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



The above observations seem to indicate that Aphelinus 

 places but one egg in a host, but that it is incapable of deter- 

 mining whether a given host harbors a parasite already until 

 the ovipositor is inserted. The above habit is decidedly in its 

 favor when its efficiency as a parasite is considered in contrast 

 to some of the more wasteful species like Aphidius, which gen- 

 erally places a number of eggs in a single host, but only one of 

 the resulting larvae matures. 



Number of Eggs Laid per Day and Night. — To determine 

 the number of eggs laid per day and night over the period of 

 egg production, experiments were carried out with a single 

 Apheliniis confined with a given number of nymphs from the 

 first to the third instar. Dissections were made on these both 

 in the evening and morning, and a fresh supply of parasite-free 

 aphids placed in the cage for the parasite to oviposit in for the 

 succeeding period. During the night, the cages were kept in a 

 dark chamber so that practically absolute darkness prevailed 

 until the time came to change to light. As nearly equal periods 

 of light and darkness were obtained as was possible; likewise, 

 other factors, such as temperature and humidity, were fairly 

 uniform. All experiments were carried out in room 107 of the 

 Botany and Zoology Building, in a temperature of from 70 to 

 75 degrees. 



Owing to the extreme minuteness of the specimens dealt with, 

 considerable difficulty was experienced in carrying a single 

 parasite through its total life without its escaping or being 

 accidently killed in handling. This was so great that only one 

 specimen went through its total period of egg production to a 

 natural death. Two others were carried for seventeen and 

 eighteen days respectively before they escaped or were acci- 

 dentally killed. The results of these experiments appear 

 graphically in Figure 1. 



Feeding. 



It is quite evident from observations made that the com- 

 monest means of sustaining life in the adult Aphelinus is by 

 its habit of feeding at the puncture holes made by the ovipositor 

 in the young aphids. 



This habit is not restricted to Aphelinus alone, but seems to 

 be rather common among chalcid parasites in general. The 



