174 



THE STUDY OF INSECTS 



beetles because they cultivate fungi, commonly called ambrosia, upon 

 which they feed; and timber-beetles, because they burrow in the solid wood. 



The galleries of the ambrosia-beetles can be distinguished from those 

 of other wood-boring insects by the fact that in all of their ramifications 

 they are of uniform size and free from wood-dust and other refuse, and their 

 walls are stained black i >r 1 >r< >wn by the fungus that is grown upon them. 



The galleries of different species differ in form; but usually there is a 

 main gallery, which extends deeply into the solid wood and is often 

 branched; and extending from the sides of the main gallery there are 

 short chambers, termed cradles, in each of which an egg is laid and a 

 larva reared (Fig. 308) . In some species, the female deposits her eggs loosely 

 in the galleries, and the young and old live together in the same quarters. 



Fig. 308. — Gallery of Monarthrum mail in maple. (From Hubbard.) 



The galleries are excavated by the adult beetles. In some species 

 the gallery is started by a single female, in others the males assist the 

 females in this work. The entrances through the bark to the galleries 

 are similar to those made by the bark-beetles and like them are known 

 as " shot-holes." Under favorable conditions colonies may continue their 

 excavations during two or three generations. 



The fungi upon which these beetles feed are carefully cultivated by 

 them. So far as is known, each species of ambrosia-beetle cultivates 

 only a single species of fungus, and only the most closely allied species 

 have the same food-fungus. The fungus is started by the mother-beetle 

 upon a carefully packed bed or layer of chips. It is probable that some 

 conidia are brought for this purpose from the gallery in which the female 

 was developed. The excrement of the larvae is used in some and prob- 

 ably in all the species to form new beds for the propagation of the fungus. 



In those species in which the larvae are reared in separate cradles, 

 " the mother-beetle is constantly in attendance upon her young during 

 the period of their development, and guards them with jealous care. 

 The mouth of each cradle is closed with a plug of the food-fungus, and 

 as fast as this is consumed it is renewed with fresh material. The larvae 

 from time to time perforate this plug and clean out their cells, pushing 

 out the pellets of excrement through the opening. This debris is promptly 

 removed by the mother and the opening again sealed with ambrosia. 

 The young transform to perfect beetles before leaving their cradles." 



