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IN an examination of stock cultures of the red-rust flour beetle, Tribolium castaneum:1 Herbst, in connection with experimental population studies, a certain individual was found which possessed eyes completely lacking black pigment in certain ommatidia. The eyes of this form appeared white or pearly when contrasted with the eye of a normal Trib oliumn, which is entirely black. This suggested at once that the unusual eye pattern might be due to some kind of heritable variation, since the failure of pigment to develop seems to be an effect quite commonly produced by gene mutation. In order to study this character genetically, a number of pupae were segregated from the stock culture and sexed (for technique see Park, 1935) and then set aside and kept in a virginal condition until examined. Out of this group of sexed pupae one pearl eyed male and one pearl eyed female were found which appeared exactly, with respect to eye pigmentation, like the original pearl eyed beetle. These two pearl forms were mated together and their progeny studied. The progeny were all pearl eyed like their parents and when bred with themselves for the purpose of multiplying the pearl stock gave all pearl eyed forms. It seemed patent, on the basis of these results, that this eye abnormality was an inherited characteristic and certain genetic crosses were made to determine the mode of inheritance of the mutation which is. to the best knowledge of the

A gene, designated "paddle," is described for the flour beetle Tribolium castaneum, and shown to be inherited as a single, sex-linked recessive. The somatic effect of the gene is to cause varying degrees of fusion of the three segments constituting the antennal club. In addition, male mutant beetles show a reduction in the number of antennal segments from the eleven characteristic of the genus to a modal number of nine.

ALTHOUGH scattered observations on the life span of many vertebrates and invertebrates are legion, the accurately Collected mortality. data necessary for the construction of a life table are, apart from mnan, few indeed. For the insect group, life tables in complete or abridged form have been published for representatives of four orders: the Orthoptera (Blatta orientalis), the Lepidoptera (Telea polyphtemis and Acrobasis caryae), the Diptera (Drosophtila melanogaster and various of its mutants), and the Coleoptera (Tribolit am1 coonfusumt). Reference to the first three orders will be found in the papers of Pearl and AMiner (1935 and 1936); to the last order in Pearl, Park alcd Mliner (1941). The present paper reports a life table for another, and hitherto little studied, flour beetle, Tribolimi qnadens. The details of life table construction, the significance of the life table for many pleases of population biology and a review of the literature dealing with mortality in infra-human populations are not considered pertinent for this short paper. If interested, the reader can find further information in Bodeniheinier (1938), Dublin. and Lotka (1936) and Pearl (1940). The flour beetles (Tribooliulml cojifusutm and Triboliamn;^ castaneum) are proving to be appropriate organisms for experimental populations studies (see Ford, 1937, and Park, 1941). It is hoped that, as more backg-round data 1 I wish to express my sincere thanks to Dr. Alfred J; Lotka, of the Metropolitail Life Insurance Compally, whose advice has been inv-aluable. I am also greatly iiidebted to Mr. Albert W. Buzicky, of The University of Miimesota, for furnishilgg me with a culture of Triboltm macdens as well as for a ilnunber of suggestions. This investigation has beeni aided by a grailt from the Dr. Wallace C. adll Clara A. Abbott Meioriml Funid of the University of Chicago.

