Fighting dengue fever? Let native ‘butiki, gagamba, palaka’ do it

Mosquitoes are the cause of the dreaded diseases such as malaria or dengue, whose cases in the Philippines continue to rise to alarming levels.

The exponential increase in the mosquito population can be attributed to a number of factors. This includes the extinction of their natural predators – they can be your friendly neighborhood spider, or gagambang bahay, lizards or butiki that occasionally crawl on your ceiling to hunt insects, and frog, or palaka that lives in your favorite potted plant.

reed toad

Alarming health situation

The Ministry of Health reported that 92,343 people were infected with the dengue virus on July 23. This is an increase of 118 percent from the 42,294 cases recorded in the same period last year.

Apparently, this prompted the Department of Environment and Natural Resources (DENR), specifically the Biodiversity Management Bureau (BMB), to warn the public about eliminating mosquitoes by releasing biological control agents such as frogs or fish, saying that such practices can do more harm than good.

Releasing frogs and fish into swamps and standing water to combat dengue could disrupt the ecological balance of the environment, according to director Natividad Bernardino of the DENR-BMB.

diverse diet

Fish and frogs have varied diets and aren’t too fond of eating mosquitoes alone, Bernardino said.

Citing a 2016 study by biologist Jodi Rowley on the effectiveness of frogs in fighting the Zika virus, Bernardino said that “mosquitoes make up only less than 1 percent of the frog’s diet, referring to the cane toad (Rhinella marina ).

In a press release, the DENR-BMB chief said that releasing potentially harmful biological control agents such as frogs or fish is not a scientifically proven effective solution to get rid of dengue-causing mosquitoes.

Invasive Alien Species

There are frogs or fish species that are actually considered invasive alien species that can cause the extinction of other native species, disrupting the ecological balance in a particular ecosystem.

Some local government units, Bernardino said, are allegedly releasing cane toads to fight dengue, unaware they are one of the worst invasive alien species in the world

“When introduced to a new environment, non-native species of frogs and fish can become invasive and alter the area’s biodiversity,” she warned.

New species, new disease

The Convention on Biological Diversity defines invasive alien species as “organisms that are not native to an ecosystem and that may cause economic or environmental damage or adversely affect human health.”

It’s true that invasive species can negatively impact human health by directly infecting people with new diseases, serving as vectors for certain diseases, or causing wounds through bites, stings, allergens or other toxins, Bernardino warned.

Zoonotic diseases – infectious diseases transmitted between species from animals to humans, or vice versa – can cause a global outbreak that could lead to massive economic setbacks or worse, declare a public health emergency requiring extreme measures, such as community quarantine or lockdowns to prevent death as with the Covid-19 virus.

Timely and appropriate

International biodiversity expert Theresa Mundita S. Lim, executive director of the Asean Center for Biodiversity, said the BMB’s advice is quite good.

The increasing incidence of dengue cases has once again provided several creative ways to tackle this public health problem, Lim told BusinessMirror via Messenger on Aug.

“This is not the first time authorities have resorted to introducing predators to control pest populations. In most cases, this has led to unintended tragic consequences, such as the extinction of wild populations of an entire species, citing the case of the Partula snail in the Polynesian islands, she said.

mosquito fish dilemma

Closer to home, Lim noted that in the past, when she was still with the DENR, there were also introductions of the so-called mosquito fish (Gambusia affinis) by a fisheries agency.

The purpose of releasing the mosquitofish is to feed on mosquito larvae in creeks, but apparently the move was not well coordinated with the government agency involved, such as the DENR-BMB.

“We drew the agency’s attention at the time and pointed out that the fish, due to its aggressive and predatory behavior, has been recorded as negatively impacting small fish populations through predation and competition,” Lim, a former director of DENR-BMB , said.

Environmental Impact Study

Lim said that before a non-native species is released, an environmental impact study should be conducted, including assessing the potential or actual impacts of the release on fisheries, on biodiversity and on ecosystem services.

“In a healthy, balanced ecosystem, there are a large number of natural predators that control the population of pests naturally occurring in the area,” she said.

According to Lim, controlling pests and emerging diseases requires an integrated solution to ensure the survival of natural predators and fulfill their ecological functions.

Habitat Protection, Threat Reduction

She said a variety of actions — such as protecting natural habitats, reducing threats and pollution, and proper waste disposal, such as reducing mosquito breeding grounds — should be considered before releasing non-native species into the wild.

Lim noted that integrated solutions include tackling poaching and illegal wildlife trade, such as the case of the tokay gecko population several years ago due to over-collection that has been linked to an increase in mosquito-borne diseases, as reported in a paper by dr. Angel Alcala, et al, in 2012.

Introducing invasive species could not only affect the natural population of predators, but also lead to predation and depletion of other vulnerable species that are not targeted by pests intended for control, she warned.

According to Lim, there should be an institutionalized coordination mechanism between the different sectors that will take into account links between public health, the health of pets and wildlife and the health of the environment when planning and implementing a prevention programme.

‘Destroy’ breeding ground

For his part, Gregg Yan, founder of Best Alternatives Campaign, said there are more ways to fight dengue. One is by destroying the breeding ground of mosquitoes.

“The best way to fight dengue fever is to leave as few places as possible for mosquitoes to breed. This means removing standing water puddles or ships that could collect rainwater in and around our homes,” Yan told BusinessMirror on Aug. 9.

According to Yan, biological control mechanisms, such as releasing fish into waterways, have been shown to be somewhat effective in reducing mosquito populations in other countries.

“However, Best Alternatives cautions against doing this locally, as the fish used are usually not native to a particular country, such as the guppies, mollies and mosquito fish introduced into Philippine waterways to eat mosquito larvae,” Yan added.

‘Green’ control measures

For biological control mechanisms to be truly “green,” it should have as few unintended effects on the environment as possible, he said.

“We recommend doing research on native species that eat mosquito larvae. It doesn’t have to be fish. Many of our native bats, lizards and amphibians also like to buffet mosquitoes,” he said.

“So the next time you see a ‘rough-looking’ gagamba or butiki on your wall, please think twice about killing it. It may have protected you from dengue or malaria all along,’ he said.

Image Credits: Wikimedia, Wikimedia Commons

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