EVALUATION OF INFRARED THERMOMETRY AS A NONDESTRUCTIVE METHOD TO DETECT FEEDING ON CORN ROOTS BY THE WESTERN CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE)

Infrared thermometry was investigated as a diagnostic tool to detect r oot injury in corn caused by feeding of the western corn rootworm, Dia brotica virgifera virgifera LeConte. Plots were infested with 50-1000 eggs per plant, and the study was conducted over 2 years. Differences (P<0.05) in canopy temperatures were detected in severely infested plo ts in 6 out of 13 days and 7 out of 11 days on which measurements were made during the period of feeding by rootworm larvae in 1989 and 1990 , respectively. Temperature differences between the air and leaves fro m infested plants were never greater than 3.5-degrees-C and usually oc curred within +/- 1-degrees-C. Feeding by rootworm larvae at infestati on levels of less than 200 eggs per plant could not be detected with i nfrared thermometry. Above densities of 200 eggs per plant, increases in canopy temperatures corresponded with increases in the level of inf estation with rootworm eggs, and with reduced plant height, and lower grain yield. Losses in grain yield due to rootworm infestation were ma nifested through smaller cobs and fewer seeds per cob. Kernel weight w as not affected by rootworm feeding. Crop maturity was delayed at infe station levels of 1000 eggs per plant. Elevated canopy temperatures in duced by rootworm feeding were detected through infrared thermometry i n commercial com fields, however differences (P<0.05) in canopy temper atures were noted only after 10 July. Although these data show that el evated canopy temperatures induced by rootworm feeding can be detected with infrared thermometry, some inconsistency in results was observed . Various reasons for why the technique was not more reliable are disc ussed.