REAL-TIME X-RAY INSPECTION OF WHEAT FOR INFESTATION BY THE GRANARY WEEVIL, SITOPHILUS GRANARIUS (L.)

A high-resolution real-time x-ray imaging system was assembled using a low-energy, high-current x-ray source, a low-energy x-ray image intensifier, and a CCD camera interfaced to a PC. Overall system resolution was measured at 5 line pairs per mm (100 .m), sufficient for identifying infestations of the granary weevil, Sitophilus granarius (L.) in kernels of wheat. The field of view for imaging of the system was 6 cm2, large enough to image approximately 350 kernels of grain in a single frame. The exposure time for a single frame was 149 ms, yielding a maximum potential throughput rate of around 2500 kernels per second. For this study, 1500 wheat kernels were x-rayed, both on film and with the system described above. Of the imaged kernels, 682 contained infestations ranging in maturity from the egg to the adult life stage of the granary weevil, while 818 were uninfested. Both film and digital images were presented to human subjects to compare recognition of the infested kernels. Overall recognition results averaged 84.4% for the images from the intensifier system vs. 90.2% for the film observations. However, when considering only infestations more advanced than the 3rd larval instar, errors for both sets of images fell below 2% and were not significantly different.

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