BURliAU Ok' ENTOMOLOGY. 331 



t'HVctive type of (lustiii<r iiiachinciv. This qiu'stioii has been so im- 

 portiint that a s[)Ocial hiilletin (farmers" Bulletin lODs) has l)een 

 issiu^l for the use of l)oth farmers and manufactiirers. 



Mucli work has been conducted on cotton varieties in relation to 

 weevil injury, weevil hibernation, etc. In addition, the weevil dis- 

 ])ersion line for the fall of 1919 Mas determined. 



A Department Bulletin. No. 875, "Cotton Boll Weevil Control by 

 the I^se of Poison," prepared during the fiscal year 1920, has been 

 issued since the close of the year. 



A study of the field biology of the cotton boll weevil has been com- 

 pleted at the field station of the bureau at ISIadison, Fla., and the 

 manuscript has been prepai-ed for publication. 



During the year a thorough studj' of the relationship of tempera- 

 ture to the immature stages of the boll weevil was untlertakcn, with 

 special reference to the application of control measures. During 

 the month of June, 1919, the high soil temperatures at Madison. Fla., 

 caused a morlality of 98 per cent among weevils of the first genera- 

 tion. In other words, there were no more weevils in the field on the 

 r)th of .July than were present on the 5th of June, in spite of the 

 fact that time had elapsed for the first generation. These studies 

 indicated that for certain localities in the southeastern Gulf Coast 

 States control experiments could have been inaugurated on the 5th 

 of July with just as good chance of success as had such experiments 

 been performed on the 5th of June. 



The field biology of the boll weevil was found to present a con- 

 siderable variation compared with the biology under insectary condi- 

 tions. The a^erage time from egg to adult under insectary condi- 

 tions is approximately 14 days. The studies in the field show that 

 the time tVom v*^^ to adult, where the weevils are allowed to hatch 

 on the soil beneath the plants, is approximately 22 days. This im- 

 portant discovery has a ver}^ direct bearing on the application of 

 methods of control, especially where the time interval betAveen appli- 

 cations of poison is concerned. 



A good (leal of attention has been gi\en to the possibilitj^ of grow- 

 ing sea-island cotton under boll-weevil conditions. Sea-island cotton 

 has been abandoned in almost every section w'here the weevil has 

 made its ai)peai-ance. The studies at Madison. Fla., indicate a possi- 

 bility of making a very profital)le crop on certain of the light sandy 

 soils. The studies alon«r this line are beinj; continued and it is 

 expected that some very valuable information will be gamed. 



T(tnAcco INSECTS. — The tobacco hornworm continues to be the most 

 imj)oitan( insect i)est of tobacco in Kentucky and Tennessee. The 

 shortage u( labor and the consequent high wages affect the problem 

 of control. Tender former conditions i^rowers did nuich hand worm- 

 ing during certain periods when labor could thus be advantageously 

 emjdoyed, but under present conditions labor is so scarce that the 

 control of the hornworm can be better accomj>lished by the use of 

 dusting machinery, even when worms are not very abundant. This 

 condition has brought the machinery problem to the front, and has 

 resulted in the devising of a mule-drawn duster which ai)pru'S the 

 dust i)oisons to two rows at the same time and much more thoroughly 

 and with much less labor than with the hand duster. This machine 

 will be thoroughly tested and developed during the coming summer. 



