Establishment and phenology of the parasitoid Microctonus hyperodae (Hymenoptera : Braconidae) in New Zealand

The South American weevil Listronotus bonariensis (Kuschel) (Coleoptera: Cu rculionidae) is one of New Zealand's worst pasture pests causing between NZ $78 -251 million damage per Fear. Accordingly, the South American parasitoi d Microctonus hyperodae Loan (Hymenoptera: Braconidae. Euphorinae) was rele ased at Lincoln, Canterbury, in 1991 as a biological control agent fort. bo nariensis. M. hyperodae was first recovered from the held in January 1992 a lthough noticeable population growth did not occur until a year Later after which rates of parasitism increased very rapidly, although these rates dec lined over time. Under field conditions, M hyperodae completed 3 generation s per year after postdiapause development in September. Peak numbers of egg s occurred in late December, early March, and mid-May, respectively; the 3r d generation was much smaller than the first 2. A notable decline in percen t parasitism between the 1st and 2nd generations (mid-December and mid-Febr uary each year) was related to a large influx of Ist summer Generation adul t weevils during an intergenerational absence of adult parasitoids. Second parasitoid generation infection rates of the weevils were very high (>90%) by early March but soon declined as protracted autumnal (April-May) emergen ce of weevils, combined with immigration from surrounding uncolonized areas . increased the proportion of unparasitized weevils. The small 3rd generati on of M. hyperodae may be important for parasitizing these late emerging we evils. Host and parasitoid phenology conformed approximately to an existing phenological model. Analysis of field data indicated that the day-degree r equirements of M., hyperodae egg and Ist, 2nd, 3rd,, and 4th larval stages above a threshold of 10.2 degrees C were 14 154 28, 19, and 11, respectivel y.