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 I 

 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 longicoriiis (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 



