THE CHALCIDOID GENUS PEEILAMPUS. 51 



cTiseta adults issued from February 2 to February 14. Perilampus 

 adults issued from the same lot April 1 to April 6, approximately two 

 months later. 



In this instance the puparia were not kept at an even temperature. 

 During the night, especially, it was frequently cool. Another lot of 

 puparia collected at about the same time but not placed in cold 

 storage or exposed to frost produced Perilampus adults November 30 

 to January 30 and adult tachinids January 22. Under these con- 

 ditions the first Perilampus issued a month earlier than its host, as 

 opposed to two months later when kept in cold storage until about 

 the middle of January. It is apparent from the above that Penlam- 

 jms adapts itself to changed conditions much more readily than does 

 VaricJiseta. Indeed it is a necessity that it should be able to do this, 

 being a parasite of other parasites which normally complete their 

 development during either spring, summer, or fall, as the case may be. 



EFFECT OF PARASITISM UPON HOST. 



(Fig. 26.) 



The Perilampus j)lanidium, even before it begins to feed, exerts a 

 very marked effect upon its host, especially in case the host is a tachinid. 

 As mentioned on a preceding page, these planidia while living inter- 

 nally within the host larva do not seem to cause it the slightest incon- 

 venience, and it is impossible to distinguish between a parasitized 

 and an unparasitized larva before the planidium emerges, excepting, 

 of course, where the secondary parasite itself is visible. Immediately 

 pupation takes place in the host and the planidium becomes ectopara- 

 sitic, the effect of the parasitism becomes evident, especially after the 

 host pupa has been subjected to warmth. Instead of responding to 

 the increased temperature in the usual way — that is, instead of develop- 

 ing pigment in the imaginal eyes and bristles upon the body — it takes 

 on a peculiar transparent appearance, principally in the cephalic and 

 thoracic regions. The eyes and appendages develop very slightly 

 and the imaginal head reaches scarcely one-half the size of that 

 attained in the unparasitized pupa. These pupse now present a very 

 characteristic appearance (see fig. 26), and in opening a series of 

 puparia one may recognize the parasitized individuals at a glance, 

 even before Perilamjms has begun to feed. This peculiar effect is 

 noticeable to a considerably less extent where Limnerium acts as 

 a host. 



The pathological nature of tliis unusual condition of the para- 

 sitized pupse has not been investigated as yet. It is apparently an 

 arrested histogenesis, but in what manner tliis is brouglit about we 

 can not say. Only a single case has come under observation where 



