SECTIONS PROFITING MOST BY NATURAL CONTROL. 63 



Many of the conclusions which might be drawn from Table XUT 

 have already been stated in connection with preceding tables. The 

 last column shows that southern Texas enjoys the benefits of natural 

 control to a larger degree than does any other section. In that seel ion 

 62.6 per cent (nearly two-thirds) of all stages found had been de- 

 stroyed. One half of this mortality was accomplished by ants, the 

 other half by heat and parasites combined. Central Texas stands 

 next, with a total mortality of 45.5 per cent. In this section, while 

 the effectiveness of heat and of ants had decreased, that of parasites 

 had considerably increased. The increase in parasite attack, however, 

 was by no means sufficient to counterbalance the decrease from the 

 other two factors. Western Louisiana and eastern Texas, with 43.2 

 and 41.4 per cent of total mortality, respectively, show very close 

 agreement in the proportions of mortality from each factor. This 

 close agreement might be anticipated because of the similarity in 

 soil, climatic, and cultural conditions prevailing in those adjacent 

 sections. The principal reason for separating the localities into 

 these two sections w T as to facilitate a comparison of the recently 

 infested territory of Louisiana with the older-infested sections of 

 Texas. In this respect, also, but little difference exists between east- 

 ern Texas and western Louisiana. In analyzing the factors producing 

 the closely similar total percentages of mortality in western Louisi- 

 ana and in central Texas it will be seen that there were very essential 

 differences. In western Louisiana nearly 70 per cent of the total 

 mortality found was due to ant attack, while in central Texas only 

 43.5 per cent was due to ants. It is evident that in central Texas 

 may be found the conditions which are most favorable to parasite 

 attack. An extended study is being made of the entire field of para- 

 sitic attack upon the boll weevil, and part of the results previously 

 obtained may be found in Bulletin 73 of this Bureau. By far the 

 lowest proportion of total mortality is that found for southwestern 

 Texas. Most of the localities included in this section have but 

 recently become infested. It would appear, however, that' in the 

 higher altitude of those localities heat may not be quite as effective 

 and that ants may not be as abundantly distributed as they are in 

 other sections of the State. The observations in this locality have 

 not extended over a sufficient period to justify any general conclu- 

 sions regarding the result of the smaller degree of natural control 

 which would appear from the observations made. It is quite possible 

 that other factors than these which are here considered may serve t<> 

 check the weevil in this section. Such a condition as a much larger 

 mortality during the hibernation period might hold the weevils largely 

 in check in spite of the smaller mortality during the summer. 



