June, '12] TOWNSEND: WHITE SCALE OF COTTON 259 



The parasites just mentioned are able to dominate the scale by the 

 end of the humid season, aided by other agencies to be described 

 shortly. They resume activity in May and June and increase steadily 

 during the ensuing humid months. As a rule in October and Novem- 

 ber 'very little living scale is 1,0 be found on the cotton plants, a very 

 great part being parasitized, even up to 95 and 98 per cent in spots. 

 But not all the scales succumb to the parasites and allied agencies, 

 and here lies the flaw in ordinary parasite and natural enemy work 

 against coccids in this region. The verj'" few scales that escape, 

 being relieved from the activity of their enemies, multiply in ever- 

 increasing ratio from December to May, until the plague has assumed 

 practically the same proportions as before. Thus the parasites and 

 other enemies have lost all they gained, have all their work to repeat, 

 and the scale has been present in damaging force for half the year. 



It may be stated here that spraying and all kinds of insecticidal 

 operations are practically out of the question in the cotton fields of 

 Peru, not only on account of the large extent of the plantations 

 making the total cost of treatment exorbitant and the present impos- 

 sibility of securing concerted action, but also particularly because 

 of the methods of cultivation and irrigation in vogue, which are 

 peculiarly w^ell suited to the prevailing conditions and could only 

 wdth the greatest difficulty be changed and which do not allow the 

 use of- work-animals and machinery in the fields. Moreover work- 

 animals are not to be had, at least for the present, and all cultural 

 and insecticide w^ork would have to be performed by hand-labor, 

 which is scarce. • Thus the only feasible mode of procedure against 

 the scale for the present lies in parasite, coccinellid or other natural- 

 enemy work. 



Cutting back once a year would greatly reduce the seriousness of 

 the pest, but the favorite native Peruvian and perennial variety of 

 cotton is not amenable to this practice. Annual planting would 

 similarly reduce the injury, but greatly increase the cost of production. 

 Moreover both conflict with the season of irrigation in the Piura 

 valley, which is without flowing surface water for half the year, and 

 with the established cropping seasons in the whole region. Neither 

 would greatly reduce the pest, which flourishes in especial abundance 

 on wallows, castor-bean plants, pigeon-pea, beans, and many others, 

 all of which would need similar treatment. All of these and still 

 other conditions emphasize the natural-enemy plan of work as the 

 sole tenable mode of procedure. 



It must now be noted that no doubt a considerable part of the 

 nearly complete mortality of the scale at the close of the humid season 

 is due to natural physiological causes inherent in the host and not 



