Submitted to: American Journal of Agricultural Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 27, 2014
Publication Date: June 14, 2014
Repository URL: http://dx.doi.org/10.7726/ajast.2014.1006
Citation: Peiris, K.S., Drolet, B.S., Cohnstaedt, L.W., Dowell, F.E. 2014. Infrared absorption characteristics of Culicoides sonorensis in relation to insect age. American Journal of Agricultural Science and Technology. 2(2):49-61. DOI:10.7726/ajast.2014.1006. Interpretive Summary: Biting midge Culicoides sonorensis is the vector that transmits Bluetongue viral disease in domestic and wild ruminant animals. Only female adult insects can transmit the disease. Determination of the age structure of female insect population is important before adopting control interventions in that control of the disease becomes more effective only when the proportion of adult insects is high in the insect population. Present methods of age determination of Culicoides midges are laborious and time consuming. Therefore, we investigated the absorption of mid- infrared light in relation to the age of insects. We noted that systematic changes in infrared absorptions at specific wavelengths occur with the age of insects. As a result, infrared spectroscopy can be used to determine the age structure of insect populations. This will enable rapid determination of the age composition of midge populations which will help implementation of insect control programs to manage dissemination of Bluetongue disease effectively.
Technical Abstract: 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.