A Research Blog

Julien Pompon, molecular entomologist and Assistant Professor in the Emerging Infectious Diseases Programme at  Duke-NUS Medical School shines a light on his work with mosquitoes and what attracts and repels these pesky (but resilient) insects.

MosquitoHow do you test for behaviour in mosquitoes?

We observe mosquito behaviour primarily while they feed, which corresponds to the transmission phase. Mosquitoes are observed in real time by a researcher who rates their behaviour - such as the mosquito’s landing, insertion of the proboscis, imbibing of blood, number and time of each probe, etc. Real-time behaviour is then used to compute several important parameters that help us to assess the impact of different factors on mosquito biting success.

What do the different behaviours and preferences of mosquitoes mean?

Different species of mosquitoes have evolved to specialise on feeding on different animal species. Aedes aegypti is an almost obligatory human feeder, while Aedes albopictus can feed on many different warm blood animals, although it still feeds on human even in presence of other animals. It is because of this proclivity to bite humans that Aedes aegypti is the main vector of most of the arboviruses.

Could you tell us a bit more about your work on mosquito saliva?

Our team is set to identify the whole proteome (all the proteins) and transcriptome (all the mRNA from which the proteins are generated) from the mosquito saliva. It is critical to identify the proteins from the saliva as they could play a key role in the infection during a mosquito bite.

Although some previous studies have identified few proteins from the mosquito saliva, we are going to use cutting-edge high sensitivity technology which will provide us with unprecedented level of sensitivity. We are also going to identify how dengue, Zika and chikungunya infection are regulating the proteome and transcriptome. We hope to characterise the function of such regulation by the virus. The main hypotheses are either that the virus highjacks the mosquito physiology for its benefits or that the mosquito mounts an immune response to limit the fitness impact of virus replication. We also hope that our study will identify novel targets to design new drugs or compounds to break the transmission cycle of these deadly diseases.

What attracts and repels mosquitoes?

Mosquitoes from the genera Aedes, those that transmit dengue, chikungunya and Zika, are attracted to human by visual and olfactory cues. Once they get close to their feeding target, they will further select their target using olfactory cues produced by skin as well as the bacteria present on the skin. After that, they will detect the higher level of CO2 produced by humans around their skin.

Mosquito repellents can include synthetic chemicals or plant extracts. Although none of the mechanisms of any repellent has been determined so far, it is hypothesised that mosquitoes are either repelled by the strong odour of a compound or that the compound  masks human scent or CO2.

Currently, DEET is the most commonly used synthetic repellent. Discovered for use in agriculture in the United States in the 50's, DEET has been used throughout the world ever since. Consequently, it has a very good safety track record. Although few cases of side effects have been reported, it is usually the consequence of inappropriate use, such as over application or ingestion. A recent study conducted with over 500 pregnant women at the border between Myanmar and Thailand demonstrated no negative impact of daily use of DEET for both the women and their children.

Picaridin and IR3535 are the latest synthetic compounds that have been discovered. Although their efficacy is similar to DEET, they are effective for a shorter amount of time.

Plant-derived compounds are essential oils. Eucalyptus is the most effective, and was the source to purify PMD (p-Menthane-3,8-diol), which is as effective as DEET but lasts for a much shorter time. Overall, essential oils are not totally safe because they require regular application since their effectiveness doesn’t last for very long which, in turn, has the potential for more severe side effects.

Anything else you would like to share with us about your mosquito research?

The Duke-NUS Insectary is a unique space in Singapore. It provides mosquitoes the setting to grow in a controlled environment and allows investigators to conduct infection with defined conditions. Further, we have established a functional platform to test the impact of gene silencing on any aspects of behaviour or infection. We are striving to push the molecular edges of entomology to decipher precisely how mosquitoes transmit viruses.

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