Combining transinfected Wolbachia and a genetic sexing strain to control Aedes albopictus in laboratory-controlled conditions.

The global expansion of Aedes albopictus has stimulated the development of environmentally friendly methods aiming to control disease transmission through the suppression of natural vector populations. Sterile male release programmes are currently being deployed worldwide, and are challenged by the availability of an efficient sex separation which can be achieved mechanically at the pupal stage and/or by artificial intelligence at the adult stage, or through genetic sexing, which allows separating males and females at an early development stage. In this study, we combined the genetic sexing strain previously established based on the linkage of dieldrin resistance to the male locus with a Wolbachia transinfected line. For this, we introduced either the wPip-I or the wPip-IV strain from Culex pipiens in an asymbiotic Wolbachia-free Ae. albopictus line. We then measured the penetrance of cytoplasmic incompatibility and life-history traits of both transinfected lines, selected the wPip-IV line and combined it with the genetic sexing strain. Population suppression experiments demonstrated a 90% reduction in population size and a 50% decrease in hatching rate. Presented results showed that such a combination has a high potential in terms of vector control but also highlighted associated fitness costs, which should be reduced before large-scale field assay.

High-throughput sequencing of complete genomes of ipomoviruses associated with an epidemic of cassava brown streak disease in the Comoros Archipelago.

Using high-throughput sequencing of small interfering RNAs (siRNAs), virion-associated nucleic acid (VANA), and double stranded RNAs (dsRNAs), we have determined the complete genome sequences of Comorian isolates of two ipomoviruses, cassava brown streak virus (CBSV) and a divergent isolate of Ugandan cassava brown streak virus (UCBSV-KM) representing a new strain of this virus. While the large ORF of CBSV shares the highest nucleotide sequence identity (95.9%) with a Tanzanian isolate of CBSV, the large UCBSV-KM ORF shares the highest nucleotide sequence identity (77.5%) with a Malawian isolate of UCBSV. This low value is near the species demarcation threshold for the family Potyviridae (<76%). Phylogenetic analysis confirms that UCBSV-KM represents a new lineage that is genetically distinct from the currently described UCBSV strains.

Tomato leaf curl Mahé virus: a novel tomato-infecting monopartite begomovirus from the Seychelles.

This is the first description of the complete genome sequence of a new monopartite begomovirus isolated from tomato with symptoms of tomato (yellow) leaf curl disease collected in the Seychelles. The DNA-A-like nucleotide sequences share the highest nucleotide sequence identity (84%) with tomato leaf curl Anjouan virus (ToLCAnjV) from the Comoros islands. Phylogenetic analysis confirmed its recombinant nature and its relationship to Old World monopartite and bipartite begomoviruses. This discovery of a new member of a species confirms the high genetic diversity of begomoviruses in the south-western Indian Ocean islands.

Optimization of Dieldrin Selection for the Genetic Sexing of Aedes albopictus.

The mass production of mosquitoes at an industrial scale requires efficient sex separation, which can be achieved through mechanical, genetic or artificial intelligence means. Compared with other methods, the genetic sexing approach offers the advantage of limiting costs and space by removing females at the larval stage. We recently developed a Genetic Sexing Strain (GSS) in Aedes albopictus based on the sex linkage of the rdlR allele, conferring resistance to dieldrin, to the male (M) locus. It has been previously reported that dieldrin ingested by larvae can be detected in adults and bioaccumulated in predators, raising the question of its use at a large scale. In this context, we performed several experiments aiming at optimizing dieldrin selection by decreasing both dieldrin concentration and exposure time while maintaining a stable percentage of contaminating females averaging 1%. We showed that the previously used dieldrin exposure induced an important toxicity as it killed 60% of resistant males at the larval stage. We lowered this toxicity by reducing the dose and/or the exposure time to recover nearly all resistant males. We then quantified the residues of dieldrin in resistant male adults and showed that dieldrin toxicity in larvae was positively correlated with dieldrin concentrations detected in adults. Interestingly, we showed that the use of reduced dieldrin exposure led to a dieldrin quantification in adult males that was below the quantity threshold of the Gas Chromatography-Mass Spectrometry detection method. Presented data show that dieldrin exposure can be adjusted to suppress toxicity in males while achieving efficient sexing and lowering the levels of dieldrin residues in adults to barely quantifiable levels.

Development of an automated mosquito pupae counter.

The production of mosquitoes for control programs or basic research is facilitated by the standardization of rearing conditions allowing the daily manipulation of thousands of individuals. It is crucial to develop mechanical or electronic systems for controlling the density of mosquitoes at each development stage with the aim of reducing costs, time, and human errors. We present herein an automatic mosquito counter using a recirculating water system allowing rapid and reliable counting of pupae without detectable increased mortality. Using Aedes albopictus pupae, we determined the density of pupae and the time of counting for which the device is most accurate, and evaluated the time saved using this device. Lastly, we discuss how this mosquito pupae counter can be useful in small-scale or mass-rearing contexts enabling a number of applications for research purposes as well as operational mosquito control programs.

Contribution of historical herbarium small RNAs to the reconstruction of a cassava mosaic geminivirus evolutionary history.

Emerging viral diseases of plants are recognised as a growing threat to global food security. However, little is known about the evolutionary processes and ecological factors underlying the emergence and success of viruses that have caused past epidemics. With technological advances in the field of ancient genomics, it is now possible to sequence historical genomes to provide a better understanding of viral plant disease emergence and pathogen evolutionary history. In this context, herbarium specimens represent a valuable source of dated and preserved material. We report here the first historical genome of a crop pathogen DNA virus, a 90-year-old African cassava mosaic virus (ACMV), reconstructed from small RNA sequences bearing hallmarks of small interfering RNAs. Relative to tip-calibrated dating inferences using only modern data, those performed with the historical genome yielded both molecular evolution rate estimates that were significantly lower, and lineage divergence times that were significantly older. Crucially, divergence times estimated without the historical genome appeared in discordance with both historical disease reports and the existence of the historical genome itself. In conclusion, our study reports an updated time-frame for the history and evolution of ACMV and illustrates how the study of crop viral diseases could benefit from natural history collections.