Insect herbivores associated with the invasive herb Senecio madagascariensis (Asteraceae) in its native range in KwaZulu-Natal, South Africa and their potential as biological control agents in invaded countries

Abstract

ABSTRACTNative to southern Africa, Senecio madagascariensis Poir. (fireweed, Asteraceae) has invaded agricultural lands and disturbed areas in several countries worldwide and is currently a target for biological control in Australia and the USA (Hawaii). Quantitative surveys of the plant in KwaZulu-Natal, South Africa, considered the origin of the Australian and Hawaiian populations, revealed several insect herbivore taxa that are frequently associated with the plant’s foliar, floral and structural tissues. These largely comprised ectophagous sap suckers (34%), chewers (29%) and root feeders (1%), but also endophagous stem borers (21%), capitulum feeders (13%) and leaf miners (2%). Many of these taxa were encountered only occasionally or rarely during sampling, with some displaying low to very low abundance. Based on these surveys and earlier precedents in biocontrol programmes against other invasive Asteraceae, 15 taxa were shortlisted as candidate agents. Of these, four were prioritised for host-range assessments which are currently in progress. These include the capitulum-feeding Homoeosoma stenotea Hampson (Lepidoptera: Pyralidae), the stem-boring Gasteroclisus tricostalis (Thunberg) (Coleoptera: Curculionidae) and Metamesia elegans (Walsingham) (Lepidoptera: Tortricidae) and the root-feeding Longitarsus basutoensis Bechyné (Coleoptera: Chrysomelidae: Alticinae). Although the diversity of native Senecio species in Australia may present challenges during routine host-specificity testing, prospects for the biocontrol of S. madagascariensis in Hawaii appear very promising, since the native flora does not include any species in the tribe Senecioneae.