102 F. W. DRY. 



Another explanation of the action of the roping method which has been put forward, 

 is that the caterpiUars, becoming weary of being repeatedly knocked off the plants, 

 migrate from the field. A watch was kept for such migration from the field under 

 discussion, but caterpillars were only found crawling out of the field where the flax 

 had been stripped of leaves right up to the edge of the field. Where the flax offered 

 plenty of food, the caterpillars remained there. It seems probable that the roping 

 method, in so far as it does reduce the number of caterpillars, acts not by driving 

 them out of the field, but by bringing about their death in the field. 



The conditions involved in the success or failure of this method seem, therefore, 

 to be : — 



(1) Kind of rope and frequency of roping. 



A heavy rope has more effect than a light one. The more times the field 

 can be gone over in a day the better. If caterpiUars are present in sufficient 

 numbers to do appreciable damage, once or twice a day would do little 

 good. 



(2) Size of the caterpillars. 



On small caterpillars the roping method has an effect both directly, by 

 injury, and indirectly, by placing them at the mercy of ants. On large 

 caterpillars there is Httle effect by either means. 



(3) Numbers of the caterpillars. 



Against an outbreak in which the caterpillars were very numerous, I doubt 

 the efficacy of this method, unless, possibly, roping were done more times 

 a day than would be feasible on a farm. Very little success has been 

 reported against bad outbreaks, and in the light of the field 

 observations just recorded this is not surprising. For, 

 {a) It appears that roping produces its effect by bringing about the death of 



only a small percentage of caterpillars each time the rope passes. 

 {b) Unless the numbers of ants or other predators attacking the caterpillars on 

 the ground are increased by immigration, the larger the numbers of 

 caterpillars, the less potent proportionately wih the ants be to reduce the 

 numbers of the caterpillars. 

 These facts, I believe, explain the different reports on the roping method — some of 

 success, some of failure — which have come to hand. If the caterpillars are big before 

 roping is started, if their numbers are very large, if the rope is too light, or if it is not 

 passed through the field often enough, failure may be expected. But if the cater- 

 pillars are small and not present in excessive numbers, roping, properly carried out, 

 will, I believe, meet the case. 



It will thus be seen that there are distinct limitations to the roping method, and 

 it is, moreover, a laborious one. Undoubtedly, it will be replaced by something more 

 effective, and at present fiax-growers are paying attention to various mechanical 

 devices invented by several settlers for removing the caterpihars from the crop, while 

 the search for other methods is being continued by the Division of Entomology. 



