Video tracking mosquitoes

Malaria is a widespread disease, resulting in much illness and even death in tropical and subtropical regions. In Africa particularly, the death toll caused by malaria is high. As we all know, the disease is transferred person-to-person by malaria mosquitoes (Anopheles gambiae); therefore, much research is being done to find effective, but also economical, options to prevent malaria. Common options include bed nets and insect repellants, but many mosquitoes are now resistant to these repellants. To protect more people from malaria, research into an effective pesticide is needed. Researchers have also turned to assessing mosquito behavior (flight patterns, landing sites, ability to find holes in bed nets), as this is also important in battling malaria. Video tracking technology is an important tool in this research. This page features some examples of studies that use video tracking. 

How mosquitoes find their host

Why is it that some people are covered in mosquito bites while their roommate stays unharmed? Assessments of mosquito behavior have revealed that there are many different cues that mosquitoes use to find their host. How you smell is only one. 

In 2013, Jeroen Spitzen and his colleagues studied host-seeking behavior of malarial mosquitoes inside of  a wind tunnel, using EthoVision XT video tracking software to assess flying behavior in the tunnel. To get a better understanding of exact flight path, Track3D software was used for 3D path construction and analysis. 

Heat and smell

The results showed that the mosquitoes use both odor and heat to find their host; either of these two stimuli alone is not enough. In presence of foot odor and heat, the mosquitoes alter their flight path and fly in a zig-zag pattern to the odor source. This indicates that they make use of gradients in heat and odor concentration and scan the odor plume intensely to fly to its source. Armed with this knowledge, methods to control malaria mosquitoes can be improved; for example, a heat source could be added to an odor baited mosquito trap.

Read more about this study in this blog post

A new approach in the battle against malaria

Bed nets, and especially those that are treated with insecticide, have been very effective in the battle against malaria. However, the standard way of testing if a pesticide is effective (World Health Organization, WHO), is to keep mosquitoes in a small enclosure, forcing them to touch a piece of net with the pesticide. Due to the forced nature of these studies, and lack of escape options for the mosquito, we have to ask the question: would the mosquito stay away from the bed net if possible? 

Wind tunnel assays

Jeroen Spitzen and his colleagues again used wind tunnels to compare the results of WHO standard bioassays with an assay in which the natural flight behavior of both normal and pesticide-resistant mosquitoes towards bed nets was studied. The mosquito flight behavior in the wind tunnel was automatically analyzed with the video tracking software EthoVision XT. All mosquitoes quickly flew towards the bed nets, indicating that the pesticide-treated nets are not repellent to them. However, in the WHO studies, mosquitoes had to spend at least 3 minutes touching the pesticide-treated nets; in the current study, mosquitoes spent less than 3 minutes voluntarily in contact with the bed nets. Not surprisingly, mortality rates were lower in the wind tunnel test, indicating a more realistic estimate of bed net effectiveness. It also revealed interesting differences in flight behavior between normal and pesticide-resistant mosquitoes. All of this can help to make better bed nets to protect people against malarial mosquitoes.

Read more about this research in this blog post

Smarter mosquitoes due to pesticide resistance?

Not everyone has access to bed nets. And even for those that do, they may still be bitten anyway due to holes in the nets. 

To investigate the effectiveness of bed nets with holes, Malal Diop and colleagues used a free-flight approach in a wind tunnel to see whether malarial mosquitoes could reach an attractive odor source through a 1 cm hole in a bed net. Video tracking was done with EthoVision XT. The bed net was either untreated, or treated with common insecticides (the synthetic pyrethroids Permethrin or Deltamethrin). They tested normal mosquitoes (susceptible to pyrethroids) and two strains that were either partially or completely resistant against pyrethroids. 

Mosquitoes are smart

Mosquitoes are smart: at least 50% of the mosquitoes were able to pass through the 1cm hole in the bed net, regardless of genotype. As expected, treated bed nets were unable to kill the completely resistant mosquitoes. Surprisingly, partial resistant mosquitoes were the best at finding and passing through the hole, yet due to their only partial resistance were killed more easily than conspecifics.  

So while insecticide-resistant mosquitoes have a high resistance against synthetic pyrethroids, this resistance comes with a fitness cost. The partially resistant mosquitoes may have best of both worlds.

Why investigate this?

This study shows that it is important to study more than just the mortality of different strains of malarial mosquitoes. The partially resistant strain was easier to kill than the resistant strain, but they are better at searching for ways in. These types of insights are valuable in the search for tools against malaria. 

Read more about this research in this blog post

Even mosquito larvae can help

Most of us are familiar with DEET as an insect repellent. In 2012, the Zwiebel lab (Vanderbilt University) found a possible new and stronger bug repellant calledVUAA1. This repellant seems to turn on all the receptors in the mosquito’s “nose”, effectively overloading the odor-sensing system so they have no way to locate any odor source...including humans!

Testing the behavior of larvae

To study the effectiveness of VUAA1 and some analogues, mosquito larvae were exposed to VUAA1, DEET and two other compounds that are known to affect larval mobility: 3MP and ACP. Larval activity was measured in 6-well plates with EthoVision XT in a DanioVision chamber. As expected, based upon knowledge of the compounds, 3MP increased larvae activity, as does DEET, while ACP decreased it. And, in accordance with previous findings, VUAA1 increased activity significantly more than DEET.

This study shows promising findings for the creation of better mosquito repellants and thus in limiting the spread of malaria and other diseases that can be transferred by insects.

Read more about this study in this blog post.

References