NO. l8 SENSE ORGANS OF COLEOPTERA MclNDOO 43 



niercial Derris product, consisting mostly of pyridine ; cresol, U. S.P. 

 (i cc. shaken in 400 cc. water) ; 40 per cent nicotine sulphate in 

 water (i to 400) ; and heta naphthol (i gm. powder in 400 cc. water; 

 powder not all in suspension) (table 11). 



The results given in table 11 show that the repellents more or less 

 protected the leaves, Init not sufficiently so to prevent them from 

 being eaten. The Derris product and beta naphthol were the only ones 

 which might be considered promising, yet their protective value was 

 about equal to that of lead arsenate, as already shown in table 7. 



III. THERMOTAXIS- 



After having searched the literature for references on other 

 tropisms not yet discussed, the writer found a few more concerning 

 Coleoptera, but only two of these references pertain to the orientation 

 of beetles to temperature. Much exj^erimental work on various tem- 

 peratures, particularly as control measures, has been done, but very 

 little of it can be discussed from the tropic point of view, 



I. REVIEW OF LITERATURE 



Fulton (17) devised a crude temperature gradient with which he de- 

 termined that the choice of temperature of adult click beetles is much 

 below the usual maximum temperature in open fields during summer. 

 He also says that negative phototaxis causes the beetles to seek dark 

 hiding places during the day. Wire worms, or the larvae of these 

 beetles, were found more resistant to heat than were the adults, but 

 they did not voluntarily seek higher temperatures. Seasonal move- 

 ments of the larvae may be closely correlated with changes in soil 

 temperature. 



Grossman (21) tried three methods to determine the orientation of 

 cotton boll weevils to heat stimuli, but decided that only the results 

 obtained by using a new apparatus were reliable. This {ipparatus was 

 constructed by using 16 copper bars ^ inch wide and iV inch thick, with 

 ^4 inch insulating space between each two bars. Using only two 

 variables, temperature and light, 126 boll weevils were tested 1,993 

 times. The average tem^^eratures to which they reacted definitely were 

 130° F. at the hot end of the apparatus and 26° F. at the cold end. 



B. Sensory Receptors 



Since tropic responses are brought about largely by external stimuli 

 aflfecting either the special sense organs or others not definitely known 

 and localized, called the general sense organs, it is only natural to 

 discuss the tropic res^xjuses and sensory receptors in the same paper. 



