30 



.5 10 1.5 20 2.5 30 



SLAB THICKNESS (IN.) 



Figure 2. — X-ray exposure curves for v)ood and bark slabs' (lodgepole pine) of different 

 thickness and moisture content when the X-ray unit is operating at 25kV, 5mA, 

 using a 51-am (1 inch = 2.54 cm) target film distance (from Arrman and Rasmussen, 

 J. Econ. Entomol. 62:631-634, 1969).^ 



Radiographs were processed and then interpreted independently by two observers. A 

 light table, on which all light except for a 15.2-cm2 area had been blocked out, was 

 used for radiograph interpretation. Insects and their identification were recorded on 

 mattex acetate placed over the radiograph. Counts of insects and stages were made from 

 the overlays. 



Data were analyzed by means of analysis of variance. The comparisons made between 

 radiographic and bark-removal sampling were based on averages of estimates obtained by 

 both observers. 



4- 



