DOST Seeks to Control Dengue Mosquito Population via Sterile Insect Technique

By EDD K. USMAN, SDN, Twitter @edd1819, Instagram @bluestar0910, Facebook: SDN — Science, Digital & Current News


— Philippine Nuclear Research Institute (PNRI) doing Sterile Insect Technique (SIT) to control dengue-carrying mosquito.

— Rendering mosquito sterile (baog in Pilipino) to suppress its population succeeded in Guandong, China.

— PNRI plans to released gamma-sterilized male mosquitoes to be released in the wild to mate with Aedes aeqypti, the vector for dengue, chikungunya, and Zika viruses.

(SDN) — DENGUE infections in the Philippines have soared to alarming rate in 2019.

News reports in the past few days showed infections of the deadly virus at over 100,000 victims as of June, and a death rate of over 400 as of July.

Is there a way to contain, control, the national menace?

Is the government up to the challenge posed every year by the female mosquito Aedes egypti, the vector for the deadly disease?

Perhaps, not coincidentally, the dengue carrier is the same insect that causes chikungunya, and Zika ailments.

Filipinos can only hope.

Whether the government has the capability — hopefully, complemented by the private sector — to scale down the number of victims, many of them young, even very young, children, the Department of Science and Technology (DOST) has something up its sleeve.

To be sure, it is not to be taken as a silver bullet against the increase in population of the dengue-carrying mosquitoes and, therefore, a lower incidence of dengue hemorrhagic fever.

Through one of the DOST’s 18 attached agencies, the Philippine Nuclear Research Institute (DOST-PNRI) headed by Director Dr. Carlo Arcilla, the government is conducting a study to reduce the number of dengue-vector mosquitoes through a project dubbed Sterile Insect Technique, or SIT.

SDN — Science and Digital News, spoke with PNRI Scientist 1 Glenda Obra, award-winning head of the institute’s Agriculture Research Section, during the opening on July 17 of the week-long DOST National Science and Technology Week (NSTW) at the World Trade Center (WTC), Gil Puyat Avenue, Pasay City, Metro Manila.

aa PNRI Glenda Obra

Award-winning Scientist Glenda Obra at the PNRI exhibit booth for the DOST National Science and Technology Week (NSTW) 2019 at World Trade Center, Pasay City, Metro Manila. Curious students look at captured female and male mosquitoes. She is leading a research on rendering mosquitoes sterile (baog in Pilipino). (Photo: SDN)

The mosquito SIT Project at the PNRI started a few years ago, and was initially funded by the National Research Council of the Philippines (DOST-PNRI).

Recently, the PNRI has acquired a new gamma irradiator that can sterilized mosquitoes within minutes.

Only the male mosquitoes will be treated with a certain dose of irradiation, Obra said. Only female mosquitoes bite humans and animals.

Male mosquitoes do not bite, they only mate with their female counterparts. Female mosquitoes lay the eggs that soon transform into a full-blown mosquitoes.

The insect produces from 200 to 500 eggs. Mosquitoes’ life cycle may last one and a half months.

At the present time what her team is doing is more on rearing mosquitoes in the laboratory.

aa PNRI audience

A PNRI researcher giving students lessons on mosquitoes at DOST NSTW. (Photo: SDN)

“It’s because increasing the number of mosquitoes (through rearing) is important to Sterile Insect Technique using artificial control environment. Those are the ones we are going to irradiate.

“So, that’s what we are doing now,” Obra says.

Obra pointed out that they have a study on the population dynamics of mosquitoes about their number, adding they want to see the fluctuation of their population on a weekly basis. She said this is a continuing research until they will get the needed sample size in a certain area in Metro Manila.

“It’s important that we learn what species are there, and how many.”

The DOST-PNRI scientist said they have completed with forming a colony in the laboratory. “We are (now) rearing mosquito species in the laboratory. We are improving our protocol so that we can produce good quality mosquitoes for irradiation.”

Obra emphasized the importance of having “good quality” male mosquitoes for the SIT project, for release in the wild.

“Good quality” in reference to the SIT means they are “competitive, strong, healthy, as they will compete for the female mosquitoes in the wild to mate with them.”

She said the sterile male mosquitoes need to be in good shape, strong, and healthy because they will compete with the males in the wild for the “love” of the female gnats.

If the SIT mosquitoes are not competitive, they will not get to mate with the female species in the wild. 


PNRI shows that male mosquitoes do not bite. (Photo: SDN)

“If we produce good quality mosquitoes they can compete for the females for mating,” she explained.

“Once everything is settled, like the sterilizing dose, the population dynamics for reference point, and any changes that may occur which we have to remedy, then the irradiation can be conducted.”

