Search

PREVIOUS PREVIOUS investigations (Park, 1934, 1935, 1936) have analyzed certain effects of conditioned flour upon the fecundity and fertility of the beetle, Tribolium confusum Duval. "Conditioned flour" represents a medium which is produced by the beetles in the normal course of their existence and is obtained, for experimental purposes, by using flour which has been inhabited by dense populations of Tribolium. It is, therefore, an inevitable product of population activity which owes its existence entirely to the cumulative effects of the breeding and general behavior of the beetles themselves. More specifically, conditioned flour differs from fresh or unconditioned flour in that the beetles inhabiting it have reduced its nutritive value through constant feeding and have added certain by-products, such as excretory and metabolic wastes, not present in the original medium. It was shown in one of these previous reports (Park, 1934) that, if the fecundity of Tribolium females was assayed while the forms were living in a heavily conditioned flour and contrasted with the fecundity of a control or fresh-flour group, the former beetles had a drastically lower rate of egg production than the latter. In a later paper (Park, 1936) the heavily conditioned flour (i.e., flour from a dense Tribolium population) was "diluted" with fresh flour so as to form a series of mediums composed of 25, 50, and 75 per cent conditioned flour. The effects of these environments on the beetles' fecundity were tested against a fresh-flour control and an all or heavily conditioned flour control in order to see if differential conditioning of the environmenti.e., a lighter or partial conditioning-was equally effective in changing oviposition rates. The results indicated that, in general, there was a proportionate relationship between the degree of conditioning and the number of eggs produced. In other words, the beetles in the fresh flour laid the most eggs; those in the 25 per cent conditioned flour and the 50 per cent conditioned flour laid eggs at the next highest rate; those in the 75 per cent followed; and the forms in all-conditioned or "undiluted" mediums produced the fewest eggs. This was not a perfectly proportional relationship; the greatest difference came between the fresh-flour controls and the 25 and 50 per cent series. (The beetles in the latter two environments produced eggs at a statistically similar rate.) In other words, there was a bigger difference, as far as fecundity was concerned, between the fresh-flour controls and those living in the most lightly conditioned medium (the 25 per cent) than there was between any of the other combinations. This immediately suggested that it might be instructive to investigate the influence of more lightly conditioned flours upon Tribolium productivity and to try to relate these facts to the data previously obtained. The emphasis of the present paper is directed toward this end with the special hope that certain generalizations about the decline of Tribolium populations will be forthcoming. VOL. X, No. 2, APRIL, 19371 197

This paper reports further studies of cannibalistic predation as it occurs in populations of two species of flour beetles, Tribolium confusum and T. castaneum. There is by now an extensive literature about this subject, and comprehensive summaries appear in Park et al. (1965); Mertz and Davies (1968); Park, Mertz, and Nathanson (1968); Mertz and Robertson (1970); Park et al. (1970); Ryan, Park, and Mertz (1970); and Prus and Park (1973). For a general orientation about Tribolium populations, from both the ecological and genetic points of view, the reader is referred to the recent review by King and Dawson (1972). For a discussion of the "Tribolium model" in terms of its empirical and mathematical aspects, the paper of Mertz (1972) should be consulted. A new book by Sokoloff (1972) provides a