Nuclear magnetic resonance spectroscopy for studying the development and detection of the grain weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae), within wheat kernels

A novel non-destructive method was devised for studying the development of insects hidden within individual wheat grains using a standard nuclear magnetic resonance (NMR) spectrometer. The development of Sitophilus granarius (L.) at 25°C and 70% RH was studied from egg-laying to emergence by NMR, X-radiography and weighing. The results of the three methods correlated quite well. Neither the NMR nor the X-radiation appeared to harm the insects. The NMR method did not usually detect the insects until they were in the third larval instars, but after that the areas of the two NMR peaks observed with each infested grain followed a pattern which was readily interpreted in terms of the insect development. The major NMR peak was found to be due almost wholly to water and the minor peak to lipid, and the size of the major peak obtained with adults was close to that expected on the basis of their water content. The movement of some of the insects within the grains was observed for short periods and appeared to be characteristic of each developmental stage. Preliminary work with a less sophisticated NMR machine showed that it is possible in a single scan to detect ten grains infested with S. granarius larvae in a batch of 500 grains, but further work is required to see whether single eggs can be detected. The results obtained in this study were sufficiently encouraging for a wide variety of other areas to be suggested in which use of NMR might help to solve some entomological problems.