Predicted impact, establishment and distribution of Heikertingerella sp. (Coleoptera, Chrysomelidae), recently released for the biological control of Tecoma stans in South Africa

Abstract

Abstract Biological control practitioners are required to demonstrate that candidate agents are not only safe for release, but will establish widely in their new range with a significant impact on the target weed. We conducted this study in quarantine to provide insight into the impact and distribution of the root‐feeding flea beetle Heikertingerella sp. (Chrysomelidae), released in early 2023 against the invasive tree Tecoma stans (L.) (Bignoniaceae) in South Africa. We studied the effects of low and high beetle densities on plant growth and biomass, and F1 progeny production by the beetle. There were significant reductions in plant growth and biomass accumulation in the beetle‐exposed plants, relative to the controls. P1 adults damaged significantly more leaflets, with significantly higher F1 progeny production, at high beetle densities. The MaxEnt model predictions suggested that most of South Africa is climatically highly suitable for Heikertingerella sp., particularly along the southern and eastern coasts where the weed is most prevalent. Only the inland regions of the Northern Cape Province, depicting the driest and hottest part of the country where the weed does not occur, were predicted to be unsuitable for Heikertingerella sp. The beetle's thermal physiology, as determined by its critical thermal minimum and maximum temperatures and lower and upper lethal temperatures (LT50), suggests tolerance to temperature extremes in at least four of the eight provinces that fall within the range of T. stans in South Africa. Our results further justify the release of Heikertingerella sp. in areas predicted as suitable in South Africa.