1554 INSECTS PESTS. - MEANS OF PREVENTION AND CONTROL 



the end of July or the beginning of August. In Great Britain the insect 

 is single [brooded, but in certain regions of Nortli America there are two 

 broods.' i;^ 



The number of eggs laid varies a good deal. In America apparently 

 the average number does not exceed 80, while in England the average 

 is about 37,2 eggs per female. 



The genus Aphelimis is placed among the parasitic Hymenoptera 

 and belongs to the sub family Aphelininae. This sub-family is very widely 

 distributed, species being known from almost all parts of the globe, with 

 the exception of the colder temperate and polar regions. A list of the 

 localities in England in which it occurs is given in this paper. 



The larvae of the ApheUnae are either exclusively parasitic or para- 

 sitic and partially predaceous. They confine their attacks almost exclu- 

 sively to the Rhynchota, the Coccidae and the Aphididae being their prin- 

 cipal hosts. 



Several hosts are mentioned as being subject to the attacks of this 

 parasite in various regions. The author gives detailed descriptions of di- 

 verse stages in the two sexes, of parthenogenesis, of oogenesis, and of the 

 external and internal morphology. Experiments in breeding have been 

 successfully carried out in the Manchester University Biological Experi- 

 ment Ground, in specially constructed breeding cages, with a view to in- 

 vestigating the biology of the parasite. 



The life history of the parasite can be summarised as follows : in one 

 year it passes through two generations, and the adults are almost, alwa3's 

 females. Out of 750 indi\dduals reared only 10 were males, about i per cent. 

 Reproduction takes place almost entirely by means of parthenogenesis. 

 The adults very rarelj^ fly, and have extremely limited powers of migration. 

 In the first generation the adults appear in greatest frequency between the 

 third week in June and the middle of July. The female laj^s a single egg on 

 the dorsal or ventral surface of the body of the immature host, only the scaly 

 covering of the latter being perforated. The newly hatched larva closely 

 resembles the fully grown stage in form, and during larval life the insect is 

 an ectoparasite of its host. The second generation of adults mostly appear 

 between the middle of August and the first week in September. They para- 

 sitise the sexually mature hosts, and the resulting larvae hibernate through 

 the winter, giving rise to the first generation of adults of the following year. 

 The results of the first generation of parasitism are complete, the affected 

 hosts invariably dying in consequence. In the second generation of pa- 

 rasitsm the affected hosts usuall^^ deposit a small number of eggs before 

 succumbing ; its results, therefore, are partial and incomplete. The pa- 

 rasite exercises an inhibitory effect upon oviposition, the essential reduction 

 in the number of eggs not being primarily due, as stated by previous 

 observers, to their destruction by the Aphelinns larvae. Assuming that 

 every 100 hosts lay on an average 37 200 eggs, the net results of a 3'^ear's 

 parasitism entails a reduction of about 2600 in the number of eggs laid, or 

 7 per cent. The efl&cienc}^ of the parasite, therefore, is far below that of the 

 most effective insecticides. This is primarily due to four factors : 1) its 



