Research Accomplishment Reports 2007

S1029 Improved Methods to Combat Mosquitoes and Crop Pests in Rice Fields

S.L. Dobson
Department of Entomology

 

Project Description

We address crucial information gaps about the ecology and biology of crop pests and mosquitoes, especially recent invaders. This information is central to developing effective control strategies that minimize chemical use. We will perform laboratory tests of Wolbachia as a biopesticide for mosquitoes.

Wolbachia are intracellular bacteria that are estimated to naturally infect up to 28% of mosquito species. Wolbachia have excellent potential as biological control agents and as a vehicle for driving desired genotypes into disease vectors. Suppression and gene replacement strategies are based upon the ability of Wolbachia to cause early embryonic death through cytoplasmic incompatibility (CI). Wolbachia-based insect suppression strategies are similar to that of traditional sterile insect technique, except that CI males are released instead of sterile males. The Wolbachia strategy eliminated a medically important Culex field population in Myanmar. However, application of this technique to additional mosquito populations has been restricted by an inability to identify appropriate Wolbachia strains. An example is Aedes albopictus, an invasive, important disease vector of multiple arboviruses and filaria. This mosquito has spread through much of the southern region. Ae. albopictus field surveys demonstrate that individuals are uniformly superinfected with two Wolbachia types (wAlbA and wAlbB). Thus, Wolbachia-based strategies to reduce Ae. albopictus populations will require artificially generated incompatible infection types.

Population suppression will require the release of males that are bidirectionally incompatible with the naturally superinfected Ae. albopictus population. Bidirectional incompatibility occurs when different Wolbachia types infect the same host insect population. It results in embryo mortality whenever mating occurs between individuals with differing infection types. Models predict that two or more incompatible Wolbachia types within a panmictic population will quickly reduce to a uniform infection type. Releases of incompatible insects into the population prolong the co-occurrence of bidirectionally incompatible infections. Since male mosquitoes do not blood feed or transmit disease, large numbers of males may be released.

Impact

Transfer of Wolbachia ('transfection') is accomplished via microinjection of Wolbachia infected cytoplasm in embryos. KAES used a transfection technique for Ae. albopictus that segregated the naturally occurring Wolbachia superinfection, resulting in an artificial wAlbB single infection (HTB strain). The HTB strain is not useful for applied strategies, but shows that the technique will work. KAES recently generated an artificial Wolbachia infection useful for Ae. albopictus suppression (HTR line). The HTR line is bidirectionally incompatible with both natural infections and the previously generated artificial infection. Initial trials show that releases of HTR males into laboratory cages of superinfected populations result in reduced egg hatch. KAES will generate additional Wolbachia infected mosquitoes and conduct laboratory experiments to create strategies to suppress important mosquito populations.

Efforts have recently succeeded in generating an additional infection via the transfer of the Wolbachia infection from Ae. polynesiensis into Ae. albopictus. Experiments characterizing the CI level and pattern and other impacts of the Wolbachia infection are currently in progress.

Publications

Xi Z., Gavotte L., Xie Y., Dobson S. L.: (2008). Wolbachia Host Transcriptome Effects and Impact of Angiotensin Converting Enzyme on Cytoplasmic Incompatibility. BMC Genomics. (In Press)

Benedict M., D'Abbs P., Dobson S., Gottlieb M., Harrington L., Higgs S., James A., James S., Knols B., Lavery J., O'Neill S., Scott T., Takken W., Toure Y.: (2008). Guidance for Contained Field Trials of Vector Mosquitoes Engineered to Contain a Gene Drive System: Recommendations of a Scientific Working Group. Vector-Borne and Zoonotic Diseases. (In Press)

Brelsfoard C. L., Sechan Y., Dobson S. L.: (2008). Interspecific Hybridization Yields Strategy for South Pacific Filariasis Vector Elimination. PLoS Neglected Tropical Diseases, 2(1):e129.

Sanogo Y. O., Dobson S. L., Bordenstein S. R., Novak R. J.: (2007). Disruption of the Wolbachia surface protein gene wspB by a transposable element in mosquitoes of the Culex pipiens complex (Diptera, Culicidae). Insect Mol Biol, 16:143-154.

Dobson S. L.: (2007) Transfection of Wolbachia pipientis into Drosophila Embryos. In: Current Protocols in Microbiology. Edited by Downey T: John Wiley and Sons, Inc.