76 



IVAR TRAGARDH. 



But, on the other hand, one might safely presume that these conditions did not 

 alter the relation between the time of emergence of the host insect and its parasites. 

 Further there existed certain known data as to the relation of N enteritis cremastoides, 

 Hlmg., Ephialtes glabratus, Eatz., and Bracon sp. to Laspeyresia strobilella, L. This 

 greatly simplified matters. The first thing to be done was to see how these parasites 

 grouped themselves around their host. If other parasitic species grouped themselves 

 round one or the other of the phytophagous species, it might safely be concluded 

 that they were the parasites of these. 



40 % 





"4 



18 



19 



20 



21 



22 



23 



24 



25 



26 



27 



2S 



29 



30 



'/a 



2 



3 



4 



5 



6 



30% 

















■ n:o 1 



































\ 



/ 









n:o 2 



































\ 



/ 





















,n:o 3 























































70% 



























^ 



/ 



^ 



N 



\ 





























> 





/ 



1 '■ 













\ 











Fig. 1. Diagram i-howing the percentages of Perrisia strobi, Winn. (No. 1), 

 Laspeyresia strobilella, L. (No. 2), and Torymus azureus, Bhn., bred from spruce- 

 cones from 17th April to 6th May 1916; material from Kungsor, Koping. 



The success of the method, however, depended on the phytophagous species not 

 appearing contemporaneously, but in a certain succession. Fortunately the latter 

 was the case. Figs. 1 and 2 are diagrams showing the number of Perrisia strobi, 

 Winn. (No. 1), Laspeyresia strobilella, L. (No. 2) and Torymus azureus, Bhn. (No. 3), 

 calculated as a percentage of the whole number of each species, bred from two 

 different localities. 





'It 



10 



11 



12 



13 



14 



15 



16 



17 



IS 



19 



20 



21 



22 



23 



24 



25 



26 



27 



2S 



29 



30 



30% 

 20°A> 

















:o 1 









n:o 



j 























































h 



J 



:o 3 



















































10"lo 





















































Fig. 2. Diagram of the same species bred from 3rd to 30th April 1916 ; material 



from Forshem, Kinne. 



We notice in fig. 1 that the gall-midges start hatching on the 17th of April and 

 increase rapidly in number, so that on the 19th, 30 per cent, emerged ; on the 20th 

 the number decreased, on account of the number of males rapidly diminishing before 

 the females have reached their maximum. On the 21st also 30 per cent, emerged, 

 the number subsequently rapidly diminishing. 



