Mosquitoes are the bane of many people’s existence, especially since their bites aren’t just an annoying itch; They can also spread deadly parasitic diseases. Even the larvae of some 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 has captured the unique attack tactics of these cannibal predators in a high-speed video, revealing how they capture their prey with swift strikes, according to a recent study published in the Annals of the Entomological Society of America.
Co-author Robert Hancock, a biologist at Metropolitan State University of Denver, became fascinated by predatory mosquito larvae when he first saw them sting their prey under a microscope during an entomology class in college. He was impressed by the sheer speed of the attacks: “The only thing we saw was a blur at work,” he recalls. Scientists have long studied these caterpillars because they are very effective in controlling populations of other mosquito species. Only one predatory larva can eat up to 5,000 predatory larvae before reaching adulthood.
Hancock first attempted to capture the remarkable behavior of larvae in 16mm film by outfitting a device with a microscope and camera in the 1990s — a process he said led to a lot of films being lost, given the film’s spoiled speed. strikes. Now as a university professor, he was able to exploit all the advances in video and microscopy technology that had been made since his college years to learn more about the biomechanics involved.
Hancock and colleagues focused on three types of mosquito larvae in their experiments. Toxorhynchites amboinensis Native to Southeast Asia and Oceania; The lab obtained adults from Ohio State University and collected the hatchlings weekly from special black plastic egg-laying cups. surophora cilia Larvae were collected from shallow irrigation canals in citrus orchards in River County, Florida. and samples from Sabethes cyaneus It came from a colony first established in 1988 at Ohio State University, where adults and larvae were collected from Mag Island in Panama.
The researchers caused blows by placing predatory larvae in water-well slides, then presenting live prey larvae with jeweler’s forceps. The striking behavior was captured on video using high-speed micro-imaging. They used heat-shield filters for hot, bright flashing lights under the microscope, otherwise the heat would have cooked up the live larvae. The researchers even wore dark sunglasses for protection. Finally, they analyzed the resulting video clips to gain insight into the anatomy of the larvae and the sequence of movements involved in their strokes.
Both TX. ampoenensis And the note. cilia They are what are known as “committed” predators, that is, they need to eat the larvae of other insects. “Despite their different association in different tribes of Culicidae and divergent life histories, predators obligate TX. ampoenensis And the note. cilia It apparently converged with a similar mechanical strategy for predation on mosquito larvae,” the authors wrote. This involves abruptly extending the neck to launch the head toward its prey, like a harpoon—a movement that appears to be generated by the release of pressure built up in the abdomen of the predatory larva.
Septis It is an “optional” predator that occasionally feeds only on other caterpillars; They can also live on microorganisms, and therefore have developed a markedly different strategy for catching prey. There is no harpoon-like launch of the head. While that, Septis The caterpillars use their tails — known as siphons, because they also serve as breathing tubes for the larvae — to sweep prey into their lower jaw.
The strokes of the three types studied in the experiments lasted 15 milliseconds. According to Hancock, this time scale indicates that the behavior is almost reflexive in nature, similar to blows by the act of swallowing, which involves the coordination of many small muscles. “All of these things have to work collectively — we all do it automatically,” he said. “And that’s exactly what mosquito larva strikes should be. It’s a package deal.”
DOI: Annals of the Entomological Society of America, 2022. 10.1093/aesa/saac017 (about DOIs).