The common light trap for monitoring mosquitoes, such as this historical example from the Centers for Disease Control and Prevention, has remained largely unchanged for decades. A new study, however, shows that replacing the incandescent light source with light-emitting diodes of specific wavelengths can improve the trapping of mosquitoes known to carry and transmit malaria. (Photo credit: James Gathany, CDC Public Health Image Library)

By Andrew Porterfield

For more than 50 years, the light trap—an incandescent light source attached to an insect collector—has been the standard for sampling potentially disease-carrying mosquitos. The U.S. Centers for Disease Control and Prevention and other insect control agencies and organizations worldwide have used the light-bulb trap apparatus to attract and count a wide variety of mosquito species, using this data to estimate the risk of disease.

Andrew Porterfield

More recent studies have shown that light-emitting diodes (LEDs), which emit specific wavelengths instead of the entire visual spectrum (and beyond), can be more efficient at attracting mosquitoes, allowing public health and insect control agencies to make more accurate assessments of mosquito populations and better predictions of the spread of mosquito-borne diseases. However, not much data exists on LED light traps and their ability to attract (and allow counting of) the malaria-carrying anopheline mosquitoes.

Malaria is carried largely through mosquitoes in the genus Anopheles, which is made up of 465 species and distributed in tropical, subtropical, and temperate regions of the world. The disease is a major public health problem in Brazil, for instance, afflicting about 300,000 people a year there, and it accounts for 42 percent of all malaria cases in Latin America and the Caribbean region. Worldwide, more than 3 billion people live at risk of contracting malaria, which is spread by the Plasmodium parasite carried by Anopheles mosquitoes.

In a paper published today in the Journal of Medical Entomology, insect biologist Francinaldo Silva and his colleagues at the Federal University of Maranhao in Brazil report on the effects of specific LED wavelengths of anopheline mosquito behavior. They found that the CDC-type light traps, when modified with LEDs emitting two distinct wavelengths, attracted significantly more anopheline mosquitoes than did light traps with incandescent bulbs.

Working on a farm in northwestern Maranhao, Brazil (a semi-humid, tropical area that is partly endemic for malaria), the researchers set up six LED light traps, with two emitting 520 nanometer (green) and another two emitting 470 nanometer (blue) lightwaves. The remaining two traps contained standard incandescent bulbs and were used as a control. Two sampling sites on the farm were selected: one in open pasture with a pig pen and cattle corral and the other that had a pig pen and was next to a forest.

About 1,845 specimens making up eight species of anopheline mosquitos were collected. The green light was most attractive to the mosquitos, responsible for 43 percent of all insects collected. Blue light accounted for 31.8 percent of attracted mosquitos, followed by the control (incandescent) light at 24.9 percent. The LED trap attraction was significantly improved over the incandescent control, even when controlling for phases of the moon, which commonly interfere with incandescent light traps.

Species collected were Anopheles (Nyssorhynchus) evansae at 35.2 percent, followed by Anopheles (Nys) triannulatus at 21.9 percent, Anopheles (Nys) goeldii at 12.9 percent and Anopheles (Nys) argyritarsis at 11.5 percent.

Light traps have marked an improvement over human or animal bait traps, which expose collectors to potential pathogens and introduce human error to sampling techniques. Other methods of attraction have included chemical techniques like carbon dioxide and sweat volatiles. Silva’s study shows that specific wavelength-based light traps can better sample mosquitos that appear attracted to those light waves. LEDs are also cheaper, make for a more efficient light source, are more difficult to break, and have a longer operating life than do incandescent bulbs. The LEDs are also more efficient at delivering light, since incandescent bulbs emit light in infrared regions and expend 95 percent of their radiation as heat, both of which are invisible to most insects. Determining the population of any anopheline mosquito can provide data needed to target eradication efforts that can reduce the incidence of malaria.

“The efficiency of LEDs improves light trapping results, and the use of LEDs as an attractant for anopheline mosquitos should be taken into consideration when sampling anopheline mosquitos,” Silva and his colleagues write.

Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.