Genetic control ofHylemya antiqua III. Differences in pupation ability between two strains

Summary Some relevant traits of a wild (L) and a laboratory (C) strain ofHylemya antiqua (Meigen), determining differences in their pupation ability under experimental conditions have been investigated in relation to genetic control. The wild strain showed an intrinsic higher pupation ability than the laboratory strain. The minimum feeding period was 0.6 days longer for the C strain. The minimum larval dry weight was different for the two strains. With a normal feeding period C larvae pupated on average 1.63 days later than L larvae. By the shortening of the larval feeding period an acceleration of the larval development of both strains was observed: the acceleration of development was more marked for the wild strain. This result has been contrasted with published works onDrosphila. The consequences of these differences as far as the competitive ability of each strain is concerned, have been discussed in relation to genetic control.     

Postmetamorphic growth, survival, and age at first reproduction of the salamander,hynobius nebulosus tokyoensis Tago in relation to a consideration on the optimal timing of first reproduction

Summary The postmetamorphic growth and survival of the salamanderHynobius nebulosus tokyoentis Tago were surveyed in the study site located in Habu village of Hinodemachi, a suburb of Tokyo City, during 1975–1981. A laboratory experiment on the growth rate of juveniles was conducted in parallel with the field survey. The result indicated that this salamander grew at the rate of 8,mm in s.v.l. per year during the juvenile stage, but its growth rate decreased markedly as low as 1.8 mm for males and 1.1 mm for females, once it had attained sexual maturity. According to the “capture-recapture” procedure the annual survival rate after metamorphosis was found to be quite high; that is, approximately 0.7. By using the growth rate of juveniles and the difference between the sizes at metamorphosis and sexual maturity, the age at first reproduction was estimated to be 4 year for males and 5 year for females. From the data obtained in this study, the intrinsic rates of increase (r) were calculated for various values of age at first reproduction under different survival schedules, and the relationship between the age at first reproduction and fitness as measured byr was examined. The result indicated that an optimal age maximizing fitness always existed under respective survival schedules, and the observed age at first reproduction of this salamandei was found to coincide well with the predicted optimal age.     

Contest and scramble competitions inCallosobruchus maculatus (Coleoptera: Bruchidae) II. Larval competition and interference mechanisms

Summary Competition between contest and scramble strategists was examined using two strains ofCallosobruchus maculatus, the contest strain (iQ) and the scramble strain (tQ). The direct larval interference experiment within each strain showed that the contest strain performed strong direct interference throughout its larval stage against the conspecific opponent(s). The scramble strain also performed its interference, but only during the 3rd and the 4th larval stages. The inter-strain larval competition experiments inside a large and small mung bean (Vigna radiata) showed that the contest strain was, in general, superior to the scramble strain in competition, but the competition results were density- and frequency-dependent. In the large beans, the proportion of adult emergence of the contest strain increased with the increase of its own initial density but decreased as the initial density of the scramble strain increased. The shape of the proportion of adult emergence became nonlinear in the small beans. The cause of the complexity of inter-strain competition results was discussed in the light of the difference in larval interference ability between the two strains.     

Competition between laboratory populations of green leafhoppers,Nephotettix spp. (Homoptera: Cicadellidae)

Summary Intra- and interspecific competition between laboratory populations of four green leafhoppers,Nephotettix spp. was studied in the laboratory under three different temperature regimes of 24°C, 27°C and 30°C. For the single-species population of the three tropical species, the equilibrium density increased as the temperature increased. On the other hand, for the temperature speciesN. cincticeps, the highest equilibrium density was at the intermediate temperature and the lowest at high temperature. Interspecific interactions between two tropical (N. virescens vs.N. nigropictus), a tropical and a temperature (N. virescens vs.N. cincticeps) and a rice-feeding and a grass-inhabiting (N. virescens vs.N. malayanus) Nephotettix species were also studied in the laboratory at the three temperature regimes. Temperature differentially affected the outcome of competition between twoNephotettix species. BetweenN. virescens andN. nigropictus, the latter was more successful over the former at low and intermediate temperatures, while the former was more successful at high temperature. BetweenN. virescens andN. cincticeps, the temperate species inhibited the growth of the tropical species at low temperature while the tropical species inhibited the growth of the temperate species at high temperature. At intermediate temperature, the population ofN. virescens persisted at a slightly higher density over the population ofN. cincticeps. Between the rice-feedingN. virescens and the grass-inhabitingN. malayanus, regardless of temperature the population density of the latter was greatly reduced and later became extinct while the population of the former continued its growth. These consequences of competition between twoNephotettix species conformed fairly well to those predicted by theLotka-Volterra model using demographic parameters specified for each species.     

