CLASSIFICATION AND DESCRIPTION OF COMMON INSECTS 343 



The systems of tunnels show much variation in shape but are often 

 distinctive of the individual species. They may be simple longitudinal, 

 simple transverse, irregular elongate, irregular short, forked, radiate, 

 cave, pith or ambrosia. In some forms the egg-tunnels originate from 

 a small cavity, the nuptial chamber, at the base of the entrance hole. 

 The eggs are laid in niches along the sides of the egg-tunnels, and the 

 larvae make slender mines leading away from the egg-tunnels. At the 

 ends of these mines are the enlarged pupal cells. The adult beetles, 

 in emergence, bore round holes through the bark. 



With most of the destructive bark-beetles, there is but one brood, 

 or a partial second one, each season. They pass the winter as adults 

 and larvae in the dying trees entered by the parent adults early in the 

 same season. 



While most of the bark-beetles breed in dying and dead trees, 

 some species attack sound trees. The latter are, therefore, called 

 "primary" and the former "secondary" enemies. Some species, how- 

 ever, fall into both classes as they are known to attack both sound 

 and dead and dying trees. 



Natural Control. — Several natural factors operate in checking the 

 development of bark-beetles. These are {a) weather conditions, such 

 as cold and wet seasons; {b) certain hymenopterous and mite parasites; 

 (c) certain predaceous beetles; {d) wood-peckers; and {e) certain para- 

 sitic fungi. 



Control Measures. — ^Epidemic and sporadic outbreaks often occur 

 in spite of the operation of the natural control factors mentioned above,- 

 especially in districts swept by fires, or subjected to careless lumbering 

 operations where much "slash" is left. If, however, the slasli is 

 burned in winter or the trees injured by fire are cut during the first 

 winter after the fire, and got into water or sawn before spring opens, 

 most of the beetles will be destroyed, if the slabs are burned. 



The cutting and barking of infested trees, with the burning of the 

 bark during winter or early spring, may be adopted as a control meas- 

 ure. Sometimes cutting and charring the bark will be found sufficient 

 to destroy the beetles. 



-. Hymenoptera (Ants, Bees, Wasps, et al.) 



/^^, .:,,.'.-• Principal Groups and Families 



A. Trochanter with two segments; female with ovipositor. 

 B. Abdomen sessile or joined broadly to thorax. 



