138 STATE BOARD OF AGRICULTURE. 



For two scaxms tlio fiiowors of wlu'iil, tsix-ciidly those in tlic iiorllicni jiart of the 

 State. Imve l)ocii troubled witli tlie Hessian lly. iind as no detailed aceount of thi.s insect 

 and its niethod of \voii< lias been publislied in tlie Alidiigan bulletins for many years, 

 a description of tlie pest may ])rove of interest. 



As long ago as 1779, the Hessian fly was reported as doing injury in New York. It 

 was for some time sn])])osed that the insect was introduced into this country, in 

 straw, by the Hessians eiii]iloyed by the British in o>ir Revolutionary war, hence the 

 name '"Hessian lly.'' This explanation, however, lias been shown since to be a ques- 

 tionable one. In 1837 the lly appeared at Paw Paw, Michigan, and has been trouble- 

 some from time to time in our State ever since. 



Usually the first intimation a farmer lias that the fly is present is the "lodging" 

 of his wheat. An exaiiiiiial ion of an inj\ire(l wheat jilant is made and just below the 

 l)oint where tlie break occurs, usually just al)ove the first, second or third joint, are 

 found one or more little dark brown bodies (Fig. 1.5, c) about one-eighth of an inch in 

 length. These are the pujiaria. often called the "flax-seeds," and correspond to the 

 cocoons of many moths or the chrysalids of butterflies. 



This brintrs us to the (luestion of the stages through which insects pass in a 

 lifetime. Most insects pass through four iiriiicijial stages or what correspond to them, 

 viz. — the egg. the larva (caterpillar or grub) stage, the chrysalis ( cocoon or pupa ) stage, 

 and the adult stage. Now the third of these stages, the chrysalis or cocoon, is usually 

 a (|uiescent one. the insect haA'ing little or no power of motion. In some cases it is 

 only during this jx'iiod tliat we can effectually combat some particular insects which 

 do injury in some one of the other stages. In the case of the Hessian fly, the eggs 

 are laid usually on the upper side of the leaf, singly or in small groups of two or 

 three. In about four days they hatch and the minute maggots which come from them 

 work their way down between the sheath of the leaf and the stem, where they com- 

 mence to feed and to grow, at the expense of the plant. After a time the maggots 

 become full grown and ready to pass into the pu])al or flax-seed stage, when the outer 

 skin becomes hard and rigid, forming a protecting shell, inside of which the insect 

 can become a winged fly. Tliis ])upal or flax-seed stage is the one most likely to be 

 first noticed. After a time the sliell liursts and out comes a delicate fly of very minute 

 ))roportions. the female (ly ordiiiavily measuring one-tenth of an inch in length and 

 the male slightly less. 



The life cycle is probablj^ passed through twice a year in Michigan, though in some 

 states more time seems to be required and in others lefts.* For the winter brood the eggs 

 are laid some time in late August. September, or early October, on fall wheat, usually 

 just coming up. The young grubs go down to about the level of the ground and 

 soon become full grown, ready to become pupae for the winter. In the spring they 

 come out as adult, winged flies, and in April or IVIay they lay their eggs on the young 

 wheat. The young grubs of the spring brood behave just like those of the fall brood, 

 except that they do not go so low down in the plant, usually working just above 

 the first, second or third joint. All the adult flies do not come out at once, but 

 occupy some time in doing so, with the result that the l)roods are not so distinct as 

 ■would be expected. 



>-.\TURAL EXEjriES. 



Fortunately this insect is kejit in check ordinarily by other insects which prey upon 

 it. These other insects belong to the group of parasitic hynienoptera and are very small. 

 They lay an egg in the body of the maggot or on the ])upa. which egg gives forth a 

 still smaller grub that subsists on the living body of its host, after a time passing 

 through a pu])al stage and finally becoming an adult winged insect inside the remains 

 of the Hessian fly maggot. At tlie proper time this winged insect, resembling a minute 

 wasp, comes out and lays more eggs in other flies. These parasites usually keep the 

 Hessian fly under control, but occasionally for some reason, climatic or otherwise, the 

 parasites become reduced in numbers or are unable to devour all the flies, and then 

 our wheat, rye. etc., suffer. If we know what a goodly su])]ily of ])arasites are ))resent 

 in the fields, it is best to wait for them to destroy the flies and not to resort to meas- 

 ures which would destroy friend as well as foe. The presence of the parasites is best 

 known by the small holes left in the w^heat stem through which they emerge from the 

 pupa of the fly. The fly itself, wlien uninjured by parasites, cracks open the shell of 

 the flax-seed and crawls up between the sheath and stalk. l)ut the parasite bores a 



* Dr. Paul Marchal (Les C'ecidoiiiyies (leg f'ereales et leurs Parasite Ann. de la Soc. Ent. ile France, 

 1897) says they may be six l)roM(leil under the most favorable conditions. 



