RELATIONSHIP OF FACTORS OF CONTROL. 21 



may 1)0 I'ouiul as ^iv(>n l)y Mr. AV. I). IMcrcc^ in Biill(>tin No. T^r^f tlio 

 Bureau of Knl()ni()k)«^y. 



For nuiny> years the cotton leaf ^\()rnl {Aldlxinid unjUldctd) has 

 been considered as an important cotton pest throughout the Soutli, 

 thou^li the severity oi its injury to the crop has been less durin<^ 

 recent years than it Avas formerly. It now aj^pi^ars in destructive 

 numbers only ilurinu: the latter part of th(> season, usually after the 

 eroj) begins to matur(\ and is not infrecpient ly a welcome visitor. 

 Especially in rank late cotton its destruction of the foliage enal)les 

 li*:ht and air to [XMietrate more n^ulily, thus prcventin^j; the decay of 

 l)olls lyin^ on or nc^ar the *^round and ^n^atly facilitating^; the maturity 

 of the crop. For this reason comparatively few planters now look 

 upon the leaf worm as a pest to be controlled by the ap|)lication of 

 insecticides. Succe(Hlin^ tj:eneTations of the caterpillars remove an 

 increasingly large proportion of the foliage until the plants may be 

 finally stripped bare repeatedly before the close of the season. 



The significance of the leaf worm in the control of the boll weevil 

 rests directly upon its effect upon the food supply of the latter species. 

 As the weevil has no other food plant than cotton, its final multi- 

 plication before the end of the season is usually limited directly by 

 th(^ abundance of squares and bolls within which it may breed. The 

 defoliation of the cotton by the leaf worm stops immediately the 

 formation of squares and the subsequent possibility of the setting of 

 bolls. F\irther development of the weevils is thus abruptly checked. 

 The maturing bolls may continue to give out weevils for some weeks, 

 and previously infested squares may add to the number of adult 

 weevils for from one to two weeks, but the sudden removal of the 

 food supply and of the shelter usually enjoyed by the adults causes 

 great mortality among them. Many weevils leave the bare fields in 

 search of food, and thus, in various ways, the number of weevils in a 

 field where the leaf worms work abundantly and thoroughly becomes 

 very greatly reduced. If the leaf worms continue to strip the cotton 

 until late in the fall there will be no possibility of an increase in the 

 number of weevils. The leaf worms may actually accomplish what 

 is practically a more or less complete early destruction of the cotton 

 plants and a cleaning up of leaf rubbish in the field. Where this is 

 the case it is safe to assume that so few weevils will survive or hibernate 

 that a very positive benefit may be experienced during the following 

 season, and if climatic conditions should favor the growth of cotton, 

 a crop may be secured with comparatively little injury by the weevil. 



Defoliation by the leaf worm may be especially effective if it should 

 ha})pen to be followed b}" winter climatic conditions which are 

 exceptionally severe, so that only those weevils which found the most 

 favorable hibernation shelter would naturally survive. The leaf 

 worm does not, however, often occur abundaiitly during two succes- 

 sive seasons in Texiis. Its work is often local and only partial in the 



