Rearing mosquito colonies for research's sake

Menchie Manuel: Rearing mosquito colonies for research’s sake
By Tan Ruilin, Writer

Manuel in the breeding section of the mosquito insectary where she works. // Credit: Norfaezah Abdullah, Duke-NUS

Few people would spare half a thought for a mosquito’s welfare—mosquitoes being one of the species that most of us would be gladly rid of. That is, unless you are Menchie Casayuran Manuel.

Deep within the controlled confines of the Duke-NUS insectary, Manuel begins her day with a routine that is anything but ordinary.

Tasked with the meticulous care of thousands of mosquitoes, her daily diligence is crucial in the fight against some of the world’s most dangerous viruses.

For Manuel, these tiny creatures are not merely pests, but pivotal players in scientific breakthroughs that could one day save countless lives.

Describing caring for the mosquitoes that she rears, Manuel said, “It’s me and only me.”

Every day, Manuel—the laboratory technologist at the Duke-NUS Insectary—monitors the laboratory and oversees her blood-sucking charges. When she rears a colony, she must adapt her workflow to the mosquito lifecycle. For example, when she has mosquitoes in the pupae stage, she must come the next day to collect them, transferring them safely into the cages before they can emerge from the pan as flying mosquitoes.

Mosquito pupae growing in a larval pan in the insectary. // Credit: Menchie Casayuran Manuel, Duke-NUS

“These skills are not easy to learn, and we really need time, focus and a steady hand to collect them—especially as they are so tiny. So I took a lot of time to practice dissecting mosquitoes.”
Menchie Manuel

The insectary facility, managed by Manuel since 2013, is positioned to support researchers who are interested in conducting studies on mosquito-borne viruses such as dengue, Zika and chikungunya. In order to better understand the transmission of infectious diseases that are spread by mosquitoes, as well as discover new ways of disease- and mosquito-control, the insectary trains researchers both within and outside of Duke-NUS, supplying them with mosquitoes and helping them to analyse, quantify and process their samples.

Working in a mosquito insectary presents several challenges. Manuel points out, in particular, that maintaining the precise environmental conditions necessary for the insects to thrive is tricky. Mosquitoes require very specific temperature, humidity, and lighting levels, and even minor fluctuations in any of these can disrupt their life cycle.

A one-woman show, Manuel specialises in the rearing, maintenance and handling of mosquito colonies for research purposes and is responsible for the care of mosquitoes throughout all life stages, from eggs to larvae, pupae, and adults. And to complete the circle of life, she harvests the eggs from adult colony cages, drying them so they can be preserved for later use. The dried eggs remain viable for two to three months and it is this store on which she relies to restart her work when she returns from a long vacation. Because before she goes on a long vacation, she must kill all the mosquitoes and disinfect everything in the laboratory.

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Besides ensuring the mosquitoes’ health and availability for experiments, Manuel is skilled in laboratory techniques such as dissection, species identification, intrathoracic inoculation (a highly effective means of infecting mosquitos with a virus that is injected directly into their chest cavity) and mosquito oral infection, which she does in between maintaining the strict biosafety protocols of the lab—including sterilising the laboratory, ensuring the proper disinfection of equipment and workspaces, and managing inventory to keep supplies well-stocked.

Among her wide-ranging duties, testing both her logistical acumen and fine motor skills, Manuel’s favourite part of the job is also the most challenging.

“Dissection remains the hardest part—some of the requestors want us to collect parts such as the mosquitoes’ salivary glands, which are very fine and minute organs, invisible to the naked eye. These skills are not easy to learn, and we really need time, focus and a steady hand to collect them—especially as they are so tiny. So I took a lot of time to practice dissecting mosquitoes.

However, my favourite part of the job is applying and refining my technical skills, particularly in dissection, intrathoracic inoculation and molecular techniques, where the precision and detail required allow me to fully utilise my expertise. Ultimately, it’s hugely rewarding to see my skills directly contribute to the success of research and disease prevention efforts.”

An adult mosquito enclosure of Aedes aegypti mosquitoes in the insectary. // Credit: Norfaezah Abdullah, Duke-NUS

Finally mastering the art of dissection, Manuel states, gave her such a full-fledged feeling of satisfaction. Taking two to three months to become adept at it—practising whenever she had time to spare from her duties in the insectary—was a process of repeatedly refining her skills.

“When I was not yet an expert, requests for collecting salivary glands, or the mid-gut, would be time-consuming—it would take me several minutes to get the salivary glands. Now, however, it takes me mere seconds.” The dissections are completed using a microscope, needle and forceps.

