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Infrared absorption characteristics of Culicoides sonorensis in relation to insect age

Peiris, Kamaranga H. S., Drolet, Barbara S., Cohnstaedt, Lee W., Dowell, Floyd E.
American Journal of Agricultural Science and Technology 2014 v.2 no.2 pp. 49
Culicoides sonorensis, Fourier transform infrared spectroscopy, absorbance, absorption, age, age structure, chloroform, eclosion, females, habitats, insect cuticle, insect vectors, livestock, midges, pathogens, potassium bromide, prediction, proteins, rapid methods, reflectance, vector competence, vector-borne diseases
Biting midges can transmit diseases that significantly impact livestock in many parts of the world. The age structure of an insect vector population determines its likelihood of transmitting pathogens because the older insects are more likely to be infected than younger ones. Understanding the insect age distribution allows for predictions of their behavior, habitat, vector competence and the vector-borne disease epidemiology. Most insect age grading techniques are laborious and slow, thus we investigated the novel application of mid-infrared (MIR) spectroscopy to determine insect age. Female biting midges (Culicoides sonorensis) were anesthetized with chloroform at 1, 4, 7, 10, 13, and 16 days after eclosion. MIR Attenuated Total Reflectance (ATR) spectra of desiccated insects were collected using a Fourier Transform Infrared spectrometer. Transmission spectra of 1, 7, and 13 day old midges were also taken via potassium bromide (KBr) disks prepared with homogenized desiccated insects in each age group. ATR and transmission spectra had identical bands and provide chemical information about the whole insect. The ratio of absorbance of ATR spectra at 1634/1540 cm(-1) showed a systematic change with increasing insect age. A similar trend was also observed in the transmission spectra. These absorption bands may be due to the absorbance of chitins and proteins. Therefore, the observed changes in absorption ratios may reflect qualitative or quantitative changes in insect cuticle and/or body proteins in relation to chronological age. When using absorbance data, insects were classified as young (<= 7 days) with 89.2% accuracy, and old with 63.5% accuracy. These results suggest that infrared spectroscopy may be used to develop a rapid method for age grading of midges.