Article V. — An Experimental I nvestigation of the Relations of the 

 Codling Moth to Weather and Climate. By Victor E. Shelford. 



INTRODUCTION. 



The varied effects of the variable weather of current and preceding 

 seasons on the rate of development of an insect, and hence on the time of 

 appearance and period of continuance of each of its stages, and even on 

 the number of generations in a year and the number of individuals in each 

 generation, are often causes of uncertainty as to the best time to take steps 

 for the control of an injurious species and as to the necessary intensity of 

 control measures; and heavy losses often occur because the times chosen 

 and the activity and thoroughness of the operation do not fit the pattern 

 of the seasonal life history. It has hence become necessary to learn for 

 each important insect species the facts of its life history imder normal or 

 usual conditions and the effects of unusual weather to retard or hasten its 

 transformations and to diminish or increase its numbers. 



This problem was brought to a crisis in Illinois in 1914, when an 

 unusually hot and dry summer in combination with other favorable condi- 

 tions in the southern part of the state so accelerated the development of 

 the codling moth and so increased the number of the third generation and 

 other late larvae, usually economically insignificant, that the most intelli- 

 gent and careful apple growers suff'ered heavy losses, due to a lack of 

 harmony between their standard spraying program and the larval periods 

 of the successive generations of the codling moth. (Sprays are effective 

 only if applied so as to have the poisons on the apples early in the larval 

 period.) A serious study of the life history of this insect under field 

 conditions was consequently begun, in the fall of 1914, and was continued 

 with an elaborate equipment through the three following years. The 

 results were published by the State Entomologist's Office* and the State 

 Natural History Survey**, in 1916 and 1922, respectively. 



These studies added materially to dependable information on this 

 subject, but as they could deal only with such weather conditions as hap- 

 pened to occur in these years, their range was far too limited to warrant 

 final conclusions concerning the effects of ever)' kind of season likely to 

 occur in Illinois. 



The questions involved in so complex a problem called for long con- 

 tinued research by a climatologist provided with an ample equipment by 

 which various kinds of weather could be artificially imitated in labora- 

 tories where the insects studied could be maintained under otherwise 

 normal conditions. The present paper is the product of a series of such 



• Life history of tlie codling moth, by Stephen A. Forbes and Pressley A. Glenn. 

 29th Report, pp. 1-21. (1916) 



•• CodlinpT moth investig-ation.<5 of the State Entomologist's Office, 1915-1917, by 

 P. A. Glenn, Vol. XIV, Art. 7. (1922) 



