86 FOREST ENTOMOLOGY. 



As the respective genera and species show variation in life-history 

 and markings, it would perhaps be well for the student to study the 

 salient features of a typical bark -beetle, as regards the formation of a 

 brood, and its subsequent life-history. 



With regard to the formation of the brood, there is one important 

 point to be noted — viz., that some genera are monogamous, whilst 

 others are polygamous. In the case of the former, the initial opera- 

 tions are always conducted by the females, whereas, in the latter, they 

 are always made by the males. 



Take a typical monogamous species. Both sexes hibernate during 

 the winter months, but the female awakes first, and betakes herself 

 to a suitable tree, where she scoops out a small chamber, and then 

 takes a sort of nuptial flight, as it were, for she returns generally 

 accompanied by the male, and copulation takes place either within 

 the chamber or immediately outside it. The female then com- 

 mences her work in earnest. She makes a straight tunnel, and 

 deposits eggs right and left alternately. Her presence can always 

 be recognised by the frass, or bore dust, made by the workings, 

 which is deposited outside the burrow. The male is generally 

 found just at the entrance of the burrow. As the female moves 

 along, she often makes little bore-holes over her tunnel, for the pur- 

 pose of ventilation. 



In due time the larva hatch out, and moving along their respective 

 galleries, which broaden according to larval growth, they finally 

 scoop out a chamber, and then pupate. It is important to note, as 

 we shall consider presently, that it is the particular angle made by 

 the junction of the larval with the maternal galleries which gives the 

 peculiar markings of the respective species. The fully formed beetle 

 eats its way through the bark, which, after the swarming or flight 

 period, looks as if it had been riddled with shot. The holes made by 

 the exit of the beetle can, however, by careful inspection, be distin- 

 guished from those made by the mother for ventilation, as the latter 

 are always made over her own tunnel. 



In those cases where the initial operations are conducted by the 

 males, the excavation is a sort of circular chamber, where several 

 females, generally from four to six, assemble, and within which 

 copulation takes place. Hence it is called by the Germans " Rammel- 

 kammer," or brood-chamber. The females then make their respect- 

 ive galleries, all radiating from the brood-chamber. The male very 



