Ut5KAKY 
 
 STATE PLANT BOARD 
 
 October 1953 ET-3: 
 
 United States Department of Agriculture 
 
 Agricultural Research Administration 
 
 Bureau of Entomology and Plant Quarantine 
 
 A TECHNIQUE FOR ESTABLISHING ATTACKS 
 OF ISOLATED BARK BEETLES 
 
 By Ro Z. Callaham 
 Division of Forest Insect Investigations 
 
 Recent investigations have shown that pine species show a differential 
 resistance to various species of bark beetles. These investigations have 
 emphasized the need for a study of the responses of different species as 
 they attack the same tree; they also have emphasized the need for a 
 genetic study of certain species of the bark beetle genus Dendroctonus . 
 For undertaking such investigations it would be necessary to have seme 
 satisfactory method of inducing isolated beetles to attack the host mate- 
 rial. One such m.ethod is to insert the insects into nail holes in the bark 
 and to cover the opening with screen to prevent their escape.— This 
 method obviously does not allow the beetles to choose whether or not to 
 attack, or to select either the place of attack or their mates. 
 
 A mjore satisfactory technique recently has been devised and tested 
 in connection with studies of the host factors affecting the success of 
 bark beetle attack. Pieces of 16-mesh metal screen are cut as shown 
 in figure 1, and the straight margins are stapled together to form a 
 cone. The cone apex is left open. Next a portion of the bark on the 
 tree is smoothed with a 1-inch wood chisel, to provide a base for 
 securing the cone. Care should be taken to complete this operation 
 with the least possible disturbance of the natural bark surface to be 
 enclosed within the cone. A thin layer of cotton' is placed on the 
 smoothed bark surface, and the basal margin of the cone is attached 
 by means of staples driven through the screen and cotton into the bark. 
 Finally, the insects are placed in the cage through the open apex of the 
 cone, and the opening is closed by means of staples (fig. 2). 
 
 Western pine beetles ( Dendroctonus brevicomis Lee.) were used to 
 test this technique. Adults that had recently emerged were taken in 
 flight in a rearing room. Sex determinations were made on the basis 
 of general size (from any one piece of brood bark the females were 
 
 1/ Method developed in 1931 by W. D. Bedard, of this Bureau. 
 
UNIVERSITY OF FLORIDA 
 
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 noticeably larger than the males) and the shape of the seventh abdominal 
 tergite as described by Hopkins (1^, p. 36). Care was taken to avoid 
 bunching the insects together, for if given an opportunity the beetles 
 clipped the legs and antennae from their neighbors. 
 
 The object of the experiment was to investigate the behavior re- 
 sponses of single males, single females, and pairs of beetles. No less 
 than six replications of each condition were made. An examination of 
 the galleries made by the paired beetles and the single females revealed 
 normal attacks, egg galleries, and broods. Hence, it seems logical to 
 assume that the technique described herein can be used in studies of 
 host resistance and in genetic investigations of the genus Dendroctonus 
 where attacks and broods of individual pairs of beetles are studied. As 
 expected, single males did not attack. Males observed under natural 
 conditions usually enter the galleries of the females and do not partic- 
 ipate in the boring activities. 
 
 Literature Cited 
 
 (1) Hopkins, A. D. 
 
 1909. • The genus Dendroctonus . 
 Pt. I, 164 pp. 
 
 U. S. Dept. Agr. Tech. Ser. 17^ 
 
 n 
 
 Figure 1. --Pattern for screen cones. 
 
 Figure 2. --Screen cone 
 installed on a pine log.