Larvae of the common malaria mosquito (Anopheles quadrimaculatus), shown here among pollen in their aquatic habitat, showed low survival rates in a lab study when provided a diet of corn pollen or pine pollen. However, the southern house mosquito (Culex quinquefasciatus) fared well on the pollen diet. The findings suggest corn pollen could help the latter species—key vector of West Nile virus in the U.S.—thrive in habitats near agricultural areas. (Photo by Don Yee, Ph.D., BCE)

By Paige Embry

Paige Embry

Food makes the mosquito. Young (larval) mosquitoes need both enough food and the right amounts of carbohydrates, proteins, amino acids, and fats to grow into adults, and some food provides what they need better than others. Although most of the 3,500 or so species of mosquitoes aren’t a problem for humans, figuring out what foods help the problematic ones reach adulthood is an important scientific pursuit.

A study published last week in the Journal of Medical Entomology looks at both corn and pine pollen to see if they might be a hidden source of sustenance for two important mosquitoes in the United States: the southern house mosquito (Culex quinquefasciatus), the vector for West Nile virus and a variety of other human pathogens, and the common malaria mosquito (Anopheles quadrimaculatus), the primary vector for malaria in the U.S. before it was eradicated.

Don Yee, Ph.D., BCE

Taka Nah Jelah

Larval mosquitoes live in water but breathe air. Some must live at the surface and find their food there, while others can dive down and use more of the water column as a potential pantry. None of the larvae can chew, so they need food small enough to take in whole. Donald Yee, Ph.D., BCE, a professor at the University of Southern Mississippi (USM) and co-author of the study, says, “If you look at a close-up of a mosquito larva, most of them have big mustaches around their face, around their mouth. They’ll whorl those in kind of a cyclical motion to create vortices in the water that draws material to them.” And then they suck it up. Where they can feed in the water column impacts what food they can bring in with their vortex-inducing “mustaches.”

One potential, and often abundant, food that has received little attention is pollen. Corn is one of the most widely grown crops in the world and produces copious amounts of pollen at certain times of the year. Similarly, pine trees grow widely and produce large quantities of pollen. Corn pollen has been shown to be a viable food source for the two Anopheles species in Africa that are the primary vectors of malaria, so Yee’s student Taka Nah Jelah decided to investigate whether pollen was a potential food source for important U.S. mosquitoes for her senior thesis. Taka is from Cameroon and says that, as someone who grew up in a malaria-stricken country, it was important to her that she had “the opportunity to do research to add to the literature that could have potential importance in the control of mosquitoes.”

For the experiment, each mosquito species was given one of three diets: lactalbumin (an artificial diet used in mosquito rearing), pine pollen, or corn pollen. For each pollen type, the mosquito larvae received either low, medium, or high levels of pollen with a bit of strained ditch water to get the microbial life going. They also looked at the levels and stable isotopes of carbon and nitrogen (key nutrients) in both the pollen and the larvae. The researchers wanted to see how the different diets affected development time, body mass, and survival.

An. quadrimaculatus did poorly on both pollen diets, with 25 percent making it to adulthood on corn pollen and a meager 3 percent on pine. These results differed from what had been found for An. quadrimaculatus’ African cousins. One reason for the difference may lie in where in the water column the Anopheles species feed. The U.S. species lives and feeds only at the surface. If the food sinks, it is lost to them. And indeed, the pollen did sink in the experiment—and quickly. Both African species, however, can feed throughout the water column. It’s a trait they share with Cx. quinquefasciatus, and the U.S. Culex survived well on both pollen types. Survival rates were high (approximately 69 percent) for all levels of the corn pollen diet, and they also did well on the medium and high levels of the pine pollen diet.

The authors say that the results of the study were unexpected—both that the Anopheles did poorly, unlike the African species, and that the Culex did so well. Consequently, they write, the association of Culex larvae in habitats near corn fields warrants further research, particularly in the west north central part of the country (e.g., Iowa, Kansas, Minnesota, Nebraska, North Dakota, South Dakota). Those states grow 59 percent of U.S. corn and often have high levels of West Nile virus. Yee says that the Culex doing so well on corn pollen “has some real ramifications for disease because we have a lot of agriculture in the U.S. … and we grow a lot of corn, and often times that corn is associated with the kinds of habitats where Culex can develop.”

Paige Embry is a freelance science writer based in Seattle and author of Our Native Bees: North America’s Endangered Pollinators and the Fight to Save Them. Website: www.paigeembry.com.