Movement patterns of threeAthalia sawflies in relation to the spatio-temporal distributions of their habitats

Summary I compared the differences in the movement intensity of three species of sympatricAthalia sawflies,A. japonica, A. rosae andA. infumata feeding on cruciferous plants. Mark-release-recapture census was conducted to estimate movement distance, sex ratio and age composition of adult sawflies. In addition, the sex ratio of newlyemerged adults was examined by rearing field-collected larvae until adult emergence. Age composition and longevity of adults were estimated experimentally. The movement intensity was evaluated mostly with the indirect information thus obtained. Females moved more actively than males in all three sawflies.A. japonica females of all age classes moved actively in spring and autumn, but in summer they disappeared. Also,A. rosae females of all age classes moved actively in spring and autumn. In summer, in contrast withA. japonica, A. rosae females moved most actively among the three species in all seasons.A. infumata females, in particular the young females, moved most actively among the three species, exceptA rosae in summer. The movement patterns of the three sawflies were deduced in relation to the spatio-temporal distributions of their habitats. In spring and autumn, when host plants were abundant,A. japonica andA. rosae females were dispersed among the host patches within the census are. In summer, however, when host plants were scarce,A. japonica entered diapause, whereasA. rosae migrated to neighboring areas. On the other hand,A. infumata, in particular young famale, innately dispersed to seek for temporary host plants throughout the census seasons.     

Egg cluster size variation in relation to the larval food abundance inLuehdorfia puziloi (Lepidoptera: Papilionidae)

Summary Mean egg cluster size ofLuehdorfia puziloi yessoensis varied among habitats. The mean egg cluster size tended to be large when abundance of the larval food leaves expressed as the fresh weight of leaves per unit area at a given habitat was high. Since this variation was observed among closely located study plots (butterflies can easily move between study plots), the egg cluster size variation among habitats is likely to be a result of flexible response by females to varying food abundance for larvae.     

Population fluctuations and natural mortalities of the pine-moth,Dendrolimus spectabilis

Summary Annual changes in the population of the pine-moth,Dendrolimus spectabilis Butler, were studied in Kashima district. The insect completes two generations in one year, and the adult emerges in early summer and again in autumn. The insect population showed fairly drastic fluctuations in the past years, and a conspicuous peak was recorded in three times, in 1950, 1955 and 1961. It was noted in each of those three years that a great number of adults of the summer generation emerged in autumn. The main reason for this great abundance of the insect population seemed to be high survival rate of the young larvae in summer. It was suggested that the climate in July had powerful influence upon the survival f thos e young larvae. The effects of natural enemies were usually the greatest on the egg population of the pine-moth in either generation. Much greater number of insects in the overwintering generation was destroyed by parasites and diseases than in the summer generation. Finally, a rapid increase of the insect population in autumn was considered to be caused by a combined effect of climatic conditions and of natural enemies.     

Variation in offspring size within a population of the web-building spiderAgelena limbata

Within a population of the web-building spiderAgelena limbata, the weight of the first instar nymphs ranged from 1.187 to 6.559 mg. Both intraclutch and interclutch variation were recorded. The mean weights were different among clutches and the coefficients of variation within a clutch ranged from 3.3 to 29.2%. Variation in the nymphal weight was certainly derived from variation in the egg weight because there was a high correlation between the two weights. Factors affecting interclutch variation in nymphal weight were examined by multiple regression analysis. Nymphal weight was positively correlated with the body size and food conditions of female parents, and negatively correlated with the clutch size. Among these three factors, the food conditions of female parents had the largest apparent effect on the interclutch variation. The results suggest that females with larger body size and more food produce larger offspring, and that there is a trade-off between offspring size and clutch size. Heavier nymphs had larger body size (carapace width) and may have larger energy reserves. Heavier nymphs survived experimental starvation for a significantly longer period.     

