No abstract

Insect-transmitted plant-pathogenic bacteria may alter their vectors' fitness, survival, behavior, and metabolism. Because these pathogens interact with their vectors on the cellular and organismal levels, potential changes at the biochemical level might occur. "Candidatus Liberibacter asiaticus" (CLas) is transmitted in a persistent, circulative, and propagative manner. The genome of CLas revealed the presence of an ATP translocase that mediates the uptake of ATP and other nucleotides from medium to achieve its biological processes, such as growth and multiplication. Here, we showed that the levels of ATP and many other nucleotides were significantly higher in CLas-infected than healthy psyllids. Gene expression analysis showed upregulation for ATP synthase subunits, while ATPase enzyme activity showed a decrease in ATPase activity. These results indicated that CLas stimulated Diaphorina citri to produce more ATP and many other energetic nucleotides, while it may inhibit their consumption by the insect. As a result of ATP accumulation, the adenylated energy charge (AEC) increased and the AMP/ATP and ADP/ATP ratios decreased in CLas-infected D. citri psyllids. Survival analysis confirmed a shorter life span for CLas-infected D. citri psyllids. In addition, electropenetrography showed a significant reduction in total nonprobing time, salivation time, and time from the last E2 (phloem ingestion) to the end of recording, indicating that CLas-infected psyllids were at a higher hunger level and they tended to forage more often. This increased feeding activity reflects the CLas-induced energetic stress. In conclusion, CLas alters the energy metabolism of its psyllid vector, D. citri, in order to secure its need for energetic nucleotides.IMPORTANCE Insect transmission of plant-pathogenic bacteria involves propagation and circulation of the bacteria within their vectors. The transmission process is complex and requires specific interactions at the molecular and biochemical levels. The growth of the plant-pathogenic bacteria in the hemolymph of their vectors indicated that the hemolymph contains all the necessary nutrients for their growth. In addition to nutrients, "Candidatus Liberibacter asiaticus" (CLas) can take up energetic nucleotides, such as ATP, from its vector, Diaphorina citri, using ATP translocase. In this study, we found that the CLas pathogen manipulates the energy metabolism of its insect vector. The accumulation of ATP in CLas-infected D. citri psyllids indicated that CLas induces ATP production to fulfill its need for this energetic compound. As a result of ATP accumulation, a shorter life span and altered feeding behavior were observed. These findings increase our knowledge of insect transmission of the persistent-circulative-propagative type of plant pathogens vectored by insects.KEYWORDS huanglongbing, Diaphorina citri, "Candidatus Liberibacter asiaticus," energy metabolism, ATP, adenylated energy charge, HPLC, electric penetration graph, electropenetrography

No abstract

SummaryNatural plant products have been studied for potential use as in-hive fumigants for suppression of parasitic mites and other pests. A more direct application through direct feeding of bees would avoid problems with fumigant volatility in cold climates and provide a more systemic route of exposure for the target pest. However, there must be a balance between toxicity to hive pests and toxicity (safety) to the bees. We focused on adult bee toxicity when testing ten products: cineole, clove oil, formic acid, marjoram oil, menthol, oregano oil, oxalic acid, sage oil, thymol, and wintergreen. Each product was tested at several concentrations in a sugar syrup fed to bees over several days, and dead bees were counted daily. Oxalic acid was the most toxic of the products tested. Menthol and cineole had mortality levels no different from controls fed plain syrup after 8 days of treatment. At 14 days of treatment, wintergreen was the least toxic, but neither menthol nor cineole were a part of the testing that went to 14 days. Our results indicate that the tested products could all be used safely for treating bees orally if dose is carefully managed in the hive.Toxicidad oral de aceites esenciales y ácidos orgánicos en la alimentación de la abeja de la miel (Apis mellifera) Los productos naturales de plantas han sido estudiados para su uso potencial como agentes fumigantes de represión de ácaros parásitos y otras plagas. Una aplicación más directa a través de la alimentación de las abejas evitaría problemas como la volatilidad de los fumigantes en climas fríos y proporcionaría una vía más sistémica de exposición para las plagas. Sin embargo, debe haber un equilibrio entre la toxicidad para las plagas y la toxicidad (seguridad) para las abejas. Nosotros nos hemos centrado en la toxicidad sobre abejas adultas de diez productos: eucaliptol, aceite de clavo, ácido fórmico, aceite de mejorana, mentol, aceite de orégano, ácido oxálico, aceite de salvia, timol y aceite esencial de wintergreen (salicilato de metilo). Cada producto fue probado con diferentes concentraciones en un jarabe de glucosa que alimentó a las abejas durante varios días, las abejas muertas fueron contadas diariamente. El ácido oxálico fue el producto más tóxico de todos los analizados. El mentol y el eucaliptol presentaron niveles de mortalidad similares a los controles, que fueron alimentados únicamente con jarabe después de 8 días de tratamiento. Tras 14 días de tratamiento, el aceite esencial wintergreen fue el menos tóxico, pero ni el mentol ni el eucaliptol se incluyeron en el análisis a los 14 días. Nuestros resultados indican que todos los productos testados pueden ser utilizados con seguridad por vía oral para el tratamiento de las abejas si la dosis es administrada cuidadosamente en la colmena.