Integrative Systematics of the Bemisia tabaci species complex (Hemiptera: Aleyrodidae) and their parasitoids (Hymenoptera: Aphelinidae)
This project will use machine-learned morphological image analysis, combined with multigene DNA sequence analysis, to distinguish between 30 species in the Bemisia tabaci whitefly species complex and also their associated parasitoid wasps.
The studentship starts October 2019 and is funded by NERC.
Bemisia tabaci is among the most important plant pests globally, especially in the tropics and subtropics. As well as causing direct damage to a wide range of crops, it transmits more than 200 plant viruses.
Among the plants most susceptible to damage by B. tabaci are cassava, the main staple crop in sub-Saharan Africa and increasingly elsewhere in the Old World tropics, cash crops such as cotton and poinsettia, and a wide diversity of horticultural, vegetable and other crops.
B. tabaci has recently been shown to be a complex of more than 35 distinct biological species. Until a recent pilot study by A. Polaszek, N. MacLeod and R. Canty it was not possible to distinguish the species morphologically. Image recognition software developed by N. MacLeod can now distinguish 6 species tested so far.
The proposed project will extend this study to the species of economic importance (about 30 species), analyse adult B. tabaci for the first time, and test whether the shape recognition software is effective in distinguishing the whiteflies' parasitoids, some of which also appear to be cryptic species complexes.
In many parts of the world, several of these parasitoids have effectively controlled B. tabaci, but further studies are needed on the degrees of host-specificity among cryptic parasitoid species, a pre-requisite to their effective use as control agents.
A recently completed preliminary study funded by the Bill & Melinda Gates Foundation, and involving the present NHM team, enabled the establishment of live cultures of all species of economic importance at a quarantine facility at the Natural Resources Institute, and this material will continue to be available to the research team.
Different biological species of B. tabaci show very different kinds of host plant association, and virulence, especially with regard to virus transmission. Developing a rapid machine-learning protocol for distinguishing the developmental stages (something impossible until now) will facilitate the rapid identification of species, eventually enabling this to be done on living specimens in field situations, something that has previously depended on DNA barcoding.
Identification of parasitoids has also been difficult in the past, relying on a combination of adult morphology and DNA sequence analysis. A non-destructive DNA extraction protocol developed by the lead supervisor now permits DNA sequencing (including whole genome NGS) while preserving a perfect specimen for image analysis and other technologies that depend on intact specimens (e.g. confocal laser scanning microscopy).
The main current attempts at controlling B. tabaci, especially the cassava-associated species in sub-saharan Africa, are focussing on the use of resistant plant races, including GM varieties. It has been shown unequivocally that B. tabaci is a complex of species capable of rapid local adaptation and eventually speciation, traits that suggest plant host resistance may not be the best option for controlling this particular pest. Focussing on natural enemy species that may themselves be able to adapt to changes in host behaviour and biology would appear to be an essential element of a more integrated control strategy.
To be eligible for a full award a student must have:
- British Citizenship or;
- Settled status in the UK, meaning they have no restrictions on how long they can stay,
- Been ‘ordinarily resident’ in the UK for 3 years prior to the start of the studentship - (For non-EU citizens, this must NOT have been in full time education.)
This means they must have been normally residing in the UK (apart from temporary or occasional absences). This does not apply to UK nationals.
For more information, download this PDF.
How to apply
Applications for the PhD are processed through the Natural History Museum.
To apply please send the following documents to the Postgraduate Office at email@example.com:
- Curriculum vitae.
- Covering letter outlining your interest in the PhD position, relevant skills training, experience and qualifications for the research, and a statement of how this PhD project fits your career development plans.
- Names of two academic referees.
The deadline for applications is 8 January 2019.
This is a joint project between The Science and Solutions for a Changing Planet (SSCP) Doctoral Training Partnership at Imperial College London and The Natural History Museum.