Marching across and beyond West Africa: First record of the stem-galling fly Cecidochares connexa (Diptera: Tephritidae) in Central Africa and the implications for biological control of Chromolaena odorata (Asteraceae)

Abstract

The Neotropical invasive plant Chromolaena odorata R.M. King and H. Robinson (Astera ceae) is a serious weed in West and Central Africa and two biological control agents that have been introduced into West Africa to help reduce its impacts on agriculture and biodiver sity, have established. The stem-galling fly, Cecidochares connexa (Macquart) (Diptera: Tephritidae), has spread widely across West Africa since its release in only Coˆte d’Ivoire, occurring in six countries. This study aimed to investigate whether the gall fly had spread fur ther across West Africa and into Central Africa. Here, we surveyed C. odorata for C. con nexa galls in Cameroon between October 2018 and October 2020, along roadsides, on farms, residential areas, and abandoned plots, encompassing various vegetation types. Additional surveys were conducted across four countries (Ghana, Togo, Benin Republic and Nigeria) in West Africa that we considered the probable pathway for the spread of the gall fly into Central Africa. Cecidochares connexa was present at five of the six locations sur veyed in Cameroon, albeit in varying abundance. In Africa, these findings represent the first ever report of C. connexa outside of West Africa. In West Africa, we recorded significant expansion in the geographic range of C. connexa, as reflected in the absent-present record of C. connexa in two locations in Nigeria and one in Ghana, as well as its occurrence in all locations surveyed in Benin Republic and Togo. Clearly, Ghana, Togo, Benin Republic and Nigeria served as the dispersal pathway of C. connexa from the release sites in Coˆte d’Ivoire into Cameroon, covering over 2,300 km. Following the spread and establishment of C. con nexa into Cameroon, we anticipate that it will continue to spread further into other parts of Central Africa which are climatically suitable. Cecidochares connexa is currently the only biological control agent for C. odorata in Central Africa. Given that it has significantly reduced populations of C. odorata in other countries where it has established, it is expected to have a similar impact in Central Africa.