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Ecologist and biology professor Todd Livdahl investigates how mosquitos native to the U.S. defend their territory again foreign invaders. In Biology 201, he takes students into the field to learn about the ecology of the Atlantic shore. |
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Mosquitoes bite
Professor Todd Livdahl's research
"Mosquitoes* cause more human suffering than any other organism with over one million people dying from mosquito-borne diseases every year." --American Mosquito Control Association
Ecologist Todd Livdahl and his research team have determined that a mosquito native to the U.S. may defend its territory by cannibalizing the young of non-native mosquitoes.
Livdahl has been studying the behaviors of three different mosquito species, only one of which, Ochlerotatus triseriatus,** is native to the United States. Aedes aegypti and the most recent immigrant,Aedes albopictus, are not native, but like to breed in habitats occupied by their native cousins.
Livdahl knows that the globalization of trade has the potential to alter local ecologies. Something as simple as a mosquito inadvertently hitching a ride to the U.S. on a Japanese-made automobile tire--thought to be the means of transport for Aedes albopictus--can threaten the delicate balance within a plant and animal community.
Since these three types of mosquitoes also contribute to the spread of diseases that afflict humans, it is especially important to understand the conditions that cause them to thrive. Ochlerotatus triseriatus carries the La Crosse encephalitis virus, Aedes albopictus is associated with dengue viruses, and Aedes aegypti with both dengue and yellow fever.
Treehole mosquitoes compete for resources
The mosquitoes being studied are "container" dwellers who like to lay their eggs in the quiet pools of water that collect in the bottom of treeholes. As the rainwater drips down the tree and into the hole, it collects nutrients that the mosquitoes use for food. But if treeholes are not available, any container that collects rainwater water--from cemetery urns to discarded tires† to aluminum cans--will do as a breeding area.
Livdahl's research team knows that, because these mosquitoes favor the same type of habitat, they compete among themselves for the resources necessary to their survival. In fact, the larvae of Aedes aegypti and Ochlerotatus triseriatus have been known to eat earlier-stage larva under certain conditions, and the team wanted to know if the larvae of Aedes albopictus, the most recent of the three to come to the United States, will also resort to cannibalism.
An experiment to understand species interaction
The researchers created an experiment to explore the way these three species interact. Plastic cups filled with treehole water were used as the breeding environments. Each container simulated one of 48 different environmental conditions created by varying
- The amount of food. Some environments were food-poor while others were food-rich.
- The degree of environmental complexity. In some containers, refugia (places where larvae could conceal themselves) was added, while others were free of refugia.
- The species of prey (victim). In each container, 1st stage larva† of one mosquito species served as prey.
- The species of predator. In each container, 4th stage larva of one mosquito species served as predator.
Each of the 48 environments was simulated five times. Several containers containing prey, but not predators, served as control groups. After 24 hours, the researchers counted the number of prey larvae remaining in each container.
Mosquito cannibalism
Based on their observations, Livdahl's team determined that:
- Aedes albopictus, the most recently arrived species, was the least likely to cannibalize, and the most likely to be victimized. In fact, it was unclear whether Aedes albopictus predator larvae engaged in cannibalism at all. The difference in larval deaths when the Aedes albopictus predator larvae were present, versus when no predator was present at all, was not quite statistically significant.
- Ochlerotatus triseriatus larvae were the most likely of the three species to eat younger larvae, and the least likely to be victims of cannibalism.
- Of all the species, only Ochlerotatus triseriatus' cannibalizing was affected by the amount of food available. When more food was available, it was less likely to prey on other larvae.
- Surprisingly, while Ochlerotatus triseriatus was more successful cannibalizing in a refugia-free environment, Aedes aegypti was more likely to cannibalize in an refugia-present environment if food was scarce.
The aggressive cannibalizing tendencies of Ochlerotatus triseriatus may help it compete against the two non-native species. However, more research is needed to determine if the effect of this behavior will be offset by the higher hatch and growth rates of Aedes albopictus and aegypti.
*Mosquito comes from the Spanish word "musketas."
*Ochlerotatus triseriatus was, until recently, known as Aedes triseriatus
†Scientists and public health officials are especially concerned about the increasing number of tires that are inappropriately discarded.
††Like all insects, mosquitoes have four developmental stages: egg, larva, pupa and adult. Mosquito larvae go through four stages (instars) and they shed their skins between each.
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Additional Resources
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The neato mosquito! See the life cycle of a treehole mosquito. 
Ochlerotatus triseriatus
Aedes albopictus
Aedes aegypti
Closeups of larvae engaging in cannibalism. Click 
Red areas indicate counties with confirmed presence of Aedes albopictus in 2000. 
Distribution of Aedes aegypti in North and South America in 1997. 