Experiments with cyanide showed a remarkable insensitivity to this inhibi- 

 tor, both in developing and resting pupae. In contrast Avith reported observa- 

 tions on other species (e. g. Schneiderman & Williams, 1954) the develop- 

 ing pupae seem to be less sensitive than the resting pupae are. It remains a qu- 

 estion, however, if the 1олу activity of cytochrome с may account for these cont- 

 radictory results. 



200 240 days 



120 160 200 days 



Fig. 3. Abscissa: number of days of chilling. Ordinate of the left figure: emergence of the 

 host after pupation. Ordinate of the right figure: emergence of the parasite -larva after 



puliation of the host. 



Physiological aspects of synchronism. The larva of Eucarcelia ru- 

 tilla Vill. {Tachinidae) hibernates within the host pupa and is apparently ac- 

 tivated when adult development of the host begins. The synchronism of life 

 cycles in the field, as reported by Klomp (1958), is maintained under experi- 

 mental conditions (Fig. 3). This synchronism, if it has a physiological basis, 

 must depend upon an activating or an inhibiting influence of the host on the 

 parasite larva. Activation could possibly be brought about by the host's 

 cerebral neurosecretory cells or prothoracic glands. Parasite larvae, however, 

 are able to start their development in early decerebrated pupae; these pupae 

 themselves are not able to terminate their experimentally induced diapause. 

 The question presents itself whether chilling merely removes the inhibition 

 exerted by the host or directly effects the larva. 



This iuA^estigation is supported by the Netherlands Organization for the 

 Advancement of Pure Research (Z. W. 0.). 



263 



