PRE-RELEASE RESEARCH ON BIOCONTROL AGENTS FOR CHROMOLAENA IN SOUTH AFRICA

Abstract

With the establishment of two leaf-feeding agents on Chromolaena odorata in South Africa, some success in biocontrol of the weed has been achieved, but there is a need for additional agents. Current research is focused largely on stem-attacking insects. The two broad groups that have been targeted are (i) candidate agents which originate from the region of the Americas in which plants resembling the biotype of C. odorata invading southern Africa are present, and (ii) those which originate in regions which have a similar climate to the area in southern Africa invaded by C. odorata and which have a biology allowing them to withstand a prolonged dry season and/or fires. Promising agents in South African quarantine at present include a stem-tip galler, Dichrorampha n.sp. (Lepidoptera: Tortricidae), a stem-tip wilter Carmenta n.sp. (Lepidoptera: Sesiidae) and a stem borer Recchia parvula (Coleoptera: Cerambycidae). Field host-range surveys that have been carried out on three species, viz. the stem galler Conotrachelus reticulatus (Coleoptera: Curculionidae), Carmenta n.sp. and the root feeder Longitarsus sp.(Coleoptera: Chrysomelidae), and which are under way for a fourth, the stem-tip wilter Melanagromyza eupatoriella (Diptera: Agromyzidae), in the neotropics have proved valuable. Longitarsus sp. was rejected as a biocontrol agent due to an unacceptably wide host range, while the stem tip galler Mescinia n.sp (Lepidoptera: Pyralidae) and the stem galler Polymorphomyia basilica (Diptera: Tephritidae) were reduced in priority status due to rearing difficulties and the prioritization of more promising agents. Potential pathogens collected from C. odorata in Jamaica did not perform well in quarantine, but trap plants to be planted in Jamaica may attract compatible fungi.