A new field demonstration from Peru suggests that we might be able to co-opt adult mosquitoes into applying insecticides for us, and that they are far more efficient at doing this than humans are.
Researchers from Rothamsted Research, an institute of the Biotechnology and Biological Sciences Research Council in the UK, working with the health authority in the Peruvian Amazon, have pioneered a new way of controlling the mosquito that carries the potentially deadly dengue virus. They forced adult Aedes aegypti mosquitoes to transfer insecticides to their own breeding sites, thereby killing any larvae developing there.
The juvenile stages of all mosquitoes develop in aquatic habitats. Emerging adults have to return there to lay their eggs and continue the life cycle. These habitats are key targets for mosquito and disease control campaigns but, because of the cryptic and myriad nature of potential breeding sites, their treatment with insecticides is usually difficult, time consuming, and expensive.
Scientists were able to achieve almost total coverage of the aquatic larval habitat by treating a small proportion of the area where adult mosquitoes rest with a safe, potent and persistent insecticide. This insecticide can be carried by adult mosquitoes but only kills juvenile stages. Amplification of the effect occurs because every adult mosquito completes several resting and egg-laying cycles during its lifetime. This results in multiple opportunities for contamination of the aquatic habitat.
The use of the adult mosquito as the transfer vehicle ensures that the larvicides are very accurately targeted: the more popular the breeding site, the greater the transfer of insecticide and the more effective the control.
The technique is truly novel, and could be implemented immediately. One of the researchers at the Ifakara Health Institute in Tanzania has developed a mathematical model of the process to explore how the Peruvian team might apply their technique to the mosquito species which carry malaria and filariasis.
Notes to Editors
» Globally, 50,000,000 annual dengue virus infections result in 500,000 cases of dengue haemorrhagic fever (DHF) and 22,000 deaths. The majority are transmitted by the mosquito, Aedes aegypti.
» In the context of the environmental effects of larvicides, it is worth noting that they will be applied anyway - whether conventionally disseminated or using this new method. The targeted water bodies are urban: from discarded tins to sewage seeps. These are not important ecologically and, in any case, the risk posed by the mosquitoes that breed there is far greater than any environmental hazard to non-target insects.
» Pyriproxyfen, the insecticide used, is a juvenile hormone analogue. It is already registered for public health use. It has drinking water approval from the WHO of 300 ppb which is 1000 times the dose needed to control Aedes aegypti.
» The work took place in the Peruvian Amazon, in the city of Iquitos: the most populous city in the world that cannot be reached by road. It has an intractable dengue problem. Biologists and technicians from the local health authority helped conduct the trials. The lead biologist was Elvira Zamora Perea.
» Greg Devine from Rothamsted Research led the investigation whilst working with the US Navy and the University of California Davis. He lived in Iquitos between 2006 and 2008, supported by the Deployed War Fighter Protection Program, administered by the US Armed Forces Pest Management Board.
» Amy Morrison, an epidemiologist from UC Davis, based in Iquitos and Jeff Stancil, a US Navy entomologist from the Naval Medical Research Center Detachment in Peru, were co-applicants on the grant.
» Gerry Killeen of the Liverpool School of Tropical Medicine, based full time at the Ifakara Health Institute in Tanzania created a simple model that helps interpret the technique and suggests that it might have applications for the control of malaria vectors.
Rothamsted Research is based in Hertfordshire and is one of the largest agricultural research institutes in the country. It is sponsored by the BBSRC.
Contacts: Greg Devine (firstname.lastname@example.org) Tel. 01582 763133 ext 2329. For further information, please contact the Rothamsted Research Press Office Tel: 01582 763133 ext 2485 or email Mary-Louise Burnett (email@example.com) or Adelia de Paula (firstname.lastname@example.org)
Source: Rothamsted Research