August, '22 HOWARD: Mexican bean beetle 271 



resulted the past season in the occurrence of the peak of infestation in 

 late July and early August. In the late summer and early fall the 

 beetles became extremely active. One field of beans was carefully 

 picked free of adults almost daily in October, and during 24 hours 

 adults flew in from other fields which had been destroyed. 



Artificial Control 



The Mexican bean beetle feeds in both larva and adult stages on the 

 underside of the leaves of bean and other food plants. The larva 

 consumes relatively greater quantities of leaf tissue and consequently 

 is the more destructive stage. Since the larva does not leave the plant 

 under normal conditions, because of its great susceptibility to direct 

 sunlight, which causes it to succumb in a few minutes where shade 

 temperatures are over 90° F., the proper distribution of a stomach poi- 

 son to the underside of the leaves is essential. 



The susceptibility of bean foliage to injury from arsenical treatm.ent 

 is well known and the practical application of arsenicals must be made 

 with this in mind. Injury to bean foliage is probably a complex result 

 of at least several contributing factors. The season's observations 

 indicate: (1) That the water-soluble arsenic content of an arsenical 

 is an important factor; (2) that the stability of the arsenical is probably 

 a factor; (3) that the soluble mineral content of water used when wet 

 sprays are applied is an important factor-; (4) that there are seasonal 

 variations in the susceptibility of bean plants to injury; and (5) that 

 the vigor of the plants appears to be a factor. Plants withstood spray 

 applications better in early spring and late fall than during the heat 

 of the Slimmer, even when applications were made with arsenicals and 

 water from the same source. Wet sprays were almost consistently 

 more injurious than dusts, even though the application of the latter 

 as practiced in the experiments distributed more of the arsenicals per 

 acre. 



Where wet sprays were used without serious injury to the foliage, 

 better insect control was obtained than with dusting and this was 

 undoubtedly due to the more effective distribution of the arsenical to 

 the lower surface of the leaves, and the better adhesion of the particles. 



Arsenical Sprays 



The commercially available arsenicals tested, viz., calcium arsenate, 

 zinc arsenite, lead arsenate, and Paris green, used as wet sprays, caused 



^Valuable assistance was received in this phase of the work from Dr. Wm. Moore 

 and Mr. C. M. Smith of the U. S. Bureau of Entomology. 



