244 



HABITS AND INSTINCTS IN LEPTINOTARSA. 



same time throughout the whole season eggs, larvae, and adults, so that it 

 seems on first sight that there are a large number of generations in every year 

 in the tropics. In all the species of the genus the only difference between the 

 two generations is that the second does not develop the germ-cells until after 

 a period of rest, while the other develops them at once, or soon after 

 emergence. 



The length of the season during which any given species is active varies 

 greatly in the different species, and also in the different parts of the continent 

 of North America, the season being longest in the moist regions of Vera 

 Cruz, Chiapas, and southward, and shortest in the arid semidesert and desert 

 regions of northern Mexico and the southwestern United States. The 

 lengthening of the period of reproduction is the cause of the long time during 

 which these beetles are found active in the more humid districts, and, vice 

 versa, the reduction of the length of the reproductive period is responsible for 

 the lessened period of activity in the more dry regions. Nowhere, however, is 

 the duration of the embryonic period, of the larval life, or of the pupal stage 

 subject to any great amount of variation. The time of the appearance of the 

 different generations, their duration, and various other data have been con- 

 densed into the following table : 



Table 106. Compilation of data concerning generations in the genus Leptinotarsa. 



