Risk assessment to interpret the physiological host range of Hydrellia egeriae, a biocontrol agent for Egeria densa

Citation

Smith R, Mangan R & Coetzee JA (2019) Risk assessment to interpret the physiological host range of Hydrellia egeriae, a biocontrol agent for Egeria densa. BioControl, 64 (4), pp. 447-456. https://doi.org/10.1007/s10526-019-09942-4

Abstract
Egeria densa Planchon (Hydrocharitaceae) is a submerged macrophyte native to South America. It forms part of a new suite of invasive aquatic plants that has benefited from open nutrient-rich freshwater systems following the successful biological control of floating aquatic plants in South Africa. The specificity of the leaf-mining fly, Hydrellia egeriae Rodrigues (Diptera: Ephydridae) was tested, using traditional laboratory host-specificity testing (i.e., no-choice and paired choice). Only one non-target species, Lagarosiphon major Deeming (Hydrocharitaceae) supported larval development during pair-choice tests. In order to avoid the rejection of a safe and potentially effective agent, continuation (i.e., multiple generations) tests were conducted to measure the ability of the non-target species to nutritionally support a population indefinitely. None of these species could sustain a viable agent population for more than three generations. Laboratory host-specificity tests are limited as they exempt certain insect-host behaviours. To enhance the interpretation of host-specificity results, a risk assessment was conducted using agent preference (i.e., choice tests) and performance (i.e., choice and continuation tests) results. The feeding and reproductive risk that H. egeriae poses to non-target species is below 2%. Based on these findings, permission for its release in South Africa has been obtained.

Keywords
Submerged aquatic weed; Ephydridae; Continuation test; Multiple generation test

Journal
BioControl: Volume 64, Issue 4