v 



INSECTS AFFECTING PARK AND WOODLAND TREES 395 



species whose young are reared in separate cells or cradles. All the grow- 

 ing- parts of the fungus are extremely succulent and tender ; the conidia 

 specially are pellucid and glisten like pearls or drops of dew. These are 

 produced in great abundance during active growth, sometimes appearing 

 singly at the end of short, straight stems as in figure 105, and sometimes as 

 grapelike clusters among interlacing branches [fig. 54]. The fungus 

 appears at such times like hoarfrost on the walls of the galleries, and the 

 very young nip off the tender tips somewhat as calves eat heads of clover, 

 while the older larvae and the beetles devour the whole structure which 

 soon springs up again. Mr Hubbard compares the growth of these fungi 

 to asparagus, which remains succulent and edible only when cropped, and 

 when allowed to go to seed is no longer useful for food. The ambrosia 

 must be constantly fed on ; otherwise it ripens, the cells burst and dis- 

 charge their granules in such abundance as to fill the galleries, and the 

 beetles may be overwhelmed and destroyed by the growth. 



Disturbances in conditions necessary to growth are apt to promote the 

 ripening of the fungus, a danger to which every colony of ambrosia beetles 

 is exposed. Checking the natural increase of a populous colony of beetles 

 also' results in overproduction of fungus and disaster, because the super- 

 abundant growth chokes the galleries and often suffocates the remaining 

 insects. The same untoward results may be brought about by closing the 

 outlet of the galleries through the bark, or by spraying with kerosene or 

 some other liquid. This throws the inmates of the galleries into a panic, 

 and like other social insects, they gorge themselves with food and exhibit 

 great concern at the threatened loss of this their most precious possession. 

 They rush hither and thither, trampling on and crushing young, eggs and 

 larvae, breaking down the delicate lining of the brood chambers and pud- 

 dling it into a slush, which is pushed about and accumulates in the passage 

 ways, completely blocking them. Breaking down of the fungus follows, 

 and in a few days the galleries are filled with masses of spores or mycelium 

 threads. 



The limited conditions under which these fungi can be grown restricts 



