252 University of California PuUications. [Entomology 



Olla ociilata Fab., Olla ahdominalis Say, Cycloneda sanguinea 

 Linn., and Adalia hipunctata Linn. 



The writer makes no assertions with respect to the validity of 

 any of the above-named species. The belief is quite general that 

 Hippodamia ambigiia is a varietal form of Hippodamia conver- 

 gcns, and the same claim has been advanced regarding Olla ah- 

 dominalis with respect to Olla oculata. Investigations are now 

 under way to determine the exact status of these forms. 



Laboratory Methods 



At the time the investigations were undertaken an extensive 

 series of tests was made to determine the most satisfactory method 

 of caging the individuals during the period covered by the ex- 

 periment, in order to secure as nearly as possible ideal conditions. 

 Potted plants infested with aphis and covered with chimney 

 glasses were used for a time, but did not fulfill the requirements, 

 due to the fact that moisture often collected on the inside of the 

 glass, and also because the adult beetles showed a strong ten- 

 dency to ascend to the top of the glass and there remain inactive, 

 rather than to feed normally on the infested plant as desired. 

 Later plaster of paris containers, jelly glasses, etc., were used 

 but with indifferent success. By far the best results were finally 

 secured by confining the individuals under observation in ordi- 

 nary three-inch vials with cotton stoppers. Experiments upon 

 larvae necessitated the covering of the stoppers with thin tissue- 

 paper to prevent injury through entanglement in the cottony 

 fibers. The stoppers used were light enough to permit a reason- 

 ably free passage of air, thus maintaining approximately outdoor 

 conditions as regards temperature and humidity. 



In the feeding tests, both with larvae and adults, a certain 

 definite number of aphids of as nearly a standard size as pos- 

 sible were placed in each vial early in the morning and the count 

 made at the corresponding time the following day. The number 

 of live aphids present was determined, and this number sub- 

 tracted from the original luimber gave the total for the day. 

 Check vials containing one hundred aphids each were also main- 

 tained to determine the approximate mortality from imtural 

 causes, and the proportion determined subtracted from the total 

 of all records for the current day. 



