For the first time, scientists have revealed how hungry mosquito larvae pursue and kill prey in aquatic ecosystems using stunning high-speed video footage.

This new study, which was just published in the Annals of the Entomological Society of America, sheds light on behavior that has previously proven to be too small and too quick to investigate.

Mosquitoes spend their early years under water, whether it’s in flood plains or flowerpots, before they learn to fly. Some mosquito larvae are predators that prey on other aquatic insects, including other mosquito larvae, but the majority of mosquito larvae consume algae, bacteria, and other microbes.

For a large portion of his career, Robert G. Hancock, Ph.D., professor of biology at Metropolitan State University of Denver, has been fascinated by these predatory animals. As an undergraduate, he first saw their strikes under a microscope in a medical entomology class.

“It was so incredibly fast,” he remarks. “The only thing that we saw was a blur of action.”

Hancock and his students have been able to pause that motion and get a glimpse into an universe that no one has ever seen before thanks to breakthroughs in video and microscope technology over the years.

Hancock provides ten videos of mosquito larvae strikes in Annals of the ESA and examines the anatomical details and actions involved. Five of the videos depict two species, Toxorhynchites amboinensis and Psorophora ciliata, that are obligate predators—that is, their diet requires eating other insect larvae—and whose biology and behavior are highly adapted for capturing prey. These two species use a similar technique to capture prey. The other five films show the Sabethes cyaneus species, which is a facultative predator that eats both microorganisms and occasionally other larvae and has developed a very different method of predation.

Both Toxorhynchites and Psorophora species have larvae that attack prey by abruptly extending their necks and launching their heads away from their bodies and at the prey. When it strikes the victim, its mandibles and several brushes that resemble whiskers spread out and close quickly. According to the researchers, the distinctive, harpoon-like head-propulsion movement appears to be produced by the larva first generating pressure within its abdominal segments and then quickly releasing it.

Hancock remembers being amazed the first time the strike was successfully documented on camera. “I saw it first and my jaw dropped, and it still does every time I watch it,” the researchers says.

Sabethes mosquito larvae lack the mechanism for head elongation. A Sabethes larva snares prey instead by sweeping it toward its head with the help of its tail. As the prey is brought in, the larva expands its mandibles and maxillae (mouthparts that resemble pincers) and clamps onto the prey. Hancock claims that the use of the tail—known as a “siphon” because it allows mosquito larvae to breathe while hanging upside down at the water’s surface—was also unexpected.

In all three of the study’s species, both strike types require roughly 15 milliseconds. Hancock claims that this rate of movement is an indication of a fixed-action pattern, a highly established and nearly reflexive activity. He compared it to the swallowing motion, which requires numerous, tiny individual muscle movements. 

“All of this stuff has to work in concert—we all do it so automatically,” he adds. “And that’s exactly what these mosquito larvae strikes have to be. It’s a package deal.”

The predatory nature of Toxorhynchites and Psorophora mosquitoes is widely documented. Toxorhynchites species, in particular, have been researched as a potential tool for mosquito control because a single Toxorhynchites larva can consume up to 5,000 prey larvae before maturing into maturity. The adult Toxorhynchites and Psorophora species are among the largest mosquitoes in the world as a result of their larval diet. Sabethes cyaneus, on the other hand, are less fearsome predators, but as they get older, they develop broad, feather-like paddles on their legs and an iridescent blue hue.

Hancock says that the initial footage of Toxorhynchites and Psorophora strikes was recorded on 16-millimeter film using a microscope and camera equipment he developed while he was a student at the University of the Cumberlands in the 1990s. He joined the initiative again in 2020 with students from MSU Denver, this time filming Sabethes strikes using a digital high-speed camera set up similarly. Hancock explains that because the lights used to magnify mosquito larvae are so hot and brilliant, heat-protective filters are needed “to not just cook” the larvae and “the darkest sunglasses I could buy” to protect the researchers’ eyes. However, the development of digital cameras has made studying mosquito larvae more simpler and more sophisticated. The new digital camera can take more than 4,000 frames per second, whereas the high-speed film camera could only capture up to 600 frames per second. Hancock estimates that a 32-gigabyte SD card can store around $12,000 worth of film and development.

Hancock has spent the majority of his career on mosquitoes, and he frequently employs them as model organisms in the research projects his students do. The videos, according to him, may help people become more aware of the ecosystems that can be found in even the smallest bodies of water. He claims that this new understanding of how predatory mosquito larvae capture prey can be a tool for “continuing to unveil mysteries of nature around us, especially in anything that’s aquatic.” “Small containers of water that don’t move are primarily the domain of mosquitoes,” he says.

Source: 10.1093/aesa/saac017

Image Credit: Getty

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