HOST-PLANT PHENOTYPE AND THE IMPACT AND DEVELOPMENT OF CARMENTA-MIMOSA, A BIOLOGICAL-CONTROL AGENT OF MIMOSA-PIGRA IN AUSTRALIA

The influence of host plant phenotype on the impact caused to Mimosa p igra L, (Mimosaceae) plants by the feeding activity of larvae of Carme nta mimosa Eichlin and Passoa (Lepidoptera, Sesiidae) and the relation ship between plant phenotype (through plant quality) and larval develo pment were investigated under controlled conditions. Plants grown unde r conditions of reduced light availability were most prone to the detr imental effects of the feeding activities of C. mimosa larvae. The rel ative growth rate (RGR) of most plant phenotypes could be reduced when infested with C. mimosa larvae compared to uninfested plants, Small p lants infested with C, mimosa and grown under reduced light availabili ty exhibited significant reductions in RGR sooner than large plants gr own in full sun. The physical quality of stems was correlated with the severity of impact, i.e., whether stem breakage occurred. Little larv al-induced mortality of plants was observed, suggesting that vascular tissues remained sufficiently intact to allow translocation. Systemic stem death arose through infection by secondary pathogens. Differences in biomass of infested versus uninfested plants of all phenotypes wer e associated with the loss of stems and to a lesser extent leaves, The phenotype of plants had a significant effect on the development of C. mimosa larvae. Larvae in stems of plants with good access to reserves of soil moisture reached more advanced stages of development sooner t han did those in plants which were often water stressed. This response was mediated through the combined influence of availability and nutri tional quality of food. The implications of these findings to the impa ct of this agent in the field and the factors which may significantly influence its population dynamics are discussed.