91 



opening in the upper side of the scale, made by the larva in order to 

 facilitate the extrusion of the pupa half-way through the opening, in 

 which position the midge emerges. The biological significance of this 

 peculiar mode of pupation becomes evident when it is remembered 

 that the seeds fall to the ground, whereas the cones remain on the 

 trees. If they remained in the seeds and fell to the ground with them, 

 the midges would have a considerable distance to travel to find another 

 individual to mate with or suitable places for oviposition, besides 

 being exposed to numerous enemies. Pupating in the cone-scales they 

 emerge in the crown of the trees and close to the spot where their eggs 

 are laid, being, moreover, well protected in the scales during the pupal 

 period. The fact that pupation takes place in the scales is therefore 

 doubtless an adaptation which ensures the protection of the species. 

 Platygaster {Triplatygaster) contorticornis, Ratz., was bred by Ratzeburg 

 from spruce cones and was suspected by him of being the parasite 

 of P. strobi, but until now this had not been definitely proved. 

 The larva of Platygaster is parasitic in that of Perrisia, but does not 

 kill its host until it has left the seeds and formed the cocoons in the 

 base of the scales, the inflated skin of the larva serving as an extra 

 cocoon for the parasite. Platygaster is present with its host all over 

 the country, though it was very remarkable that in 1916 in the 

 northern part of the country it was not bred in those localities where 

 Perrisia was very abundant, whereas in the south of Sweden a high 

 percentage of Perrisia always corresponded to a high percentage of 

 Platygaster. The majority of those localities from which the cones 

 gave a low percentage of Platygaster being situated in the north of 

 Sweden, these data seem to justify the inference that in this part of 

 the country climatic conditions have been favourable to the re- 

 production of Perrisia but not of its parasite. That this species is a 

 very efiective parasite of Perrisia is shown by the fact that in 25 per 

 cent, of the localities the percentage of midges killed by it was 1 1-20 ; 

 in 13 per cent., 21-30; in 10 per cent., 31-40; in 14 per cent., 41-50; 

 and in 5 per cent. , over 50 per cent. Its value is increased by the fact 

 that the females are far more numerous than the males, while in 

 Perrisia the number of both sexes is about equal. 



At the beginning of the investigation it seemed very likely that 

 some species of the genus Megastigmus would be found in spruce seeds, 

 two species of this genus being recorded in Germany with this habitat. 

 It is, therefore, very remarkable that during the investigation of these 

 14,000 cones the author entirely failed to breed any species of 

 Megastigmus, the part played by this genus in Central Europe being 

 evidently taken in Sweden by Torymus azureus, Boh. The mode of 

 pupation of Torymus seems to be the same as that of Perrisia, the 

 burrows of the former being, however, easily distinguished from those 

 of Perrisia owing to the absence of white cocoons. When the adult is 

 ready to emerge, the pupa does not become extruded half-way through 

 the opening, but remains in the burrow, the adult biting a circular 

 hole through the wall. 



The two sexes of Aprostocetus strobilanae, Ratz., were described as 

 two difierent species by Ratzeburg, who called the male Geniocerus 

 erythrophthalmus and the female Eulophus strobilanae. This mistake 

 has not hitherto been corrected, Schmiedeknecht in the " Genera 

 Insectonim " referring the male to Tetrastichus and placing the female 



(C452) A.2 



