The African citrus psyllid : An efficient vector of Liberibacter asiaticus.

Introduction: Huanglonbing (HLB) is the most serious disease of citrus in the world, associated with three non-cultivable phloem-restricted bacteria Liberibacter asiaticus (Las), L. africanus (Laf) and L. americanus (Lam). Las is transmitted by the Asian citrus psyllid , and has spread to several countries. The African psyllid , the vector of Laf occurs in Africa and neighbouring islands. Only two major citrus-growing regions - Australia/New Zealand and the Mediterranean Basin - are still HLB-free in the world. However, has recently been introduced into continental Europe (Portugal and Spain) and has become a potential threat to citrus production. The transmission of Las by had been postulated but never tested. To evaluate the risk of transmitting Las, comparative transmissions of Las by and were assessed.

Methods: Transmission tests were performed on excised leaves and seedlings of with different inoculation access periods (in series) for both insect species. Quantifications of bacterial titers were made in excised leaves, seedlings three and six months after inoculation and on individual insects.

Results: Our results showed that was able to efficiently acquire Las. Furthermore, carried significantly higher bacterial titers than , and was able to efficiently transmit the bacteria to seedlings at a similar rate that highlighting the high risk of spread of the most aggressive variant of HLB (Las) by in Europe.

Discussion: Thus, extreme precautions to prevent any entry of Las into Europe should be adopted.