(UNESCO / Japan Young Researchers' fellowships programme)

Molecular characterization of Bemisia tabaci (Homoptera: aleyrodidae) for a durable management

Summary of research carried out: 
Molecular characterization of Bemisia tabaci (Homoptera: aleyrodidae) for a durable management

The Bemisia tabaci (Gennadius) whitefly is a major pest in cotton and vegetable crops in Burkina Faso, in Africa and throughout the world. The complexity of controlling B. tabaci is linked to the biodiversity of this polyphagous pest and its capacity to pullulate rapidly and transmit viruses. If an effective Bemisia tabaci control method is to be put in place, knowledge of its bioecology must be improved. Little information is available to date on the biotypes found on crops in Burkina Faso and in West Africa generally. It is still not known whether the cotton whitefly is the same as the tomato whitefly.

This study aimed, firstly, to conduct mitochondrial gene amplification to characterize 13 B. tabaci populations and PCR (absence/presence) tests to find the various symbiotes associated with the various populations. The various PCR tests and the search for the various symbiotes required some 600 DNA extractions.

To conduct our study, as a first step, the mitochondrial gene coding for Cytochrome Oxydase I was sequenced in order to characterize B. tabaci populations by host plant and by geographical site. The findings point to biotype variability depending on the geographical region. In Burkina Faso, the presence of the Q1 biotype was recorded on cotton in Farako-Ba and Lena and on aubergine in Kuinima. Two sympatric biotypes, Q1 and ASL (Sub-Saharan Africa Silver Leafing), were found on tomato and courgette plants. Only the Q1 biotype was found in the centre and in the east, on tomato and cotton respectively.

The new Q3 biotype was found on tobacco in the west and on Lantana camara. In Benin and Togo, the presence of ASL was recorded on cotton and on tomato plants. Secondly, the study dealt with interaction among biotypes and the frequency of association with B. tabaci secondary symbiotes (SS) by geographical site and by host plant. Hamiltonella and Wolbachia were spotted only with populations of the Q1 genetic group, while Arsenophunus (750 pb) were found with the Q biotype ASL genetic group and with the Sub-Saharan non Africa Silver Leafing (AnSL) biotype. The new genetic group harboured Rickettsia and Aersenophonus (750 pb). Cardinium and Fritschea were not found in the tested populations. The results for this part of the study shows strong correlation between symbiotic status and biotype, but populations were less infected than European populations. This study has increased knowledge of B. tabaci bioecology in West Africa, which, should doubtless contribute to the introduction of a strategy to control this major agricultural pest.

Keywords: Bemisia tabaci, biotypes, characterization, CO1 gene sequencing, secondary symbiotes, sustainable management.


22 April 2009

Translated from French by UNESCO