52 RESULTS FROM GIPSY MOTH PARASITE LABORATORY. 



the host pupa developed the characters of the adult to any extent. 

 During ]\Iarch, 1909, a puparium of Varichseia was dissected and 

 found to contain a very small pupa of Perilampus, only about three- 

 fourths natural size but fully developed and apparently healthy in 

 every way. The astonishing thing in this instance was the fact that 

 the tachinid pu])a had developed to a stage where it had taken on 

 the characters of the adult. Even the bristles were well formetl. 

 This is the only case out of several hundred puparia examined where 

 development had not ceased soon after the formation of the pupa 

 and is rather difficult to explain. It is possible that for some reason 

 the planidium did not respond to the usual stimulus, histolysis, and 

 remained internal within tlie pupa, giving the tachinid an 0])por- 

 tunity to develop considerably further than normally before the 

 secondary parasite changed its mode of life to external feeding. 

 There were many other puparia subject to the same conditions and 

 they all responded in the usual way, so that the above case must be 

 considered as abnormal. 



The retardation of development in the parasitized hosts is of course 

 brought about by the presence of the planidium, but whether in- 

 directly or directly has not been ascertained. That it may be due to 

 a glandular secretion is not impossible, but this liardly seems to be an 

 adequate explanation, as nothing resembling glands of this kind have 

 been found, although a careful study of the planidium has been 

 made witn the oil-emersion objective. In the opinion of many 

 zoologists an insect during the process of pupation is in a very critical 

 condition and is more susceptible to injury at this time than during 

 any other period of its life. It does not seem improbable that in this 

 supposition lies the explanation of the condition brought about in its 

 host by Perilampus. The larva or maggot is able by reason of its 

 great vigor to withstand the presence of the secondary parasite, but 

 immediately histolysis and histogenesis begin to take place the 

 weakened condition of the host makes itself apparent in the form of 

 a cessation of development of pupal or imaginal organs and append- 

 ages and occasionally in certain instances death ensues. The develop- 

 ment of Limnerium invariably ceases soon after the exit of Perilam- 

 pus, although the latter does not emerge until the host larva has 

 tUscharged its meconium and the formation of the pupa has begun. 

 In one instance the planidium was observed located in the imaginal 

 eye of its host, which becomes visible as a darker spot some time 

 before the larval- skin is discarded. 



PERCENTAGE OF PARASITISM. 



The percentage of parasitism of Varichseta and Limnerium by 

 Perilampus in 190.S was not very higli. Large numbers of the 

 cocoons and puparia were opened, or reared through in the laboratory, 



