12 CIRCULAR 5 7 5, U. S. DEPT. OF AGRICULTURE 



in the experiments in 1939 with nymphs. Thus it is possible to recom- 

 mend to farmers and control agencies that cricket bait should be spread 

 only during migrations. This automatically excludes periods during 

 which the insects are clustered or in shelter, as in the early morning and 

 when they are roosting on vegetation during the heat of the day. The 

 recommendation also applies to a lesser extent to first- and second- 

 instar nymphs. During the period of these instars little migration 

 has been observed, little feeding was recorded on pan baits, and less 

 satisfactory results from field baiting were obtained than with later 

 instars. 



FIELD DEMONSTRATIONS OF CONTROL BY THE USE 

 OF POISONED BAIT 



Broadcasting bait in field plots was begun in May 1938 for first- to 

 third-instar nymphs. Five baits were used in these early tests, al- 

 though not all the five were used in each series. The baits consisted 

 of standard bran to which was added 2 or 4 pounds of sodium fluosili- 

 cate, with and without oil, or 2 quarts of sodium arsenite. Results 

 were uniformly poor, because continued rains and low temperatures 

 inhibited the normal activities of the crickets. As little was then 

 known concerning the correct time for baiting, most of the bait was 

 broadcast when the insects were not active, and poor kills resulted. 



This work was continued during June on large-scale plots in which 

 samples (obtained from the wing pens) were taken from the baited 

 area. The crickets at that time were mostly in the sixth and seventh 

 instars. More favorable weather conditions were encountered and 

 the kills averaged from 67 to 97 percent. 



Field baiting was continued throughout July and August when 

 adult crickets were present. In all, about 1 ton (dry weight) of the 

 bran and sodium fluosilicate bait was used. At this time the results 

 obtained were exceptionally good in all instances. 



Early in the spring of 1939 baiting was begun on a large scale on 

 first- to fourth-instar nymphs, in cooperation with the Mormon 

 cricket control unit of the Division of Domestic Plant Quarantines 

 of the Bureau of Entomology and Plant Quarantine. A total of 

 4,300 pounds (dry weight) of cricket bait was spread over 418 acres 

 of infested areas in Washington, Nevada, and South Dakota. Of 

 this 3,400 pounds was with standard bran as the carrier, while the 

 remaining 900 pounds consisted of 1 part mill-run bran to 3 parts 

 sawdust. The latter was all used in South Dakota. All baits con- 

 tained 4 pounds of sodium fluosilicate per 100 pounds of carrier. 

 Results were generally satisfactory, although in some instances it was 

 difficult to estimate kills because the small size of the first- and second- 

 ins tar nymphs made it extremely hard to see the dead ones. 



In the large-scale tests in South Dakota, where the mill-run bran- 

 sawdust carrier was compared with standard bran, samples taken by 

 the wing-pen method showed kills of from 72 to 90 percent, with the 

 mill-run bran-sawdust giving the higher kill in every instance. Closely 

 supervised experimental tests have not substantiated these results, 

 although it has been found that during periods of relatively high 

 temperatures and little soil moisture results with the mill-run bran- 

 sawdust mixture approach those obtained with the standard bran. 