Overwintering ecology of two social halictine bees,Lasioglossum duplex andL. problematicum

Summary Overwintering of two social halictine bees,Lasioglossum duplex (Dalla Torre) andL. problematicum (Blüthgen), was studied. InL. duplex many females stay near the old nests, each female preparing a hibernaculum separated from the natal nest. InL. problematicum most females overwinter communally within the natal nest. This difference in overwintering habits relates to the social structure in the next spring.L. duplex is nearly always solitary in spring although later becoming eusocial, whereas many nests ofL. problematicum are polygynous, beginning in early spring.L. duplex overwinters much deeper ( ) in the soil than doesL. problematicum ( ), but both species are safe from drops in soil temperature, which is above 0°C even in midwinter, and the bees' supercooling points are lower than −6°C. This cold resistance and the storage of sufficient food in the crop are reflected in the winter survival, which is much higher (79%) than the rate of successful nests in the spring active phase (25%). Bionomics of the eusocial halictine beeLasioglossum duplex VII. Contribution No. 2654 from the Inst. Low Temp. Sci.     

Drug resistance in an age-of-infection model

ABSTRACT

In the case of a disease spreading over a time-scale comparable to the average lifetime in a host population, when the infectiousness of individuals depends on the tine since the onset of infection and when infections involve both drug-sensitive and drug-resistant strains of a pathogen, resistance may develop during the treatment of drug-sensitive strains. If increasing the treatment rate reduces the reproduction number of the drug-sensitive strain to a value below the reproduction number of the drug-resistant strain, then the disease may persist at a boundary equilibrium where only drug-resistant infection is present.     

Interspecific competition between two species of Trichogrammatidae III The analytical study on the competition

Summary The experiment was carried out in order to analyze the results of interspecific competition which were mentioned in the previous reports (Sasaba 1964, 1965). The following definite tendencies were obtained and an account was given with regard to the process of competition. (1)T. minutum had a higher reproductive rate thanT. japonicum at a lower density of the parent wasps. (2) The parasitic efficiency ofT. minutum was high as compared withT. japonicum. (3)T. japonicum was consistently superior toT. minutum in the interspecific competition at larval stage. Contribution from the Entomological Laboratory, College of Agriculture, Kyoto University, No. 384.     

The effect of larval age range on survival of twoTribolium castaneum strains in mixed cultures, through pupal cannibalism

Summary The effect of larval age range on survival of twoTribolium castaneum strains in mixed cultures was studied in an experimental situation in which other selective forces were reduced to a minimum. Increasing the difference in larval age setween the strains by one day resulted in a reduction of survival of the faster-developing mutant strain, because more of its earlier pupae were cannibalized by the larvae. General aspects of the effects of pupal cannibalism by larvae on the outcome of intra-specific competition (sensu lato) inTribolium are discussed.     

Damped oscillation of population density at equilibrium

Summary It has been theoretically assumed that the population density at the equilibrium oscillates with damping from generation to generation. In the adult population of the southern cowpea weevil,Callosobruchus maculatus, it was exemplified. But, it was not so clear in the adult population of the azuki bean weevil,C. chinensis as seen in that ofC. maculatus. This difference seems to be due to the scramble type of competition that occurs in larval stage inC. maculatus, instead of in the egg stage asC. chinensis. Comparing with the oscillation from generation to generation obtained in the present experiment to that ofLucilia population found byNicholson, the oscillation inLucilia population is composed of the cycle in a generation and the descending phase of each cycle of it is not regulated density-dependently. The present result seems to be more appropriate for the demonstration of the theory of self-adjustment of population. Contribution from the Entomological Laboratory, Kyoto University, No. 404. Supported by a grant in aid for Scientific Research from the Ministry of Education.