Generales

In an attempt to find effective methods for reducing vector populations, researchers from Universidad de Antioquia and the Medellín-based CES University, are currently exploring alternative strategies for controlling Aedes aegypti mosquitoes. Overall results are satisfactory.

Researchers from UdeA and CES University recently conducted a series of field studies to test the effectiveness of ovitraps in reducing mosquito populations. Ovitraps are devices intended for controlling the populations of mosquitoes that carry diseases such as dengue fever and chikungunya. The study took place in several areas of Medellín and Colombia’s Urabá region, an area known for mosquito-borne diseases. 

Pregnant Aedes aegypti mosquitoes, a primary carrier of chikungunya virus, prefer to lay eggs in containers that hold clean, stagnant water including water tanks, rain buckets and vases. Ovitraps are cylindrical containers made of plastic that mimic ideal egg-laying conditions. The traps are filled with water as well as an insecticide that prevent the eggs from reaching the larval stage.

The researchers evaluated to what extent ovitraps can help reduce mosquito populations and thus lowering the spread of chikungunya.

Mosquito traps

The lack of effective vaccines against dengue - a disease that in 2014 killed at least 88 people nationwide -, and chikungunya - an incapacitating, nonfatal disease with high morbidity rates – has led to explore alternative prevention methods such as the use of insecticides and elimination of breeding sites.

Ovitraps are designed to attract female mosquitoes so that they lay their eggs in there. The traps are filled with water and an insecticide that kills both the eggs and larvae.

The average life span of a female mosquito is 35 to 40 days and they can lay up to 100 eggs at a time. They prefer to lay eggs in sites containing clear water and in different breeding sites to ensure the survival of their offspring.

The studies took place in several areas of Medellín and Colombia’s Urabá region, and were led by Marcela Quimbayo, a researcher in the UdeA Medical Entomology Research Group (GEM), and Dr. Gabriel Parra Henao, of the Colombian Institute of Tropical Medicine (ICMT) at CES University.

Field studies

Testing was conducted in the Medellín hillside neighborhood of Aranjuez, an area with high presence of Aedes aegypti mosquitoes and high dengue risk. Ovitraps were filled with either water or an attractant hay infusion. A piece of fabric impregnated with an insecticide (deltamethrin or permethrin) was placed inside the trap so that eggs are laid there.

“The most effective ovitrap is that which contains the largest number of eggs and the lowest number of larvae”, says GEM researcher Marcela Quimbayo. The traps were placed in 30 homes in the Aranjuez neighborhood. Ovitraps containing water and deltamethrin were the most efficient in laboratory tests. In field tests, the ovitraps combining deltamethrin and a 10% hay infusion proved to be the most effective.

“Ovitraps are an effective tool to measure vector populations. Mosquito densities decline or increase depending on the time of the year, however, ovitraps help determine when population will increase,” Quimbayo said.

Between September 2009 and March 2010, 519 ovitraps were randomly placed in several areas at the municipalities of Carepa and Apartadó, Colombia. The traps contained bacillus thuringiensis var. israelensis (Bti), a bacterial agent that kills mosquito larvae when ingested. Vector resistance to some chemical pesticides has led researchers to explore alternative low-cost, environment-friendly measures for controlling mosquito populations.

Studies conducted in Brazil, Cuba and Costa Rica showed that ovitraps are a useful tool to detect the presence of mosquitoes in less time than traditional methods including household index, container index and Breteau index, as these don’t provide reliable information about risk levels for mosquito infestation or vector density.

A study found that while household infestation index was relatively low (below 10%) at certain times of the year, the number of positive ovitraps rose to 60% during the same period. Therefore it is safe to say that traditional measurement methods focus on mosquito populations rather than eggs and larvae.

The results showed that ovitraps are an effective method for measuring mosquito populations and reduce the number of disease-vector mosquitoes. The traps destroyed 502,000 eggs in the region of Urabá.

“Although ovitraps have become a major strategy for controlling mosquito borne-diseases, these devices are not a definitive solution for mosquito problems. These are used as an important tool in community-based dengue prevention programs as they provide useful information about mosquito densities and help create risk maps for dengue occurrence,” the researchers said.