Pest control methods implemented around the world have been able to reduce malaria mortality rate to a mere fraction of what it used to be. These methods include indoor residual insecticide spraying and insecticide nets. However, over a long enough period of time, mosquitoes will develop resistance to these measures. In order to test how this resistance develops, researchers at the Kasetsart University in Bangkok needed a technique that would allow them to breed wild-caught female mosquitoes in a laboratory setting.

Currently, there are several classes of insecticides used to control mosquito populations, with pyrethroids being the most commonly used. They are safe for humans and they are approved for use in insecticide nets by the World Health Organization. However, mosquitoes are developing a resistance to this class of insecticides, and mosquito populations have managed to adapt to them in most southeast Asian countries. This has driven the development of new insecticides, but the degree of resistance has to be tested before they can enter mass production and be approved for use. This is where inducing egg-laying in wild mosquitoes comes in.

The technique used by the researchers to achieve this result was called forced oviposition (egg-laying) with a slight modification. The original method was developed in 2010 by John Morgan and his colleagues, and it involved confining blood-fed female mosquitos in small vials that have moistened filter paper inside them. The stress of this confinement will induce the female mosquitoes to lay eggs.

The researchers at the Kasetsart University wanted to apply this method to mosquitoes caught in the wild so they could have a new generation to test them for resistance to insecticides. They used the Anopheles species, with four lab strains and five field strains. The researchers found that the forced oviposition method was successful in breeding wild strains of mosquitoes, with 85 to 100 percent of the pupae created this way becoming adults.

The modified method employed by the researchers at the Kasetsart University used larger containers for the females however, and this resulted in a smaller number of eggs being laid. They came to the conclusion that smaller confined spaces led to more stress, and thus the females laid more eggs.

Thanks to this research, scientists will now be able to breed wild populations of mosquitoes for a variety of experiments, including those that would help in the development of new mosquito control methods. For now however, we will have to stick to the classics when it comes to controlling mosquitoes in residential areas.