NO. l8 SENSE ORGANS OF COLEOPTERA — McINDOO 21 



beetles caught in 39 traps in 1926 was about 2,000,000, one trap 

 catching 13,476 in one day. These traps were used also in connection 

 with ecological investigations, and to obtain data on the degree of 

 infestation at different points in different years. Beetles are caught in 

 the traps before any are observed in the immediate neighborhood. As 

 a result of these investigations various types of traps have been put 

 on the market by commercial firms. In the 1929 report on the Japa- 

 nese beetle, Smith (78) has the following to say about geraniol and 

 traps : 



Several years ago chemotropic investigations revealed that geraniol, one of 

 the higher alcohols, was extremely attractive to the Japanese beetle. Few, if any, 

 other insects have been found to be attracted to any degree by this chemical and 

 it is apparently a specific for this insect. In commerce it is commonly used as 

 an ingredient in the cheaper perfumes. Geraniol has been utilized in several 

 ways in the control of the beetle ; these include combining it with poisoned baits, 

 as a means of concentrating the beetles in a small area where they may be killed 

 with contact sprays, or more often as a constituent of baits used in mechanical 

 traps. The Japanese beetle traps have come into wide use by residents in the 

 suburban area around Philadelphia. In conjunction with spraying, the traps are 

 useful in capturing large numbers of beetles. During the summer of 1929, 500 

 traps were placed on a is-acre estate in the heavily infested district near 

 Roxborough, Pennsylvania. The record of collections in these traps during the 

 period between July 9 and August 23 gives a total of 1,874^ pounds of adult 

 beetles and represents approximately 10,000,000 individuals. Many types of 

 beetle traps are now on the market, ranging in price from 10 cents upward. 

 The traps have not yet become sufticiently effective to warrant their use on 

 farms. In fact, the presence of large numbers of traps may attract many 

 beetles which are not captured, with the result that the grub population in the 

 soil, in the vicinity of the traps, is greatly increased over what it would have 

 been had the traps not been used. 



During the past few years traps have come into general use for 

 catching large numbers of Japanese beetles, but for various reasons 

 a large percentage of the insects attracted to the traps are not caught ; 

 therefore, Mehrhof and Van Leeuwcn (49) devised and perfected 

 an electric trap (pi. 2) which not only attracts the beetles but kills 

 practically all of them that come to it. This trap, in the form of a 

 hollow cube, is 3 feet on each side, with parallel wires, f inch apart, 

 on all four sides and on the top. The most effective bait was geraniol 

 emulsion, sprayed on peach foliage which was suspended in the center 

 of the trap. By this method beetles were at times attracted from a 

 distance of one-fourth mile. 



Siegler and Brown in 1927 (74) first published on the idea that 

 attractive baits might be used advantageously in scouting for in- 

 jurious insects. During the season of 1929 the Federal Plant Quaran- 



