W. Ritchie 199 



have issued that the outer bark layer is broken and the wood surface 

 exposed to view. 



NATURAL ENEMIES OF C. ABIETIS. 



From observations made in the field during the last two years I am 

 of the opinion that the bark fungi play little or no part in controlling 

 the numbers of C. abietis. Only on a few occasions have I found beetles 

 killed by fungoid attack. 



The larvae are destroyed in numbers by the larvae of a Hymeno- 

 pterous parasite belonging to the family Chalcididae. On the removal 

 of a piece of the outer bark layer of a badly infested branch or twig one 

 repeatedly met this parasite either in the larval or pupal stage. Only 

 one parasitic larva was found on each host. No cocoon is spun by this 

 Chalcid larva prior to pupation but the pupa lies naked in the Cryphalus 

 gallery or pupal bed. As soon as these parasites have reached the adult 

 stage each gnaws a minute puncture through the outer bark and escapes 

 into the open. 



From some Silver Fir branches badly infested with C. abietis which 

 I collected in Aberdeenshire in October, 1916, large numbers of these 

 Chalcids issued from July 21st to August 6th, 1917, just at a period when 

 large numbers of these C. abietis larvae would be found on infested 

 branches. 



The number of these Chalcids varied to a great extent in different 

 localities. From one lot of badly infested material collected in one 

 particular area in the Aboyne district only a few parasites issued. On 

 the other hand, from badly infested material collected from another area 

 a little over a mile from the first exceedingly large numbers of parasites 

 issued. In a single day as many as 30-40 individuals escaped from a 

 few pieces of badly infested material. In this particular case I estimate 

 about 75 per cent, of the larvae of the beetles must have been destroyed. 



The abnormal conditions prevailing in our forest areas during the 

 past three years have undoubtedly been the means of creating an ex- 

 cessive number of breeding places for our bark-boring beetles. Foresters 

 throughout the country ought therefore to be on the alert. The intensive 

 study of the life-history and habits of this beetle and of other such 

 forms is for this reason of more than usual interest at the present time. 



In conclusion my thanks are due to Dr R. Stewart MacDougall for 

 the encouragement and facilities he has given me throughout this work. 



