Studies of Behavior of the Tribolium Flour Beetles. I. Contrasting Responses of T. castaneum and T. confusum to Fresh and Conditioned Flours

Abstract

The studies set out in Part Fi of this series contrast the behavioral responses of Tribolium castaneum Herbst., and T. confusum Duval, to two markedly differing conditions of the flour medium: fresh whole-wheat flour, and whole-wheat flour of the same origin that has become heavily conditioned by supporting the growth of high populations of Tribolium in stock rearings. The conditioning of a flour medium by beetles living within it is a process involving at least 3 factors: depletion of the nutritive value of the medium; accumulation of cast larval skins, dead imagoes, and similar debris; and finally and most markedly, accumulation of the quinones given off by Tribolium imagoes and taken up by the flour. Conditioning is a progressive, cumulative process, so that a flour is more, or is less, conditioned depending on its occupancy by larger, or smaller, numbers of beetles for longer, or shorter, periods. Interest in the behavior of these 2 Tribolium species arises primarily from their use by Dr. Thomas Park, of the University of Chicago, in a biologic model of interspecies competition (Park 1954). The model is meaningful in view of the close relation between these species and their ability to survive indefinitely as single-species control populations under identical conditions of husbandry. As Park (1954) has pointed out, these are species exhibiting marked ecological similarity, between which the struggle for survival in competition might be presumed to be severe. In confirmation, Park has found that under 6 different combinations of temperature and humidity, elimination of one or the other species follows invariably when they are placed in competition. Study of their behavior offers one important route by which we may now assess the degree to which these species are, in fact, ecologically similar. The results of competition between these beetles are better known and better documented than they are for any other species, so that by assessing their ecological similarity we may also hope to assess the importance of ecological similarity itself as a factor in competitive elimination. A substantial literature of Tribolium studies has arisen partly because these insects are admirably suited to laboratory investigation of ecological problems, and also partly because they have been of considerable economic importance as pests of stored food. Economic interest has led to a number of studies of the gaseous secretion that is the principal cause of the conditioning of the flour medium. Roth and Howland (1941) found that last instar larvae and prepupae exposed to the gas gave rise to variously aberrant adult beetles. Roth (1943) found that there was no detectable secretion of the gas in larvae of all instars or in prepupae, but that tests for gas were positive among some very late pupae and in all adults an hour after emergence. In this same year Alexander and Barton (1943) identified the main part of the volatile secretion of T. castaneum as ethylquinone and noted that the same substance could be obtained from T. confusum. A decade later, Loconti and Roth (1953) provided the presently most exact determination of the composition of the secretion of T. castaneurn. They found that 3 quinones were present in the odorous secretion: 80-90% 2-ethyl-1, 4-benzoquinone; 10-20% 2methyl-1, 4-benzoquinone; and a trace of 2methoxy1, 4-benzoquinone. Loconti and Roth introduced a new approach to the study of this gaseous secretion by performing qualitative repellency tests with the 3 quinones isolated from adult beetles, using T. castaneum as the test animal. Their test method was based on the strong attraction of starved beetles to flour. The introduction of the ethyland methyl-quinones into the flour repelled starved beetles, whereas the methoxyquinone did not. It may be supposed that, had they also performed these repellency tests with T. confusurn as the test animal, they would have noted the single most striking observation from the present studies-that, unlike T. castaneum, T. confusum is strongly attracted to conditioned flour. This emerges in the present study as a major facet of behavioral dissimilarity affecting the ecological relations of these species. 1 These studies have been aided by fellowships from the University of Chicago and currently by P.H.S. Grant M-5561 (A).