June, '13] TOWNSEND: COTTON SCALE 319 



it northward up both valleys. The waters of the two rivers flowing 

 south and west, transporting it constantly into the fields during irri- 

 gation, have carried it generally southward especiallj'' in the Piura 

 valley, and this in direct opposition to the prevailing strong winds. 

 This explains its late invasion of the lower Piura valley. 



Conditions Encountered in Piura, Including Enemies 



This insect, like most diaspine coccids, if left undisturbed, is able 

 to breed quite continuously under all the climatic gradations from 

 warm humid to hot arid, provided onlj' that its host-plant remains 

 phj'siologically active. The cotton plant is active throughout the 

 year in Piura Department, the climate is excessively arid from Decem- 

 ber to Alay and with considerable atmospheric humidity from June 

 to November during the nights and forenoons. Practically no rain 

 falls at any time of year. This climate is not duplicated anywhere 

 in the world, and is only approached in a few districts like certain 

 parts of northwestern Mexico, western Australia and perhaps south- 

 western Africa. The Piura region is much dryer than the central 

 coast region of Peru. It is exceedingly interesting, therefore, from 

 both the economic and biologic standpoints, to note what has taken 

 place with reference to this insect and its enemies under the almost 

 unique climatic conditions in question. 



Having gained access to the Piura region, the insect either brought, 

 wdth it or was met there by certain microhymenopterous parasites 

 common to diaspine scales in tropical and suljtropicai countries and 

 by others especially American, as well as by still other enemies largely 

 native to the countr^^ The parasites and enemies now at work in 

 some force on Hemichionaspis minor in Piura Department are as 

 follows : 



(1) Aspidiotiphagiis citrinus — -Tropicopolitan to temperate. Found 

 in 1909 in both Piura and Lima. Known to oviposit in the active 

 young of the scale, and thus possibly brought into the Piura region 

 by the host, though more probably generally distributed with other 

 scale insects before the advent of the piojo bianco. Abundant and 

 evenly distributed. Both Piura and Chira valleys. 



(2) ProspaUeUa peruviana — Peruvian. Found in 1909 in both 

 Piura and Lima. Not nearl}^ so abundant as the first, and while 

 distributed everywhere it occurs unevenly and in fluctuating numbers. 

 Both Piura and Chira valleys. 



(3) ProspaUeUa aurantii — Tropicopolitan to temperate. Not found 

 in Lima, and not in Piura till 1910 after liberations from North 

 America in 1909. Its presence in Piura is therefore perhaps the 



