The first release of the biological control agent Listronotus appendiculatus on the invasive Sagittaria platyphylla or Delta arrowhead was done last year October by Dr Mabizela, Debbie Muir (DFFE) and Dr Grant Martin. This release was done in Makhanda in the Botanical Gardens. Since that first release, our team led by Dr Lenin Chari released 460 adults at the site. Releases were also done in KwaZulu Natal led by Dr Daniella Egli.
The sites have been monitored monthly since October 2023. At the Makhanda Botanical Gardens, the team had yet to find an adult at the site since March 2024. Since then they had not seen any insect activity at this site, and they anticipated that the weevil was overwintering (in diapause) nearby, awaiting spring. As of this month, they confirmed that the weevil has survived the cold weather and overwintered, the insects are actively feeding again!
In KZN, they released a total of 729 adults at two sites: Kranzkloof Nature Reserve and PMB Botanical Gardens between October and December 2023. They also stopped seeing the weevil closer to winter, but much later than the Makhanda site. They started seeing adults in the field in September 2024.
Since March this year, our team has been rearing insects in the lab/quarantine and harvesting flowers and fruits from the release site to feed the culture, with varied success. It is from this lab cultures and the now thriving field sites that the CBC hope to spread the weevil to other infested sites around the country this summer.
