October, '21] morrill: nicotine dusts 399 



An attempt was made to overcome the interference of high winds and 

 to reduce the amount of material needed per plant by using a canvas 

 cover to confine the dust. Areas about three feet square were covered 

 with eight ounce duck held 2 to 4 inches above the leaves of the vines 

 and with side pieces extending to the ground. From one-fifth to one- 

 fourth of the amount of dust normally required was used per plant, 

 discharging the dust at different parts of the enclosure in different tests. 

 These results did not encourage the belief that the use of covers could be 

 used to advantage with the dusting process. 



In the Imperial Valley late in May and early in June, with maximum 

 daily temperatures ranging between 93 degrees and 103 degrees, nicotine 

 dusts containing approximately 75% sublimed sulphur caused burning 

 of canteloupe plants. 



A single infested watermelon plant treated with such a dust May 29th 

 showed no injun,', the aphids being completely eradicated. Pure sulphur 

 applied as a check to canteloupe plants on June 1 had caused no notice- 

 able damage two days later but on June 5 it was noted that the dusted 

 vines were badly burned. While nicotine sulphur dusts may not cause 

 any dam^age to canteloupes where the temperatures are more m.oderate 

 than in the Im.perial Valley it appears safer to avoid the use of dusts on 

 this crop containing more than 10% sulphur. 



Special mention should be made of the relation between nicotine dusts 

 for the melon aphis and the natural enemies of this pest. During the 

 period mentioned above, adult lady bugs were very abundant in the 

 melon fields but there were very few eggs and larvae present. Hymen- 

 opterous parasites were remarkably scarce. The most active natural en- 

 emy was a species of syrphus fly . A similar situation with regard to melon 

 aphis natural enemies was noted at Burbank near Los Angeles, during 

 July. The adults and larvae of lady birds {Hippodamia convergens) and 

 the larvae of the syrphus flies (species unknown) were apparently un- 

 effected by the nicotine dusts used in the experiments. 



In tests of nicotine dusts against the melon aphis near Los Mochis, 

 Sinaloa, Mexico in March 1921 it was noted that the adults of hymen- 

 opterous parasites (Aphidius testaceipes) were apparently not affected 

 by dusts which were satisfactory against the aphis. The aphids which 

 survived the dust, located mostly in curled leaves, received the concen- 

 trated attack of the parasites resulting in almost complete eradication 

 of the pests. 



