Culicoides anopheles

This is the fourth post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2014. This particular post was written by Sarah Prammer she had titled "The Mosquito's Karma" on a midge that sucks blood the belly from mosquitoes (you can read the previous post about how leaf-cutter ants defend themselves against parasitoid flies here).

Photo from Figure 1 of the paper

Very few people are lucky enough to escape the bloodsucking appetite of a mosquito - most would have been bitten by those insects at some point in their life. It seems now, however, we can say the same of the mosquitoes themselves. A type of midge, scientifically known as Culicoides anopheles, has been recorded feeding on the blood of at least nineteen different species of mosquito. It only attacks mosquitoes that are already engorged with blood, so typically leaves males and ‘empty’ females alone. Although this study was located on the Chinese island province of Hainan, these midges have also been found in Papua New Guinea, Sri Lanka, Myanmar, Thailand, Vietnam, Indonesia, and on almost three quarters of Anopheles stephensi mosquitoes in India.

This particular study took place last year (2013) in Haikou, a populous city in Hainan. An unfortunate cow was used as bait inside a net trap to capture mosquitoes. Upon examining the caught mosquitoes, the researchers noticed that one of them, an Anopheles sinensis specimen, was being parasitised by the midge. This happened again the next day. The researchers chloroformed the animals and videotaped their behaviour underneath a microscope. The midge had pierced the front of the mosquito’s abdomen with a specialised tube-like mouthpart called a proboscis, and its own abdomen increased in size as it stole the stolen blood directly from the mosquito. It was significantly smaller than the host which probably gave it easier access and prevent the mosquito from pulling it off.

Notably, the midge had trouble detaching itself; it had to rotate its body a few times in order to unscrew itself from the host. The researchers hypothesised that the midge’s proboscis has evolved to remain firmly inside the mosquito, which allows it to continue feeding at leisure even while the host is flying. This is supported by other studies which show that the midge can hang off the mosquito for almost two and a half days. A paper about a study done in Papua New Guinea described one midge still embedded in its mosquito even after being sedated, killed, and preserved. Although the mosquitoes can tolerate the midges for a few hours with apparent indifference, they appear to eventually grow agitated of being a blood meal, sometimes flying about erratically when infected. One mosquito was observed to suffer organ damage from this type of parasitism. Up to three midges have been found on a single mosquito.

Because mosquitoes are often carriers of disease, the midge is considered a component in further spreading pathogen in both humans and other animals; it is effectively a transmitter between transmitters. The pathogens it can potential spread include the Bluetongue, Oropouche, and Schmallenberg viruses, which are transferred by the midges themselves, as well as the Dengue, West Nile, and Japanese encephalitis viruses, which carried by the mosquitoes. It is not known just how much the Culicoides anopheles midges contribute to the spread of these diseases. Similarly, there is little other information on their behaviour or genetics.

Reference:
Ma, Y., Xu, J., Yang, Z., Wang, X., Lin, Z., Zhao, W., Wang, Y., Li, X. & Shi, H. (2013). A video clip of the biting midge Culicoides anophelis ingesting blood from an engorged Anopheles mosquito in Hainan, China. Parasites & Vectors, 6: 326.

This post was written by Sarah Prammer