Embryo development and sex determination in the Cassava whitefly (Bemisia tabaci)

The cassava whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), is a highly invasive and destructive agricultural pest, with a global distribution. B. tabaci insect has evolved resistance to multiple insecticides, and therefore, new control methods will have to be developed to control this insect. The self-limiting system, which produces a female-specific lethal heritable element and causes population suppression, works well for control of mosquitoes. The goal of this thesis is to assess the feasibility of creating a self-limiting system in B. tabaci. The self-limiting system requires generating transgenic insects, and this is done via injection of constructs into eggs at the pre-germ-line cell stage (around blastoderm formation), this enables stable germline transformation. However, there has been limited research into B. tabaci early embryogenesis stages, and therefore it is unclear when transformation constructs will have to be introduced. In this thesis, I conducted confocal microscopy studies to determine the timing of early embryogenesis stages in B. tabaci MED. Unexpectedly, I revealed that early embryogenesis in B. tabaci starts before the eggs are oviposited, unlike in mosquitoes and fruitflies. Therefore, injecting laid B. tabaci eggs is too late for obtaining stable transgenic whitefly lines, though somatic transgenics may be obtained. Past self-limiting transgenic insects used genes found in the sex determination pathway, for female-specific lethality, as these were expressed early and had sex-specific splicing. Genes of the sex determination pathways in B. tabaci and other hemipteran are largely unknown. Hence, I conducted a genome-wide search of 11 publicly available hemipteran genomes to identify their sex determination genes. Also, I conducted single-embryonic RNA-seq experiments in B. tabaci to assess if these genes undergo sex-specific splicing at the early embryogenesis stages in males and females. These results identified sex determination genes in B. tabaci and other hemipterans and revealed potential targets for future genetic control methods

When a discriminating dose assay is not enough: measuring the intensity of insecticide resistance in malaria vectors

Background Guidelines from the World Health Organization for monitoring insecticide resistance in disease vectors recommend exposing insects to a predetermined discriminating dose of insecticide and recording the percentage mortality in the population. This standardized methodology has been widely adopted for malaria vectors and has provided valuable data on the spread and prevalence of resistance. However, understanding the potential impact of this resistance on malaria control requires a more quantitative measure of the strength or intensity of this resistance. Methods Bioassays were adapted to quantify the level of resistance to permethrin in laboratory colonies and field populations of Anopheles gambiae sensu lato. WHO susceptibility tube assays were used to produce data on mortality versus exposure time and CDC bottle bioassays were used to generate dose response data sets. A modified version of the CDC bottle bioassay, known as the Resistance Intensity Rapid Diagnostic Test (I-RDT), was also used to measure the knockdown and mortality after exposure to different multipliers of the diagnostic dose. Finally cone bioassays were used to assess mortality after exposure to insecticide treated nets. Results The time response assays were simple to perform but not suitable for highly resistant populations. After initial problems with stability of insecticide and bottle washing were resolved, the CDC bottle bioassay provided a reproducible, quantitative measure of resistance but there were challenges performing this under field conditions. The I-RDT was simple to perform and interpret although the end point selected (immediate knockdown versus 24 h mortality) could dramatically affect the interpretation of the data. The utility of the cone bioassays was dependent on net type and thus appropriate controls are needed to interpret the operational significance of these data sets. Conclusions Incorporating quantitative measures of resistance strength, and utilizing bioassays with field doses of insecticides, will help interpret the possible impact of resistance on vector control activities. Each method tested had different benefits and challenges and agreement on a common methodology would be beneficial so that data are generated in a standardized format. This type of quantitative data are an important prerequisite to linking resistance strength to epidemiological outcomes

Spotlight on the Roles of Whitefly Effectors in Insect–Plant Interactions

The Bemisia tabaci species complex (whitefly) causes enormous agricultural losses. These phloem-feeding insects induce feeding damage and transmit a wide range of dangerous plant viruses. Whiteflies colonize a broad range of plant species that appear to be poorly defended against these insects. Substantial research has begun to unravel how phloem feeders modulate plant processes, such as defense pathways, and the central roles of effector proteins, which are deposited into the plant along with the saliva during feeding. Here, we review the current literature on whitefly effectors in light of what is known about the effectors of phloem-feeding insects in general. Further analysis of these effectors may improve our understanding of how these insects establish compatible interactions with plants, whereas the subsequent identification of plant defense processes could lead to improved crop resistance to insects. We focus on the core concepts that define the effectors of phloem-feeding insects, such as the criteria used to identify candidate effectors in sequence-mining pipelines and screens used to analyze the potential roles of these effectors and their targets in planta. We discuss aspects of whitefly effector research that require further exploration, including where effectors localize when injected into plant tissues, whether the effectors target plant processes beyond defense pathways, and the properties of effectors in other insect excretions such as honeydew. Finally, we provide an overview of open issues and how they might be addressed

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background: Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods: The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results: NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion: As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population