August, '22 



FENTON & HARTZELL: BORDEAUX AND LEAF HOPPERS 



297 



Table II. — Effect of Bordeaux Mixture on Empoasca mali Nymphs 



In not a single case did any of the nymphs feeding on sprayed leaves 

 become adults. In some instances the insect would moult once but 

 very often death occurred directly after the casting of the exuvium or 

 even before the n3^mph could completely extricate itself. Bordeaux 

 mixture acted comparatively slowly, some of the older nymphs living 

 as long as nine days. In general the younger the insect the quicker 

 death resulted upon being confined on a sprayed leaf, the length of 

 time ranging from approximately two days in the case of the first 

 instar to about six for the fifth. 



Careful observation disclosed the fact that the nymphs were not 

 dying from starvation because they were either unable or refused to 

 feed from the sprayed leaves. Once placed on a leaf well coated with 

 Bordeaux, the hopper at first wandered about but sooner or later 

 settled down and began to feed. In fact, very often the dead nymph 

 would be found with its proboscis firmly fixed in the leaf tissue. Often 

 twenty-four hours or more before death the insects would become 

 affected, appearing sluggish and partly paralyzed. The fact that 

 they were confined to shell vials apparently had little to do with it 

 because in almost every case the nymph could be raised to maturity 

 under these conditions on unsprayed leaves. Nymphs placed on 

 sprayed potted plants in the insectary soon disappeared but whether 

 they died or not is a question. 



Similar tests with adults were carried out but as yet our data is 

 insufficient on this subject. In the few vials observed some adults 

 lived for over two weeks and this would appear to show that Bordeaux 

 mixture is at least not very toxic to the adults and possibly it may 

 not affect them at all in this respect. 



Field Experiments 



The insecticidal value of Bordeaux mixture in the control of the 

 potato leafhopper was also shown by results obtained from field plots 

 at Ames. These plots consisted of a number of rows of potatoes of 

 two varieties, namely: Green Mountain and White Blossom Irish 

 Cobbler. These rows were sprayed with self-prepared Bordeaux 

 miixture 4-4-50 formula alone and also in combination with black leaf 



