Insects, etc., Injurious to the Plum. 



369 



[F. E. 

 FIG. 243. FLIGHT HOLE (A) OF SHOT BORER BEETLE 



(Xyleborm dispar). 



When ready to hatch the pupse are packed fairly close together, 

 and this accounts for the presence of so many beetles packed like 

 shot in the tunnels. 



The maggots feed on a grey and black layer lining these tunnels, 

 a substance called by 

 Sch mid berger and others 

 " Ambrosia." This lining 

 has been described by Eich- 

 hoff as formed from the sap 

 which soaks out of the walls 

 of the tunnels and which 

 thickens into a white egg- 

 like coagulation, and on 

 this a coating of fungus 

 develops ; after a time the surface of the circular galleries becomes 

 black. He tells us that these coagulations and fungoid growths 

 serve solely as the food of the Shot Borer Maggots. As many as 

 thirty or forty ova are laid by each female. These are laid at 



different times on till June. Thus 

 \ve find maggots of various sizes 

 close together and all derived from 

 the same parent. 



The tunnel formed by this insect 

 is at first made to the centre, and 

 then another is cut horizontally, run- 

 ning part of the way around the stem 

 or branch, about \ inch across, this 

 circular tunnel may be close under 

 the sapwood or right in the wood ; 

 from this horizontal gallery others 

 are drilled at right angles both up 

 and down the stem, these may reach 

 1 inch in length. 



It is in these tunnels in which 

 we find the beetles packed like shot 

 in September, and here the beetles 

 feed as well as the maggots. The 

 beetles seem to occur with us in 

 January, February, May, September, on to December. The larvae 

 appear to grow rapidly, and by mid June beetles appear. During 

 the year 1908 some hatched in November. 



When first hatched they are soft and reddish, and they 



2 B 



[Horace Knight. 



FIG. 244. SHOT BORER BEETLE 

 (Xyleborus dispar). 



