506 journal of economic entomology [vol. 9 



Economic Importance 



During the present (19 16) season Bucculatrix thurheriella has been 



one of the few major pests of cotton in the Imperial Valley. One 



hundred cotton leaves were gathered on June 2 from a field heavily 



infested with this species, and the infestation was computed as follows: 



Leaves (total) 100 



Leaves free 22 



Leaves supporting larvae' 4 



Leaves supporting pupae' ■ 32 



Leaves showing work 42 



Percentage infestation 78 



Subsequent to the above date infestation reached an even higher 

 degree, but by the first of July was somewhat checked by the work of 

 parasites. The Bucculatrix larvae, however, attained the ascendancy 

 again about the first of August and at the present date (August 8) 

 are probably the most abundant that they have been at any time dur- 

 ing the season. In some fields not a leaf is free from the work of the 

 species. Table I presents the results from the examination of 20 

 leaves picked at random about a field at El Centro, California. 



Table I. Occurrence of Imjutire Stages ok Bucculatrix thurheriella on Cotton Leaves 



The pest has been found in fields at El Centro, Imperial, Brawley, 

 Westmoreland, Calipatria, Meloland, Seeley and Calexico, which 

 demonstrates that it occurs in every cultivated part of the Valley. 



The tineid caterpillar may be found in virtually every cotton field, 

 but it appears to thrive best on plants which, for some reason, are 

 stunted and non-vigorous. A 5-acre field of cotton, "volunteering" 

 from last season's roots which had received no water since the occur- 

 rence of a rain in March, was early seen to be veiy severely attacked. 

 A small plot of seedling cotton (see PI. 36, fig. 1), growing near a hedge 

 of tall eucalyptus trees, remained stunted for weeks, and these plants 

 became very heavily infested. Tall cotton is similarly attacked (see 

 PI. 36, fig. 2) but is better able to withstand the work of the pest. 

 When present, cotton clearly shows the effect of the caterpillar, the 

 foliage being riddled and perforated, often, until little more than veins 



' Also showing damage. 



