The Effects of Reduced Atmospheric Pressure on Populations of Tribolium castaneum and Tribolium confusum

Abstract

Using pressure chambers, two spp. of beetles, Tribolium castaneum and T. confusum. were studied in simulated altitudes of 8000 and 14,000 feet with a control group maintained at Chicago altitude (593 feet) for comparison. Closely similar treatments were imposed on replicated cohorts of each spp. simultaneously and five categories of responses were assayed in each of the three altitudes as follows: (1) Fecundity and fertility, (2) rate of development and survival of the immature stages, (3) single population patterns with respect to total population weights and numbers, the latter being broken down into numbers of imagines, pupae, large larvae and small larvae, the total census history covering a period of 660 days, (4) changes arising in the population pattern resulting from the transfer of populations which had lived for a year at high simulated altitude to Chicago altitude and vice-versa, (5) mixed species competing population patterns. Statistical tests showed that (1) both spp. laid significantly fewer eggs under conditions of reduced atmospheric pressure, the effect being most pronounced in T. castaneum, (2) length of larval period but not of egg and pupal periods was increased in each sp., (3) as shown by census histories, both spp. were reduced in numbers and total population weight, with the larval period showing the most drastic changes, (4) in T. castaneum the reduction in numbers was compatible with population survival while in T. confusum there was a tendency (not demonstrated statistically) for the populations to become extinct for as yet incompletely known reasons, (5) the patterns of competition were essentially the same in all three conditions, (6) no tendency to become acclimated was detected in either sp. in either of the low pressure atmospheres.