INJURIOUS AND BENEFICIAL INSECTS OP CALIFORNIA. 



369 



This is unfortunate, as control measures are difficult and poorly worked 

 oid. Pasturing the fields or destroying all clover and alfalfa heads 

 m the winter, as well as the destruction of the straw after threshing, 

 are the check measures recommended. Infested seed should not be sown. 



THE WHEAT JOINT-WORM 



Isosoma tritici Fitch 20 " (Family Eurytomida; ) 

 (Figs. 366, 367) 



Description. — The adults are very small, shiny-black, four-winged 

 insects. The joints of the legs, feet and two spots on the shoulders are 

 yellow. The females are 

 about 4 inch and the males 

 1-9 inch long. The full- 

 grown larvae or grubs are 

 legless, yellowish or whitish 

 with brown mouth parts and 

 about ^ inch long. The 

 pupae are about the same 

 size as the larvae and at first 



the same color, but 



gradually become 



darker as they 



mature. 



Life History. — 

 The w inter is 

 passed in the larval 



stage in cells within the stems of the wheat. The larvae 

 pupate in the spring and issue as adults in April and May. 

 The females deposit their eggs in the uppermost joints of the 

 stems of the growing wheat, by means of the sharp ovipositor. 

 The eggs hatch very soon and the larvae feed within the stalks 

 at or near the joints, producing knots or swellings. The 

 entire summer is spent within the stems, the larvae becoming 

 full-grown when the grain ripens. The cells for hibernation 

 are made at this time. There is but a single brood 

 a year. 



Nature of Work.— The work of the wheat joint- 

 worm is very characteristic and consists of various 

 knots, swellings or other distortions of the stems near 

 or between the joints. An angle of thirty degrees 

 may lie formed in the main stalk at the place of attack. 

 The stems become very brittle at these points and 

 break easily. Thus much of the wheat may fall before 

 harvest time. In threshing, hard, broken bits of the 

 straw remain with the wheat, greatly reducing its value. 



Distribution.— This insect was reported at Sacramento as early as 

 1895. 267 Woodworth 268 also lists it in his work on California insects. 

 However, the insect does not appear to be a serious pest in California. 



M0 Prof. R. W. Doane reports to have collected this fall (1914), in Shasta County, 

 what he believes to he the larvae of the wheat straw-worm, Isosoma grande Riley. 

 -'■ 7 Rept. Cal. Agrcl. Exp. Sta., p. 245, 1N''4-.V 

 -""Woodworth, C. W., Guide to Cal. Insects, p. 120, 1913. 



24—13664 



Fig. 366. — Adult of the wheat joint-worm, 

 Isdsoir.a tritici Fitch. Natural size is shown by 

 t'li- line at the light. (After Howard, V. S. 

 D« pt. Agi ic. i 



Fig. 367.— W'heat 

 stem showing the 

 work of the wheat 

 joint-worm, Isosoma 

 tritici Fitch. Re- 

 duced. (After Web- 

 ster, U. S. Dept. 

 Agric.) 



