10 



most usual condition for success and no case exists in Britain- 

 is where there are great climatic differences between different 

 parts of a country. Thus, in certain parts of the U.S.A., Lady- 

 birds migrate to the mountains in the autumn and spend the 

 winter in large colonies, only working down to the low ground 

 again when warmed by the spring weather. Naturally the warm 

 weather first reaches the valleys while the mountains are still 

 cold and thus pests, which have spent the winter in the valley, 

 get a start and can breed for a time free from their Ladybird 

 enemies. By collecting the Ladybirds from the hills, where they 

 occur together in millions, they can be brought to the valleys 

 and sold by the pound ! They are then released as soon as the 

 pests begin to appear in spring. 



A second case in which artificial assistance can be given to the 

 control of pests by parasites is where it is necessary to collect by 

 hand large numbers of the pest. The best instance of this is 

 shown by the Apple Blossom Weevil* (Anthonomus pomorum, L.), 

 which causes " capped blossom," and is one of England's most 

 serious apple pests. If the capped blossoms are collected 

 before the beetles have emerged, many of the blossoms will 

 contain, not weevils, but an Ichneumon parasite (Pimpla 

 pomorum, Ratz.) which has killed the weevil. In the case of one 

 Cambridge orchard, Immsf has shown that as many as 26 per 

 cent, of the destroyed blossoms contained Ichneumons-. Now, if 

 instead of burning the collected blossoms, they are placed in a 

 muslin cage, the Ichneumons can all be released and the weevils 

 killed, with the result that far more parasites should be available 

 next year to kill a smaller number of pests. This method of 

 dealing with Blossom Weevil has never been tried in England, 

 but in France, in one case at all events, success is claimed. 



Yet another condition favourable to the encouragement of 

 parasites is sometimes found when pest and parasites leave their 

 pupae at different seasons. In the case of the Gout Fly, for 

 instance, it appears that whereas the fly comes out about harvest 

 time, the parasites remain within their pupae in the barley, 

 which are threshed out in the drum and appear in the 

 " cavings." If the latter are burned, the parasites only are 

 destroyed, while, if left, they will come out later and assist in 

 controlling the fly. 



Lastly, conditions for success may be found in the case of 

 plants grown under glass. If a really destructive parasite of any 

 of the more serious glass-house pests such as the White Fly 

 can be discovered it would pay to keep a stock going to 

 distribute when needed in any infested house. The discovery 

 of the parasite in this case is of course the first step. 



These cases are all mentioned to show that while it is 

 necessary to be sharply on the look-out for any means of 



* See Leaflet No. 15, to be obtained from the Ministry and also- 

 included in Sectional Volume No. 2, price Wd., post free, 

 t (Annals of Applied Biology, Vol. IV., p. 211). 



