August, '22 HOWARD: Mexican bean beetle 273 



unless diluted, and only the best grades must be used. 



Nicotine dusts, contining from 1 to 10 per cent of nicotine sulphate, 

 by weight, gave no control. 



Pyrethnim, or insect powder, is a powerful contact insecticide, 

 especially against the adult bean beetle. A good grade may be diluted 

 as much as one-half with cornstarch or hydrated lime. It is not so 

 effective against the larva, and does not affect eggs or pupae under 

 field conditions. The cost and scarcity, as well as the impracticability 

 of a contact insecticide against an insect of this natiu^e, prohibit its 

 general use either for farm or garden. 



Derris, while superior to pyrethrum powder, falls in the same category. 



Use of Sprayed Beans as Food 



Chemical analyses of beans which had been wet-sprayed by a grower 

 7 days previous to picking prove that little danger of arsenical poisoning 

 results from the application of arsenicals in the relative proportions 

 of 2 pounds of lead arsenate to 50 gallons of water. From a quart of 

 green heaps picked June 3 from a field which had been sprayed thorough- 

 ly May 27, less than one-fiftieth of what is ordinarily considered a lethal 

 dose of arsenic was present in very careful washings, and one-hundredth 

 of a lethal dose was left on the beans. Nine other samples from exper- 

 imental plots treated with various arsenicals as dusts and sprays showed 

 less than 10 milligrams of arsenic expressed as AS2O5 in very careful 

 washings from a quart of green beans, picked 21 days after the last 

 aresenical treatment. All visible traces of insecticides should be wash- 

 ed from green beans, however, before cooking. 



Cultural Practices and Crop Substitutes 



All stages of the beetle are destroyed by covering them with one inch 

 or more of clay soil during the summer. In cases of heavy infestation, 

 fields should be plowed under. 



About Birmingham, Ala. in 1921, early planting was impracticable 

 because the beetles were afield before the last frosts. Very early 

 plantings of bush snap beans, however, produced a crop in locations 

 where infestation was not so heavy. 



The discovery of a number of wild host plants'* in addition to those 

 already recorded, and in addition to the cultivated hosts already record- 

 ed, indicates the futility of attempting to eradicate this species by 

 discontinuing the planting of garden beans. 



^Analyses by Mr. R. W. Allen, field assistant. 



*Meiboma tortuosa, M. canescens, M. viridiflora, Galadia volubilis, Lespedeza 

 virginica. 



