Mosquitoes are the bane of many people’s existence, especially since their bites are not only annoyingly 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, and revealed how they capture their prey with lightning-fast strikes, according to a recent study published in the journal Annals of the Entomological Society of America.
Co-author Robert Hancock, a biologist at Metropolitan State University in Denver, became fascinated by predatory mosquito larvae when he first saw them preying on them under a microscope during an undergraduate entomology class at the university hit He was impressed by the sheer speed of the attacks: “The only thing we saw was a blur of action,” he recalled. Scientists have long studied these larvae because they are so efficient at controlling the population of other mosquitoes. Just one predatory larva can devour as many as 5,000 deer larvae before they reach adulthood.
Hancock first attempted to capture the larvae’s distinctive behavior on 16-millimeter film by destroying a setup with a microscope and a camera back in the 1990s — a process he said took too much lost film led, due to the blistering speed of the strike. Now a college professor, he was able to take advantage of all the advances in video and microscope technology that had been made since his undergraduate years to learn more about biomechanics.
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 receives adults from Ohio State University and collected instars weekly from special black plastic cups for laying eggs. Psorophora ciliata The larvae were collected from shallow irrigation ditches in the citrus groves of River County, Florida. In samples of Sabethes cyaneus came from a colony first established at OSU in 1988, with adults and larvae collected from Maje Island in Panama.
The researchers induced strikes by placing the predatory larvae in well slides with water, and then presenting live predatory larvae with jeweler’s tweezers. The striking behavior was captured on video using high-speed microcinematography. They used heat protection filters for the hot and bright lights under the microscope, because otherwise the heat would have cooked the live larvae. Even the researchers donned dark sunglasses for protection. Finally, they analyzed the resulting videos to gain insight into larval anatomy and the sequence of movements involved in their strikes.
Both Tx. amboinensis in the PS. ciliata they are what are known as “obligate” predators, meaning they must consume the larvae of other insects. “Despite their different relationships in different tribes of the Culicidae and different life histories, the obligate predators Tx. amboinensis in the PS. ciliata have apparently converged on a similar mechanical strategy for preying on mosquito larvae,” the authors wrote. This involves suddenly extending the neck to launch the head at its prey, like a harpooning motion, which through the Release of the built-up pressure is generated in the abdomen of the predatory larvae. At the same time, the jaws open, snap shut on impact, to catch the prey.
Sabethes is a “facultative” predator that only occasionally feeds on other larvae; they can also live on microorganisms and thus have developed a distinctly different strategy for capturing the cat. There is no harpoon-like launch from the head. Instead, Sabethes The larvae use their tails—known as siphons because they also function as breathing tubes for the larvae—to draw prey into their mandibles.
The strikes of all three species studied in the experiments lasted 15 milliseconds. According to Hancock, this time scale shows that the behavior is almost reflexive in nature, as compared to the act of swallowing, which involves the coordination of several small muscles. “All these things have to work at the same time – we all do it automatically,” he said. “And that’s exactly what these mosquito larvae have to be. It’s a package deal.”
DOI: Annals of the Entomological Society of America, 2022. 10.1093/aesa/saac017 (About DOIs).