A STUDY IN HYPERPARASITISM 31 
PLEUROTROPIS TARSALIS (ASHMEAD) 
This species differs from all the other hyperparasites treated in this 
bulletin, except Pleurotropis nawaii, which is considered next, in its 
unusual habit of being essentially a tertiary parasite. The writers 
have had no difficulty in breeding it in the laboratory as a secondary 
on Apanteles melanoscelus; but in the field it has appeared of little 
importance in this réle, occurring most frequently as a tertiary. 
Several hundred cocoons from which Pleurotropis emerged were dis- 
sected to determine to what extent the species had been secondary © 
and to what extent tertiary. It was found that in 97 per cent of 
these cocoons P. tarsalis had developed as a parasite of the second- 
aries Kurytoma, Dibrachys, Dimmockia, Eupelmus, Hemiteles, and 
Habrocytus, and in only a very few instances as a parasite of Apan- 
teles. However, if certain conditions should bring about a decided 
reduction in the secondary parasitism of A. melanoscelus, it is very 
probable that Pleurotropis would be more often found acting as a 
true secondary than as a tertiary. 
The female places its eggs inside the larva or pupa of the parasite 
attacked, whether that host be a primary or a secondary, and the 
Pleurotropis larva develops as an internal parasite, entirely consum- 
ing the contents of the host individual and leaving only the larval or 
pupal shell, within which it pupates. Except in rare instances it is 
solitary, only one maturing within a host irrespective of the size of the 
latter, and whether this host is a primary or a secondary. As is the 
case with most hyperparasites, the progeny of unfertilized females 
are males. 
The writers have found the species to have either one or two gene- 
rations annually. When adults emerge the same season that the eggs 
are deposited, about 28 to 40 days are required for development from 
ege to adult. Of this period about 2 days are spent in the egg, 8 to 12 
days as a larva, and the remaining time as a pupa. 
The writers have repeatedly observed that when one or two larvae 
or pupae of a gregarious secondary, like Dibrachys or Dimmockia, 
are parasitized by Pleurotropis, any unparasitized individuals in that 
cocoon fail to emerge, although they frequently reach the adult stage. 
It is difficult to understand the reason for this, since the tertiary 
larvae inside their particular hosts can hardly exert any influence 
upon the unparasitized secondaries in the same cocoon. It is curious 
that the unparasitized individuals should nearly always succeed in 
transforming to adults and yet fail to cut their way out of the cocoon. 
PLEUROTROPIS NAWAIL (ASHMEAD) 
(Fig. 10) 
This Japanese and European species of Pleurotropis has been 
commonly reared from cocoons of Apanteles melanoscelus. Like 
Pleurotropis tarsalis, it acts chiefly as a tertiary parasite. It also 
resembles that species in life history and biology, except in two 
features; it hibernates as a pupa instead of as a larva within the shell 
of its host, and whereas tarsalis produces males in parthenogenesis, 
this species is always thelyotokous. This last characteristic should 
make it more valuable than ftarsalis as a tertiary parasite. But 
the two species have been reared in approximately equal numbers. 
