Pupal Viability Research Articles

Limitation on the Pupal Development of the Eye-Spotted Bud Moth in Northeastern Wisconsin1

For several years a consistent incidence of nonparasitic mortality of pupae of the eye-spotted bud moth, Spilonota ocellana (Denis & Schiffermuller), was observed in Door County, Wisconsin, apple and cherry orchards. The pupae revealed no obvious external injury and when dissected most of them contained dried organic matter with little or no visible adult structures. A similar phenomonon has been observed with other insects (Regan 1923) ; and recently Samuelson (1961) reported a 20%-unaccountedfor pupal mortality in the cotton square borer, Strymon melinus (Hubner), and Dobson (1961) found that 19% of wheat bulb fly, Leptohylemyia coarctata (Fallen), pupae died from unknown causes. The importance of a “pupal viability”figure in experiments was recognized by Bay and Legner (1963), and Legner and Bay (1964) in culturing Hippelates eye gnats, where certain percentages of reared pupae died without development of adult structures. Pupal viability in their experiments and in current experiments by the senior author with house flies, Musca doinestica L., was influenced to a large degree by the amount and kind of food available to the larvae (Legner and Bay 1961). In nature examples of deleterious effects of severe winters and storms on insects have been noted (Carter 1961, Richards 1961, Shands et al. 1956) ; however, the existence of more discreet mortality factors in natural insect populations dining apparent optimum developmental conditions is often overlooked or ignored.

Observations on laboratory colonies of the tsetse flies Glossina morsitans West. and Glossina austeni Newstead.

(a) Glossina morsitans1. A method of maintaining a breeding colony is described. The flies were best kept singly in tubes.2. The optimum temperature and humidity ranges were 74–80° F. and 60–75% R.H., respectively. Young flies failed to tolerate a lower minimum temperature.3. A light intensity of at least one foot-candle was needed at the feeding site.4. The method of feeding the flies was of prime importance. Best results were obtained by offering food every fourth day, at a temperature of 80–81° F. The best feeding animal was sheep, but guinea-pig was useful for inducing newly emerged flies to feed. The condition of the skin at the feeding site was important, and it is suggested that frequently changing the feeding animal will lead to better feeding.5. Female flies lived longer than male flies, and in both sexes the highest mortality was during the first 20 days of life.6. The optimum age for mating was 10–14 days for males and 3–4 days for females; 90–100% of the first and second generation females were fully inseminated.7. Each generation was less virile than the preceding one. Pupa production was decreased and the abortion rate increased from each generation to the next. Pupal viability, however, remained constant throughout all generations but the mean pupal weight showed a progressive decrease, except for the pupae from the second and third generation flies.8. The mean interval without food during an interlarval period did not affect the duration of the period.9. Feeding on the day of parturition did not significantly affect the length of the succeeding interlarval period.10. The duration of an interlarval period was directly correlated with the length of the maximum interval without food during the period.(b) Glossina austeni11. A colony was maintained in a manner similar to that used for G. morsitans, but best results were obtained at 80–85° F. and 77–82% R.H.12. Feeding was more satisfactory than in G. morsitans.13. In longevity and reproduction the flies were superior to G. morsitans.

COMPARATIVE PHYSIOLOGY OF SOME CHROMOSOMAL TYPES INDROSOPHILA PSEUDOOBSCURA

Chromosomal polymorphism, in the form of simultaneous occurrence of two or more inversion types, is a widespread phenomenon in natural populations of Drosophila pseudoobscura. Dobzhansky and co-workers have carried out extensive field and laboratory studies on various local populations of this species. At Pifion Flats on Mount San Jacinto in California, two common gene arrangements in the third chromosome, Standard (ST) and Chiricahua (CH), exhibit seasonal cycles. CH increases at the expense of ST in spring, and the reverse trend occurs during summer (Dobzhansky, 1943), suggesting that in nature these karyotypes are subject to selection pressures. In the laboratory, population cage experiments carried out on flies of Pifion Flats extraction showed that different initial proportions of ST and CH inversion types approached a characteristic equilibrium frequency of about 75% ST and 25% CH at 25? C. (Wright and Dobzhansky, 1946; Dobzhansky, 1947; Dobzhansky and Pavlovsky, 1953). At 16.5? C. no significant change from the initial frequency was observed. The occurrence of a characteristic equilibrium at 250 C., rather than elimination of one of the two chromosomal types, indicates that the structural heterozygote ST/CH has an overall adaptive advantage over both homozygotes, ST/ST and CH/CH, under the conditions of the experiment. From the most recent experimental data, adaptive values have been calculated at ST/ CH 1.00, CH/CH = 0.413, and ST/ ST 0.895 (Dobzhansky and Pavlovsky, 1953). Some attempts to discover the physiological properties of the flies which may be responsible for these differences in adaptive values have been reported (Heuts, 1947 and 1948; Levine, 1952). Heuts found a differential longevity at 0 to 40 C. and at 28 to 300 C. Levine compared CH/CH, ST/ST, and ST/CH flies with regard to the effects of temperature and relative humidity on developmental and adult stages. It should be noted that in Levine's work efforts were made to raise the experimental material under optimal conditions in all cases. With his technique, no differences in the performance of egg or larval stages were observed. At some temperatures and relative humidities, differences were found in pupal viability and in the ability of adults to survive starvation. In every case of demonstrated difference, CH/CH proved least viable with ST/ST either equal or superior to ST/CH. No evidence for any superiority of the heterozygote was found. The work reported here is an attempt to discover some of the reasons for the overall adaptive advantage of the ST/CH heterozygotes by making physiological comparisons among the three karyotypes. A deliberate attempt was made to raise the experimental material under conditions more nearly approximating those in the crowded population cages. With limited environmental resources, the amount 1 Submitted in partial fulfillment of the requirements for the Degree of Doctor of Philosophy, in the Faculty of Pure Science, Columbia University. 2 Part of this study was conducted during the tenure of a fellowship from the National Cancer Institute of the National Institutes of Health, Public Health Service.