The dynamics of laboratory populations ofCallosobruchus chinensis andC. Maculatus (Coleoptera: Bruchidae) in patchy environments

Summary Experiments are described showing the long-term dynamics of two species of bruchid beetles (Callosobruchus chinensis andC. maculatus) in arenas in which the resource of 50 black-eyed beans is divided between 5, 10 or 50 ‘patches’. Both species of adult beetles exhibit clumped distributions between patches. Within a patch there is a tendency for a density dependent reduction in (1) eggs laid per female, (2) the proportion of eggs hatching per bean (C. chinensis only) and (3) larval survival which is strongly overcompensating (particularly inC. maculatus). A discrete generation model is used as a framework to draw these results together and show how the different factors affecting natality and mortality can influence the population dynamics. Finally, the importance of the resource renewal interval in influencing the period of the population cycles is discussed.     

An individual-based model for competingDrosophila populations

An individual-based model forDrosophila is formulated, based on competition amongst larvae consuming the same batch of food. The predictions of the model are supported by data for single speciesDrosophila populations reared in the laboratory. The model is used to build a simple discrete model for the dynamics ofDrosophila populations that are kept over a number of generations. The dynamics of a single species is shown to give either a stable equilibrium or fluctuations which can be periodic or chaotic. When the dynamics of a species in the absence of the other is periodic or chaotic, we found coexistence or two alternative states, on neither of which the species can coexist.     

Sex ratios in laboratory and field populations of the old field mouse,Peromyscus polionotus

Summary Males outnumbered females as juveniles but not as adults among mice captured by hand in their burrows. The higher production of male offspring together with their higher mortality rate resulted in a 1∶1 sex ratio for the adult mice. Despite the equal abundance of each sex, more males than females were caught in traps. Males must have a higher chance of encountering a trap and/or of entering a trap after finding it.     

Binomial sampling plans for estimatingBemisia tabaci populations in cantaloupes

Early season infestations of the sweet potato whitefly,Bemisia tabaci (Gennadius), on cantaloupes,Cucumis melo L., were determined by counts of the number of adults per leaf in fields near Yuma, Arizona. We used these data to develop binomial sampling plans based on the relationship between mean densities of whiteflies per leaf,m, and proportion of leaves infested with more thanI whiteflies,P _I, according to the empirical model lnm=a′+b′ ln[−ln(1−P _I)]. The models were developed for the presence-absence approach (I=0) and for a cutoff value of three whiteflies per leaf (I=3). Four independent data sets were used to evaluate the models. Both methods yielded reliable predictions at low infestation levels, but some of the higherm values were overestimated. As the tentative economic threshold forB. tabaci is three adults per leaf, which corresponds to lowP _I values, results of the binomial sampling were satisfactory for pest management purposes.     

Population dynamics of houseflies,Musca domestica, on experimentally accumulated refuse

Summary The population dynamics of the housefly,Musca domestica, on patchy and unstable habitats consisting of refuse was investigated at a waste disposal site by using sticky flypaper and mark-release-recapture technique (Jolly-Seber's method). The newly disposed garbage was favorable for breeding of the flies for about one month after being disposed, while a mixture of garbage and ash from incinerated refuse was less favorable. On the garbage under favorable conditions, the rates of population increase was 1.25–2.82 per day, and approximately 1300–1500 flies were produced per square meter within the available period of one month. The rapid decrease in the fly density was observed just after the appearance of high density peaks. The mark-release-recapture study suggested that this rapid decrease would be mainly due to the density-dependent emigration of adult flies from the patchy habitats. The emigration was also activated when the time after garbage disposition became long.     

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.     

A new method to control houseflies,Musca domestica, at waste disposal sites

Summary Investigation was carried out from 1976 to 1979 to establish a new control system against the houseflies,Musca domestica, at a sea-filling waste disposal site in Osaka Bay, Japan. Field surveys showed that the garbage was favorble for the fly breeding for 20–30 days after being disposed, while the sewage sludge and the ash from incinerated refuse were unfavorable. Comparing the fly density at the site to the reported cases of the public complaints in the urban area near to the site, a complaint threshold density of the flies at the site was estimated. Then, a control threshold density was assumed from the complaint threshold density and the reproductive rate of the housefly population. Several insecticides, as well as a surface active agent, polyoxyethylene lauryl ether (PEL), were found effective for the temporary suppression of the fly density. Based on the results obtained, the following control system was worked out. 1) Refuse is disposed onto the same area as other inorganic wastes to deteriorate the capacity of breeding sources. 2) The fly density is examined on newly disposed refuse almost everyday by landfill operators. 3) PEL is sprayed when the density slightly exceeds the control threshold density. If the density increases rather higher, insecticide should be used. 4) The disposed refuse is covered with soil or other inorganic wastes on every weekend or every other weekend by 15 cm thickness. Success in both fly control and reduction of the amounts of insecticides sprayed was achieved by a field application of this new control system.     

Population growth rates in perfect contraceptive populations

Abstract Eventually, world population must cease to grow. In many countries attempts are made to decrease population growth by providing family planning services to all who want to prevent pregnancies. In this paper we use the concept 'perfect contraceptive population',(1) - a population in which no unwanted births occur - to derive estimates of the maximum contribution that prevention of unwanted births might make toward attaining a zero rate of natural increase in population.     