It has been shown in a recent study (Park, '38) that certain aspects of the post-embryonic development of the flour beetle, Triboliumi con fusun, are noticeably affected by crowding the larvae in a constant sized volume of flour. For example, if a series of cultures are established in which the number of larvae are varied from one to 256 individuals per bottle the forms die at a higher rate and pass through their metamorphosis more slowly as their densities increase. This phenomenon was demonstrated to obtain only if the medium was not changed or altered during the period of metamorphosis. When the flour was renewed at 48 hour intervals the crowding effect was dispelled; the larvae developed essentially as rapidly at high as at low population densities. From these data the conclusion was reached that the principal density effects noted were due, not to unique behavior interactions between the larvae themselves, but to the influence the larvae exerted on their environment. The ecologic implications of such density relationships have been discussed by Park ('37; '39). In the analysis of population phenomena it is obviously necessary at times to set up experiments that possess a certain artificiality. This procedure seems justifiable if forthcoming results aid in the interpretation of population dynamics. Thus, in the experiments summarized above, it is patent that an unmolested culture of Triboliumt would rarely exist as a strictly larval population. Nevertheless, the knowledge that larval density is related to larval and pupal development is of value in appraising the mechanics of the complete population. The experiments reported in this paper are also subject to a similar type of criticism but are presented in the light that the results have significance in the understanding of the natural population. In a Triboliumt population the biotic components are eggs, larvae, pupae and imagoes. Typically, all these stages exist together in any one population for any moment of time. The thing that changes with age is the numerical frequency or density of these components. It is important, therefore, to

The flour beetles Tribolium confusum and Tribolium ccstaneum have been used in an extensive investigation of interspecies competition (Park, 1948). A finding of this study was that when no special precautions were takento eliminate the sporozoan parasite Adelina tribolii, T. confusum, as a single species, typically maintained populations about twenty to thirty per cent larger than did T. castaneim. No known differences in temperature, humidity, light, medium, or handling existed between these two series. In mixed-species populations, that is when there was competition between the two forms, T. castaneum was usually driven out by T. confusum. In the absence of the parasite, T. castaneum usually drove out T. confusum. There is some indication that in their natural distribution the two species vary in relative abundance according to latitude (Good, 1936) and to the breeding medium, whether wheat or flour (Miller, 1944). It is hoped that studies of competition may shed some light on such problems in the population ecology of the two species as well as on the general nature of interspecies competition itself. In many ways these beetles are excellent objects for the laboratory study of such phenomena. They inhabit the same ecological habitat from which they derive their entire food supply and in which their life-history, and that of successive generations. is passed. The DoDulations. includ

T KIBOLIUM CONFUSUM, the flour beetle, possesses characteristics which commend it to the attention of experimentalists. It is cosmopolitan and easily obtainable; it has a moderately short life-cycle; it is hardy and requires no elaborate equipment for its maintenance; both adults and immature forms are readily recoverable from the medium for study by a simple technique, and it spends its entire life-history in various pulverized grains such as flour. As has been pointed out before, this latter feature is particularly advantageous in many kinds of experimentation since, with a total environment such as flour, considerable stability of both intraand extramedium relationships can be obtained. By using similar flour in all experiments and by expressing this flour quantitatively in terms of weight and surface exposure, as well as surrounding the flour by as constant external conditions as obtainable, a total environment can be established which is relatively quite constant and reproducible. Despite these attractive requisites it is only recently that Tribolium has come to the attention of biologists interested in theoretical problems. The economic zoblogists have been vigorously aware of the existence of this form for many years and have done much in providing data on the general ecology of the species. However, past this point, these workers, possibly unfortunately, have seemed more interested in devising methods of exterminating the form than recommending it to the attention of experimentalists. Babcock (i9i2z), an early worker with Tribolium, used this beetle in studying the problem of metabolic water, finding the insect maintained a tissue water level about 40 per cent greater than the moisture content of an environment containing io per cent water. Davey (I9I7, 'I9), another early investigator, reported results showing that the length of life of these beetles could be prolonged if mass cultures received a small daily dosage of X-rays. Probably the principal credit in introducing Tribolium as an experimental organism, however, belongs to R. N. Chapman who in I9I8 reported on its life-history, in I9Z-4 on its nutritional requirements, and in i9z-8 on its suitability for population study. These papers will be discussed at length later: it is only important at this point to remember that they emphasized the practicability of Tribolium for experimental purposes by presenting a technique of handling the beetles as well as actual data. Since Tribolium does seem destined to merit more experimental attention, and since experimentalists need a factual background about the animal of their endeavors, it seems permissible at this stage to review fairly completely certain details about the flour beetle in the hope that such a review will be helpful and possibly stimulating to future investigators in the field. With this in mind the following general topics

During the past fifteen or so years the flour beetles Tribolium have been utilized so much in laboratory population studies (for summaries see Ford, 1937; Thomas Park, 1941) that it seems appropriate to place on record some new data on their fecundity which may be of value for future research. The present data were collected as part of a comprehensive analysis now in progress of inter-species competition in Tribolium populations.

