Use of a Miniature Optical Engine for Age Classifying Wild-Caught Coquillettidia perturbans in the Shortwave Infrared Region

Near-infrared spectroscopy (NIRS), coupled with modeling and chemometrics, has been used to age grade anopheline and aedine mosquitoes; however, NIRS has not been widely used in field studies to assign mosquitoes to age classes. One reason is the relative cost of NIRS spectrometers. We developed a spectrometer system incorporating a miniature optical engine generating spectra in the shortwave infrared region, calibrated it using laboratory-reared Aedes aegypti, and evaluated its utility to age grade wild-caught cattail mosquitoes, Coquillettidia perturbans. As a refinement of the method, we compared a scoring system based on spectral data point outliers with the typical chemometrics that have been used with NIRS. This inexpensive system (<$3,600) could reliably discriminate between age cohorts of mosquitoes and has the potential for more detailed age grading. Laboratory-reared Ae. aegypti demonstrated a decline in the fraction of spectral outliers with age, and field-collected Cq. perturbans similarly demonstrated such a decline (greater in newly emerged mosquitoes) with date of collection, consistent with their univoltine demography in Massachusetts. We conclude that an economical NIRS system may be able to provide a quantitative dichotomous (young versus old) assessment of field-collected mosquito samples, and thereby may be used to complement abundance-based analyses of the efficacy of adulticiding applications.