4:2 BULLETIN 918, U. S. DEPARTMENT OF AGRICULTURE. 



Table XXI shows that no live larvae were found during May and 

 June among those removed from seed and lint or in double seed 

 buried in the irrigated plots (Experiments Nos. 557 and 558 A to D), 

 and that 12.S per cent were alive or had emerged as moths under the 

 same conditions in the nonirrigated plot (Experiments Nos. 560 and 



561 A to C). No live larvae were found in bolls buried in irrigated 

 plots from March 10 (the first examination) until June 6 in Experi- 

 ment No. 559 A, and none in bolls buried in nonirrigated plot (Experi- 

 ment No. 562 A) after April 24. The surrounding soil had been irri- 

 gated and when the last examination was made on June 7 the soil in 

 the nonirrigated plot was found moist about 3 inches below the surface 

 from water that had seeped in from below. From this experiment 

 6.2 per cent survived till April 24. There was less mortality in the 

 bolls when left on the surface of the ground than when buried. In 

 the irrigated plot (Experiment No. 559 B) live larvae were found in 

 bolls left on the surface of the ground at the last examination on 

 June 4, 1919, and 9.7 per cent had survived or previously emerged 

 as moths on this date. On the nonirrigated plot (Experiment No. 



562 B) 50 per cent of the larvae in bolls on the surface were alive on 

 June 7, 1919. At the next examination, on July 25, all of the larvae 

 were dead. 



In all of the experiments, especially the later examinations, many 

 of the larvae were not recovered because the dead larvae were so decom- 

 posed they were not recognizable. Very few if any escaped, for the 

 buried bolls had close-mesh wire screen over the top and along the 

 sides, extending below the level of the bolls. The earth surrounding 

 the material was carefully sifted and larvae and pupal skins found 

 here counted with the others. The percentages of mortality for the 

 bolls are based on the number of larvae found in the samples at the 

 beginning of the experiments. This is not absolutely accurate, 

 because the number of larvae may vary considerably in individual 

 bolls, but it is the most reliable figure to use inasmuch as the actual 

 number of dead larvae could not be determined. 



It is seen that the mortality increases as the season advances, even 

 where the conditions were most favorable, no live larvae being found 

 as late as July 25, and that the mortality in all the experiments was 

 greater when the larvae were buried than when they were left on the 

 surface, and greater when the plots were irrigated than when left dry. 

 These experiments also show that the greatest danger for starting 

 a new infestation from material left in the fields is the old bolls 

 left on the surface of the ground. Over 9 per cent of the larvge in 

 these bolls on the irrigated plot survived till June 4 and 50 per cent 

 survived in the nonirrigated plot. At this season the cotton will be 

 large enough for oviposition to begin. Under the usual field condi- 

 tions the irrigated lands will have been cultivated before this date 



