18 SOME INSECTS INJURIOUS TO TRUCK CROPS. 



The pupa. — The pupa is illustrated by figure 5, d^ which will 

 answer better than a verbal description. The color is yellow, and the 

 .length is slightly less than that of the adult. 



The distribution of this species is probably moderately Avide and 

 additional study must be given this subject. At present we know of 

 its occurrence in the District of Columbia, in Massachusetts, and 

 probably in West Virginia. 



LITEKATURE. 



Brief mention of the occurrence of this leaf-beetle as an enemy of 

 water cress in Pennsylvania in 1893 was made by the Avriter," but 

 Mr. Frederick Knab, of this office, mentioning the same species as 

 Plagiodera riridis, has recorded ^ its occurrence in great abundance 

 upon water cress near Springfield, Mass., in 1902. The identity of 

 the species in question has been verified by the comparison of speci- 

 mens, and Mr. Knab's record was evidently made on the assumption 

 of Crotch ^' that wrughiosa was merely a variety of viridis. 



HABITS OF THIS AND A RELATED SPECIES. 



We can not at the present writing give an approximate statement 

 of the life histor^^ of Plnvdon ainiginosa, and hence must depend on 

 what is known of the related Ph. armoracia', which is common to both 

 continents.'' This letter has evidently been introduced into this 

 country, but its habits have apparently not been studied here. Tt is 

 known in England as the blue beetle and mustard beetle,'' and is of 

 considerable importance locally, in some seasons ravaging entire 

 fields of mustard, cress, cabbage, and kohlrabi. Tt passes the winter 

 as adult, reappearing in spring on cruciferous plants. Fryer stated 

 that in the three years prior to 1881 the Isle of Ely, England, suffered 

 from the ravages of this species, entire fields being injured. Mustard 

 was attacked at about the time of the formation of the seed pod and 

 after the stalks were stripped nearly to the cuticle the beetles trans- 

 ferred their attention to kohlrabi, which they completely consumed, 

 at first attacking the leaves and afterwards the bulbs, leaving nothing 

 but bare stalks. 



The water-cress leaf-beetle is doubtless no exception to the general 

 rule among most Chrysomelida? and other species of Phaxlon, in 

 laying its eggs on the under side of the leaves. Both larvie and 



oYbk. U. S. Dept. Agric. f. 1903 (1904), p. 5G4 ; & Entomological News, March, 

 1903, p. 89 ; c Crotch, Proe. Acad. Phila., 1873, pp. 54, 5-5 ; ^ Phadon armoraciw 

 L. syn. : Plagiodera cochlcaricr Pauz., Gyll. ; Phadon hetiiJw Kiist. It is not 

 the same as (■othlearuc Fab. e Fxyer and dtliors have given accounts of this 

 species in The Entomologist (Vol. XIV, pp. 44, 187, etc.). 



