Introduction

Mimosa pigra L., a prickly, perennial, woody shrub native to tropical America from Mexico to Argentina, is listed in the Global Invasive Species Database as one of the One Hundred of the World's Worst Invasive Alien Species. We refer to M. pigra in the strict sense, which excludes M. asperata, a close relative which some authors have lumped with M. pigra as one species (Heard, 2004). Outside its native range, especially Southeast Asia and Australia, untreated infestations may double in area each year (Lonsdale, 1993; Triet et al., 2004) and form dense thickets that affect both conservation areas and agricultural land (Samouth, 2004; Son et al., 2004). These reduce the diversity of plants and animals and impact negatively on agriculture by competing with pasture species, hindering mustering of livestock, and restricting access to water by humans and livestock (Braithwaite et al., 1989; Lonsdale et al., 1989).

A biological control project in Australia against M. pigra has been active since 1979 with exploration work on natural enemies from bases in Brazil then Mexico. This has led to a steady stream of agents being released in Australia between 1983 and 2007 and in Asian countries between 1983 and 1998. A total of 13 insect species and two pathogenic fungi have been released against M. pigra in Australia (Table 14.1). Both pathogens failed to establish (Hennecke, 2004; Hennecke, 2006). Few biological control projects have continued for so long and released so many agents.