SELECTION FOR TIME OF PUPATION IN TRIBOLIUM CASTANEUM

Abstract

HE totality of growth is dependent upon the period of time required for an Torganism to reach a stage of maturation. This generally has been mesaured in terms of developmental rate or developmental time. Among the insects, the genetic control of growth and rate of development is best known in DrosophiZa melanogaster; therefore, information from other species about the genetic control of developmental time is relevant, because the duration of this period is probably an important component of fitness in terms of its influence upon ultimate body size. It is the purpose of this study to provide such information concerning developmental time in Tribolium castaneum. The study was initiated in 1962 to develop, through selection, lines of T. castaneum which differed only in pupation time-i.e., early versus late pupation. The behavior of two other characters, 13-day larval weight and pupal weight, is also presented in terms of their relationship to the trait under selection. MATERIALS AND METHODS The population of Tribolium castaneum from which the selected lines were derived, was the mass mated, non-inbred stock identified as the Purdue "+" Foundation. The lines derived were: one selected for early pupation, one selected for late pupation and an unselected control, with each being replicated three times. The lines were reared in a Model 252 Jamesway incubator maintained at 33 t 1"C, with a 70 t 296 RH level. The three replications were run concurrently and were constituted from independent samples of 100 unsexed adult beetles mass mated for cne generation. Within each replication, three samples of ten pairs of adults from a single 24-hr egg collection were randomly chosen to initiate the lines described above. The procedures to be described were followed throughout the study. Parent beetles were mass mated for four days in plastic boxes (17.5 x 12.5 x 6 cm) containing 100 gm of culturing medium (95% whole-wheat flour and 5% dried brewer's yeast). The parents were then transferred to fresh medium for three successive 12-hr egg collecting periods to insure an adequate number of progeny from which the measurements of the selected trait, pupation time, and the secondary traits, 13-day larval weight and pupal weight, could be obtained. Pupation time was measured as the number of days required from egg laying (Day 0) to that of pupation, and was recorded to the nearest 0.5 day. One hundred larvae were transferred '