First report of Diaphorina citri in Kenya and in Zanzibar (TZ)
Following the recent report of Diaphorina citri (vector of ‘Candidatus Liberibacter asiaticus’ - Hemiptera: Liviidae, EPPO A1 List) in Tanzania (EPPO RS 2016/111), a survey was carried out in East Africa, focusing on Kenya, mainland Tanzania and Zanzibar. From September 2015 to August 2016, 168 sites located at various altitudes were surveyed, including large commercial citrus orchards as well as small scale citrus plantations. In addition to D. citri, the occurrence of Trioza erytreae (vector of ‘Candidatus Liberibacter africanus’ - Hemiptera: Triozidae, EPPO A2 List) was also studied. Molecular tools (DNA barcoding) were used to confirm the identity of the collected psyllids. Results showed that nymphs and adults of either D. citri or T. erytreae were collected from citrus trees at many of the surveyed sites in Tanzania (at altitudes ranging from 19 to 668 m above sea level), in Kenya (20-1666 m asl), and in Zanzibar (42-48 m asl). It was observed that D. citri and T. erytreae were sympatric at medium and high altitudes (1375-1666 m asl), but that T. erytreae or its galls were no longer observed at low altitudes (below 523 asl). T. erytreae was not found in Zanzibar. In Kenya, a total of 20 adults and 60 nymphs of D. citri was collected from the following 6 sites: Msambweni, Lunga Lunga, Machanzuni (Kwale county); Karura forest (Nairobi county); Soin, Koitaburot (Kericho county). In Tanzania, D. citri was most prevalent in the Morogoro region, but was also found in other sites around Dar-Es-Salaam (Bagamoyo, Dar-Es-Salaam and Mkuranga districts). In Zanzibar, 6 adults and 21 nymphs of D. citri were found in 3 sites (Mahonda, Kitope and Selem Station, all on Unuguja island). This is the first time that D. citri is reported from Kenya and Zanzibar.
It is hypothetized that D. citri may have been blown by storms from Indian Ocean islands (e.g. Mauritius, La Réunion) into East Africa, resulting in multiple incursion points. Another possible source of introduction could be the movement of infested plants of Murraya koenigii from Asia. It is concluded that the arrival of D. citri in Eastern Africa represents a major threat to citrus production, in particular if ‘Candidatus Liberibacter asiaticus’ became present in the region. It is recalled that this pathogen has been detected once in Ethiopia. It is considered that it is urgently needed to implement phytosanitary measures to prevent any further spread of D. citri, to establish insect-proof nurseries to produce huanglongbing-free citrus plants, to develop management strategy for the disease and its vectors, as well as to better understand the epidemiology of the Liberibacter spp. and their vectors in Africa.
Sources
Rwomushana I, Khamis FM, Grout TG, Mohamed SA, Sétamou M, Borgemeister C, Heya HM, Tanga CM, Nderitu PW, Seguni ZS, Materu CL, Ekesi S (2017) Detection of Diaphorina citri Kuwayama (Hemiptera: Liviidae) in Kenya and potential implication for the spread of Huanglongbing disease in East Africa. Biological Invasions DOI 10.1007/s10530-017-1502-5