Abstract

A multispectral polarimetric optical detection system with kHz sample rates was implemented to determine mosquito species and sex in flight. This system measures backscattered and extinguished light from mosquitoes at two wavelengths in both co- and de-polarized modes. Two Silicon and Indium Gallium Arsenide sandwiched detectors were used to collect backscattered signals from mosquitoes. These detectors collect co- and de-polarized near infrared (NIR,808nm) and shortwave infrared (SWIR, 1550 nm) light. A Silicon photodiode was also used to measure the extinction signal. The backscattered and extinguished signals were sampled at 20 kHz, with a bandwidth of the detector modules at around 4 kHz. This system was used to determine species and sex of five mosquito species (Aedes aegypti, Culex quinquefasciatus, Anopheles gambiae, Anopheles arabiensis and Anopheles quadriannulatus). One of the parameters that can be used for species and sex determination is wing-beat frequency (WBF), see Fig.1. Different parameters such as optical cross-section, melanization and absolute reflectance can be used in addition to WBF and harmonics to determine insects. The fundamental wingbeat frequency of female Anopheles gambiae shown in fig.1 is 527.3 Hz. Moreover, around 5 harmonics overtones are shown in the co-polarized NIR and SWIR signals. Specular reflection contributes to highly co-polarized backscatter, rapid details in the waveform and a content of higher harmonics. This is the reason why the higher harmonics are mainly apparent in the co-polarized NIR and SWIR backscattered signal. We encountered WBF up 950 Hz within the male Aedes aegypti species. The results of the study showed that it is possible to distinguish between species and sex when combining these parameters. The signals presented here could in principle be retrieved remotely by lidar on landscape scales [1,2]. This would allow mapping the individual movement behaviour of flying insects, identified down to sex and species. This revolutionary technique can have a huge impact on some of today’s greatest challenges: First, studying disease vectors (e.g. mosquitoes with malaria) will help researchers to understand their behaviour and apply vector control methods more precisely spatially and temporally. Second, Mapping insect pest crops will aid farmers to react timely on an incoming attack. Third, this new technique will help researchers worldwide to understand complex and detailed movements of almost all flying insects. Until now, this has been impossible to do with manual monitoring methods like traps and nets.

© 2017 Optical Society of America