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

It is evident that the methods employed in human demography have much to offer for modern population ecology. The early work of Raymond Pearl and his associates on the computation of life tables for other forms of life besides man is well known, and it may be said that these pioneer studies did much to initiate all the later work in this field. Recently, Deevey ('47), impressed by the demonstrated value of life tables in human and laboratory population research, extended this technique by applying it to field observations and expressed the hope that students working in the field would, in the future, collect their data in such a way that they could be subjected to mortalitytable treatment. The studies to which we have thus briefly referred deal in the main with the construction of life tables, which summarize in a convenient form the degree of mortality according to age. If, in addition, it is possible to measure the degree of fertility, our information in regard to a particular species or population is greatly increased and we can apply the methods of analysis which are now commonly employed in the case of human populations. The development of this branch of population mathematics is principally due to A. J. Lotka, and the biologist will find convenient summaries of the theoretical

In this paper are presented life tables for males and for females of the beetle Tribolium confusum Duval, living in regularly renewed fresh flour. The Tribolium life curves resemble in their fundamental pattern human life curves more closely than do those of any other organism for which life tables have as yet been computed. They have at the beginning of life in the imago stage a component corresponding in the time and quantitative relations of its incidence to the infant mortality component of human life tables.

Chapman ('28), working with the confused flour beetle Tribolizirn confiusumn Duval, presented evidence demonstrating that a condition of equilibrium, measured in terms of number of individuals per gram of flour, is eventually reached within each population which is approximately uniform irrespective of the environmental size or the initial population density. In table III of his paper, reproduced herewith, he has recorded data, which in addition to supporting his own conclusions, open to experimentation another phase of the problem. Allee ('3I), interested in reviewing the effects of crowding on organisms, has analyzed this data. He shows that for the first periods in the development of the beetle population, namely eleven and twenty-five days, the greatest increase in numbers, in terms of eggs and early instar larvae per female day, comes at the initial population of four, while initial populations of eight or sixteen show a more rapid increase at eleven (lays than that given when only one pair was present. About this phenomenon, Allee remarks ('3I, P. I8o), " This indicates that there is an optimum initial population-medium relationship, which, for certain volumes of medium, is different from that given by the smallest population present." Chapman's original data are presented in table I together with a recalculation to show the rate of increase per female day at all population densities tried. The work to be reported in this paper has been directed towards finding by more extensive experiments whether the initial rate of population growth is usually greater in these beetle populations when more than one pair of beetles is present. CONDITIONS OF EXPERIMENT

This report reexamines experimentally the problem of competitive indeterminacy in mixed-species populations of the flour beetles, Tribolium confusum and T. castaneum. Indeterminacy takes the form of alternative competitive outcomes: in some replicate cultures one species exterminates the other with a probability, say p, whereas in others, the opposing species wins with a complementary probability, 1-p. The conventional explanation for this is the genetic founder effect hypothesis--an explanation based on genetic stochasticity. The experiment reported here partitioned indeterminacy into founder effect and nonfounder effect components. The results implicate demographic stochasticity, not classical genetic founder effect, as a factor influencing the identity of the winning species.

Two species of flour beetles, Tribolium confusum and Tribolium castaneum, respond to neutral pith disks impregnated with aqueous extracts of their pupae in such a way that the adults and larvae tend to select the extract of the other species. These findings have implications for the population ecology of Tribolium.