Mosquitoes are the cause of the dreaded diseases like malaria or dengue, the cases of which continue to rise to alarming levels in the Philippines.
The exponential increase in the population of mosquitoes 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 crawls on your ceiling to hunt for insects, and frog, or palaka that dwells in your favorite potted plant.
Alarming health situation
The Department of Health reported that 92,343 people were infected with the dengue virus as of July 23. This is 118-percent growth from the 42,294 cases recorded during the same period last year
Apparently, this prompted the Department of Environment and Natural Resources (DENR), especially its Biodiversity Management Bureau (BMB), to warn the public against eliminating mosquitoes by releasing biological control agents like frogs or fish, saying that such practice can do more harm than good.
Releasing frogs and fish in swamps and stagnant water to combat dengue, according to Director Natividad Bernardino of the DENR-BMB, can disrupt the ecological balance of the surrounding environment.
Diverse diet
Fish and frogs have diverse diet and are not particularly fond of eating mosquitoes alone, Bernardino said.
Citing a 2016 study by biologist Jodi Rowley on frogs’ effectiveness in combatting 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 news release, the DENR-BMB chief said releasing potentially harmful biological control agents like 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 as invasive alien species that can cause the extinction of other native species, hence, disrupting the ecological balance in a particular ecosystem.
Some local government units, Bernardino said, are releasing cane toad supposedly to combat dengue, not knowing that they are one of the worst invasive alien species in the world
“When introduced to a new environment, non-native species of frogs and fishes may become invasive and alter the biodiversity of the area,” she warned.
New species, new disease
The Convention on Biological Diversity defines invasive alien species as “organisms that are non-native to an ecosystem, and which may cause economic, environmental harm or adversely affect human health.”
True enough, invasive species can negatively affect human health by directly infecting humans with new diseases, serving as vectors for certain diseases, or causing wounds through bites, stings, allergens, or other toxins, Bernardino warned.
Zoonotic diseases—infectious disease that is transmitted between species from animals to humans, or vice versa—can cause a global outbreak that can lead to enormous economic setbacks or worse, declaration of a public health emergency that requires extreme measures, such as community quarantine or lockdowns to prevent death as in the Covid-19 virus.
Timely and appropriate
International biodiversity expert Theresa Mundita S. Lim, executive director of the Asean Centre for Biodiversity said the advisory of the BMB is quite apropos.
The increasing incidence of dengue cases has again brought out various creative means to address this public health problem, Lim told BusinessMirror via Messenger on August 9.
“This is not the first time that authorities have resorted to introducing predators to try to control pest populations. In most cases, this has resulted in unintended tragic consequences, like 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 there were also introductions of the so-called mosquito fish (Gambusia affinis) by a fisheries agency in the past, when she was still with the DENR.
The purpose of releasing the mosquito fish is to feed on mosquito larvae in creeks, but apparently, the move was not properly coordinated with the concerned government agency, such as the DENR-BMB.
“We called the attention of the agency at the time, pointing out that the fish, because of its aggressive and predatory behavior, has been recorded to negatively affect populations of small fish through predation and competition,” Lim, a former DENR-BMB director, said.
Environmental impact study
Lim said before releasing a non-native species, an environmental impact study, including the assessment of the potential or actual impacts of the introduction to fisheries, to biodiversity and to ecosystem services must be conducted.
“In a healthy, balanced ecosystem, there is a good number of natural predators that keeps the population of pest naturally occurring in the area under control,” she said.
According to Lim, managing pests and emerging diseases require an integrated solution that must ensure that the natural predators continue to exist and perform their ecological functions.
Habitat protection, reducing threats
She said a variety of actions—such as natural habitat protection, reducing threats and pollution, and proper waste disposal, such as reduction of breeding grounds for mosquitoes—should be considered before releasing non-native species into the wild.
Lim noted that integrated solutions include addressing poaching and illegal wildlife trade, such as the case of the tokay gecko population some years ago owing to overcollection that has been linked to rising in mosquito-borne diseases, as reported in a paper by Dr. Angel Alcala, et al, in 2012.
Introducing invasive species may not only affect the natural predator population but also result in the predation and depletion of other vulnerable species that are not the target pests intended for control, she warned.
According to Lim, there must be an institutionalized coordination mechanism among the different sectors that will take into account links between public health, domestic and wild animal health, and environmental health in the planning and implementation of a prevention program.
‘Destroy’ breeding ground
For his part, Gregg Yan, founder of Best Alternatives Campaign, said there are more ways in fighting dengue. One is by destroying mosquitoes’ breeding ground.
“The best way to fight dengue is to leave as few places for mosquitoes to breed. This means removing stagnant pools of water or vessels that can collect rainwater in and around our homes,” Yan told the BusinessMirror via Messenger on August 9.
According to Yan, biological control mechanisms, such as releasing fish in waterways, have proven somewhat effective in curbing mosquito populations in other countries.
“However, Best Alternatives cautions against doing this locally, because the fish used are usually not native to a particular country, like the guppies, mollies and mosquito fish introduced in Philippine waterways to eat mosquito larvae,” Yan added.
‘Green’ control measures
For biological control mechanisms to be truly “green” then it should have as few unintended impacts on the environment as possible, he said.
“We recommend conducting research on native species that eat mosquito larvae. They need not be fish. Many of our native bats, lizards, and amphibians also love making a buffet out of mosquitoes,” he said.
“So the next time you see a ‘gross-looking’ gagamba or butiki on your wall, please think twice about killing it. It might have been protecting you from dengue or malaria all along,” he said.
Image credits: Wikimedia, Wikimedia Commons