COLEOPTERA. 
577 
There is considerable variation in the size and shape of 
these spots; frequently the two near the base of the wing- 
covers are joined so as to make a continuous band extend¬ 
ing across both wing-covers. The larva feeds on milkweed 
(Asclepias). 
The Diabroticas.—Several very important pests belong 
to the genus Diabrotica (Di-a-brot'i-ca). In the East they 
are known as cucumber-beetles ; but on the Pacific coast, 
where they are more feared on account of their injuries to 
fruit and fruit-trees, they are commonly called the Dia¬ 
broticas. They are chiefly greenish-yellow beetles, marked 
with black stripes or spots. The Striped Diabrotica, D. 
vittata (D. vit-ta'ta), has two black stripes on each wing- 
cover. The adult feeds on the leaves of cucumber, squash, 
and melon; and the larva, which is a slender, worm-like 
creature, bores in the stems and roots of the same plants. 
The Twelve-spotted Diabrotica, D. duodecimpunctata (D. 
du-od-e-cim-punc-ta'ta), and Diabrotica soror (D. so'ror), 
agree in having six black spots on each wing-cover (Plate t 
Fig. 2). The former is very common in the East; the 
latter occurs on the Pacific coast, and is the most destructive 
of all of the Diabroticas. Diabrotica longicornis (D. lon-gi- 
cor'nis) is a grass-green species, which feeds on the pollen 
and silk of corn and on the pollen of other plants. Its 
larva is known as the corn root-worm ; it is very destructive 
to corn in the Mississippi Valley. Its injuries are greatest 
where corn is grown on the same land year after year ; 
hence a rotation of crops should be practised where this pest 
is troublesome. The other species of Diabrotica mentioned 
above are difficult to combat, as the leaves of cucumber, 
melon, and squash are very apt to be injured by the use of 
arsenical poisons. The most practicable way of protecting 
these vines is to cover them while young with frames cov¬ 
ered with netting. Where they infest fruit-trees they can 
be fought with Paris-green ; but this poison must be used 
with great care on such trees as prune and apricot. Squashes 
38 