She said the number of the mosquitoes to be irradiated and released in the wild (in the experiment area) will depend on the estimate of the population on the field. “So, we need to know the population count so we will know how many insects are there and how many we need to release. We are still studying that.”

Obra noted that SIT is only one tool among many that can be used to control mosquito population.

Brief video of Scientist Glenda Obra, explaining the Sterile Insect Technique. (SDN)

“Our problem is the mosquito transmitting dengue, chikungunya, and Zika. Using this technology, it is sort of like a multi-vaccine because they can be controlled. In case the technique can suppress the population, it can control dengue, chikungunya, and Zika.

“Thus, our aim is to suppress the dengue mosquito vector in the area that we have plans to release.”

Obra said that the three diseases are transmitted by the female Aedes aegypti.

“We already have a proposal for the project, and we want to partner with the DOH (Department of Health).

“The International Atomic Energy Agency (IAEA) is also supporting us.”

Environmental impact

Obra assured that releasing sterile mosquitoes in the wild should not be a cause for worry.

“Sterile Insect Technique is an environment-friendly method of pest control. Released sterile males can not be established in the environment. It is species-specific so it controls only the target pest while sparing the natural enemies.

“Only females bite and transmit the virus. The sterile males will not bite or transmit the virus and will only mate with female mosquito. No offspring are produced in the process, resulting  to population decline.”

It seems the SIT method of controlling the population of mosquitoes is an effective one as shown in a CNN (Cable News Network) report on July 18 this year.

At least for the female Asian Tiger Mosquito population, as reported by CNN’s Ella Hurworth.

She reported on an experiment that rendered mosquitoes sterile conducted by the Chinese government on two islands in the southern province of Guandong.

“The experiment successfully reduced the female Asian Tiger Mosquito population — the main source of bites and disease transmission — by up to 94%, reducing the number of reported human bites by 97%.”

She also cited an experiment by Imperial College of London scientists in 2018 who “used gene-editing tools to render female mosquitoes sterile, while males developed normally and continued spreading the genetic mutation.”

The DOST-PNRI, then, appears to be in the right direction in an attempt to control the population of dengue-carrying mosquitoes.

On July 15, the Department of Health (DOH) declared a National Dengue Alert as the dreaded disease continues to afflict Filipinos in many regions.

Later, the Department of Interior and Local Government (DILG) responded by urging local government units (LGUs) to carry out clean up drives aimed at removing mosquito’s breeding areas.

The DILG said LGUs should implement this  immediately to stop dengue from spreading in their own jurisdictions.

A DOH press release showed the regions that have surpassed the epidemic threshold, such as MIMAROPA (Region IV-B); Western Visayas (Region VI); Central Visayas (Region VII); and Northern Mindanao (Region X).

The DOH also identified the regions that are being monitored because they have exceeded the threshold for alert. They are Ilocos; Cagayan Valley; CALABARZON (Region XIII); Bicol Region; Eastern Visayas; Zamboanga Peninsula; Davao; Bangsamoro Autonomous Region in Muslim Mindanao (BARMM); and Cordillera Administrative Region (CAR).

In the health department’s figures it was shown that from January 1 to June 29, 2019, most of the cases were traced in Western Visayas with 13,164; CALABARZON, 11,474; Central Visayas, 9,199; SOCCSKSARGEN, 9,107; and Northern Mindanao, 8,739.

“Dengue cases nationwide now reach a cumulative figure of 106,630 (as of July 15). This is higher 85% compared to the same period last year (57,564),” the DOH said.

“Dengue is a viral disease with no known vaccine or specific antibiotics.”

Dengue affliction, it added, has signs and symptoms that include “severe headache, pain behind the eyes, severe joint and muscle pain, fatigue, nausea, vomiting, and skin rashes.”

From the DOH website, the 4S strategy is still what it describes as the “most effective way to prevent dengue:”

  • Search and destroy mosquito breeding places,
  • Self-protective measures like wearing long sleeves and use of insect repellent,
  • Seek early consultation on the first signs and symptoms of the disease, and
  • Say yes to fogging if there is an impending outbreak.

“Dengue is preventable through the 4S strategy and early detection. Do the 4S and know its signs and symptoms,” Health Secretary Francisco T. Duque III said, as he strongly called on the public to do their share.

“We have already acquired a new irradiator for mosquito through assistance of IAEA, which will be operational by the end of the year,” said Obra, who won, along with Science Research Specialist Sotero Resilva, and Head of PNRI Irradiation Services Section Luvimina Lanuza, the 2017 Presidential Lingkod Bayan Regional Award given by the Civil Service Commission (CSC) as part of the Mango Weevil Research Team that improved the quality of Filipino mango exports. (SDN)

Featured image of a female mosquito sucking blood courtesy of Skeeze on Pixabay.

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