Maternal Contribution of Candidatus Liberibacter asiaticus to Asian Citrus Psyllid (Hemiptera: Liviidae) Nymphs Through Oviposition Site Inoculation and Transovarial Transmission

Abstract

Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), transmits Candidatus Liberibacter asiaticus (Las), the bacterial pathogen putatively responsible for citrus huanglongbing. Multiple studies have shown psyllids acquire Las more frequently, and are more likely to inoculate susceptible plants, when they acquire Las as nymphs. Understanding the transmission of Las to nymphs is critical to the Las lifecycle. The objective of this study was to determine the transmission Las by female D. citri to their offspring. Two transmission pathways were quantified: horizontal transmission (acquisition of Las via feeding at the oviposition site) and vertical transmission (transovarial). Eggs of individual, infected females were transferred to an uninfected seedling to assess vertical transmission. In a second experiment, horizontal transmission was evaluated by replacing eggs laid by infected females with uninfected nymphs. Nymphs exposed to Las via horizontal transmission of the oviposition site were more likely to acquire Las than from vertical transmission. Las deposited in flush by an infected adult female feeding during oviposition was sufficient for infecting nymphs. Combined results of both experiments suggest that vertical transmission allows Las to spread in low amounts even when infected plant hosts are not available and that inoculation of the oviposition site provides a source of Las to developing nymphs via the plant phloem. These data support the hypothesis that transmission through infected plant material via maternal inoculation is a primary pathway of Las transmission between vector and host.

Understanding psyllid transmission of Candidatus Liberibacter as a basis for managing huanglongbing

“…Mann et al 2012found a 4% transfer rate of CLas by infected D. citri males to healthy females during copulation, showing horizontal transmission. Transmission of CLas between individuals also occurs via plants, through acquisition by nymphs that feed near the oviposition site of infected mothers and at a higher rate than vertical (transovarial) transmission (Kelley and Pelz-Stelinski 2019).…”

“…Eradication of infected plants alone is not sufficient to control secondary spread, because the disease has a long incubation period and it may be several months or years until diagnostic symptoms can be perceived by inspectors. In addition, the latency of the pathogen in the plant (i.e., the time period after infection when vectors are able to acquire the pathogen from an infected plant) is much shorter than the incubation period, allowing secondary spread before eradication can be accomplished (Coletta-Filho et al 2014;Canale et al 2019;Kelley and Pelz-Stelinski 2019). Once infected, D. citri can retain and transmit the pathogen for several weeks and therefore can spread the pathogens over long distances if not controlled.…”

Development on Infected Citrus over Generations Increases Vector Infection by ‘Candidatus Liberibacter Asiaticus in Diaphorina citri’

“…After the acquisition from an infected plant, CLas spread across ACP organs and tissues, remaining within the insect for long periods of time, even after molting from one nymphal instar to the next and from nymphs to adults. Furthermore, sexual and transovarial CLas transmission has been reported, which may also contribute to increase in bacterial levels across ACP generations [3,19,29,30]. Studies have shown that CLas load in the vector rises faster when ACP acquires CLas as nymphs rather than as adults, indicating that CLas multiplies more efficiently in immature stages than in adults [5,6,18,31].…”

Infection Patterns of a Liberibacter Associated with Macrohomotoma gladiata, a Psyllid Feeding on Ficus microcarpa

“…In terms of Liberibacter transmission among psyllids, a recent study on D . citri showed that the Liberibacter deposited by ovipositing females onto the flush during feeding could be a main source of Liberibacter transmission for the nymphs ( 49 ). The data in this work showed that twigs that carry the nymphs (thus including the ovipositional sites) tend to harbor higher titers of Liberibacter ( Fig.…”