Publications

4364

The olive fruit fly, specialized to become monophagous during several life stages, remains the most important olive tree pest with high direct production losses, but also affecting the quality, composition, and inherent properties of the olives. Thought to have originated in Africa is nowadays present wherever olive groves are grown. The olive fruit fly evolved to harbor a vertically transmitted and obligate bacterial symbiont -Candidatus Erwinia dacicola- leading thus to a tight evolutionary history between olive tree, fruit fly and obligate, vertical transmitted symbiotic bacterium. Considering this linkage, the genetic diversity (at a 16S fragment) of this obligate symbiont was added in the understanding of the distribution pattern of the holobiont at nine locations throughout four countries in the Mediterranean Basin. This was complemented with mitochondrial (four mtDNA fragments) and nuclear (ten microsatellites) data of the host. We focused on the previously established Iberian cluster for the B. oleae structure and hypothesised that the Tunisian samples would fall into a differentiated cluster. From the host point of view, we were unable to confirm this hypothesis. Looking at the symbiont, however, two new 16S haplotypes were found exclusively in the populations from Tunisia. This finding is discussed in the frame of host-symbiont specificity and transmission mode. To understand olive fruit fly population diversity and dispersion, the dynamics of the symbiont also needs to be taken into consideration, as it enables the fly to, so efficiently and uniquely, exploit the olive fruit resource.

AbstractIn Florida, almost all citrus trees are infected with Huanglongbing (HLB), caused by the gram-negative, intracellular phloem limited bacteria Candidatus liberibacter asiaticus (CLas). Distinguishing between the severely and mildly sick trees is important for managing the groves and testing new HLB therapies. A mildly sick tree is one that produces higher fruit yield, compared to a severely sick tree, but measuring yields is laborious and time consuming. Here we characterized HLB affected sweet orange trees in the field in order to identify the specific traits that are correlated with the yields. We found that canopy volume, fruit detachment force (FDF) and the percentage of photosynthetically active radiation interception in the canopy (%INT) were positively correlated with fruit yields. Specifically, %INT measurements accurately distinguished between mild and severe trees in independent field trials. We could not find a difference in the Ct value between high and low producing HLB trees. Moreover, Ct values did not always agree with the number of CLas in the phloem that were visualized by transmission electron microscopy. Overall, our work identified an efficient way to distinguish between severe and mild HLB trees in Florida by measuring %INT and suggests that health of the canopy is more important for yields than the Ct value.

The potato psyllid Bactericera cockerelli (Šulc) (Hemiptera: Triozidae) is a pest of solanaceous crops (order Solanales), including potato (Solanum tuberosum L.) and tomato (S. lycopersicum L.). Feeding by high populations of nymphs causes psyllid yellows while adults and nymphs are vectors of the plant pathogen ‘Candidatus Liberibacter solanacearum’. Foliar symptoms that were consistent with either ‘Ca. L. solanacearum’ infection or psyllid yellows were observed in 2019 on tomatillo (Physalis ixocarpa Brot.; family Solanaceae) grown within an experimental plot located near Saltillo, Mexico. This study had three primary objectives: 9i) determine whether the foliar symptoms observed on tomatillo were associated with ‘Ca. L. solanacearum’ infection, (ii) identify the haplotypes of ‘Ca. L. solanacearum’ and potato psyllids present in the symptomatic plot, and (iii) use gut content analysis to infer the plant sources of ‘Ca. L. solanacearum’-infected psyllids. Results confirmed that 71% of symptomatic plants and 71% of psyllids collected from the plants were infected with ‘Ca. L. solanacearum’. The detection of ‘Ca. L. solanacearum’ in plants and psyllids and the lack of nymphal populations associated with psyllid yellows strongly suggests that the observed foliar symptoms were caused by ‘Ca. L. solanacearum’ infection. All infected plants and insects harbored the more virulent ‘Ca. L. solanacearum’ haplotype B but one psyllid was also coinfected with haplotype A. The potato psyllids were predominantly of the central haplotype but one psyllid was identified as the western haplotype. Molecular gut content analysis of psyllids confirmed the movement of psyllids between noncrop habitats and tomatillo and indicated that ‘Ca. L. solanacearum’ infection of psyllids was associated with increased plant diversity in their diet.

Abstract Culicoides biting midges (Diptera: Ceratopogonidae) are vectors responsible for the transmission of several viruses of veterinary importance. Previous screens of Culicoides have described the presence of the endosymbiont Candidatus Cardinium hertigii (Bacteroidetes). However, any impacts of this microbe on vectorial capacity, akin to those conferred by Wolbachia in mosquitoes, are yet to be uncovered and await a suitable system to study Cardinium ‐midge interactions. To identify potential candidate species to investigate these interactions, accurate knowledge of the distribution of the endosymbiont within Culicoides populations is needed. We used conventional and nested PCR assays to screen Cardinium infection in 337 individuals of 25 Culicoides species from both Palearctic and Afrotropical regions. Infections were observed in several vector species including C. imicola and the Pulicaris complex ( C. pulicaris , C. bysta , C. newsteadi and C. punctatus ) with varying prevalence. Phylogenetic analysis based on the Gyrase B gene grouped all new isolates within ‘group C’ of the genus, a clade that has to date been exclusively described in Culicoides . Through a comparison of our results with previous screens, we suggest C. imicola and C. sonorensis represent good candidates for onward study of Cardinium‐ midge interactions.