Biological control of the invasive non-native species Lagarosiphon major
The leaf-mining fly Hydrellia lagarosiphon (Diptera: Ephydridae) is being considered as a classical biological control agent against the non-native species Lagarosiphon major (Hydrocharitaceae: EPPO List of Invasive Alien Plants) in New Zealand and Ireland. L. major is an aquatic plant originating from Southern Africa. L. major can colonize freshwater lakes, water-bodies, slow-moving streams, deep reservoirs and dams. It is also reported to occur in wetlands, riparian zones as well as in canals and drainage ditches. As observed for most non-native Hydrocharitaceae species, this submerged perennial aquatic plant forms dense monospecific populations which often colonise the entire water body, restrict water movement, cut off light, produce anoxic conditions and trap sediments. L. major has been reported to outcompete native aquatic plants (e.g. Charophytes, Myriophyllum, Potamogeton) especially in Ireland, and following invasion the number of native plants decreased significantly. Historically, no leaf-mining biological control agent has achieved successful control of any submerged macrophyte. However, in the present study, under laboratory conditions larvae of H. lagarosiphon have been shown to have substantial impacts on L. major and can halt plant growth. Leaf damage varied between different larval abundances ranging from 65 leaves damaged by one larva compared to 168 damaged leaves with 5 larvae per shoot. Overall, both low and high abundances of larvae had an effect on shoot growth where shoot length was 30 to 50 % shorter compared to controls which did not receive larva. The damage incurred by the larvae, at low abundances, show that this species has potential as an effective biological control agent for L. major.
Mangan R, Baars J (2016) Can leaf-mining flies generate damage with significant impact on the submerged weed Lagarosiphon major? BioControl DOI 10.1007/s10526-016-9759-7.