40 



ON AN OUTBKEAK OF INJUEIOUS LOCUSTS IN 

 CENTEAL ILLINOIS. 



BY CLAEENCE M. WEED. 



H 



In an artick> pnblislied as one of the series of "Miscellaneous 

 Essays on Economic Entomology,"* issued from this office last 

 year, the writer recorded a few of the more important facts con- 

 cerning an outbreak of two common locusts — the red-legged lo- 

 cust {Pezoieitix femiir-rtihrum) , and the olive locust (P. differen- 

 tialis) — which occurred in Central Illinois during the summer of 

 1885. I have there reported the approximate boundaries of the 

 infested area, the extent of injury within that area, and such ob- 

 servations as I had been able to make upon the situation and 

 condition of the locust eggs at the beginning of the winter of 

 I8S5-86. It is proposed in the present paper to bring the record 

 up to the autumn of 1886, when the observations ceased, and to 

 present a few general considerations which it is hoped may form 

 a useful contribution to the subject of entomological prognostica- 

 tion. 



In the paper above cited I have shown that a considerable pro- 

 portion of the eggs had been destroyed by various insect and 

 other enemies during the autumn of 1885, — the most useful of 

 these enemies being the larvae of the ground beetles (Carabidae)^ 

 and those of the blister-beetles (Meloid?e). Late in March, 1886, 

 the region was again visited, and extended observations were made 

 upon tlie condition of the eggs. The meloid larv?e were present, 

 -though in the quiescent coarctate cooidition in which they pass 

 the winter; but many of the ca rabid larv?e had already begun to 

 work upon the eggs. The most remarkable feature of the situa- 

 tion, however, was the extraordinary abundance of the red locust 

 mite {Tromhidiiim locusi(irum) which was everywhere present on 

 and beneath the soil surface. At French Grove, March 22, these 

 mites were just beginning to come out of the ground; and in 

 many pastures from one to four of them could be seen on every 

 square foot of surface. By the roadsides they also swarmed. At 

 Monica, on the iatm of Mr. W. E. Elliot, thirteen of the mites 

 were counted within a surface area of one square foot. 



•Rep. 111. St. B(l. Agr. 1886, appendix, pp. 48-66. 