It’s a constant flurry of activity in the insectary. The colonies are replaced every month, with Manuel hatching a new batch of mosquitoes to produce eggs. The reasons for this are twofold: If a single colony is used for a long time, micro-organisms will, too, start to breed. And, in any case, a mosquito’s lifespan is just that—about a month, with male mosquitoes living much shorter than female.

As part of the insectary’s stringent quality control, Manuel checks each batch of mosquito eggs for mould. If she spots any mould, the eggs are immediately destroyed so they cannot contaminate the work // Credit: Norfaezah Abdullah, Duke-NUS

Coming into the role 12 years ago, Manuel learnt everything on the job at Duke-NUS. She recalls that, when she was interviewed, she was asked just one pertinent question: “Are you willing to work in a room full of mosquitoes?”

Memorably, in the course of her training, Manuel was personally instructed by dengue research expert Professor Duane Gubler, the founding director of the School’s Emerging Infectious Diseases Programme, in the skills needed to perform the delicate work required for many of the processes involved in inoculating and processing the mosquitoes. During her crash course on working with mosquito-borne viruses, Gubler had said, surprising her, “I think you’re ready. Now, let me see how you do intrathoracic inoculation.”

He taught her the importance of hand-eye coordination, with laboratory technologists needing to be extra-cautious not to injure themselves with the needles and forceps that are a necessary part of their trade.

Manuel takes much pride in her dissection skills—extremely fine work, all done by hand, aided by a microscope. // Credit: Norfaezah Abdullah, Duke-NUS

Incidentally, this was not Manuel’s first role handling dangerous pathogens—though it was her first time working with mosquitoes. She had previously cultured flesh-eating bacteria from fish samples for her work in the Philippines. To be able to handle life-threatening pathogen samples requires a strict adherence to protocols, and a keen conscientiousness.

Her curiosity also stemmed from the fact of working with the stinging insects themselves.

“Everyone hates them, but I’m here caring for them, feeding them… it’s fascinating. I was intrigued by the idea of working with tiny creatures that can have such a big impact on human health.”

Chief amongst the many notable aspects of rearing mosquitoes is their unique diet. Manuel feeds the insectary mosquitoes pig blood, specially obtained free of pathogens—unless, of course, a study calls for the food supply to be prepared with a virus. The mosquitoes are fed through a Hemotek feeding system, that offers mosquitoes their blood meal just how they like it: warmed to around 37 degrees Celsius, and sucked up by inserting their proboscis through an artificial skin-like membrane made from pig intestines.

In these pictures, Manuel prepares a Hemotek unit with fresh blood to feed the adult mosquitoes in the facility. // Credit: Norfaezah Abdullah, Duke-NUS

A deep love for research keeps Manuel motivated and moving—in particular, learning about how mosquitoes and their interactions with flaviviruses affect public health. Her goal for the facility is to maintain the highest standards of accuracy and efficiency in operations—a crucial factor in being successful. To advance the understanding of vector-borne diseases, Manuel strives to provide healthy mosquitoes and a safe environment.

With much affection and dedication, Manuel describes her role:

“Being in Duke-NUS helped me a lot. It’s like Duke-NUS is already my husband—my partner in raising my kids. It made taking care of them possible. That’s why I love my job. In addition, I also have very nice colleagues, and extremely supportive bosses.”

Outside of the lab, Manuel’s personal life is thriving: she has three children, all in their twenties, a much-loved daughter-in-law, and a four-year-old grandchild, with whom she spent much time during a month-long trip to the Philippines early this year.

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To decompress after work, or for the sheer pleasure of it, Manuel likes to pick up a racket for a game of tennis. And when she needs something more meditative, she opts for leisurely walks at MacRitchie Reservoir.

“Sometimes, I am enjoying myself so much, I lose track of time and continue walking for much longer than I planned to! And no—mosquitoes don’t bother me much, because I don’t stay stationary for long.”

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Manuel with her three children, daughter-in-law and grandson. // Credit: Menchie Casayuran Manuel

Whether it’s playing tennis, taking a walk or making strides at work, Manuel clearly takes not being a stationary target to heart. What keeps her moving?

It might well be the one thing that Manuel says the role has taught her—dedication. “Here in the insectary, we need to be dedicated, and focused, as you’re dealing with viruses. You must be mindful of every detail for the safety of everyone involved.”

Each day, Manuel leaves the lab knowing she has contributed to something larger than herself. Her meticulous care for these tiny vectors of disease is not just a job—it’s a commitment to public health and scientific progress.