Reproduction and egg diapause of the oriental chinch bug,Cavelerius saccharivorus okajima (Heteroptera: Lygaeidae), in the subtropical winter season in relation to its wing polymorphism

Summary Reproduction and egg diapause of the oriental chinch bug,Cavelerius saccharivorus, in the subtropical winter season were investigated in relation to its wing polymorphism. Macropterous females collected from the southern part of Okinawa Is. in the autumn season delayed their oviposition and were less fecund early in the adult life period, but survived much longer than brachypterous females collected from the same locality. The total fecundity was not significantly different between wing morphs. The diapause of eggs laid by brachypters tended to be terminated more easily at a high temperature than that of eggs laid by macropters. This indicated that the eggs laid by macropters were more intense in their diapause than those laid by brachypters. However, irrespective of the parental wing form, diapause showed considerable variation in its intensity within and between clutches.     

Relationships between body size, reproductive traits, and food resource in three species of tropical flesh flies

Summary Intra- and inter-specific comparisons in progeny size and clutch size were used to identify possible selection pressures acting on three sympatric species of ovoviviporous flesh flies. Both progeny and clutch sizes increased with body weight of the female parent in all species. There was no evidence for a simple trade-off between the two traits. In one species, the larger the female adult the smaller the relative biomass of larvae per clutch (total weight of larvae/body weight of female parent). Female flies produced similar progeny and clutch sizes over successive batches. Variation in progeny size did not influence either larval survival or duration of larval and pupal development. However, larger first instar larvae tended to form larger pupae in two of the species. The experiments testing the effect of progeny size on pupal weight under limited food conditions suggest a selective advantage for larger progeny size.     

Host plant conspicuousness and the distribution of eggs and larvae in the butterfly,Anthocharis scolymus (Lepidoptera: Pieridae)

Summary We investigated how the distribution pattern of eggs and larval on the host plant,Turritus glabra, was influenced by the oviposition behavior of the pierid butterflyAnthocharis scolymus. Females searched for the host plants visually and they frequently approached taller host plants with sparse surrounding vegetation. After encountering host plants, oviposition behavior of females was independent of host plant characteristics such as height, density, and type of surrounding vegetation. A female laid eggs singly on a host plants. Most females appeared to lay their eggs regardless of the presense of eggs on the host plant. Consequently egg and larva tended to be abundant on conspicuous host plants as measured by height or relative isolation from other plants. However, overcrowding of eggs on an individual host decreased the survival rate of larvae.     

Density-dependent growth and reproduction of the apple snail, Pomacea canaliculata : a density manipulation experiment in a paddy field

To examine density dependence in the survival, growth, and reproduction of Pomacea canaliculata, we conducted an experiment in which snail densities were manipulated in a paddy field. We released paint-marked snails of 15–20 mm shell height into 12 enclosures (pens) of 16 m² at one of five densities – 8, 16, 32, 64, or 128 snails per pen. The survival rate of released snails was 95% and was independent of snail density. The snail density had a significant effect on the growth and egg production of individual snails. This density dependence may have been caused by reduced food availability. The females at high density deposited fewer and smaller egg masses than those at low density, and consequently produced fewer eggs. The females at densities 8 and 16 deposited more than 3000 eggs per female, while the females at density 128 oviposited only 414 eggs. The total egg production per pen was, however, higher at higher snail density. The survival rates of juvenile snails were 21%–37% and were independent of adult density. The juvenile density was positively correlated with the total egg production per pen and hence was higher at higher adult density. However, the density of juveniles larger than 5 mm in shell height, i.e., juveniles that can survive an overwintering period, was not significantly different among density treatments. These results suggest that snail density after the overwintering period is independent of the density in the previous year. Thus, density dependence in growth and reproduction might regulate the population of P. canaliculata in paddies. Received: October 23, 1998 / Accepted: July 16, 1999     

An introduction experiment of an herbivorous lady beetle: Characteristics of the adult population

