April, '13] TOWXSEND: COTTON LEAF CATERPILLAR 245 



The ordinary climatic conditions of the central Peruvian coast region 

 from Chancay to Casma, in the low-lying cotton districts just back 

 from the shore line, are as follows: June to November, very humid 

 atmosphere, mist during nights and mornings, more or less continuous 

 cloud-blanket, cool temperature; December to May, less atmospheric 

 humidity in general with an approach to aridity during days, no mist, 

 generally clear sky, warm but not oppressively hot temperature, cool 

 ocean wind from south decreasing largely or dying out during the hot- 

 test part of the season. 



The season of 1911-1912 showed the following abnormal conditions 

 in this region: Very cloudy weather in general from November to 

 March; an almost constant cloud-blanket from February 14 to 22, 

 practically no sun, great atmospheric humidity with intensely oppres- 

 sive heat, an unusually strong and very hot south wind continuing 

 throughout the hottest season. This wind was evidently not the 

 usual cool south wind from off the Humboldt ocean current, but a hot 

 land wind from a general southeast direction that had followed up the 

 coast line and whose origin was probably due to extra-local causes. 

 It seems to have been strong enough to divert the south ocean wind 

 from its usual course, or was perhaps itself a diversion of that wind, 

 and was probably therefore responsible for the piling up of the unusual 

 banks of humidity hanging over the coast line in this region. 



It seems quite certain that the abnormal degree of humidity, with 

 no sun, that prevailed during the last half of February, stagnated the 

 soil of the irrigated fields by practically preventing the usual evapora- 

 tion, while the abnormal heat caused a soil fermentation to set in, 

 whereby neither the cotton plants nor the herbage in the fields showed 

 any growi;h whatever from February 15 to March 21. The cotton 

 plant was thus physiologically inactive for over a month during its 

 usual period of greatest seasonal growth, and therefore still less pre- 

 pared than ordinarily to withstand the attack of the caterpillar which 

 was at its period of greatest activity. Irrigation during this period 

 had no effect on the cotton plant, but rather made conditions worse. 



The nights of March 21 and 22 were cold, with a sea-fog, and imme- 

 diately after this sudden change in the meteorological conditions the 

 cotton plants began to show signs of renewed activity. The herbage 

 did not appear to resume growth till about March 30. 



It seems indicated that the abnormal degrees of both heat and humid- 

 ity which prevailed especially during February were most favorable 

 to the rapid development of the caterpillar, resulting in an accelerated 

 development of the stages of the insect, whose life-cycle seems to have 

 averaged shorter than usual in North America, being reduced to about 

 four weeks or even somewhat less. Three well-marked generations 