Population growth rates in perfect contraceptive populations

Eventually, world population must cease to grow. In many countries attempts are made to decrease population growth by providing family planning services to all who want to prevent pregnancies. In this paper we use the concept ‘perfect contraceptive population’,¹ — a population in which no unwanted births occur — to derive estimates of the maximum contribution that prevention of unwanted births might make toward attaining a zero rate of natural increase in population.     

Control of insecticide resistance in a field population of houseflies,Musca domestica, by releasing susceptible flies

Summary Susceptible houseflies,Musca domestica, were released at a waste disposal site to control insecticide resistance in a field housefly population. In the first experiment, a total of 163,000 pupae of the susceptible Takatsuki strain were released in October–November 1977. LD₅₀ values to fenitrothion and diazinon decreased to about one-sixth in April 1978, five months after the releases, of those before the releases. For the second experiment, a susceptible colony was derived by cross and backcross between a white-eyed substrain of the Takatsuki and a field colony. This susceptible colony consisted of whiteeyed flies with low activity and normal-eyed flies bearing no or one white eye gene. The results of large cage experiments suggested that the normal-eyed males of the susceptible colony had half the mating competitiveness of wild males. Approximately 31,000–46,000 susceptible pupae were used in each of five releases from October to November 1980. The population number of each sex, estimated by a mark-release-recapture method, increased from 12,000 in late September to 35,000–43,000 in middle November and then decreased to 5,000–8,000 in early December. The frequency of field-collected males bearing one white eye gene and those bearing one male determining factor, which were characteristics of the susceptible colony released, increased gradually during the period of releases. The susceptibility of the field population to fenitrothion and diazinon was examined five times in the period from September to December 1980. With time, the dosage-mortality regression gradually shifted towards that of the susceptible colony after starting the releases. LD₅₀ values to fenitrothion and diazinon decreased to about one-sixth and one-fifth, respectively, in June 1981, six months after the second series of susceptible fly releases, of those before the releases. Ratios of the wild flies to the released fiies were estimated to be between 4.7∶1 and 9.8∶1 in males and between 3.0∶1 and 3.9∶1 in females by taking the quality of the released colony and the population parameters of the field houseflies into consideration. Under several assumptions, the manner of resistant phenotype reduction was discussed, based on the dosage-mortality regressions and the ratios of released flies. These results showed that the releases of susceptible flies were successful in suppression of insecticide resistance in the field housefly population.     

Fluctuations of grasshopper populations on aMiscanthus sinensis grassland

Summary Population densities of the three grasshopper species onMiscanthus sinensis grassland in the Kawatabi IBP Area, Japan,Parapleurus alliaceus, Mongolotettix japonicus andChorthippus latipennis, were estimated principally by the release-and-recapture method for five years from 1968 to 1972. The total number of individuals of all three grasshopper species was about 42 per 100m² in August. The number of individuals ofP. alliaceus adult, the dominant species on this grassland, showed a tendency to decline during the five years, though the amplitude was not so large. The number of eggs laid was, however, nearly constant and the mortality from the second nymphal instar to adult was relatively low and constant during the survey period. The weather conditions during the periods of egg and the first instar, such as snowfall and temperature decreasing, are suggested to be one of the factors causing variation in numbers. Contributions from JIBP-CT No. 145. A part of this study was supported by the special project, “Studies on the dynamic status of biosphere”, sponsored by the Ministry of Education.     

Relation between exploitation and production in experimental populations ofPoecilia reticulata

Summary In order to make researches on the effect of exploitation upon fish populations, six populations of guppy were maintained during a period of 331 weeks under conditions of space, light, temperature, pH, and food controlled as much as possible. The six populations were divided into three groups two by two: a control group without exploitation, a 10% rate of exploitation group and a 20 and 33% rate of exploitation group. All the populations repeated an increase and a decrease in number and in biomass about once a year. The exploitation affected the age composition in the populations: in the non-exploited population adults occupied the largest part, and the more intensive the exploitation the larger the part fry occupied. The exploitation decreased the biomass of exploited populations, but productivity increased with increasing of of rate of exploitation. The relationship between adult and fry could be represented byRicker's reproduction curve. The form of the curve was changed by an intensity of exploitation. It was thought that exploitation acts as a preventer of aging of populations by removing old fish and results increasing number of fry and productivity.     

Elimination ofSitotroga cerealella (Olivier) bySitophilus zeamais Motschulsky from mixed laboratory cultures on maize

Summary This paper describes a series of experiments conducted to determine whySitophilus zeamais Mots. andSitotroga cerealella (Oliv.) could not survive together in maize cultures in the laboratory. The effect ofS. zeamais on different developmental stages ofS. cerealella was investigated. The presence of adultS. zeamais slightly affected moth copulation, egg laying and moth eggs in a mixed culture, but large numbers of developing moths inside maize grains were killed by the adult weevil through feeding on the grains. The major cause of elimination ofS. cerealella byS. zeamais from mixed cultures was therefore found to be damage to the immature moths in grain and such moth mortality increased as the developing moths became bigger in the grains. A weevil: grain ratio of approximately 1.4∶1 was found to be the critical weevil density at which the moth disappeared from the mixed cultures.     