In May 1971, 45 adults of an herbivorous lady beetleEpilachna niponica (Coleoptera: Coccinellidae) from Asiu Experimental Forest were introduced into a botanical garden of Kyoto University, where is 10 km south of the southern limits of its distribution with being 3–5°C warmer than the original site. The introduced population of the lady beetle was thus investigated from 1975 to 1981. Mark-release-recapture experiments were applied to individual adult beetles, to estimate population size and daily survival rate. Overwintering adults emerged from hibernation around early April, reaching peak numbers in late April to early May, then gradually declined to late June. No adults remained at the end of June. Adult survival was maintained at a high level to early May, and declined consistently until late in the reproductive season. New adults began to emerge in late June and quickly reached a peak in early July; thereafter they decreased in number and had entered hibernation by late October. In spite of seasonally deteriorating food resources and heat stress in summer, new adults showed moderately high survival during the inimical period. New adults which emerged later in the season tended to be smaller in body size than those that emerged early. The proportion of females in the new adult population gradually increased throughout the pre-hibernating period, suggesting that male-biased mortality occurred during this period. When compared to the source population, the introduced population had a higher rate of population growth. Coupled with the improved population growth, heavy leaf damage during the larval period suggested that intensive intraspecific competition was most likely to occur among larvae in the introduced population.     

Body mass changes inTrimeresurus flavoviridis (Viperidae) on Okinawa Island, Japan

Body masses of wild-caught habu,Trimeresurus flavoviridis, were measured with known error range. Habu larger than mature female size had steeper slope in length-mass regression than smaller individuals. Females outweighed males in most snout-ventlength classes and in early summer. Gravid females outweighed non-gravid ones by about 20% on the average, but the body mass ranges of the two groups overlapped. Through the body mass change in mature females, the proportion of gravid females was estimated to be about 0.5.     

Parental care and EGG size in salamanders: An examination of the safe harbor hypothesis

Summary The safe harbor hypothesis includes the suggestion that parental care causes the embryonic stage to be the safest harbor, and, therefore, egg size will increase in populations with parental care to decrease the duration of subsequent, higher risk stages. Neither the safe habor hypothesis nor r and K theory seem adequate to explain the correlation between egg size and the presence/absence of parental care among salamanders, a group in which there is a further correlation between the larval (hatchling) habitat and egg size/parental care. Pond-breeding salamanders generally have small eggs and lack parental care, and stream-breeding salamanders generally have large eggs and parental care. I argue that the fundamental difference in the food available to hatchling salamanders between lentic (plankton-rich) and lotic (plankton-poor) environments selects for relatively lower parental investment in the lentic environment. From the standpoint of parental fitness, small (more numerous) hatchlings have a greater payoff where the available food is mall and dense (zooplankton in lentic environments), and large hatchlings are selectively advantageous where the food is of large size and less dense (benthic invertebrates in lotic environments). Selection for larger hatchlings in lotic environments results in longer embryonic periods and,ceteris paribus, greater total embryonic mortality. Embryo hiding and guarding have evolved among lotic-breeding salamanders as compensatory mechanisms to reduce the rate of embryonic mortality. In this view, parental care is a consequence of selection for larger egg size and not an umbrella that allows egg size to increase, contrary to the safe harbor hypothesis. The relationship between variance in parental investment and food available to offspring, developed here for salamanders, may be of general significance. YosiakiIt?, a critic of r and K theory, independently arrived at a similar conclusion from a broader data base.     

Longevity, flight ability and reproductive performance of the diamondback moth,Plutella xylostella (L.) (Lepidoptera: Yponomeutidae), related to adult body size

Plutella xylostella in the temperate zone shows a clear seasonal change in adult body size. In the laboratory, large and small moths were produced during immature stages at 15°C and 25°C, respectively. These moths were then used to evaluate longevity, age-specific flight ability, flight ability of mated and unmated females, and the influence of flight experience on the subsequent reproductive success. The large moths lived longer and displayed a greater flight ability over 3 weeks. Irrespective of body size, unmated females flew for a longer time than mated females, and flight experience affected their subsequent reproductive success. Females of both sizes mated and laid eggs soon after emergence, without any obvious pre-reproductive period. More flight experience did not delay oviposition, but did reduce egg production. It is likely that large moths with a longer adult life span and greater flight ability are better fitted for long-distance flight and more fecund than small ones. These experimental results may explain why long-distance migration ofP. xylostella is mostly seen during cool seasons, when relatively large moths with long forewing appear in the field.     

