Seasonal abundance of insect biocontrol agents of Mimosa pigra in the Northern Territory

Nine insect species endemic to tropical America have been released into the Northern Territory as biological control agents for Mimosa pigra L. (Mimos aceae). To date, few studies have been published that quantify the abundanc e of these agents post-release. Hence, populations of adult agents in three stands of ill. pigra were monitored using Malaise traps. Trap catches freq uently contained the lepidopteran agents Carmenta mimosa Eichlin and Passoa and Neurostrota gunniella (Busck). Neurostrota gunniella, which was first released in 1989, was the most abundant of all the agents caught, irrespect ive of the: stand of M. pigra where trapping was conducted. The three coleo pteran agents (namely Acanthoscelides Schonherr spp., Chlamisus mimosae Kar ren and Coclocephalapion Wagner spp.) were caught less frequently. Two rece ntly released beetles, Chalcodermus serripes Fahraeus and Sibinia fastigiat a Clark, were not caught. Trap catches of Acanthoscelides spp. were greates t during the late dry season with smaller catches during the mid- to late w et season. Chlamisus mimosae was most abundant during the dry to dry-wet tr ansition. Neurostrota gunniella was generally most abundant during the dry season. The abundances of Cn. mimosa and Coelocephalapion spp. exhibited li ttle seasonality. Malaise trapping is recommended as part of a long-term mo nitoring program to quantify agent populations and their impact upon M. pig ra.