Why doLuehdorfia butterflies lay eggs in clusters?

Summary Luehdorfia butterflies lay eggs in clusters. Clones of their host plants (Asiasarum andHeterotropa) are distributed pacthily among the understory of deciduous forests. Groups ofLuehdorfia larvae often exhaust the clones and may wander over the forest floor seeking new clones. The highest mortality observed is during this wandering period. To elucidate whyLuehdorfia butterflies lay eggs in clusters, a simulation experiment was made for hypothetical populations which lay eggs in clusters or singly. Field data on larval mortality, consumption, density of host clones and leaf weight forLuehdorfia japonica were incorporated into the model. The predictions of the simulation were: (1) When the egg density is low, the single egg type could leave many more pupae than the egg clustering type, but when the egg density is high, the former might leave smaller number of pupae than the latter; and (2) There are optimal sizes of egg clusters for different egg densities and the optimal size becomes larger as the egg density increased. This work was supported in part by Grant-in-Aid No. 439017 and No. 56480039 from the Ministry of Education, Science and Culture, Japan.     

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     

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.     

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.     

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.     

Population dynamics of a migrant skipper butterflyParnara guttata (Lepidoptera: Hesperiidae) II. Survival rates of immature stages in paddy fields

Summary Survival rates and mortality factors of a migrant skipperParnara guttata were censused in paddy fields in 4 localities of central and western Japan during 1975–1980, and 10 life tables were developed for 3 generations. Mortality rates of eggs, older larvae and pupae were high but those of younger larvae were very low. The high mortality rate was caused by parasitoids. Ten primary and 6 secondary parasitoids were recorded. Out of three egg parasitoids,Telenomus sp. was predominant. Larval parasitoids,Apanteles baoris andPediobus mitsukurii which are specific to genusParnara were predominant in wet land habitat, i.e. paddy land. On the other hand, tachinid flies which have a wide host range and a high searching ability were predominant in dry land habitats. Mortalities of eggs and pupae contribute more to the change in the total mortality of immature stages than those of other stages. egg parasitoids which are the major mortality factor of eggs acted density-dependently but larval and pupal parasitoids did not do so. The total mortality of immature stages occurred more or less density-dependently. Larval density on rice plants scarecely affected the survival rate of larvae.     

Receptivity of female remating and sperm number in the sperm storage organ in the bean bug,Riptortus clavatus (Heteroptera: Alydidae)

This study examines the relationship between the number of sperm in the seminal receptacle (spermatheca) and the receptivity of female remating in the bean bugRiptortus clavatus Thunberg. On the 21 st day after the first mating when receptivity to remating was > 70%, females receptive to remating had significantly fewer sperm ( < 40 on average) in the spermathecae than females reluctant to do (about 150 on average). However, averages of the number of eggs laid by receptive and reluctant females within 21 days were almost same. The proportion of fertilized eggs for receptive females at 15–21 days after copulation was significantly lower than that for reluctant females. Spermatozoa transferred from a male to a female’s spermatheca were detected 5 min after copulation and then increased continuously to about 500 with the first hour. When copulation durations were manipulated artificially, the shorter the copulation period (=females had less sperm in their spermathecae), the higher the remating rate became. Females may perceive the number of sperm in their seminal receptacles and then determine whether they copulate or not. These results support the hypothesis that females mate multiply in order to replenish inadequate sperm supplies to fertilize all eggs produced.     