Age structure of six populations of old-field mice,Peromyscus polionotus

Summary An accurate age-estimating technique, based on biochemical changes in eye lens protein, was used to study age structures of six populations of the old-field mouse,Peromyscus polionotus. A new mathematical procedure permitted quantitative comparisons of these populations. Four inland populations had essentially the same median ages (75–84 days), maximum ages (248–297 days) and relative production rates (56–58% of the surviving population had been born in the 100 days prior to sampling). Approximately 50% of the females were old enough to have weaned a litter. One inland population had a lower median age (49 days), a lower maximum age (181 days) and a higher relative production rate (73%). Relatively fewer females (38%) could have weaned a litter. The single beach population was also different, with higher median age (180 days), and lower relative production rate (2%). All females were old enough to have weaned a litter. Maximum age was essentially the same as for the four similar, inland populations. Factors which may have contributed to observed differences in these populations are discussed.     

Variability in food consumption rate of natural populations in the spider,Nephila clavata

Summary Mean daily food consumption and total lifetime food consumption of the spider,Nephila clavata, were estimated in natural populations. Daily food consumption in the late adult stage was 27–150 mg wet weight, which was nearly equivalent or slightly larger than that in other large web-building spiders. Considerable variation in food consumption was found among habitats or years. The largest variation among habitats in the same year was 7 and 5 fold for daily and lifetime consumption, respectively, while that among years in the same habitat was 3.5 and 2.5 for daily and lifetime consumption, respectively. Feeding conditions evaluated from the food consumption per body weight of spiders declined during the period from mid-July to mid-September in almost all the populations, which suggested that they faced to severe food limitation in this period.     

Searching preference of the parasitoid,Anisopteromalus calandrae (Howard) for different stages of the host,Callosobruchus maculatus (F.) in the laboratory

Summary The functional response parameters of the parasitoid,Anisopteromalus calandrae (Howard) to the third instar, the fourth instar and the pupae ofCallosobruchus maculatus (F.) were estimated from the Random Parasitoid Equation. By modifying this equation for a two host situation and using the parameters estimated above, a no switch model could be obtained. This model was then used to test for switching. In the preference experiments where two stages of the host were presented to the female parasitoid, a definite preference for the fourth instar followed by the pupa and the third instar, respectively was shown. There was, however, no evidence of switching. There was also no evidence that the data fitted the no switch models which suggests that when the parasitoid is searching in an environment with two or more hosts, its searching behaviour is more complex.     

The genetic heterogeneity of deer mouse populations ( Peromyscus maniculatus ) in an insular landscape

A survey of the genetic variability in deer mouse populations was performed using specimens collected from six different islands on a lake covering approximately 50 km². Random amplified polymorphic DNA (RAPD) was used to measure the extent of the genetic differences in this insular system. An analysis of molecular variance (AMOVA) revealed that populations are clearly separated at this microgeographic scale (F _st = 0.13863; P < 0.001). The homogeneity of molecular variance test (HOMOVA) indicated that within-population levels vary greatly (B _p = 0.76831; P < 0.001). The within-population molecular variance was found to be mainly correlated with the accessibility of the islands, computed as the inverse of the geographic distance separating an island from the lakeshore (r = 0.916; P < 0.003). Received: March 5, 1999 / Accepted: July 16, 1999     

The role of vole populations in prevalence of the parasite (Echinococcus multilocularis) in foxes

Effects of population fluctuation of the gray-sided vole(Clethrionomys rufocanus) on the prevalence (infection rates) of the parasiteEchinococcus multilocularis in red fox(Vulpes vulpes) populations was investigated from 1985 to 1992 in eastern Hokkaido (Abashiri, Nemuro, and Kushiro area), Japan. This parasite needs two hosts to complete its life cycle; the gray-sided vole as its intermediate host and the red fox as its final host. We found that: (1) Infection rates in foxes depended on the current-year abundance of voles in all three study areas, particularly in Abashiri. (2) In addition to this direct density-dependence, delayed density-dependence between the infection rate and the prior-year abundance of voles was detected in Nemuro and in Kushiro. (3) The regional differences in density-dependence pattern were related to regional differences in the winter food habits of red foxes: in Abashiri the proportion of voles in the fox’s diet greatly decreases in winter, while the proportion remains high in winter in Nemuro and in Kushiro, probably because of shallower snowpack. These results suggest that infection rates in foxes in Abashiri were less influenced by the prior-year prevalence, since the infection cycle might be interrupted in winter, when voles became less important in fox’s diet. In contrast, the state of the prevalence may carry over from year to year in Nemuro and in Kushiro, because red foxes continue to eat a considerable amount of voles throughout year. The regionally contrasted results for the relationship between infection rate in foxes and vole abundance were parallel to the regional difference in fluctuation pattern of vole populations, which are highly variable in Abashiri area, but less variable in Kushiro-Nemuro area. Drastic change in vole populations appears to affect the host-parasite system.