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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Citrus and Other Subtropical Products Research » Research » Publications at this Location » Publication #360897
Title: CLas titer in ACP, not infected citrus, is the driving force for the spread of HLB

Author
item McCollum, Thomas
item Hall, David
item LUO, W - North Carolina State University

Submitted to: International Research Conference on Huanglongbing
Publication Type: Proceedings
Publication Acceptance Date: 2/7/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Transmission of Candidatus liberibacter asiaticus (CLas), presumptive causal agent of Huanglongbing (HLB), from one generation of asian citrus psyllid (ACP) adults to the next requires the insects transmit the pathogen through citrus where it can subsequently be acquired by progeny ACP. Our results indicate that it is not the CLas infection status of citrus trees that drives generational transmission of CLas, but rather, CLas titer in progenitor insects is the driver. These results support the importance of proactive ACP control to prevent development of HLB epidemics.

Technical Abstract: Transmission of Candidatus liberibacter asiaticus (CLas) from Asian citrus psyllid (ACP) progenitor to progeny (generational transmission) requires that CLas pass through citrus. Transovarial transmission of CLas is apparently insignificant. Acquisition of CLas by ACP from citrus occurs more efficiently by nymphs than by adults, presumably as a result of nymphs feeding for longer durations in close proximity to sites where eggs were laid, and where CLas was originally transmitted to citrus by infected progenitors. Adult ACP not only acquire CLas less efficiently than nymphs, but ACP that acquire CLas as adults are less efficient at transmission than nymphs. All of these observations suggest that citrus is merely a conduit for generational transmission of CLas and that CLas titer in citrus trees may not play an important role on CLas dispersal. We conducted experiments to determine how generational transmission of CLas is impacted by titer in progenitor ACP adults, and in citrus. Our results indicate that CLas titer in ACP is the major driver in generational transmission. The probability of successful transmission starts to increase when CLas titers in progenitor adults exceeds ca. 10^3 copies per insect, the probability of infection increases dramatically to over 80% when CLas titer exceed 10^4 per insect. In both ACP nymphs and adults CLas titer increased with time after initial acquisition; titers of 10^6 copies per ACP adult were not uncommon. This increase in CLas titer during development occurred regardless of infection status of the tree prior to exposure to CLas infected progenitors. CLas titer in ACP in adults also impacted the titer of CLas detected both in leaves on whole trees or on detached leaves. In a comparison of transmission when CLas-infected progenitors were placed onto citrus either free of or infected with CLas, there was no significant difference in transmission efficiency in the experiment. Our data support the hypothesis that infection status of trees has little significance in generational transmission.