THE WESTERN CABBAGE PLEA-BEETLE. 11 



mated more nearly the soil temperature in the field. Much below 

 this the larvae did not develop well and above 80° there was a con- 

 siderable increase noticeable in the death rate. If too much mois- 

 ture accumulates in rearing jars or "cages", the air becomes satur- 

 ated during the day and at night cools off and condenses. This is 

 detrimental to the larvae, as they often become submerged in drops 

 of water. 



The young larvae feed on the hair roots of their food plants and the 

 older ones feed also on the main stalk and branches. 



It was necessary to supply fresh roots every two or three days as 

 decay is apt to set in. Parts of the crown of small turnips were sup- 

 plied to the larvae as food and they fed on this readily but did not 

 seem to do as well as on fresh radish roots. 



Upon reaching maturity the larvae cease feeding and crawl rest- 

 lessly around for a day or so before entering the soil. They make 

 a distinct pupal cell with the inside compact and tightly cemented. 

 Larvae were observed in these cells, in a number of cases, for several 

 days before they began to shorten. The contracted prepupal 

 period ordinarily lasts 4 or 5 days. 



Several times soil was secured in the field and brought to the 

 laboratory and examined for larvae or pupae of this flea-beetle. In 

 no instance was any larva or pupa observed. A number of ex- 

 aminations for larvae and pupae were made by digging around the 

 roots of growing turnips and radishes, but neither was ever found 

 in the field. 



Since the eggs and larvae in the laboratory seemed to be so sus- 

 ceptible to excessive moisture, the opinion was reached that it 

 might be possible to control the species in the egg, larval, and pupal 

 stages in the field by the practice of irrigation. Whenever the 

 plants are irrigated, the soil around the roots is quite thoroughly 

 soaked and it seems likely that the eggs, larvae, and pupae may not 

 be able to withstand this. 



LIFE CYCLE. 



In working out the life history of the western cabbage flea-beetle 

 adults were captured in the field and confined in cages consisting of 

 battery jars and glass-covered boxes. The lid of a small tin salve 

 box, filled with moistened earth, was placed in each cage, and in 

 this earth the beetles deposited their eggs. The lids containing the 

 earth were removed daily or at intervals of two or three days and 

 placed in larger salve boxes. Food was supplied the larvae by 

 placing sprouted radish seed on the surface of the earth in the boxes. 

 As the larvae neared maturity most of the earth was removed from 

 the lids in order to enable a close observation of the pupae. 



