212 E. A. HARTLEY Vol. XXII, No. 8 



standard lantern globe cage used in rearing aphids, and a 

 specially designed celluloid cage. The celluloid cage was found 

 to be far superior to the lantern globe in ventilation and its equal 

 in all the other factors. However, both were used with success 

 throughout the work. 



Myzus persiccE Sulz., a common aphid on dock and crucifers, 

 was used for a host in practically, all the experiments, although 

 several other species were carried along for the purpose of 

 testing the parasite in other hosts. This aphid proved to be 

 quite satisfactory in every way; since it was the natural pre- 

 ferred host of Aphelimis semiflavus, reproduced readily through- 

 out the winter on a number of common plants, and was attacked 

 by practically every other aphid parasite. Dock {Rumex 

 cripus, and R. obtusifolius) was found to be the best host plant 

 for this aphid, and was also very satisfactory from an exper- 

 imental standpoint; being easily grown, and having large smooth 

 foliage which greatly facilitated observation and handling. 



Parasite-free material was obtained by rearing in tight 

 cages. 



In all experiments, a few specimens confined in a small, neat 

 cage gave better and more accurate results than many in a large 

 cage. Too many aphids to start with would multiply so rapidly 

 that they would kill the plant before the experiment could be 

 closed, making it necessary to transfer them, which always 

 resulted in loss of material. 



For development studies, a number of parasites were con- 

 fined with parasite-free aphids for a few hours and then removed. 

 A number of these aphids were dissected at intervals to deter- 

 mine the stages reached by the parasite in a given time. These 

 dissections were made in normal salt solution held in a hollow 

 ground slide under a binocular microscope. Very fine sewing 

 needles mounted in matches served as excellent instruments. 

 When the parasites had killed the aphids, they were removed to 

 gelatin capsules marked with the number of the cage and 

 date of removal. These were then filed in small cardboard 

 boxes, by the month, for further reference, in watching their 

 development from then on. These developments in the capsules 

 were checked by cage rearing and found to coincide. Gelatin 

 capsules were made use of as containers for all the material 

 that was retained for future reference. 



