Elad Orbach : reverse engineering and enhancing mosquito moth led suction trap

There was the hum of a mosquito, a bite and an itch. I had to do something about it.

I started with one of the cheap 5 V USB mosquito traps sold online. The idea is simple: several LEDs attract the insects and a small fan pulls them into the collection chamber.

After opening it, I found a damaged resistor and temporarily replaced it with a wire. The motor and LEDs are all powered directly from the 5 V USB input.

I could not understand why the outlet had such a dense plastic barrier. It might help keep insects inside when the power is off, but while the fan is running it adds a lot of resistance to the airflow.

There are two common fan designs. Static pressure fans use closely spaced blades to push air through restrictions such as heatsinks. High airflow fans use more open blades to move a larger volume of air through an unrestricted space. This trap used a small inexpensive DC motor and fan, so the dense grille was working against it.

I covered half of the trap with fabric so that I could take repeatable measurements with an anemometer. Removing the white plastic barrier roughly doubled the air speed at the measurement point. That does not automatically mean twice as many mosquitoes, but it confirmed that the original grille was restricting the airflow.

I also measured the LEDs with a spectrometer. Their output was close to 400 nm.

Building a larger version

After seeing how much the original trap could be improved, I built a 12 V version from parts I already had:

A 12 V computer fan

A telescoping air guide

A nominal 3 W, 400 nm LED mounted on a star heatsink

A DC to DC LED driver

A mosquito net

A plastic storage box to hold the insects and diffuse the light

A round cover to guide the airflow

Wooden sticks and hot glue

I also considered replacing the LED driver with a voltage dropping power resistor. The resistor would waste some power as heat, but the heat might provide another attraction source for mosquitoes.

The small motor and low power consumption also make this kind of trap suitable for batteries or a small solar panel.

Mosquito vision

A 1992 study of female Aedes aegypti reported sensitivity from ultraviolet at 323 nm to orange red at 621 nm, with peaks around 323 to 345 nm and 523 nm. The eye has poor spatial resolution but high overall light sensitivity and some ability to distinguish wavelengths.

Lynda E. Muir, Malcolm J. Thorne and Brian H. Kay. Aedes aegypti Vision: Spectral Sensitivity and Other Perceptual Parameters of the Female Eye. Journal of Medical Entomology 29(2), 278 to 281, 1992.

https://www.researchgate.net/publication/21660763_Aedes_aegypti_Diptera_Culicidae_Vision_Spectral_Sensitivity_and_Other_Perceptual_Parameters_of_the_Female_Eye

The LED is close to the edge of the UVA range. Unlike visible light, ultraviolet can expose the eyes without appearing very bright, so I avoided looking directly into it.

Original trap, airflow measurements and DIY version below.