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Helicosporidium parasiticum 
when the material is collected. In rainy weather the larvae leave the flooded 
parts of the tree’s wounds and penetrate into the fissures of the tree; in the 
meantime, the wound is thoroughly washed by the rain and is freed from the 
collected sap which usually contains dead and dying larvae infected with 
Helicosporidium. When the normal conditions are restored and the wound is 
once more covered with freshly exuded sap, the larvae crawl again from their 
hiding places and invade the wound. If the sap is collected at this time, very 
few infected larvae will be found. On the contrary, in damp weather with 
the absence of much rain, when the old sap remains in the wound for a 
prolonged period, the number of diseased larvae increases. Finally, the sap 
collected from the wounds and kept in jars in the laboratory gives a still 
higher proportion of diseased larvae, as in this case the non-infected larvae 
rapidly become infected from contact with their diseased companions. 
7. Stages of the host susceptible to infection. 
In all its larval stages Dasyhelea obscura is susceptible to infection with 
Helicosporidium. This is undoubtedly due to the feeding habits of the larvae 
remaining uniform throughout its life. Very small larvae, hardly 1*5 mm. 
long, were often found with the body cavity filled with spores of the parasite, 
the spores showing already completely formed spirals and the three sporozoites. 
In a single instance a full-grown larva, almost ready to pupate, showed only 
the schizogonic cycle of the parasite, a condition which indicates a recent in¬ 
fection. Between these two extremes all the intermediate phases are met with. 
Only a few pupae of Dasyhelea were found infected and this infection is almost 
certainly derived from the larval stage: a full-grown larva became infected just 
before pupating, when all its imaginal discs were already completely formed 
and the pupation took place before the parasite had time to make a destructive 
invasion. Such infected pupae are eventually killed by the parasite. In no case 
have I observed the parasite in the adult insect. 
III. Other Hosts of Helicosporidium parasiticum. 
1. Mycetobia pallipes Meig. (Diptera, Rhyphidae). 
The larvae of Dasyhelea obscura are usually found associated with a number 
of other Dipterous larvae living in the same medium. According to their 
feeding habits, these larvae can be separated into two groups: 
(1) Saprophagous larvae which like Dasyhelea feed upon the decomposed 
sap e.g. Rhyplius fenestralis Scop., Mycetobia pallipes Meig., Aulacogaster 
rufitarsis Meig. and the larvae of Eristalids. 
(2) Carnivorous larvae such as Systenus adpropinquans Loew, and Pliaonia 
cincta Zett. 
I have frequently examined large numbers of larvae of all these different 
species for various parasites and only once have I found the spores of 
