230 HABITS AND INSTINCTS IN LI^PTINOTARSA. 



In all the species of this genus the beetles on emergence from hibernation 

 or aestivation, or when freshly hatched from the pupa, are sexually immature 

 and do not seem to possess any attraction for the opposite sex. In both tem- 

 perate and tropical regions, when the different species of Leptinotarsa emerge 

 in the springtime from the dormant condition in which they have passed the 

 winter or the dry season, as the case may be, they are emaciated, weighing 

 less than half as much as they did when they disappeared in the autumn 

 before. Moreover, the germ cells are not developed, and the scent glands con- 

 nected with the reproductive organs are inactive and devoid of secretions. At 

 this time the sexes mingle as so many individuals, without the least trace of 

 interest in each other. They fly or move about their food plants or in the 

 observation cages in search of food and water, and when they find them they 

 set upon them with a most ravenous appetite, so that large quantities are 

 devoured in a short time. But after feeding for several days, or perhaps 

 longer, the beetles have become well nourished, the germ-cells have matured, 

 the reproductive organs are ready for use, and the characteristic habits of 

 the mating period begin to appear. The changes which take place in this 

 interval between emergence from hibernation or aestivation and the beginning 

 of reproduction will be considered in the second division of this paper. 



As soon as the beetles have attained sexual maturity they become exceed- 

 ingly restless and active. They move about in search of the opposite sex, and 

 if it is not to be found this restlessness results often, especially in the males, 

 in movements so violent and prolonged that the anim.als become completely 

 exhausted, and death not infrequently follows. If during the neutral period 

 the sexes be separated and allowed to attain maturity in separate observation 

 cages, they will, after the period of neutrality, show a great and increasing 

 activity. This is manifested in both sexes by a cessation of feeding and an 

 incessant, aimless wandering about at a rate of movement so excessive that 

 complete exhaustion and death may follow in a day or two. When thus sepa- 

 rated the females are less violent in their activities than are the males, and 

 both sexes show large individual differences in their manifestations of 

 uneasiness at the absence of the opposite sex. 



The experiment was tried, with rather interesting results, of keeping the 

 sexes separated entirely throughout the breeding period. When decemlineata 

 was thus experimented upon some of both sexes died in a few days, but 

 others, especially among the females, lived for two or even three months when 

 kept in proper conditions of temperature and moisture and given food of 

 good quality. All experiments of this kind are summarized in the following 

 table, in which is shown the duration of life of the two sexes when separated 

 and not allowed to breed . 



