1959 - Gaines, R. C, L.D.Newsom, J. S. Roussel, and N. W. Earle. Rearing and 



treating successive generations of boll weevils. J.Econ. Ent. 52(4):555-557. Aug. 



In studies of boll weevil resistance to chlorinated hydrocarbon insecticides, 

 10 generations were reared from September 1956 to September 1958 and 4 to 6 

 generations were treated topically with insecticides. There was no indication 

 of reversion to susceptibility in the untreated strains when tested with endrin. 

 Endrin applied to resistant and susceptible strains increased the LD-50 and 

 LD-90 and gave some changes in slope of lines. A mixture of equal parts of 

 endrin and Guthion (0,0-dimethyl S- (4-oxo-3H- 1,2,3,-benzotriazine- 3 methyl) 

 phosphorodithioate) and Guthion alone gave no changes in LD-50, LD-90, or 

 slope. However, this does not prove that resistance will not develop with con- 

 tinued selection in large populations of boll weevils. 



1959 - Roussel, J. S„, M. S. Blum, and N. W. Earle. Joint action of DDT and other 



chlorinated hydrocarbon insecticides against resistant boll weevils. J. Econ. 

 Ent., v. 52(3):403-409. 



The joint action of DDT in combination with toxaphene, endrin, or lindane 

 against boll weevils differing in susceptibility to the individual insecticides was 

 studied in the laboratory. Weevils were treated topically or exposed to a residual 

 film for mortality studies. These were either laboratory reared or field collected. 

 Penetration and metabolism of DDT was studied when applied alone or in mixtures 

 with other insecticides. 



Mixtures of insecticides exhibited additive effects only for boll weevils 

 susceptible to chlorinated hydrocarbon insecticides. However, when weevils 

 resistant to these insecticides were used, the mixture of toxaphene-DDT exhibited 

 synergistic effects. Mixtures of endrin-DDT and lindane-DDT exhibited additive 

 effects only. 



Penetration of DDT appeared to be equal for both strains. Separate applica- 

 tions of toxaphene and DDT to different sites of the weevil were as effective as a 

 single application of the mixture. DDT applied as late as 96 hours subsequent to 

 an application of toxaphene resulted in high mortality of weevils. However, 

 repeated applications of toxaphene failed to give much of an increase in mortality. 



Weevils did not metabolize DDT as rapidly when treated with the mixture 

 as when treated with DDT alone. The metabolism of toxaphene is unknown. 

 Although the toxaphene-DDT mixture exhibits synergistic activity against resist- 

 ant boll weevils, the combination was not so effective against resistant boll weevils 

 as toxaphene, alone, against susceptible boll weevils. 



1960 - Burkhalter, G. F., and F. S. Arant. Boll weevil susceptibility to toxaphene, 



endrin, and Guthion in five Alabama localities. J. Econ. Ent., v. 53(2):3 1 1-3 13. 

 Laboratory experiments were conducted in 1956 and 1957 to determine the 

 susceptibility of the boll weevil to toxaphene endrin, and Guthion (O, O-dimethyl 

 S-(4-oxo- 1,2,3, -benzotriazine-3-(4H)-ylmethyl) phosphorodithioate) in 5 Alabama 

 localities. The technical insecticides were dissolved in acetone and applied 

 topically to 2-day-old weevils reared from cotton squares. Mortalities were de- 

 termined at the end of 72 hours. Approximately 25,000 weevils were used in the 

 experiments. During 1957, LD-50 values varied among populations from different 

 localities as follows: for toxaphene, from 12.5 to 61.8 fig. per gm. of boll weevil; 

 for endrin, from 0.8 to 3.5 fig. per gm; for Guthion, from 0.9 to Z.Zflg. per gm. 

 There was no evidence of acute resistance of the boll weevil from any of 5 

 localities to any insecticide tested. Mortality variations between times of year 

 and between the 2 years were as great as among locality groups. 



1960 - Parencia, C. R., Jr., and C. B. Cowan, Jr. Increased tolerance of the boll weevil 

 and cotton fleahopper to some chlorinated hydrocarbon insecticides in central 

 Texas in 1958. J. Econ. Ent. 53(l):52-56. 



The boll weevil and cotton fleahopper ( Psallus seriatus Reut.) showed in- 

 creased tolerance to several of the chlorinated hydrocarbon insecticides in 

 central Texas in 1958. Topical application studies on weevils reared from 

 squares collected from one field in July indicated increased tolerance to 



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