August, '22] FENTON & hartzell: bordeaux and leaf hoppers 295 



the nymphs contained less of the toxic substance than the adults, a 

 fact not bom out by previous experiments^ where it was shown that 

 the nymph is the more toxic of the two. Undoubtedly some difference 

 in procedure not noted at the time may have been the cause of this. 

 Failure to produce burning in all cases may have been due to inability 

 to force enough of the liquid into the plant by means of the hypodermic 

 needle. This represented a real difficulty in our earlier inoculation 

 tests as the natural turgidity of the leaf made it almost impossible 

 to force much of the extract in. The difference in the amount of ex- 

 tract injected into the leaves as a result of this turgidity may explain 

 the difference in the effects of the toxin in the leaf. That the negative 

 results of the earlier experiments may have been due to the failure 

 to introduce enough of the hopper extract to produce burning because 

 of the natural turgidity of the leaves is also indicated by the success 

 of the tests with a potometer. Another factor entering in was the 

 difficulty of getting very much of the toxic substance into solution 

 by a mere maceration of the insects in distilled water. Apparently 

 not all or perhaps not even much of the toxic substance was extracted 

 by this method as was indicated by the highly toxic action on potato 

 leaves, of the residue composed of macerated insects after the clear 

 solution had been drawn off. That the live nymphs do contain this 

 toxic substance was demonstrated a number of times by crushing them 

 over a leaf abrasion. Very distinct lesions as already described re- 

 sulted in every case. 



The above tests need to be repeated on a larger scale and some better 

 method devised for getting the toxin into the solution. Furthermore, 

 extracts prepared from other insect species should be injected into 

 the leaves as it is well known that insect sera often contain toxic prin- 

 ciples. 



EFFECT OF BORDEAUX MIXTURE ON EMPOASCA MALI 

 By F. A. Fenton and Albert Hartzell, Iowa State College, Ames, Iowa 



Since the establishment of the fact that Empoasca mali LeB. is the cause 

 of potato tipbum, it was found that Bordeaux mixture in some way 

 prevented this foliage disease by its action on this insect. It was 

 thought at first that it acted as a repellent^ because plants sprayed 

 with this fungicide were noticed to have comparatively few leafhop- 

 pers on them. The senior author^ demonstrated later that this com- 



iPenton, F. A. loc. cit. pages 76-77. 



2Fluke, C. L. Journal of Economic Entomology, Vol. 12, 1919, pages 256-257. 



^Fenton, F. A. Journal of Economic Entomology, Vol. 14, 1921, pages 71-79. 



