Establishment and dispersal of two biocontrol agents one year after their release: Management of the invasive weed, Parthenium hysterophorus, at two locations in Ethiopia

Parthenium hysterophorus is an invasive weed in many regions of the world. In Ethiopia, the weed poses significant threats to crop production, biodiversity, human and animal health. Leaves and pollen produce allelochemicals that inhibit the growth of other plants. To combat this weed, a biological control program led by Virginia State University and funded by USAID has released two bioagents, the leaf-feeding beetle (Zygogramma bicolorata) and stem-boring weevil (Listronotus setosipennis) in Ethiopia in 2017. The objective of this study was to determine the establishment and spread of two agents one year after they were released at two regions of Ethiopia. The release locations were assessed twice (July, September) in 2018. At Arba Minch, no L. setosipennis was found, only Z. bicolorata was established and the number of eggs per plant varied from ~ 2 to 7 at the release site and from 0.5 to 0.7 at the dispersal site. At Mojo, only L. setosipennis was established with 4 – 11 eggs/plant at the release site and 9 – 15 eggs/plant at the dispersal site. After one year, L. setosipennis and Z. bicolorata were found 51.7 ± 3.9 m and 94.1 ± 13.7 m away from the release sites, respectively. The results showed that the biocontrol agents have started to establish and have dispersed at the two locations in Ethiopia. Agents responded differently to conditions at Arba Minch and Mojo, Ethiopia.  Predatory, plant quality, and soil type were different between sites that may affect biocontrol agents' establishment.