Biological Papers. 



315 



leave its host. It then cuts out a neat circular piece near the caudal 

 end of the body and emerges head first. 



The writer first found this parasite at Manhattan, Kan.. Novem- 

 ber 17, 1907, in Mr. Moore's east greenhouse. The infestation of 

 aphids in this house was found to range from three to four on each 

 rose plant. In another house about 100 yards west the infestation 

 was so great that parts of the rose plants were covered with lice. 

 On inquiry it was found the same methods and same preparation 

 were used for fumigating both houses. In the house without the 

 parasite Mr. Moore found it necessary to fumigate at least once 

 every week, while in the other he fumigated only once every 

 month, and then more as a precaution than as a remedy. His rea- 

 son for the difference in the apparent killing power of the smoke 

 in the two houses was that the west house, being more open, did not 

 retain the smoke long enough to kill the aphids; the other, being 

 less open, retained the smoke much longer. Careful examination 

 of the west house revealed no signs of the parasite 



On December 2 five females and two males of Lys^phleh'S cer- 

 asaphis which had not been seen in copulation were introduced. 

 The females began at once to sting the aphids, bat no signs of 

 parasitism appeared until January 6, 1908. From this time on the 

 parasite increased in numbers very rapidly, so that by April 1 the 

 percentage of unparasitized aphids was exceedingly small. The 

 number of both parasitized and unparasitized aphids on ten leaf- 

 lets were counted with the following result: 



Percentage of aphids parasitized, 87.3. 



By May 25 it was almost impossible to find any unparasitized 

 aphids in this house, and Mr. Moore said he had not "smoked" 

 since the middle of March. In these observations neither tempera- 

 ture nor moisture records were kept. 



On April 12 the Lysiphlebus cerasaphis was found in two green- 

 houses in Topeka, Kan. In these it was almost impossible to find 

 any unparasitized aphids, while in another greenhouse in Topeka, 

 where no signs of parasitism were found, the rose plants were very 

 badly infested with lice. On inquiry it was found that the owners 

 of all three houses used the same material for fumigating; but 

 while apparently so effective in the two where the parasites were 

 found that fumigation was unnecessary oftener than once in three 



