I9C8.] 



Large Larch Saw- Fly. 



651 



The females begin to deposit their eggs almost immediately 

 after emerging from the cocoons, especially if the weather is 

 warm and sunny ; as they reproduce parthenogenetically 

 there is no necessity for them to await fertilisation by the male. 

 The eggs are deposited on the stems of the fresh green terminal 

 shoots in small slits made by the saw-like appendages of the 

 ovipositor. The slits are made along the shoots with the 

 result that the green terminal shoot is killed by the numerous 

 wounds and curls round in a characteristic manner (Fig. 3). 

 The presence of these brown and curled dead terminal shoots is 

 often a means of detecting the presence of the larvae when they 

 do not occur in sufficient numbers to indicate their presence by 

 much defoliation of the twigs. The eggs appear to be deposited 

 chiefly on the lower branches of the trees, as I found that on 

 the trees which were only moderately attacked the larvae were 

 most numerous on the shoots of the lower branches and these 

 usually showed signs of defoliation before the branches nearer the 

 top of the tree. The beginning of the attack on the lower 

 branches is probably explained by the fact which has already been 

 mentioned, namely, that the females begin to lay almost im- 

 mediately after emergence ; they would naturally on emerging 

 from the cocoons lying beneath the turf, &c, fly on to the 

 lower branches first. 



As Packard's detailed description of the different stages of the 

 life-history has been given in a summarised form by MacDougall,. 

 I shall not repeat those of my results which are merely con- 

 firmatory. In one respect, however, my experiments did not 

 agree with those of Packard. He found that the larvae moulted 

 three times, that is, there were four larval stages. The larvae 

 which I reared and kept under observation, several hundreds 

 in number, moulted five times, there being six larval stages. 

 This difference in our results may be due to the fact that the 

 observations were made in different countries, and in the case of 

 saw-fly larvae, as also in lepidopterous larvae, one cannot be 

 dogmatic with regard to the number of larval stages. The 

 larvae hatched out in eight to ten days after the eggs had been 

 deposited. The larval life extended over a period of three to 

 four weeks, each larval stage lasting from three to four days. 

 A typical life-history (Exp. No. N. 2) was as follows : — 



2 T 2 