A host shift from wild blue cohosh to cultivated potato by the phytophagous ladybird beetle, Epilachna yasutomii (Coleoptera, Coccinellidae)

Life history traits of the phytophagous ladybird beetle Epilachna yasutomii were compared between a nonpest population feeding on wild blue cohosh and a pest population feeding on cultivated solanaceous crops, mainly potato. Newly emerged adults of the nonpest population entered diapause early in midsummer when blue cohosh withered, while adults of the pest population were found in tomato and eggplant fields until late autumn. The pest population had larger females, a higher population growth rate, a shorter larval developmental period, and reduced longevity of overwintered females, compared with the nonpest population. ANOVA indicated that all these life history traits were influenced by the food plant, and that the number of eggs laid per female and the longevity of overwintered females were also affected by the population type. These findings suggest that the life history pattern of E. yasutomii changed to high fecundity with a short life span from low fecundity with a long life span as a result of the host shift from wild blue cohosh to cultivated solanaceous crops. Received: May 22, 1998 / Accepted: January 13, 1999     

Why does onlyAthalia Japonica enter summer diapause among three sympatricAthalia sawflies feeding on crucifers?

Summary This report assesses the primary factor for the evolution of summer diapause of the three species of sawfly,Athalia japonica, A. rosae andA. infumata that feed on cruciferous plants and coexist in the same area.A. japonica has two discrete spring and autumn generations, butA. rosae andA. infumata 5–6 generations. OnlyA. japonica enters summer diapause in response to the long daylengths in spring. Although these three sawflies usually feed on the same cultivated crucifers, they differ markedly in the utilization of wild crucifers. They oviposit only on young leaves.A. japonica mainly usesCardamine plants which sprout in spring and autumn.A. rosae andA. infumata primarily use hosts with new leaves all the year round, i.e. cultivated crucifers andRorippa indica, respectively. The thermal threshold for development is lower inA. japonica than in the other two species. The low heat tolerance ofA. japonica is adapted only to cool shady habitats whereCardamine grows. Presumably, summer diapause ofA. japonica is adaptation to the deterioration of the primary host plants rather than unfavorable climatic conditions. This interpretation is supported by the movement patterns of the threeAthalia sawflies, alternative means to escape from deteriorated habitat conditions.     

Spatio-temporal variation of natural and sexual selection in breeding populations of the coreid bug,Colpula lativentris (Heteroptera: Coreidae)

Spatio-temporal variations of lifetime reproductive succes (LRS) of both male and female individuals of a coreid bugColpula lativentris were measured and analyzed using the multiple regression method of Arnold and Wade (1984a, b). The standardized variance of LRS was larger in males than that in females as males often to secure mates for a long period whereas females could easily find mates and oviposit simply dependent on ovarial maturation. LRS was partitioned into 4 consecutive fitness components: (1) reproductive lifespan, (2) copulating efficiency, (3) guarding efficiency (for males) or oviposition efficiency (for females), and (4) number of eggs per clutch. In males copulating efficiency was the largest determining factor of LRS, whereas in females reproductive lifespan was the most important factor. Such tendencies were stable on both a yearly and local basis. Patterns of relative contribution of natural selection (reproductive lifespan and number of eggs per clutch) and sexual selection (copulating efficiency and guarding or oviposition efficiency) to LRS were clearly different between males and females. This sexual difference is, at least to some extent, thought to be brought about by sexual selection among males for mating opportunity, though no physical fight was observed among males. Directional selection on body length was found only in relation to the clutch size of females because large females tended to lay larger clutches. No significant directional selection was found in other fitness components.     

Possible influences of habitat characteristics on the evolution of semelparity and cannibalism in the hump earwigAnechura harmandi

The possible influences of life history and habitat characteristics on the evolution of semelparity and cannibalism in the hump earwigAnechura harmandi were studied. This species is univoltine and overwinters as an adult. Females laid single egg-batches during winter in nests under stones at a riverside in a valley. They took care of the eggs which hatched in early spring and the offspring ate their mother before dispersing. The valley was sometimes flooded in summer. Nymphs emerged as adults and dispersed to elsewhere before the rainy season arrived. They returned to the riverside after the rainy season. The flooding and/or summer heat seemed to be the selective force for the evolution of dispersal behavior and semelparity in this species. The cannibalism of the female parent by her offspring seemed to have readily evolved after the evolution of semelparity. The unfavorable environmental conditions seemed to have a large effect on the evolution of semelparity and cannibalism in this species.     

