Pre-release evaluation of the flea beetle Heikertingerella sp. (Coleoptera: Galerucinae: Alticini), a potential biological control agent for the invasive weed Tecoma stans L. (Bignoniaceae) in South Africa.

Abstract

The root-feeding beetle Heikertingerella sp. (Coleoptera: Chrysomelidae) was introduced into quarantine in South Africa for evaluation as a biological control agent of the invasive tree Tecoma stans L. (Bignoniaceae). Larval feeding damages the roots, potentially reducing the weed’s growth and reproduction. Pre-release studies in quarantine included several aspects. Studies on the beetle’s biology and host specificity were conducted to confirm its safety for release in South Africa. The impact of varying beetle densities on plant fitness was assessed to determine its likely impact in the field. The effect of local climate on the beetle’s potential to establish throughout the weed’s range in South Africa was predicted using climate-modelling software. The interaction between Heikertingerella sp. and a leaf-feeding agent already established in South Africa was investigated. Finally, the effect of host-plant age and nutrient enhancement on mass-rearing activities was studied, to optimize beetle numbers for releases. The beetle proved host specific resulting in the granting of permission for its release in South Africa. There were significant reductions in plant growth and biomass accumulation in the beetle-exposed plants, relative to the controls, indicating that Heikertingerella sp. is sufficiently damaging. Climate matching revealed that Heikertingerella sp. is likely to perform best at coastal sites in South Africa, with the colder, more inland, areas within the weed’s range proving less suitable. The beetle proved compatible with a defoliating agent established in South Africa, with evidence of positive interactions that are likely to enhance their combined impact on the weed. Trials involving plants of varying age and nutritional enhancement revealed that 3-year-old plants, which were supplemented by either medium or high levels of fertilizer, were best suited for F1 progeny production and therefore for the mass-rearing of Heikertingerella sp. for releases. The results of this study should also benefit other countries in Africa and elsewhere in the world, where the plant is invasive.