61 



in Bulletin 14, Iowa Experiment Station. The most important results 

 may be here stated. In an experiment upon a plat of grass land a por- 

 tion was treated with the tarred sheet on May 29; the remainder of the 

 plat, or rather a corresponding portion on the opposite side of a nar- 

 row roadway, was left untreated. On June 9 a trial by running the 

 tarred sheet over a strip 3 rods in leugth on each plat, it was determined 

 that by actual count the leaf-hoppers were more than five times as plenty 

 on the plat that had been untreated as on the treated plat. And July 

 2, when the hay was cut on each plat, the yield from the treated plat 

 was 34 per cent better than that of the untreated plat. 



On June 20 the tarred sheet was tried on another part of the lawn, 

 and, "in moving 55 feet with the dozer, the number of leaf-hoppers taken 

 was estimated by counting the insects on three sections of the dozer, 

 each 6 inches long and extending the entire width of the dozer. The 

 counts were 183, 319, and 226, respectively, which averages 243 for each 

 section, or 4,131 on the whole pan. At this rate about 376,000 in sects 

 would be caught per acre. 



" Another test was made at the same time, dragging the dozer over 

 66 feet of lawn. This time five sections of 6 inches each were counted 

 off and averaged, instead of three, which resulted in giving 2,805 insects 

 on the dozer, or 213,089 would be taken on an acre." 



In previous reports I have given some estimates as to the number of 

 these leaf- hoppers that may occur on an acre of grass land, and it will 

 be seen that these trials not only give confirmatory evidence as to the 

 great numbers of these pests that live in grass, but show that they can 

 be captured successfully by the hopperdozer plan. Since the latter 

 trials were made in hot weather and when most of the insects were 

 AA'inged, it was impossible to capture all of the hoppers, and it is prob- 

 able that the actual number of hoppers on the land averaged well up 

 to 1,000,000 per acre. By selecting best conditions, it will be possible 

 to capture a larger percentage, and the profit of securing even half of the 

 hoppers in the grass will, I believe, well repay all expense and trouble 

 of treatment. 



A very interesting occurrence of the year was the remarkable in- 

 crease of a parasite (Apanteles glomeratus) affecting the common Cab- 

 bage-worm (Pier is rapce). 



About the 1st of May I received from you some parasites imported 

 from En gland, but they were already issuing from the cocoons and 

 there had been no cabbages planted at the time in this locality, so that 

 my only hope of getting them established here was to place them on 

 Black Mustard growing wild, and even here I had little hopes of getting 

 them established, as P. rapce had only begun to appear in the imago 

 and there was little possibility of larvae being ready in time for oviposi- 

 tion of Apanteles. About the 1st of August I was somewhat surprised 

 to have brought to me a number of rapce larvae with cocoons of a para- 

 site that resembled exactly the Apanteles. When the imagos issuecf. 



