A TECHNIQUE FOR SAMPLING POPULATIONS 

 OF THE MOUNTAIN PINE BEETLE 



Robert W . Carlson and Walter E . Cole 



Suitable sampling techniques are basic to the determination of relations between an insect 

 and the host plant. Development of suitable sampling techniques is part of intensive studies on 

 the population dynamics of the mountain pine beetle, Dendroctonus monticolae Hopk. , in lodge - 

 pole pine, now actively underway in the intermountain area of Utah and Wyoming. 



This paper reports results of research designed to develop a procedure for sampling pop- 

 ulations of the bark beetle during the mature larval and pupal stages. The experimental design 

 tested for variation between sample sizes and shapes, locations on the tree, and trunk diame- 

 ters, as well as testing for the nature of the statistical distribution. 



The study areas selected, though widely separated geographically, were bioclimatically 

 equivalent as defined by Hopkins' Law. One was on the Wasatch National Forest in Utah and the 

 other on the Teton National Forest in Wyoming. The populations sampled in both areas can be 

 considered as epidemic. The Wasatch population has been epidemic in numbers since 1938. 

 The Teton population has shown cyclic tendencies of recurrent epidemics; the present cycle 

 began about 1958. The affected timber stands differ. The Wasatch stand, in general, consists 

 of smaller diameter trees, as old as those in the Teton stand, or older, but less vigorous. The 

 Wasatch population was characterized by low brood density and a current static trend. The 

 Teton infestation showed a definitely increasing trend. 



EXPERIMENTAL DESIGN 



The experimental work in the two stands was replicated as closely as possible. Three 

 variables were measured (counts): (1) density of attack, (2) length of egg gallery, and (3) den- 

 sity of brood. All existing stages of brood were recorded: mature larvae, pupae, and callow 

 adults. Only successful attacks and consequently successfully constructed egg galleries were 

 recorded. 



Sample size: Six sample units were superimposed in a nested fashion at each point sam- 

 pled (fig. 1). The six units were: four rectangular- -1/10, 1/4, and 1/2 sq. ft. --and a sample 

 proportional to tree diameter; and two circular- -1/10 and 1/4 sq. ft. Brood counts were made 

 only for the rectangular samples. 



Sample location: Each tree was sampled at six points: on the north and south aspects at 

 breast height, 5 feet below the height of infestation, and midway between these two points. 



Tree size: Ten trees in each of the following d.b.h. categories per plot were used: 6-9, 

 9-12, 12-15, and greater than 15 inches. Only 13 trees per plot were sampled for brood, 

 because of the stage of brood development and imminent adult emergence. These trees were 

 selected randomly. 



