The suitability of Neochetina bruchi and Neochetina eichhorniae as biocontrol agents for Eichhornia crassipes in Ethiopia
Eichhornia crassipes (Pontederiaceae: EPPO A2 List) was reported around 60 years ago in Koka Lake and Awash River in Ethiopia (ET), and has since spread to many waterbodies within the country. The two weevils Neochetina bruchi and Neochetina eichhorniae have been utilised as biocontrol agents against E. crassipes throughout its invasive range. The weevils are host specific and cause considerable damage to the invasive population with cases of spectacular success. For example, in Uganda the two weevils reduced the biomass of E. crassipes on Lake Victoria by nearly 80 %. The efficacy of the two weevils in controlling E. crassipes has shown differences from country to country. Often the difference in efficacy is due to varying climatic conditions. In Benin, N. eichhorniae has been shown to be more effective whereas in Uganda N. bruchi became the dominant species. To evaluate the suitability of both weevil species in the Rift Valley, Ethiopia, populations were imported from Uganda and mass reared for the subsequent experiments. The egg hatching period of N. bruchi (4–10 days) was shorter compared to that of N. eichhorniae (8-12 days) as too was larval development (N. bruchi 32-38 days: N. eichhorniae 52-60 days). Both species significantly reduced the vigour and development of E. crassipes where N. bruchi showed a 72 % reduction in plant fresh weight compared to a 66 % reduction by N. eichhorniae. The study concludes that N. bruchi could be considered a promising candidate for the biological control of E. crassipes in Ethiopia.
Sources
Fireman Y, Struik PC, Lantinga EA & Taye T (2015) Adaptability of two weevils (Neochetina bruchi and Neochetina eichhorniae) with potential to control water hyacinth in the Rift Valley of Ethiopia. Crop Protection. 76, 75-82.