Large Aperture Optoelectronic Devices to Record and Time-Stamp Insects’ Wingbeats

Abstract

Recording and analysis of wildlife sounds with regard to monitoring biodiversity is a developing trend in ecology. Automatic audio-based units are commonly used to record field vocalizations of birds, bats, cetaceans and amphibians. The wingbeat of insects produces audible but feeble tones. Practical automatic recording units for the wingbeat of insects are still pending. In this work we present a complete system to record the wingbeat of insects based on large aperture optical sensors that turn the light fluctuations (caused by the partial occlusion of light from the wings) into sound. Wide apertures are useful when tracking the movement of fast flying insects and the full motion of the beating wing in the case of tethered insects. The system detects a wingbeat event, auto-triggers the recording process, time-stamps the event and stores the permanent record in-situ. When the sensor is inserted in an insectary it effortlessly produces massive datasets of wingbeat recordings. We discuss implications for novel studies that are impractical to carry out manually, as they involve large numbers of insects. We also suggest potential applications such as smart insect traps that count, recognize and alert for the presence of insects of economic and public health importance.

Affordable Bimodal Optical Sensors to Spread the Use of Automated Insect Monitoring

“…In [21], we presented an approach that is based on modulating the insect wingbeat signal to high frequencies, cleaning the lower frequencies contaminated with all sorts of electromagnetic interferences, and demodulating back the insect's frequencies. This approach is kept in the new recorder as this equipment needs to function in laboratories that have several sources of optical and electromagnetic interference.…”

“…The benefit of a large receiving aperture compared to a single LED or 1D array of diodes is that fast-flying insects spend more time in front of the PV and, therefore, offer more information on the flight process. The PV of the sensor reported in [21] is a volume of 70 mm × 59 mm × 11 mm, whereas in the setting of Figure 2, we have a cylinder π × 25 2 mm 2 × 70 mm, regarding the extinction mode and π × 25 2 mm 2 × 50 mm for the scatter mode. Both types of receivers (light guide and Fresnel lenses) have the advantage of having a smooth, compact, surface; there are no gaps in the receiving surface of both sensors that could potentially lead to false frequencies when a fast insect passes through the PV.…”

“…The construction of the sensor becomes easier, perfectly repeatable, and more compact. A Fresnel lens provides collimation of light, and in Figure 1, we use a single LED as an emitter and a single photodiode as a receiver as opposed to [21], where 11 photodiodes make a linear array for receiving the light and 42 LEDs make an array that emits a light plane with the help of a diffuser. Using a single photodiode results to small capacitance and lesser noise in the transimpedance amplifier (TIA).…”

“…Using a single photodiode results to small capacitance and lesser noise in the transimpedance amplifier (TIA). Due to collimation, we do not face the loss of optical power that can be a subsidiary effect of using a diffuser as in [21]. Therefore, one needs much less power to achieve the same SNR.…”

“…Moreover, both at the emitter and the receiver of light, we make use of cost-effective acrylic Fresnel lenses that are able to provide collimated light and a probe volume (PV) that allows the reception of high-quality wingbeat recordings of fast-flying insects. The advantage of the Fresnel lens compared to a light guide used in [21] is significant as collimation of light provides better signal to noise ratio (SNR) at lower power consumption and allows the construction of a more compact and easier to assemble sensor in comparison with a light guide. Acrylic lenses are cost-effective compared to other kind of lenses used in laser applications.…”