320 NATURAL HISTORY OF ARTHROPODS. 



Among the many insecticides which are used to reduce the numbers of Doryphora, 

 Paris green and London purple are generally considered best. Paris green, or as it is 

 sometimes called Scheele's green, is an arseniate of copper often used as a pigment. 

 It is extremely poisonous, and is diluted with twenty times its weight of flour and 

 sprinkled with a sieve upon the potato-plants. London jjurple, which is a •vf^'Ste 

 product of anilin manufacture, contains about forty per cent of arsenic, and although 

 very much cheaper than Paris green it is still more poisonous, and is used in the same 

 wa;y, diluted with about thirty-six parts of flour. In all cases where these poisons are 

 used cattle should be carefully excluded from the fields. 



Severe cases of poisoning from handling the beetles themselves, in quantity, have 

 been reported ; likewise the vapor arising when they are killed by scalding is said to 

 be poisonous. While such cases of poisoning are apparently authentic and are not 

 improbable, yet the question of the poisonous nature of Doryphora is one that requires 

 much further careful investigation than it has received. 



Very closely related structurally to Doryphora, which is itself sometimes retained 

 in the genus Chrysomela, is C. clivicollis and G. scalaris. G. clivicollis, which is 

 often called C. trimaculata, is about 0.4 inch long, with deep blue head, 

 thorax, antennas, legs, and under-side, while the elytra are reddish orange 

 with a few blotches of black upon them. Its reddish larva, which re- 

 sembles in form that of Doryphora, feeds, like the imago, upon species 

 ¥ia.S66. — civry- °^ milk-wecd (Asclepias). G. scalaris is one of a gi-oup of chrysomelids 



'cMil? "^^"'^ which have the elytra covered with curious hieroglyphic stripes and mark- 

 ings, whence they have been given by some authors the generic name of 

 CaUigrapha. The greenish-black and white imago, which is about 0.3 inch long, after 

 passing the winter under leaves and in rubbish, appears early in the spring upon elm 

 and linden trees and on the alder. Its eggs are deposited in May and June, and the 

 larvae of the first brood reach full growth by the end of the latter month. The lai-vje 

 have similar form to those of Doryphora, but are whitish, somewhat spotted with black. 

 Similar species of GaUigrapha are found on the hazel ( Gorylus), on Viburnum, and 

 on willow (Salix). 



In southern Europe the larva of Ghrysomela diluta is nocturnal, as is the case with 

 some lepidopterous larvae, and comes out of its hiding places where it spends the day 

 to feed upon a species of plantain {Plantago coronopus) at night. The larvte of a few 

 chrysomelids have a habit, when disturbed, of forcing out upon the tips of spines which 

 are arranged in rows along their bodies, little drops of a disagreeably odorous milky 

 fluid. These drops of a secretion, which is, of course, defensive in function, can be 

 again withdi-awn into the spines when danger is past. Professor C. Glaus found 

 salicylic acid in the larva of G. populi, the European species in which this peculiar 

 secretion has been most studied. In America larv£e of Plagiodera scripta, D. lap- 

 pontca, and P. tremulce have similar secretions. 



Gastrophysa polygoni is an oblong beetle, about 0.15 inch long, of which the 

 prothorax, legs, and basal joints of the antennae are reddish brown, the rest of the 

 insect shining blue, except in the case of females when they are much distended with 

 eggs ; then the portions of the distended abdomen which the elytra cannot cover are 

 yellow or yellowish brown. This beetle is very abundant from April to September 

 upon common knotgrass {Polygonum aviculare) both in Europe and in America. 

 The groups of yellow eggs on the leaves of the knotgrass hatch in from eight to eleven 

 days. The yellow larvae resort to the ground for pupation. There are two or three 



