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Walton (W. R.). The Hessian Fly and how to prevent Losses from 



it. — U.S. Dep. Agric, Washington, B.C., Farmers' Bull. 1083^ 

 March 1920, 16 pp., 13 figs. [Received 7th July 1920.] 



Much of the matter contained in this bulletin has already been 

 noticed {R.A.E., A, iii, 416]. In the chief winter- wheat growing regions 

 of the United States the Hessian fly, Mayetiola {Phytojpliaga) destructor^ 

 is the most injurious enemy of the wheat crop. Damage by this pest 

 amounting to £20,000,000 in a single year has been known to occur. 

 Barley and rye are injured to a less extent, and oats are not attacked. 

 The larvae feed on the stems under the sheath. In severe infestations 

 much of the yoimg wheat may be killed outright, particularly in the 

 case of the autumn brood larvae ; otherwise as the wheat head grows 

 heavy with grain the stem bends, or even brealcs ofi at the weakened 

 spot, and the head falls to the groimd out of reach of the harvesting 

 machinery. Infested plants are usually of a darker colour, with 

 shorter, ranker leaves. 



The insect has adapted its hf e to varying cHmatic conditions in that 

 the SI mmer pupal stage is short in the north and long in the south. 

 The effect of cold on the fly seems to have been overestimated. Eggs 

 are laid in quite cold weather, and frosts seem only to delay their 

 hatching. The immunity of late -sown wheat is not due to frost, 

 but to the fact that most of the flies have disappeared by the time that 

 severe frosts occur. Larvae in the puparia have been known to ^ 

 survive for more than two years. By apphcation of the biocHmatic 

 law [R.A.E., A, viii, 87, 278] it is indicated that the first general I 

 colouring of the foUage is as a rule coincident with the safest and best i| 

 time to begin sowing wheat on any farm within the range of winter .j 

 wheat culture. I 



Parasites play a very important part in the control of the Hessian 

 fly. Often one species will almost exterminate the pest in a particular 

 locaUty. They cannot however be depended upon for control. Polyg- 

 notus Jiiemalis is perhaps the most useful, and Eupelmus allyni is 

 known to be of considerable importance, though it sometimes functions 

 as a hyperparasite. More than twenty species of insect parasitesof th e 

 Hessian fly are now known, but many of them are apparently of httle 

 importance under most conditions. 



Once estabhshed the Hessian fly cannot be reached by any control 

 measure, though the apphcation of a quickly acting fertiliser to increase 

 the vigour of the plants may be beneficial. Preventives however 

 have an important efiect ; crop rotation lessens the activity of all 

 wheat pests and should be carried out where practicable ; stubble 

 should be ploughed deeply, and the surface roUed or harrowed, to 

 prevent the flies emerging ; but this should not be practised, under 

 existing systems of rotation, wherever it seriously interferes with the ^ 

 growing of clover or the forage grasses necessary for maintaining i^ 

 the proper tilth of the soil. Self-sown wheat, which acts as a breeding 

 place, should be destroyed. Everything possible should be done to 

 ensure a strong crop by care in preparing the seed-bed and conserving, 

 moisture, and the use of the best seed and of fertilisers. 0^ving to the ^ 

 fact that the majority of the flies of the autumn brood survives for IM 

 about a week only, it is possible so to time the seeding of wmter wheat 

 as to avoid the pest, and this is one of the most effective measures that 



