21 



just above the joint. The eggs, as with those of the spring- brood, hatch 

 in a short time, and the larvae reach maturity b}^ the time the straw 

 has become too tough and dr}" to afford further nutriment. The larva 

 at this time usually gnaws its wa}^ down into, or at least partly into, 

 the joint, and without forming cell or cocoon, about October passes 

 into the pupal stage. 



DESCRIPTION. 



ADULTS OP SUMMER FORM. 



{Isosomu grande Riley.) 



Length of body, 4.2 mm. ; expanse, 7.6 mm. Antenna3 rather more slender and 

 less clavate than in the spring form and but half the length of the thorax. Thorax 

 with the mesonotum slightly more rugulose; wings larger and less hyaline than in 

 the winged specimens of the spring form, with the veins extending to the outer 

 third, the submarginal nearly four times as long as the marginal; legs with the 

 femora less swollen. Abdomen not so long as the thorax, stouter than in the spring 

 form, ovate-aouminate, ajjproaching typical Eurytoma. Less hairy than in the spring 

 form, esi^ecially al)out the legs, the haiis about the abdomen l)eing less numerous, 

 less regular, and shorter. Coloration similar to that of the spring form, but brighter 

 and more highly contrasting, the promotal spot larger and l)righter yellow, the 

 pedicel of the antennte yellow, and the femora with a delinitely limited suboval 

 yellowish spot below, near the tip, extending two-fifths the length of the femur on 

 front pair, smaller on middle pair, and still shorter and less definite on posterior 

 pair. 



Larva greenish yellow in color. Average length, 6 mm. ; otherwise of same pro- 

 portions and structure as in spring form.« 



Piqm, average length, 5 mm. Except in larger size and ample wingpads undis- 

 tinguishable from that of the spring form, mhiutum. 



Egg of the ordinary ovoid form with pedicel about twice as long as the bulbous 

 part. The apical end is furnished with a distinct hook, perhajas for the purpose of 

 holding the egg in place while the ovipositor is being withdrawn from the plant. 



ADULTS OF SPRING FORM. 



(Isosoma minutum. ) 



Length of body, 2.8 mm.; expanse of wings, 4 mm.; greatest width of front wing, 

 0.7 mm.; antennae, subclavate, three-fourths the length of thorax; whole body 

 (with exception of metanotum, which is finely punctulate) highly "[polished and 

 sparsely covered with long hairs toward the end of abdomen; abdomen longer than 

 thorax and stouter. Color, pitchy black; scajae of antenna?, occasionally a small 

 patch on the cheek, mesoscutum, femoro-tiljial articulations, cox?e above and tarsi 

 (except last joint) tawny; pronotal spot large, oval, and pale yellowish in color; 

 wing veins dusky yellow and extending to beyond middle of wing; submarginal 

 three times as long as marginal; postmarginal very slightly shorter than marginal, 

 and stigmal also shorter than marginal. (See Riley, Am. Nat., 1882, p. 247.) 



Larva, length, 4.5 mm.; of the shape indicated in fig. 3; color pale yellow; mouth 

 parts brownish. Antenn;e appearing as short two- jointed tubercles. Mandibles 

 with two teeth. Venter furnished with a double longitudinal row of stout bristles, 

 a pair to each joint. Each joint bears also, laterally, a short bristle. Stigma pale, 

 circular; ten pairs, one on each of joints 2 (mesothoracic) to 11. 



Pupa, jet black Avithout other coloring; smaller than that of summer form. That 

 is to say, the pupee wintering over in the straw and from which the spring form 

 deVelops is thus to be described; that following the larvte developing in spring is 

 understood to belong to the summer form. 



« Riley, Ann. Rept. IT. S. Dept. Agr., 1884, p. 58. 



