366 



Tfie Hessian Fly. 



Vol. IX. 



membrane, er scarf, — which, not long previ- 

 ous, was its outer skin — through which many 

 parts of the future fly maybe distinctly seen. 

 Finally, this scarf splits along the thorax, or 

 back, and the insect comes forth, both from 

 this and the pupa shell, a perfect two- 

 winged %. 



This is, in brief, the history of an indi- 

 vidual which has been so fortunate as to es- 

 cape ail the numerous enemies with which 

 its race is surrounded from the moment the 

 egg is deposited ; but of these more here- 

 after. 



In the northern and middle States, at 

 least, winter wheat is sown in September 

 or October. Soon after the plants have ap- 

 peared above ground, the Hessian fly begins 

 to lay her eggs upon them ; and this opera- 

 tion is continued during several weeks, ac- 

 cording to the season. The eggs laid on 

 the green leaves are in a few days hatched, 

 and the young larvfe crawl down the stalk, 

 and 'take their stations; generally clustering 

 around the stalk at the nearest joint below. 

 Here, by sucking the plant, they increase 

 in size, become full and hard, and pressing 

 deeply into the stalk, they impair its growth ; 

 and if their number about one joint is large, 

 the stalk is killed. Frequently the plant, 

 aHhough impoverished, advances far enougli 

 to head out ; bu^t when the grain begins to 

 fill, its own weight, or perhaps the wind, 

 causes the stalk to bi-eak down. The injury 

 done to the wheat is occasioned by the ex- 

 haustion of the sap, and by the pressure on 

 the yielding stalk. 



In five or six weeks the larvse stop feed- 

 ing, the outer skin turns brown, and within 

 this brown and leathery case the pupas pass 

 the winter — generally a little below the sur- 

 face of the earth. In April and May the fly 

 is again found depositing her eggs on the 

 same wheat,— viz: that from g>rain sown tiie 

 preceding autumn,— and also on tJie spring 

 wheat which has just come up. These eggs 

 batch, and the larvas therefrom operate in 

 the same manner as those of the autumn 

 previous. These larva; become pupfe about 

 ihe middle of June. The flies which lay 

 their eggs in the spring are probably in part 

 from tiie pupae which became such late in 

 the preceding autumn, and partly from pupie 

 contained in stubble left the preceding sum- 

 mer. The period of the existence of the 

 Hessian fly in the pup« or flax-seed state is 

 exceedingly variable. After much observa- 

 tion my own opinion is, that in general, pu- 

 pa? which become such late in the autumn, 

 evolve the winged insect partly during tiie 

 next spring, and partly in the summer and 

 autumn following. Those pupjE which be- 

 come such about June, evolve the winged 



insect partly during the next autumn and 

 partly during the year succeeding. 



The Hessian fly is attacked by numerous 

 foes, which, in various stages of its exist- 

 ence, -destroy a large part of e\'ery genera- 

 tion. Whether it has, in its winged state, 

 any enemies, except tlie ordinary destroyers 

 of flies, I know not. The eggs, while lying 

 on the leaves of the young plant, are visited 

 by a very minute four-winged insect, — a 

 species of platygaster — which lays in them 

 its own eggs. From later observation it ap- 

 pears that occasionally, as many as five or 

 six eggs of this parasite are laid in a single 

 eg^ of the Hessian fly. The latter egg 

 hatches and becomes a pupa, asAisual; but 

 from the pupa .case, instead of the Hessian 

 fly, issues one or more of these minute para- 

 sites. 



The pupa?, while imbedded in the stalk, 

 are attacked by at least three different mi- 

 nute parasites, — four-winged hymenoptera — 

 wjiieh, boring through the sheath of the stalk, 

 deposite their eggs in the body within; and 

 the latter is finally devoured by the parasite 

 larv;e. These are the principal means by 

 which the multiplication of the Hessian fly 

 is restrained within tolerable limits. 



Although the loss annually sustained by 

 the wheat growers of this country, in eon- 

 sequence of the ravage^ of the Hessian fly, 

 is severe, yet it is well nigh impossible to 

 ascertain even its probable amount. As 

 long since as 1800, Dr. S. L. Mitchell, of 

 New York, affirmed tiiat the -"insect is mor-e 

 formidable to us than would be an army of 

 twenty thousand Hessians." In 1804, Pre- 

 sident Dwight, of Yale college, remarked 

 that "this insect is feeble and helpless in 

 the extreme, defenceless against the least 

 enemy, and crushed by the most delicate 

 touch ; yet, for many years, it has taxed 

 this countay, annually, more, perhaps, than 

 a million of dollars." At the present day, 

 the amount of the injury inflicted probably 

 far exceeds what it was forty years since; 

 and to discover some feasible mode of exter- 

 minating the insect, or at least of arresting 

 its ravages, is an object of great importance 

 to this country. 



Various remedial measures have, from 

 time to time, been proposed ; most of which 

 I v.'ill here state. 



1st. Steeping the seed-wheat in elder 

 juice, solution of nitre, boiling water, or 

 other liquids; or rolling in lime, ashes, or 

 some other substance, in order to kill the 

 eggs. But as the eggs of the Hessian fly 

 are not on the seed, they will never be liurt 

 by such processes, So far as these means 

 give viffor to the plant, they may be of some 

 little service^ 



