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The whitefly Bemisia tabaci (USDA image PD USDA ARS via Wikimedia Commons)

A species of whitefly that transmits cassava mosaic virus has been detected in South Africa for the first time. The whitefly, Bemisia tabaci is a cryptic species complex containing some important agricultural pests and virus vectors. The term ‘cryptic species complex’ means that Bemisia tabaci is considered to be a complex of at least 24 different species that look almost identical but are in fact genetically different.  Researchers from a range of organisations including the University of Johannesburg, the University of Witwatersrand and ARC-Vegetable and Ornamental Plant Institute conducted surveys to investigate the diversity and distribution of Bemisia tabaci species in 8 provinces in South Africa. The study aimed to update the information regarding the different Bemisia tabaci types present in the country.

The researchers discovered two non-native types of Bemisia tabaci, one that originates in the Mediterranean (known as the “Q” type) and one that originate in Middle East-Asia (known as the “B” type). Both the “Q” and “B” type Bemisia tabaci are known worldwide as invasive species and have been observed attacking a wide range of crop plants as well as showing the ability to develop insecticide resistance, making them a major agricultural pest.

In Africa Bemisia tabaci  has been shown to colonise vegetable crops including cassava (Manihot esculenta). The cassava associated types transmit at least seven types of begomoviruses to cassava, which is a major staple food in sub-Saharan Africa. In many African countries farmers are actively being encouraging to shift to the cultivation of hardy crops such as cassava to mitigate against the effects of climate change, therefore it is very important to consider what impact Bemisia tabaci may have on increased cassava cultivation.

The results of the study demonstrated that the “B” type is currently widely established in five of the eight provinces explored in the study. The “Q” type which originates from the Mediterranean was also identified. This is the first record of the “Q” type in South Africa, posing a new agricultural threat in the country. Wider geographical sampling will provide further information on the spread and distribution of the “Q” type.

The researchers presented their findings at the 12^th International Symposium on Plant Virus Epidemiology, Tanzania, organised and hosted by the International Plant Virus Epidemiology Committee and the International Institute of Tropical Agriculture last month. The scientists suggest that the “Q” and “B” type Bemisia tabaci may have entered South Africa via trade in ornamental plant species from the Middle East and Mediterranean. There is now call for further study to establish the pest’s routes of entry into the country and to ascertain how widespread it is as these factors are crucial in the sustainable management of Bemisia tabaci as a pest and vector of plant viruses.

References:

‘Invasive Whitefly Threatens Africa’s Cassava Crops’, by George Achia, SciDev Net, February 2013 
Esterhuizen, L., Mabasa, K., van Heerden, S., Czosnek, H., Brown, J., van Heerden, H., & Rey, M. (2013). Genetic identification of members of the cryptic species complex from South Africa reveals native and introduced haplotypes
Journal of Applied Entomology, 137 (1-2), 122-135 DOI: 10.1111/j.1439-0418.2012.01720.x