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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.

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

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

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.