A survey of “Candidatus liberibacter asiaticus” and Wolbachia spp. titer in Diaphorina citri, vector of Huanglongbing, collected from four Florida citrus groves

Authors: MANN, MARINA - Cornell University; Thompson, Luke; JOHNSON, LYNN - Cornell University; Heck, Michelle

Submitted to: Phytobiomes Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2024
Publication Date: 10/28/2024
Citation: Mann, M., Thompson, L.A., Johnson, L., Heck, M.L. 2024. A survey of “Candidatus liberibacter asiaticus” and Wolbachia spp. titer in Diaphorina citri, vector of Huanglongbing, collected from four Florida citrus groves. Phytobiomes Journal. 8(4):590-597. https://doi.org/10.1094/PBIOMES-10-23-0105-R.
DOI: https://doi.org/10.1094/PBIOMES-10-23-0105-R

Interpretive Summary: In the United States, Huanglongbing (HLB), also known as citrus greening disease, is caused by a bacterium referred to as CLas. It is spread by a tiny insect called the Asian citrus psyllid during insect feeding. The Asian citrus psyllid has relationships with other beneficial bacteria, including Wolbachia. Although a lot is known about Wolbachia biology in other insects, less is known about what Wolbachia is providing to the psyllid. Whether Wolbachia is involved in the spread of CLas is not known, but some researchers are developing Wolbachia as a biotechnology tool to mitigate the spread of citrus greening. Here a survey was conducted on surveyed over 1000 individual psyllids collected from four different groves in Florida to determine CLas amounts and Wolbachia infection levels. Interestingly, even though HLB is endemic in Florida, CLas negative insects were collected from every grove sampling site, providing support for the existence of natural variation in psyllid populations for their ability to become infected with CLas. Additionally, there was a strong field effect on CLas titer which far outweighed any impact from Wolbachia or insect sex. The study highlights the importance of grove-wide sampling of psyllids for CLas in areas where the disease is emerging and future work on the role of environmental and management factors in managing HLB. A better understanding of CLas-psyllid interactions can inform policy and regulatory decisions and contribute to the development of sustainable management strategies for HLB.

Technical Abstract: Huanglongbing (HLB, or Citrus Greening disease) affects all citrus varieties world-wide. The causal agent is “Candidatus Liberibacter asiaticus” (CLas), a phloem-limited alpha-proteobacterium. The hemipteran insect vector, Diaphorina citri (Asian citrus psyllid) acquires and transmits CLas in an intracellular, circulative, propagative manner. HLB management efforts focused on controlling the vector populations to stop new tree infections from occurring are necessary, as complete vector elimination is impossible. In addition to CLas, D. citri hosts multiple symbiotic bacteria, including Wolbachia. In D. citri, Wolbachia has been sequenced and studied but its specific role is still unknown. Using well-established quantitative PCR methods of measuring bacterial titer, and sound statistical tests, we first test the hypothesis that CLas titer is correlated with field/grove-specific conditions and second, that CLas titer is also correlated with Wolbachia titer. The four field sites represent different management regimens and sample sizes, and results show that field site has the largest effect on CLas titer. Sex and Wolbachia titer had no effect on CLas titer. Our results suggest that more directed follow-up research is necessary and important to clarify the impact of specific aspects of field management regimens on CLas titer in wild-caught D. citri.