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



killed for each bait was then calculated by dividing the total number 

 dead by the total caged. This system was used during the seasons of 

 1935 and 1936, but was discarded early in 1937 because the percent- 

 ages killed from most of the baits were so nearly alike. Confinement 

 of the crickets directly on the bait apparently resulted in their eating 

 whatever was offered them with slight regard to the content of the 

 m xture. 



In 1937 the system now in use was devised, and it was not until 

 then that marked differences in the efficiency of various baits became 

 evident. This was called the "wing-pen" method. It consisted of a 

 small pen about 4.5 feet in diameter built of 10-inch galvanized iron 

 with two 16-foot wings of the same material forming a V and set in 

 front of and adjacent to it. The V was connected with the pen at its 

 apex by a 4-foot removable chute. This chute consisted of a 1- by 

 6-inch pine board with 5-inch sides of galvanized iron nailed to the 

 edges. 



Figure 2. — Series of wings, chutes, and cages used in the wing-pen method as 



modified in 1939. 



The poisoned bait was spread in front of and within the V. The 

 crickets were allowed from 20 minutes to 1 hour to feed and move into 

 the pens of their own accord. If a sufficient number had not been 

 captured at the end of 1 hour those within the V were driven up the 

 chute and into the pen, where they were held for 4 days. As before, 

 the dead crickets were removed each day and the remaining live ones 

 counted on the fourth day. The final percentage of kill was calculated 

 from the total dead and the total caged. The method was revised 

 somewhat in 1939, when a small cage was substituted for the pen 

 (fig. 2). The crickets were driven into the cage and then transferred 

 to pens at a central location. 



In the wing-pen method the crickets were not forced to feed on the 

 bait, as was the case in the first method, where they were confined in 

 the pen with the bait. Real differences between the efficiency of the 



