22 



Report on the Diseases of Wheat. 



Section XIII. — On the Wheat-Midge. {Cecidornyia tritici.) 



Nothing is more common in wheat-fields^ than to find one, 

 two, or more of the flowers, in many ripe ears, defective in the 

 grain ; even though the parts of the flower had been well formed. 

 This effect may be owing to a variety of causes ; and among 

 others, is frequently occasioned by a minute two-winged fly called 

 the wheat-midge, (Cecidomyia tritici.) This fly may be seen in 

 myriads, in the early part of June, between seven and nine o'clock 

 in the evening, flying about the wheat, for the purpose of depo- 

 siting its eggs within the blossoms. From these eggs are hatched 

 small yellow maggots, which are the caterpillars {larvce) of this 

 fly; and by these the mischief is occasioned. Mr. Kirby, the now 

 venerable patriarch of Entomologists, so long ago as 1798, gave 

 an interesting account of the habits of this insect, to which the 

 attention of naturalists had been directed by Mr. Marsham about 

 two years before. These accounts will be found in the third, 

 fourth, and fifth volumes of the " Linnean Transactions. It has 

 been supposed that the wheat-midge caterpillars feed on the pol- 

 len after it has been shed from the anthers, and thus prevent the 

 fertilization of the ovules, or young seeds ; but it seems hardly 

 likely that the pollen of one flower should be sufficient to support 

 a single caterpillar, much less several, for a month or more. Mr. 

 Kirby has suggested, what I should consider a much more plau- 

 sible theory, that the caterpillars, with their heads immersed in 

 the stigmata^ live upon the juices secreted by the ovary, and thus 

 obstruct its growth, whether it may have been fertilized or not. 

 Be this as it may, these caterpillars are certainly, in some way, the 

 cause of the non-development, or abortion of the ovary, so that the 

 grain never advances beyond the state in which it appears at the 

 time the flower first expands. A figure of the fly and its cater- 

 pillar is given in the Linnean Transactions and likewise in the 



Magazine of Natural History," vol. i. p. 227, where Mr. Kirby 

 has also given another figure, and a short notice of a different 

 species of the same genus, called the Hessian fly {^Cecidomyia 

 destructor), which is particularly injurious to wheat in North 

 America. This latter, however, does not deposit its eggs in the 

 flower, like our own wheat-midge, but near the base of the straw, 

 within which the caterpillars are hatched, and these devouring its 

 substance cause it to break off near the root. The caterpillars of 

 the wheat-midge are about the 12th of an inch in length, without 

 legs, and of a citron-yellow colour ; and when they are about to 

 pass into the chrysalis {jpupa) state, they spin themselves up in a 

 very thin and transparent web, which is often attached to a sound 

 grain, or to the inside of one of the chaff-scales. The chrysalis is 

 of a reddish orange colour. 



