Strategies for achieving widespread establishment of broom seed beetle, Bruchidius villosus (Coleoptera: Chrysomelidae), a biological control agent for broom, Cytisus scoparius

To achieve maximum efficacy of weed biological control introductions, it is important that the full benefits are realized as early as possible. The aim of experiments described here was to show how to gain widespread establishment of broom seed beetle (Bruchidius villosus (F.)) as quickly as possible. Broom seed beetle was introduced into New Zealand as a biological control agent for broom (Cytisus scoparius (L.) Link) in 1988, and since 1991 beetles have been released at 98 sites throughout the country. By summer 1998-99 the beetles had established in at least 23 of these sites. Key factors for establishing beetle populations in the field are the successful overwintering of adult beetles, and the syn-chrony of beetle development with flowering and pod development of broom. Methods are described for mass rearing beetles that require low labour input and in which 70 % of overwintering beetles survive. Reproductively active beetles have usually been released in spring or early summer when appropriate stages of broom pods are available for ovipo-sition, but new generation beetles have also been recovered from populations released in late summer, when beetles cannot reproduce until the following season. Beetles collected from the field are more abundant and easy to find for transfer to new sites in late summer or autumn, than in spring. Of several collection methods tested, the most efficient was to collect infested seed in autumn. This straightforward redistribution method can be used by farmers, foresters, and conservation managers