224 Observations on Pimpla pomorum 



unopened buds were not tightly closed, the mould appeared to gain access 

 more readily. 



The effect of the parasitism on the host is complete, the latter dying 

 in every instance whether it be in the larval or pupal stage. It is prob- 

 able, therefore, that Pimpla pomorum is an important natural aid in the 

 control of the apple blossom weevil in this country. The high rate of 

 mortality which I have shown it exacts from its host, together with the 

 general fact of its biology, clearly supports this contention. Measures 

 involving the preservation and increase of the parasite, along lines 

 similar to those conducted in France, are fully worthy of adequate trial 

 as an accessory means of controlling the weevil. The utilisation of natural 

 enemies in the control of injurious insects has led to highly encouraging 

 results in America, Italy, France and elsewhere; nevertheless, it is a 

 method which can only be advocated after a thorough scientific enquiry 

 into the life-economy of each particular species and its parasites. In the 

 case of the apple blossom weevil, among the various measures recom- 

 mended for deahng with this insect is that of jarring the trees, which 

 causes the affected apple blossoms to fall readily. Frequently, many fall 

 in the natural course of events without the trees being shaken. The 

 blossoms are then collected and burnt. With the expenditure of very 

 little extra time and labour the blossoms, after being collected, might 

 easily be placed in boxes and saved. Shallow well-fitting wooden boxes 

 are best for the purpose, and not more than six layers of blossoms should 

 be placed in a single box, as they rapidly decompose and rot in damp 

 weather. The lids of the boxes should have as large an area as possible 

 replaced by cheese cloth or butter muslin, to allow of the admission of 

 air and light. If, however, the finest holed perforated zinc be used the 

 boxes will then serve their purpose for a much longer period without 

 trouble. All that is necessary is to examine the boxes daily from about 

 the beginning of the second week in June, removing the lids thereof for a 

 few minutes to enable the parasites to fly away once they commence 

 appearing. It is advisable to jar the box sharply before doing so, in order 

 to cause those weevils which may have crawled up the sides to loose their 

 foothold and so prevent their escape. By this means the greater number 

 of the weevils are imprisoned within the boxes and eventually die, while 

 the parasites are liberated to continue their beneficial mission. Experi- 

 ments were conducted in order to ascertain whether it be possible to 

 utilise gauze of such a mesh which would allow of the liberation of the 

 parasites, and the retention of the beetles, and thus obviate the necessity 

 for the periodical removal of the fids of the boxes. Owing to the relatively 



