Megabruchidius tonkineus (Coleoptera: Chrysomelidae: Bruchinae) a potential new association biological control option for the invasive Gleditsia triacanthos L. (Fabaceae) in South Africa

Honey locust, Gleditsia triacanthos L. (Fabaceae) is a fast-growing deciduous tree native to North America. The tree has been introduced worldwide and has become invasive in South Africa. In 2017, it was listed as one of the nine fastest spreading weeds in South Africa. Once established, it competes with and displaces indigenous species and dense stands can significantly reduce stream flow. The Asian seed feeding bruchid, Megabruchidius tonkineus (Coleoptera: Chrysomelidae: Bruchinae) was unintentionally introduced into South Africa and has taken honey locust on a host plant. The beetle is damaging honey locust seeds and is therefore considered a biological control agent, despite no host specificity or impact studies ever being conducted. The aim of this study is to conduct laboratory host specificity trials to determine the host range of M. tonkineus and to determine infield impact. These results indicate that M. tonkineus does not complete its life cycle in the seeds of 24 native/economically important plant species and also has low impact 9.17% on the target host seeds. Although M. tonkineus is host specific, its impact in the field is minimal. An additional seed feeding biological control agent should be considered to control honey locust.