae are less abundant, and this may also signiÞcantly lessen the impact of the parasitoid (Barker and Addison 2006). Parasitism has been shown to severely suppress L. bonariensis ßight (Goldson et al 1999), which could lead to differential dispersal of a largely nonparasitized cohort of weevils.…”