Suitability of the leaf-mining fly, Hydrellia sp., for the biocontrol of Hydrilla verticillata in South Africa
Hydrilla verticillata (Hydrocharitaceae – EPPO List of IAP) is a submerged macrophyte plant species native to Asia and recorded as invasive in many regions of the world including Africa, Central and South America and the USA. In South Africa, H. verticillata was first discovered in 2006 where a 600 ha infestation was found at the tourist site, Pongolapoort Dam, KwaZulu-Natal. As a result of this discovery, a biological control programme was initiated against the species. A leaf-mining fly, Hydrellia sp. (Diptera: Ephydridae) was collected during surveys in Singapore and imported into South Africa under quarantine conditions to undergo host range testing. The suitability of the fly was assessed through no-choice, paired choice larval development trials and host suitability tests, using 29 plant species from 9 closely related plant families. In no-choice tests, egg to adult development was significantly higher on H. verticillata than any of the other plant species tested. Three non-target plant species (Lagarosiphon major, L. muscoides and L. ilicifolius) that supported the highest percentage of larval survival from the no-choice tests were further subjected to paired-choice tests. In these tests, all larvae which had reached the adult stage developed on the target species, with the exception of two individuals that emerged on L. major and L. ilicifolius. Host suitability and productivity tests used the two native plant species that had the highest larval development in no-choice tests, namely L. muscoides and L. ilicifolius. These tests showed that the Hydrellia fly performed better on H. verticillata compared to the two natives. It is concluded that the Hydrellia fly has a limited capacity to establish on native plant species in South Africa and therefore should be considered as a biocontrol agent for release against the invasive plant H. verticillata.
Bownes A (2014) Suitability of a leaf-mining fly, Hydrellia sp., for biological control of the invasive aquatic weed, Hydrilla verticillata in South Africa. BioControl 59, 771-780.