THE PINE INVESTIGATION. 411 



parasitic and predaceous insects as well as the injurious ones, 

 are destroyed. 



Birds may render valuable service however, in the begin- 

 ning of an outbreak of destructive bark beetles, especially 

 when there are but few trees infested ; since then their thor- 

 ough work would reduce the number of the bark beetles suffi- 

 ciently to materially check their progress, if not prevent entire- 

 ly further ravages by them. 



DISEASES, CLIMATIC CONDITIONS, ETC. 



The subject of diseases has been fully discussed on another 

 page, as has climatic and other unfavorable conditions. 



FRIENDLY ELEMENTS WHICH FAVOR THE MULTIPLICATION OF 



THIS INSECT. 



A succession of dry summers and warm winters with some 

 general mjun T to portions of the coniferous forests by snows 

 and wind storms, are probably the most favorable conditions 

 for the starting of an invasion by this destructive bark beetle. 

 It also has friends in the parasites of its insect enemies ; as, for 

 instance the parasites of Thanasimus dubius (The American 

 bark-beetle destroyer). This insect as I have found, is attack- 

 ed by at least two parasites; one, an undetermined Ichneu- 

 monid which infests the living larvae and pupae _and develops 

 in the pupa case of its victim, in which it makes its cocoon. 

 Another is an undetermined Tachinid somewhat less in size 

 but resembling the common house fly, which develops in the 

 body of the living adult. 1 succeeded in rearing one of these 

 flies from a larva which emerged from the abdomen of an adult 

 T. dubius, bi.t the wings did not develop sufficiently to enable 

 it to be identified. 



Birds are friends of the bark beetle so far as they feed upon 

 their enemies, and as 1 have observed, wood-peckers are quite 

 fond of the pupae, larvae, and adults of the European Clerid in 

 its native forest, and of the American CJerids in our own for- 

 ests. 



