1916 - Pierce, W. D. A new interpretation of the relationships of temperature and 

 humidity to insect development. Agr. Res. J. 5(25): 1 183- 1 191 . 



The effect of temperature on insect development has often been inadequately- 

 recorded, especially the higher limits, largely owing to the fact that most work 

 on the subject has been done in the North Temperate Zone where temperatures 

 sufficiently high to affect development do not occur. It is only quite recently that 

 attempts have been made to correlate the humidity factor. The author used as mate- 

 rial the records of thousands of individual boll weevils, A. grandis and A. grandis 

 thurberiae, obtained in Texas, Louisiana, and Arizona between 1902 and 1915. 



It is generally held that the activities of a species reach a maximum of ef- 

 ficiency at a certain definite temperature, but the author suggests a zone of 

 humidities and temperatures of more or less restricted areas as more probable, 

 and, in the case of the boll weevil, this lies near 83°F. and 65% relative humidity. 

 The relation of the stages of hibernation, activity, and estivation to temperature, 

 and the upper and lower fatal temperatures, have been constantly recorded with- 

 out reference to the humidity factor. 



A diagram is given showing a combination of the temperature and humidity 

 records, which result in a series of concentric eliptical areas, each of which 

 represents a stage in the progress from maximum efficiency to dormancy and 

 death. Details are given as to methods of calculations used. One of the results of 

 this method will be the necessity for discarding the conception of separate zones 

 of estivation and hibernation. The author has repeatedly noticed the impossibility 

 of differentiating between a boll weevil larva killed by heat and one killed by 

 cold. 



1925 - Yothers, W. W. Report of the frost damage. J. Econ. Ent. 18(2):425. 



"Contrary to the report that the cotton boll weevil (A grandis) had been ex- 

 terminated by the cold, an apparently healthy adult weevil was found, shortly 

 after frost, hibernating in an orange grove." 



1932 - Isely, Dwight. Abundance of the boll weevil in relation to summer weather and to 

 food. Ark. Agr. Expt. Sta. B. 271, 34 p. 



Favorable climatic conditions shorten the life cycle to an extent that ac- 

 counts for the suddenness of outbreaks of the weevil; nevertheless, unfavorable 

 weather in June and July may reduce the numbers so that potential outbreaks fail 

 to materialize. An increase in temperature from 69.8° to 87.8°F. shortens the 

 cycle from egg to adult by one-half, and an increase from 78.8° to 87.8°F. 

 shortens it by about 20%. The mean temperatures in Arkansas during the critical 

 months of June, July, and August are usually within the optimum range for de- 

 velopment (77° to 86°F.). 



Sometimes favorable temperatures are delayed until late in June, in which 

 case the fruiting of cotton is delayed correspondingly. After cotton begins fruit- 

 ing, variations in temperature may accelerate or retard the life cycle but are 

 never sufficient to change the number of generations occurring during the critical 

 period of cotton production, though they do affect the time of maturity of the first 

 2 generations. Boll weevils can survive in large numbers only between 73.4° and 

 82.2°F., the optimum apparently being 75.2° to 77°F. A rise in temperature from 

 77° to 84.2°F. results in an increase in the number of eggs deposited of about 

 70%, whereas a drop from 77° to 71.6 F. may result in a reduction of about 

 50%. 



An increase in relative humidity from 50% to 90% consistently hastens de- 

 velopment. In the field, the relation of humidity to the rate of development is so 

 over- shadowed by the effect of temperature that its importance is not readily 

 recognized. Relative humidity during the summer is the most important factor 

 affecting the survival of immature weevils. The survival of immature stages in 

 squares appeared to be negligible at a relative humidity of 50%, and near optimum 

 at one of 90%. In the field, relative humidity is probably never unfavorably high 

 but is often low enough to be distinctly unfavorable. A summer drought therefore 

 often causes potential outbreaks to fail to materialize. 



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