Public told: Stop release of invasive species in dengue fight

The Department of Environment and Natural Resources-Biodiversity Management Bureau (DENR-BMB) has warned the public against releasing potentially invasive biological control agents like frogs and fish in swamps and stagnant water to combat dengue.

Instead, the DENR-BMB said the best way to combat and prevent the outbreak of dengue is by maintaining the surroundings clean and free from dengue-carrying mosquitoes.

The DENR-BMB warning came amid the increase in dengue cases in the Philippines that breached the 90,000 mark from January to July this year alone. The Department of Health (DOH) said there were 92,343 cases of dengue from January 1 to July 2, which is 118 percent higher, compared to the 42,294 cases reported during the same period last year.

But the DENR-BMB believes releasing biological control agents like frogs or fish in swamps or stagnant water where mosquitoes breed is not an effective way in fighting dengue.

In a news release, DENR-BMB Director Natividad Bernardino said the practice could even disrupt the ecological balance of the surrounding environment.

Bernardino explained that placing frogs and fish is not an effective solution to eliminating dengue-causing mosquitoes as they have a “diverse diet from plant materials to small invertebrates.”

“While adult frogs eat a variety of things, mosquitoes do not appear to be a major part of the diet of any adult frog or toad,” she explained.

Citing a 2016 study by biologist Jodi Rowley on the effectiveness of frogs to combat the Zika virus, Bernardino said, “Mosquitoes make up only less than 1 percent of the frog’s diet.”

According to Bernardino, the cane toad, known as Rhinella marina, which is being released by some local government units supposedly to combat dengue, is 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.

The Convention on Biological Diversity defines invasive alien species as “organisms that are non-native to an ecosystem, and which may cause economic or environmental harm or adversely affect human health.”

She added that 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.

The proliferation of mosquitoes is largely attributed to environmental conditions that encourage the reproduction of disease vectors. These conditions include dirty surroundings, stagnant man-made canals and interference with natural water flows, and a decline in the quality of wetlands such as streams, creeks, rivers, swamps, and marshes due to solid wastes, invasive plants, and structures.

“The existence of natural predators in these wetland ecosystems, given that they are kept in their natural state or properly maintained, should also help control population of mosquitoes and invasive alien species should never be an option,” she said.

In a joint advisory on the use of frogs and fish to combat the dengue-causing mosquitoes, known as Aedes aegypti, the DENR, DOH, and Department of the Interior and Local Government, stressed that improving the quality of the environment is among the solutions to this water-related vector-borne disease.

The DENR advised the public to keep the surroundings clean, maintain unobstructed water flows of waterways, and keep freshwater ecosystems healthy to remove possible breeding grounds of mosquitoes.