INJURIOUS INSECTS OF 1904, 



BY F. L. WASHBURN, State Entomoloj^ist. 



THE HESSIAN FLY. 



This pest, destined to be with us always in greater or less 

 abundance, which was so troublesome last year, has hardly been 

 heard from during the season just closed. An assistant found some 

 July 2 1 St on rye in Kandiyohi county, and rumors of its occurrence 

 in Marshall, Morrison, Big Stone and Lac qui Parle counties reached 

 us during the summer, but there has been practically no injury what- 

 ever in Minnesota to wheat this year by this t^y. Owing to its very 

 general absence in localities infested last year, we have been unable 

 to secure pupse ("liaxseeds") in volunteer wheat, as we did last 

 year, showing the occurence of an extra brood in this state. Two 

 lots of volunteer wheat plants, from eight to ten inches high, were 

 sent us in November ; one lot from Marshall county and one from 

 Big Stone county, in both of which counties the fly was thought to be 

 present. Several hundred of these plants were carefully examined, 

 but, contrary to last year's experience, we found no puparia. 



Why this pest should have been so extremely abundant last year, 

 causing losses variously estimated at from 10 per cent to 50 per cent 

 and in a few cases 100 per cent, and so extremely scarce this year 

 is easily accounted for. Several minute parasites, also insects, attack 

 it, and as the fly became more abundant, naturally, from the practi- 

 cally unlimited amount of food the numbers of the parasites increased, 

 and finally became so large that the fly succumbed, and in the year 

 following the one in which the flies and also their parasites were ex- 

 ceedingly abundant, we see none. But this great reduction in the 

 numbers of the Hessian Fly removes the food of the parasites, and 

 consequently their numbers decrease also, and this gives the fly a 

 new start, its numbers increasing each year, if climatic conditions are 

 favorable, until the culmination is reached in a year when great 

 damage is done, owing to their excessive numbers. The following 

 year, for the reasons given above, but few are seen. We will prob- 