Crucial factors determining the spatio-temporal distribution patterns of threeAthalia sawflies feeding on common cruciferous plants

Summary ThreeAthalia sawflies,A. japonica, A. rosae andA. infumata, feeding on cruciferous plants, coexist in Japan. However, it is not known what ecological strategies they use and what environmental factors are crucial to such strategies. I attempted to explain these questions by examining the relationship between the spatio-temporal distribution patterns of threeAthalia sawflies and their habitats in three districts (Lowland, Intermediate and Mountain). The three sawflies have different spatio-temporal distribution patterns, though they usually used common cruciferous plants.A. japonica was abundant in spring and autumn but disappeared during summer in all the districts. In the Lowland, populations ofA. rosae andA. infumata, like that ofA. japonica, crashed in summer. HoweverA. rosae occurred mainly in summer in the Intermediate and Mountain. AlthoughA. infumata occurred in the same seasons asA. rosae in all districts, population levels ofA. infumata were always lower than those ofA. rosae. The crucial factors controlling their population patterns were the availability of host plants and temperature. Population crashes ofA. rosae andA. infumata were due to food depletion, and those ofA. japonica were due to heat stress. On the other hand, their population patterns may be interpreted as phenological synchronization with their original host plants, though they all existed on common cruciferous plants. The three sawflies may have evolved different strategies to escape from unfavorable habitat conditions. Such strategies are speculated to be summer diapause inA. japonica, long distance migration inA. rosae, and local dispersal inA. infumata.     

The role of medium conditioning in the population dynamics of the housefly

Summary The role of larval medium conditioning on the behavior of larvae and of ovipositing adults of the housefly,Musca domestica L., was investigated through behavioral preference tests. Larvae were strongly attracted to medium conditioned by themselves or other larvae, while adult females overwhelmingly oviposited in fresh medium. Medium conditioning occurs within a few hours after hatching of an egg cohort and is effective in preventing overcrowding of a single site by shutting off further oviposition within 24 hours after eggs are initially deposited. A model of medium conditioning optimizes density for developing larvae and could also provide for regulation of local larval populations. This study was carried out during the tenure of grants from the National Science Foundation (GB-35473) and The National Institutes of Health (1-R01-AI-10988-01) to the senior author.     

Contest competition inDrosophila subobscura

The role of larval intraspecific competition in laboratory populations ofDrosophila subobscura was investigated. Mortality is density-independent during the first 3 days after hatching but becomes density dependent as development proceeds to pupation. Although total biomass per patch was independent of initial egg density, competition betweenDrosophila larvae leads to the formation of smaller pupae. This resulted in a population that was dominated by suppressed individuals. Development rate ofD. subobscura larvae was not affected by high larval densities. Smaller pupae give rise to females with fewer eggs in their ovarioles. A simple simulation model, predicting the effects of intraspecific competition on the fecundity of the nextDrosophila generation is described.     

Seasonal change of nest survival and related aspects in an aggregation ofLasioglossum duplex (Dalla torre), a eusocial halictine bee (Hymenoptera: Halictidae)

Summary Nest survival in an aggregation of a eusocial halictine bee,Lasioglossum duplex, was censused through an annual cycle. Out of 2,500 nests marked at the beginning of solitary phase in the spring, only 25.5% attained eusocial phase. But 60.5% of 636 nests attaining eusocial phase successfully produced sexual offspring. This shows that solitary phase is the most vulnerable period in the annual cycle. A very low productivity in eusocial phase in the census year was clarified from examination of 99 nests in the autumn. The number of prospective foundresses surviving to the next year was estimated upon the number of brood cells in examined nests and of old females surviving these nests. Deviation between this estimate and the number of nests made in the next spring was 8.8%, confirming a drop of population size to less than one third in the next year. Some nests solitarily made in the summer by dispersed females were examined. Productivity in such nests was extremely low, hence these nests should contribute virtually nothing to the next generation. Possible factors affecting the low productivity in eusocial phase were enumerated though none of these were supported by concrete evidence. Some considerations were given on the relation between obtained results and colony life cycle in eusocial insects, particularly in halictine bees. Bionomics of the eusocial halictine bee,Lasioglossum duplex. VI.