RESULTS AND DISCUSSION 



An evaluation of the radiographic method of sampling mountain pine beetle popula- 

 tions was based on both statistical and operational considerations. 



Population estimates . --Assuming negligible location effects, no significant differ- 

 ence at the 0.05 level of probability was revealed among population estimates obtained 

 by using the bark-removal method and estimates made from radiographs for any of the 

 three sample dates (table 1) . One source of difference was noted between estimates 

 obtained by the two methods for the first sample; eggs could be counted in bark samples, 

 but not on radiographs. As observed previously (Amman and Rasmussen 1969), radiograph- 

 ing mountain pine beetles through wood precluded detection of the slight difference in 

 density of eggs. Eggs of the western pine beetle have been seen on radiographs when 

 only bark was radiographed (C. J. DeMars, personal communication July 27, 1973). The 

 authors detected no significant difference between methods for estimates of centimeters 

 of egg gallery nor of the number of gallery starts. Therefore, estimates from radio- 

 graphs appear to be comparable to those obtained by bark-removal samnling. 



Comparisons of estimates made from radiographs by the two observers revealed no 

 significant difference for brood populations and centimeters of egg gallery (table 2) . 

 However, the observers gave significantly different estimates for the numbers of gallery 

 starts (P <0.01). With the exception of gallery starts, observer differences are small 

 and adequately trained observers can be expected to give comparable estimates from 

 radiographs . 



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