Sure, mosquitoes suck blood and pass along malaria that kill more humans than any other infectious disease. But would it be good to get rid of them. They provide food for birds – one scientist suggests that elimination of Arctic mosquitoes could reduce northern bird populations by 50%. And mosquitoes pollinate flowers too, like blueberries and cranberries. See, they’re not all bad.

We can start our summer series of biology questions by continuing our discussion of taste and thermosensing. It seems that some people are bitten by mosquitoes if they peak out the front door, while other people can sit outside next to tall grass or ponds for hours with suffering a single bite. Unfortunately, I happen to be in the former category.

On the left is a drawing of the mosquito proboscis parts. Most sit in a groove of the labium, which retracts as the rest is injected into the skin. The maxillae and mandibles are like our upper and lower jaws. They are the sharp parts. The hypopharynx is what delivers the anticoagulant saliva. On the right is the parts put together. The fuzzy part is the labium and the sharp tips are from the maxillae.

Take a look at these videos taken from a 2012 PLoS One study of a mosquito biting a mouse. The squarish objects are skin cells, and the red streaks are blood vessels. The second video in the sequence shows what happens when the proboscis finds a vessel and starts to suck out the blood. Makes you respect the mosquito a bit more – these are some determined females.

But here is one of our exceptions – some mosquitoes have gotten around the need for blood meals. All 92 species of mosquito in the genus Toxorhynchites (elephant mosquito) don’t need to feed on blood. Instead, their larvae feed on the larva of other mosquitoes, and the gather the proteins they need to lay viable eggs from their larval meals. They store the amino acids in their larval and pupal bodies, until they become adults and need them to lay eggs of their own.

Compare the sizes of the elephant mosquito (left) and A. aegypti.  I’m very glad that the females of the Toxorhynchites genus don’t suck blood. They could drain people dry! Even though their size is small, species like the one on the right can consume 300 ml a day from every caribou in a herd when they are swarming.

This suggests that the elephant mosquitoes could be used to combat disease spreading mosquitoes, like the Aedes aegypti mosquitoes that spread dengue fever, yellow fever and the current disease of interest, chikungunya fever. And the elephant mosquito has been used as a natural biocontrol agent. What's weird is that A. aegypti females actually help the situation.

A. aegypti, and many other mosquitoes that lay eggs in water, have larvae that eat bacteria. So they want to lay eggs where there are a lot of bacteria. Well, the eating of larvae by Toxorhynchitesspecies leaves lots of little pieces of mosquito larva in the water, and this provides bacteria with a lot of food. A June 2014 study showed that A. aegypti females actually prefer to lay eggs in water that contain predators for their larva, because it increases the bacterial numbers so much. Thos that survive have lots of bacteria to feed on. It’s a calculated behavior – risk being eaten or risk starving.

The picture represents the transmission cycle for eastern equine encephalitis virus (EEEV). It can’t be transmitted from mammals to other animals, so they are called dead-end hosts. But it can produce disease in them. Humans most often will present with a limiting or subclinical disease, but horses have a hard time with it. The major source is in birds, and the transmission from bird to bird is by mosquitoes that rarely bite humans. The way into dead-end hosts is by a mosquito that normally bites mammals occasionally biting a bird, or the rare occasion that a bird specific mosquito will bit a mammal.

But just because they feed mostly from birds doesn’t mean they aren’t important disease transmission. They are – for horses. Eastern equine encephalitis virus is passed from bird to bird by C. melanura, so the birds, especially cardinals, are a reservoir of virus. Then, when another species of mosquito that is less particular about its host species bite a bird then bites a horse or person, the disease can be spread. There are even cases where a C. melanura will occasionally feed on a human and spread the disease directly.

On the top of this image is a general idea of semiochemicals. If they work on members of the same species (like mating signals), then they are called pheromones. If they work on other species, they are called alleochemicals. Each can be either attractive or repellant. On the bottom is a homemade mosquito trap. You might be able to see that it has been baited with old shoes and grimy socks.

Bacteria feed on the sweat, sugars and proteins that mammals exude, and they give even more semiochemicals. This can make you more or less attractive to mosquitoes. In general, people with many types of bacteria on their skin are less attractive, while those with mostly a few attractive species will get bitten more often. Having a high number of bacteria is a turn off too, probably because that would expose the mosquitoes to more possible pathogens as well. Is it possible to be so disgustingly colonized that even mosquitoes won’t land on you?

This is part of a complex figure from a 2011 scientific paper. In addition to the pretty colors used, the message is that these researchers identified TRPA1 ion channels on the proboscis of a species of mosquito. They don’t just sense heat with their antennae, but also their sucking parts. I wonder if the interior parts also have TRPA1 to help them find a vessel when the proboscis is inserted into the tissue.

On the left is a species of tick. You wouldn’t believe how big they can get when feeding on blood. Look it up – I dare you. On the right is a bedbug. The bedbug is not that closely related to the tick, since the tick is an arachnid. Count the legs on each – spiders (arachnids) have eight legs, insects have six. Both these animals feed on blood, but no one has identified a heat sensor in them.

But in birds, reptiles and insects, TRPA1 is a heat sensor. The 2009 studyshowed that the TRPA1 were expressed on the female antennae only. But that isn’t to say that only female mosquitoes have TRPA1. A 2013 study indicates that A. gambiae mosquito larvae have functioning TRPA1 so that they can sense water temperature and stay in the most comfortable water.