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Mosquitoes are the bane of many people’s lives, especially since their bites aren’t just irritatingly itchy; they can also spread potentially deadly parasitic diseases. Even the larvae of certain species can be formidable. While most mosquito larvae feed on algae or bacteria and similar microorganisms, some predatory species feed on other insects, including the larvae of other mosquitoes. A team of scientists captured the unique attack methods of these cannibalistic predators on high-speed video, revealing how they capture their prey with lightning-fast attacks, according to a recent study published in the journal Annals of the Entomological Society of America.
Co-author Robert Hancock, a biologist at the Metropolitan State University of Denver, became fascinated with predatory mosquito larvae when he first watched them beat their prey under a microscope during an undergraduate entomology class in college. He was impressed by the speed of the attacks: “All we saw was a blur of action,” he recalls. Scientists have long studied these larvae because they are so efficient at controlling the populations of other mosquito species. Just one predatory larva can devour as many as 5,000 prey larvae before reaching adulthood.
Hancock first tried to capture the striking behavior of the larvae on 16 millimeter film in the 1990s by jerry-rigging a set-up with a microscope and camera — a process he says resulted in a lot of wasted film, given the blistering speed of the strikes. Now a college professor, he was able to leverage all the advances in video and microscope technology made since his college days to learn more about the biomechanics involved.
A Psorophora ciliata larva strikes a prey larva via a sudden neck extension to launch its head away from its body and toward the prey. (RG Hancock et al., 2022)
Hancock and his co-authors focused on three species of mosquito larvae for their experiments. Toxorhynchites amboinensis is native to Southeast Asia and Oceania; the lab took adults from Ohio State University and collected stages of special black plastic egg-laying cups on a weekly basis. Psorophora ciliate larvae were collected from shallow irrigation ditches in the citrus groves of River County, Florida. And samples from Sabethes cyaneus came from a colony first established in 1988 in OSU, with adults and larvae collected on Maje Island in Panama.
The researchers induced attacks by placing the predatory larvae in well slides of water and then presenting live prey larvae with a jeweler’s rod. The striking behavior was captured on video using high-speed microcinematography. They used heat-protective filters for the hot and bright lights under the microscope, because otherwise the heat would have cooked the live larvae. Even the researchers wore dark sunglasses for protection. Finally, they analyzed the resulting videos to gain insight into the larval anatomy and sequence of movements involved in their seizures.
A Sabethes cyaneus larva attacks a prey larva by using its tail to sweep the prey towards its head. (RG Hancock et al., 2022)
Both Thx. amboinensis and ps. ciliate are so-called “mandatory” predators, meaning they must consume the larvae of other insects. “Despite their different kinship in different tribes of the Culicidae and dissimilar life histories, the obligate predators Thx. amboinensis and ps. ciliate have apparently converged on a similar mechanical strategy for hunting mosquito larvae,” the authors wrote. This involves suddenly extending the neck to launch the head at its prey, much like a harpoon movement that appears to be generated by building up pressure. reduce in the abdomen of the predatory larva. At the same time, the jaws open and close on impact to capture the prey.
sabers is an “optional” predator that only occasionally feeds on other larvae; they can also live on microorganisms and have therefore developed a distinctly different strategy for catching prey. There is no harpoon-like launch from the head. Instead of, sabers larvae use their tails — known as siphons, since they also act as breathing tubes for the larvae — to sweep prey into their lower jaws.
The seizures of all three species studied in the experiments lasted 15 milliseconds. According to Hancock, that time scale indicates that the behavior is almost reflexive in nature, comparing the blows to swallowing, which involves coordinating several small muscles. “All these things have to work together — we all do it automatically,” he said. “And that’s exactly what these mosquito larvae attacks are supposed to be. It’s a package deal.”
DOI: Annals of the Entomological Society of America, 2022. 10.1093/aesa/saac017 (About DOIs).
