Pomona College, Claremont, California 163 



change occurs. It now begins to grow at such a rate as to almost 

 double its size within twenty-four hours. The host, which here- 

 tofore has betrayed no marked injury from its enemy, now rapidly 

 shrivels up. Only five days of this voracious feeding reduces the 

 once large plump larva to an empty skin and in its place we find 

 the equally large and plump, fully grown larva of the bombyliid 

 (Figs. 3 and 4). This long retarded growth followed near the 

 end of the larval period by a relatively short period of unusually 

 rapid development seems to be a very advantageous adaptation on 

 the part of the parasite. If growth had progressed steadily from 

 the first, death of the host had surely resulted before the full devel- 

 opment of the parasitic larva. This larva now rests almost motion- 

 less for ten or twelve days (Fig. 4) when it becomes a little more 

 active ami moults about two days later, entering the pupa stage 

 (Fig. 5). In this stage it remains for fifteen to twenty days and 

 emerges as an adult (Fig. 10). 



I he work ol this parasite for the season in which it was studied 

 was quite general, about ten per cent, of the cells examined being 

 infected. So far as I observed, its work was also very equally dis- 

 tributed — about half the broods showed one parasitized larva and 

 in only one ease was there more than one found in the same brood. 

 Other parasites found were a phyeitid moth and a tenebrionid 

 beetle, both of which began their work upon the bee-bread and when 

 that supply ran short devoured the young bees. These two para- 

 sites would doubtless be much more destructive were orpifex a less 

 careful workman; for I found that where cells prepared for study 

 were not tightly sealed the pupa' were in almost every case devoured. 

 But where the partitions were left entirely intact and the glass cover 

 glued on tightly I found only one ease in which a cell was entered 

 and in this case the tenebrionid bored through the partition to 

 deposit eggs within the cell. In some cases I used bee-bread to paste 

 the glass cover over the opened cells and in every such case these two 

 parasites found their way in by feeding upon this material and 

 without fail they devoured the pupae before they emerged. From 

 my examination of cells which had not been opened before the season 

 of emergence I conclude that the injury of these parasites is slight 

 except in ease of defective construction of partitions. But they 

 were found occasionally even in the normal brood cells. 



