By Crystal Simmons
Hidden among the leaves of a bromeliad, a merciless predator awaits its next victim at the Houston Museum of Natural Science’s Cockrell Butterfly Center. Using strong, ant-like jaws to grip its prey, this aquatic hunter feeds on every pest mosquito unlucky enough to hatch in its vicinity. Dubbed the “mosquito assassin,” the Toxorhynchites rutilus mosquito has become an important ally in the war against nuisance mosquitoes.
Anita Schiller, the director of Harris County Precinct 4’s Biological Control Initiative, is at the forefront of mosquito assassin research. In the past seven years, she’s learned the ins and outs of producing these beneficial predators. She and her team now breed the insects out of Precinct 4’s 3,000-square-foot lab and release them into the wild as a natural “backyard” mosquito-control method. She hopes her latest study at the Cockrell Butterfly Center will not only shed new light on mosquito assassin behavior but also raise awareness about their benefits.
“We’re studying innovative ways to produce these insects on a larger scale,” she said. “Our goal is to deploy mosquito assassins in more areas in Harris County. These beautifully colored insects are good for the environment and pose no risk to people or butterflies. This study will give us a better idea of how fast the locally self-sustaining mosquito assassins reproduce and eliminate mosquitoes in a semi-controlled environment.”
Meet the Mosquito Assassin
Mosquito assassins are one of the many living organisms bred through the Biological Control Initiative, a program that fights biting, pest mosquitoes with native plants, insects, and parasites. Precinct 4 Commissioner began the program in 2012 to reduce the county’s reliance on pesticides and to restore native creatures that help control mosquito populations.
Unlike Harris County’s most common backyard mosquitoes – the yellow fever mosquito, Asian tiger mosquito and southern house mosquito — the mosquito assassin doesn’t feed on humans or animals. In its larval form, the mosquito assassin is one of the deadliest predators of its size. But by adulthood, the insect will take flight to live the rest of its life peacefully pollinating plants, never to kill again. These butterflies of the fly world grow about four times larger than their blood-sucking relatives and sport iridescent scales.
So just how deadly are mosquito assassins to their brethren? Depending on the season, larval mosquito assassins will consume between 200 to 4,000 pest mosquitos before pupating. More importantly, they target larval mosquitoes before they can fly, bite, and transmit pathogens that can cause such diseases as dengue, chikungunya, and West Nile.
With 56 different mosquito species in Harris County and no shortage of their ever-present, itchy reminders, it may seem puzzling that mosquito assassins aren’t more prevalent. Unfortunately, habitat loss and pesticides have depleted the native mosquito assassin population. At the same time, breeding these beneficial critters in captivity has also proven challenging.
“Our biggest research-and-development work is figuring out how to make their use economically feasible,” said Schiller. “We want to produce them in large numbers and in cheaper ways.”
Because of their insatiable nature, the insects will cannibalize each other unless they are separated before hatching, Schiller said. Accounting for these behavioral quirks, Schiller’s team has developed a strict rearing protocol published in the Journal of Insect Science. Since implementing the new protocol, the percentage of mosquito assassins that survive to adulthood has increased to 75%, up from 10%.
“A long time ago, we tried rearing them in communal groups the way literature suggested and only had a 10% survival outcome,” said Schiller. “So for every 100 eggs collected, we only managed to produce 10 adults, and that was on a good day. When we began rearing them in isolation, survival rates increased. We were also able to establish more precise rearing parameters, which has allowed us to influence and predict production numbers more accurately.”
Developing cheaper food sources for the insects is also a priority. Because mosquito assassin larvae prefer moving prey, feeding the insects can be labor intensive and costly. Schiller hopes to develop a custom mosquito assassin feed that will result in additional savings.
“No one has been able to produce them in large enough numbers that are also economically feasible, so that has been our goal,” she said. “In my lab, we know the limitations. We can’t release them across the entire United States, but they are useful in the southeastern United States and right here in Harris County. To produce them and use them, we have to have a lot of them.”
Cockrell Butterfly Center Research
In many ways, mosquito assassin research is already paying off, even in small doses. By releasing pregnant females weekly at the Cockrell Butterfly Center during the summer, Schiller was able to establish a self-sustaining population that has reduced pest mosquitoes inside the butterfly center.
“In the laboratory, we can control all the variables, and in the field study, we can’t control anything except the numbers we release,” she said. “But the semi-field study will fill in the gaps. We know the environment within the CBC; we know how many insects we release, and we know about the predators in the CBC. For example, there are a few spiders here that eat mosquito assassins, but it’s nothing like you’d find in the wild.”
Erin Mills, the director of the CBC, has been a strong supporter of the study since Schiller approached the CBC last year. She believes the insects could be ideal for environments like the butterfly center.
“Obviously, in any greenhouse situation, you’re going to have tons of pests because of all the plant life,” said Mills. “A self-sustaining population of mosquito assassins in the butterfly center will not only help control our mosquito population, but it will also spread mosquito assassin awareness.”
For Mills, introducing beneficial insects to the CBC is all part of developing a strong ecosystem in which bugs, plants, and microbes all play a role.
“The butterfly center is definitely a dynamic, living environment,” she said. “It’s not just a museum exhibit. It’s also a living environment.
“For almost any pest insect, there’s going to be a parasite, fungus, or predator that can take care of it for you. We practice that a lot already at the butterfly center. We employ an army of biological control agents in there — ladybugs, lacewings, beneficial nematodes — all sorts of things.”
How Residents Can Help
The public also has an important role to play in mosquito prevention. Schiller encourages everyone to check their yards for any water containers, including unused pools and planters.
“We’re already using mosquito assassins in small-scale efforts, but there’s plenty the average citizen can do to help,” she said. “Something as simple as monitoring your yard for water-filled containers can improve the environment for you, your family, and your neighbors.”