334 The Large Poplar Longhorn 



The Length of the Life Cycle. 



My first observations on S. carcharias in the open,, began in Aberdeen- 

 shire, in 1915, but it was not till the following year that any definite 

 experiments were begun with a view to the determination of the length 

 of the life cycle. 



On July 10th, 19] 6, in the areas where the poplars were infested with 

 this species, I noticed on examination of a number of stems of various 

 ages that quite a large number of young larvae were present under- 

 neath the outer bark layers. These larvae had not been long hatched, 

 for they had just cut the tissue close to where the eggs had been deposited 

 and had just begun to cut the horizontal portion of their galleries. To 

 facilitate observation of these larvae later on, small notches were cut. 

 Throughout the summer and autumn these marked stems were examined 

 with a view to following the making of the larval burrows. Till September 

 28th, 1916, the larvae continued to burrow in the stems, but about this 

 time they ceased feeding. In all the cases examined at this time the 

 larvae had completed the horizontal portion of their galleries, and had 

 also tunnelled the portion of their gallery in the vertical direction down- 

 wards, reaching almost the roots of the trees. In all cases the larvae 

 hibernated head downwards. Their average length at this stage was 

 18 mm. 



In the end of March, 1917, six of these marked plants were carefully 

 removed from their natural habitat and replanted in an area where they 

 could be kept under closer observation and at the same time be protected 

 from further infestation. These young trees chosen for replanting were 

 from five to seven years of age as at these ages they could be transplanted 

 without undue risk to their life. Along with these marked stems four 

 uninfested plants of a similar age were removed from the wood and re- 

 planted alongside the infested ones. Throughout the winter and early 

 spring months, October, 1916, to March, 1917, the larvae hibernated. 

 Examination of the stems on April 22nd, 1917, showed that the larvae 

 were still hibernating. From April 25th, 1917, to May 5th, 1917, they 

 showed signs of movement within their burrows, but did not recommence 

 to tunnel and extend their galleries till about May 8th, 1917. Throughout 

 the summer and autumn of 1917, the larvae continued to tunnel in their 

 burrows. On October 2nd, 1917, they ceased to feed. At this date some 

 of the larvae had attained their full growth and had completed their 

 pupal chambers. 



From October, 1917, to December, 1917, the stems containing the 



