416 



this insect in its mine, while after leaving the mines, numbers are killed 

 by spiders and birds. There are many generations with consider- 

 able overlapping, so that larvae may be found any time from May to 

 October, the dommant period being reached during July and August. 

 The Ufe-cycle is completed in a little over a month in the summer. 



Webster (F. M.). The Hessian Fly.— C/. S. Dept. Agric , Washington, 

 D.C., Farmers' Bull, no 640, 17th March 1915, 20 pp., 17 figs. 



Mayetiola destructor, the Hessian fly, causes serious damage to the 

 wheat crop in the United States. Probably two generations occur 

 during favourable seasons ; in the south heset are widely separated, 

 while in the north, in regions of spring wheat-growing, they follow 

 each other in quick succession. In autumn wheat-growing sections, 

 the winter is passed in the larval or pupal stage in the young wheat 

 just above the roots. Adults, emerging in spring, deposit eggs on the 

 wheat and the young from these pupate before harvest, passing the 

 summer in the stubble. Adults from the over-wintering larvae 

 hatch later, giving rise to a so-called supplementary second generation. 

 Eggs are deposited on the younger plants ; the larvae which emerge 

 may develop into pupae which pass the winter as such, or may 

 produce adults which give rise to another generation. In the north, 

 egg-laying begins in May and the second generation quickly follows 

 the first. In America, the insect is distributed over the eastern and 

 central States and Cahfornia ; it has also been recorded from north 

 Africa, Europe, Western Asia, New Zealand, and parts of Canada. 

 The chief food-plant is wheat, then barley and lastly rye ; it also 

 appears to breed freely on Agropyron smithii and A. repens. An 

 infested wheat plant is without stem, the leaves are short and of a 

 deep bluish-green colour, changing later to yellow or brown. In 

 summer, the effect of the fly is to cause the straw to break before 

 harvest. Most varieties of wheat are attacked when young, but the 

 second brood does not seriously injure more matured plants with 

 strong, stiff straw. Durum wheats do not seem to attract the fly, at 

 least, not the second brood. Weather conditions seem to have an 

 important influence on the fly. Heat and drought tend to keep 

 the insect in the pupal stage. Lack of moisture seems to be very 

 important in influencing distribution and development of the full 

 generation. Among the natural enemies are the Proctotrupids, 

 Platygaster herricki and Polygnotus hiemalis, and the Chalcids, Eupehmis 

 allyni, Merisus destructor, and Boeotomus subapterus. All remedial 

 measures must aim at (1) the elimination of the pest in the young 

 wheat in autunm, and (2) increase of the vigour of the young plants 

 to coimteract the injury. In northern Michigan, wheat may be sown 

 without danger from the fly in early September ; in southern Ohio, 

 after the first week in October. A corresponding delay should be 

 followed to the southward. Crop rotation compels the fly to travel 

 a greater or less distance to reach wheat plants. Burnmg the stubble 

 will destroy the fly and any other insects present. Growth of the 

 self-sown wheat menaces the crop of the following year. The 

 destruction by ploughing must take place before the larvae have 

 matured. The use of good seed and a thoroughly prepared, fertile 

 soil will enable infested plants to retain sufficient vitahty to withstand 

 the winter. 



