16 THE BLACK HILLS BEETLE. 



dying or dead trees is about three hundred and forty days. The 

 period of activity — the feeding, growing, and maturing stages — of 

 all broods of a single generation during the first summer is about 

 ninety days — July 15 to October 15 — and about one hundred and 

 fifty days from the time activity begins the following spring — early 

 in May — until the last individual has developed and emerged — early 

 in October. Thus there is a total active period of about two hundred 

 and forty days. The period of inactivity — from about October 15 

 to early in May — is about one hundred and ninety-five days, making 

 the total period of infestation of all broods of a single generation 

 about four hundred and thirty-five days. This, of course, provides 

 for an overlapping of the last broods of one generation and the first 

 broods of the next, during July, August, and September. 



NATURAL AND ARTIFICIAL INFLUENCES. 



DROUGHT AND COLD. 



It has been a common belief that the dying of the timber is caused 

 by drought, but it is now clearly demonstrated that wherever the 

 Black Hills beetle is abundant it kills the healthiest trees under all 

 conditions of dry and wet seasons, moist or dry soils, north or south 

 slopes, ridges, etc. It has also been demonstrated that it can with- 

 stand a temperature of 30° to 40° F., or more, below zero. 



LIGHTNING. 



It has been found that trees struck by lightning, or at least those 

 struck in summer, are usually attacked by this beetle, and that 

 such trees serve to perpetuate the species at times when it does 

 not occur in sufficient numbers to kill trees on its own account. 

 Such trees also serve to support the natural enemies of the beetle, 

 including insects, diseases, and birds. 



STORMS. 



Storm-felled living trees also serve as emergency breeding places, 

 and if the storm occurs at the proper time in the year to make the 

 conditions especially attractive to the beetles when they are flying, 

 they may be attracted for long distances. This concentration of 

 scattering forces breeding in felled timber may form the nucleus for 

 a destructive invasion. This has been demonstrated from time to 

 time in Europe, where even secondary enemies of the genus Tomicus 

 have been thus enabled to multiply in such great numbers as to 

 attack and kill living forests. 



FIRE. 



Our observations so far have failed to reveal much evidence that 

 this species will breed in trees injured or killed by fire in sufficient 



