August, '19] 



CAMPBELL: BEAN WEEVIL CONTROL 



287 



Table II. Compahison of the Per Cent of Weevil Infestation of Horse Beans Planted m 

 Different Months. Figures are Averages for the Three Years, 1916, 1917 and 1918 



This was further tested by experimental plantings at Alhambra and 

 Hayward during the season of 1917 and 1918, with the following 

 results : 



Table III. Averages of the Per Cent of Weevil Infestation in Experimental Plantings 

 AT Alhambra and Hayward, during 1917 and 1918 



It is plainly evident from these tables that the percentage of infes- 

 tation is very much less in crops from seed planted late in the season 

 than from crops which were planted early. The life history of the 

 insect suggests an explanation of this. It was observed that egg depo- 

 sition began about March 15, was heaviest in April and ended by the 

 middle of May. It seems reasonable to believe that pods produced 

 before or during April will be exposed to the greatest egg laying, but 

 pods produced after the latter part of April will be subject to little or 

 no egg deposition. 



Further evidence on this point is furnished by horse bean growers of 

 San Luis Obispo County. It had been the custom there, as elsewhere, 

 to begin planting in October or November and continue until May. 

 But because of severe infestation of the bean aphis (Aphis rumicis L.) 

 on the early planted horse beans for several years, and on the conten- 

 tion that horse beans acted as a winter host for this pest, propagating 

 it in great numbers, the County Horticultural Commissioner persuaded 

 the growers not to plant any horse beans until after ]March 1, in the 

 1918 season. The result is shown in Table I, with a maximum of 50 

 and 63 per cent of weevil infestation, and averages of 14.5 per cent for 

 the 1910 and 1917 crops when the seed was planted both early and 

 late, as contrasted with a maximum of only 17.2 per cent and an aver- 

 age of 2.92 per cent of weevil infestation for the 1918 crop, when no 

 seed was planted until after March 1. Many samples of this season's 

 crop were entirely free from infestation, particularly those from seed 

 planted in April and May. 



Wlicn the first observations were made on the effect of late planting, 

 it was suggested that with an abundaiice of pods available on which to 



