ST IT -L !YA
October 1953 ET1-311
United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine
A TECHNIQUE FOR ESTABLISHING ATTACKS OF ISOLATED BARK BEETLES
By R. 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 scme satisfactory method of inducing isolated beetles to attack the host material. One such method is to insert the insects into nail holes 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 more 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 'Lec.) 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 responses 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 participate in the boring activities.
(1) Hopkins, A. D.
1909. The genus Dendroctonus. U. S. Dept. Agr. Tech. Ser. 17,
Pt. 1, 16 4 pp.
Figur l.-Patten fo scren coes. igur....-.ree.con