Establishment, distribution and abundance of Mimosa pigra biological control agents in northern Australia: implications for biological control

摘要

Mimosa pigra L. is one of the most troublesome weeds in northern Australia, and is the target of a large biological control program, with 14 agents released to date. This paper describes surveys conducted between 1997 and 2004, for eight of these biological control agents. Surveys assessed the establishment of key agents. Both distribution and abundance of the most damaging agent, the stem-borer Carmenta mimosa Eichlin and Passoa (Lep.: Sesiidae), increased during the eight year period and the moth is now present in all catchments with major M. pigra infestations. The tip-borer, Neurostrota gunniella Busck (Lep.: Gracillariidae) is present in all M. pigra infestations, attacking 94% of tips. The leaf and flower-feeder, Coelocephalapion pigrae Kissinger (Col., Curculionidae) is widespread and its abundance is stable. Neither Acanthoscelides puniceus Johnson (Col., Bruchidae) nor Chlamisus mimosae Karren (Col., Chrysomelidae) were widespread or abundant when surveys commenced and populations declined during the survey period. The nocturnal beetle Malacorhinus irregularis Jacoby (Col., Chrysomelidae) was not found during these surveys, but later searches using different methods found it at three sites. Six other agents appeared not to have established, or are present at densities too low to be detected. How the results of these surveys affect management of M. pigra, and projections for future impacts against this weed are discussed. Using survey results and published literature we concluded that (1) seed and flower feeders must be capable of surviving periods of low food availability; (2) some climate matching may be beneficial before fungal biocontrol agents are released and (3) even in well studied systems such as M. pigra, the failure of an agent to establish cannot always be explained.