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Rough Science 5 Zanzibar: Ellen McCallie's diary: Call of the wild

Updated Wednesday, 2nd March 2005

Combating the mosquitoes – Ellen works to develop an effective mozzie repellant, and, in order to test it safely, she must also raise her own malaria-free mosquitoes.

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Ellen with mosquitos Copyrighted  image Icon Copyright: Production team

Day 1

This is my kind of challenge! I love it! The goal is to make a mosquito repellent and prove that it works. Everyone was taking this challenge very seriously as one of our directors, Emma, had already come down with malaria!

Today we looked for stagnant water. The people living in this area know that mosquitoes only breed in stagnant water, so they’ve worked really hard to make sure all the water around is moving. This meant we had our work cut out for us. In the end, we found one place where the water was very still – and full of mosquito larvae and pupa! I collected all I could.

Because we only have three days for the challenge, the pupae are most important, as that’s the stage right before the adults emerge. They don’t eat as pupa either, so I don’t have to worry about feeding them. It was, however, important to keep them in the water they were found in and to keep them plenty warm so they develop quickly.

Why am I collecting larvae and pupa and not going directly for the adults? Our repellent guinea pig is, once again, Kate. She’s putting her hand in the cage with the mosquitoes to test whether or not the repellent works. I can’t risk her getting malaria or another mosquito-borne disease, so I have to raise our own disease-free mosquitoes. This means two things:

  1. We have to identify the species of mosquitoes we collect and only raise up species that aren’t known to carry viruses here. If the species is known to carry viruses in this area, it can’t be used. Viruses may be passed from parent to offspring—scientists don’t know for sure yet. It would be unethical to expose Kate to mosquitoes known to carry viruses.
  2. By raising mosquitoes in cages, we can guarantee they don’t have malaria. Malaria is caused by a protozoan. Mosquitoes pick up the protozoan by biting an animal infected with it. The protozoan cannot be passed from one generation of mosquitoes to the next – too mosquitoes go from egg to larvae to pupa and emerge as adults – all malaria-free. It’s once they bite someone with malaria that they becomes a carrier and can infect others.

Day 2

About 25 adult mosquitoes emerged from the pupa. I wanted more, but this is okay. As these species of mosquitoes aren’t active during the day, they just sat on the mesh of their cages all day.

I ended up making two repellents, though the actual test only used one. I ground up and extracted the essential oils of lemongrass, commonly used in cooking, in alcohol. This type of repellent is supposed to mask the smell and carbon dioxide released from human skin. I also did the same with neem tree leaves. The chemical properties of neem tree leaves supposedly induce a vomiting reflex in mosquitoes – lovely.

As the sun was starting to set, we did the test. Not ideal conditions – later would have been better – but filming tiny insects in complete darkness wasn’t really possible, so we compromised. As soon as the mosquitoes started moving, Kate stuck one hand without repellent in one cage and the other with repellent in the other. These newly emerged mosquitoes probably weren’t at their most hungry quite yet, but they did buzz around and land on Kate’s hand – the one without repellent. Whew! The only inconvenience with natural repellents is that they have to be reapplied every 15 minutes or so.

Day 3

With my section of the challenge over, today was a beautiful day to help others. Kathy’s periscope was fantastic. Jonathan’s hydrophone worked pretty well, too. The crystals Mike grew were absolutely amazing.





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