Behavior and mortality of the southern stink bugNezara viridula in Hawaii

Summary This paper is concerned with some aspects of the ecology of the southern green stink bug,Nezara viridula, in Hawaii. Dispersal studies on adults showed an asymetrical dispersal pattern. The rate of plant to plant to movement by the adults was 3.3–6.7 feet per day. Mortality studies showed that egg predation by ants,Pheidole megancephala, was as high as 80–90 per cent. Egg parasitism byTelenomus basalis was highest during February, 1965, and adult parasitism byTrichopoda pennipes was highest during July, 1964, to January of the following year. The population ofN. viridula declined during May, 1964, to May, 1965. This decline occurred simultaneously with the decline in the number of eggs produced per female. It has been speculated that this reduction in egg production was caused by parasitism byT. pennipes. Published with the approval of the Director of the Hawaii Agricultural Experiment Station as Technical Paper No. 816. It is with great pleasure that I acknowledge with thanks the help that I received in various ways from the following: Dr. WallaceC. Mitchell, Dr. MervinKamran., Mr HarryKaya and Mr. HitoshiKamasaki.     

Spatial distribution and mortality process ofAnoplophora malasiaca (Coleoptera: Cerambycidae) eggs in citrus groves

Summary The study was carried out in two (A and B) citrus groves to clarify the spatial distribution patterns of eggs and larvae, and to analyse the mortality process of eggs. From the analysis by using the mean density and the mean crowding, it was clarified that the distributions of eggs were contagious and that larvae were more contagiously distributed than eggs. The τ andz indices showed that the operation of egg mortality was inversely density-dependent in both groves, and that the degree of inverse density-dependence was greater in A than in B grove. The spatial correlations between the emergence holes and the eggs or larvae in each tree, which were analysed by using ω index, showed that the distributions were more overlapping between the emergence holes and the larvae than the eggs. As the result of dividing trees into several groups according to the number of emergence holes, it was clarified that the survival rates of eggs were positively correlated with the number of emergence holes. In conclusion, inversely density-dependent mortality process was considered to be caused by lower mortality rates of eggs in the trees with more emergence holes. Especially in A grove, because the trees with more emergence holes were larger in diameter and more egg oviposition, the inversely density-dependent mortality process was considered to be detected more conspicuously than in B grove.     

Influence of parental density on the distribution pattern of eggs in the common cabbage butterfly,Pieris rapae crucivora

Summary To investigate the relation between the distribution pattern of eggs and the parental density in the common cabbage butterfly,Pieris rapae crucivora, the countings of egg number per plant were made on both cabbage plants cultivated in the farm and planted in the net house in which the female butterflies were released at various densities. The frequency distribution of eggs fits well to the negative binomial excepting the cases where they agree withPoisson series, and the degree of aggregation expressed as the reciprocal of the parameter, 1/k, tends to decrease as the egg or parental density increases. At the same parental density, however, the distribution of eggs can be described by the negative binomial with a common parameter,k _c, regardless of the difference in the density of laid eggs. In the case where a single female butterfly lays eggs, the spatial pattern of egg distribution is always lean, while its frequencies conform toPoisson or the negative binomial series. This lean changes toward patchy with increasing the parental density. From these results, it is concluded that the degree of aggregation in the distribution of eggs decreases with the increase of the parental density.     

Relation between plant density and arthropod density in cabbage fields

The relationship between plant density and the abundance of arthropods was examined by planting cabbages in four densities (0.25, 1, 4, or 8 plants per square meter). Four herbivorous species were examined: the small white butterfly Pieris rapae crucivora Boisduval, the diamondback moth Plutella xylostella (Linnaeus), the beet semi-looper Autographa nigrisigna (Walker), and the green peach aphid Myzus persicae (Sulzer). The number of spiders and the number of eggs of syrphid flies were also examined. The number of individuals per unit ground area increased curvilinearly with increasing plant density for most arthropods. To clarify the mechanism causing such a curvilinear increase, the oviposition behavior of Pieris rapae crucivora was examined. The oviposition process of a female was divided into three components: (1) entering the field, (2) alighting on a plant to bend her abdomen, and (3) attaching an egg on the leaf. The first and the second components curvilinearly increased with increasing plant density, while the third component was not influenced by the plant density. The analysis of the flight path of P. rapae crucivora indicated that the curvilinear increase in the frequency of abdominal bending behaviors occurs since a female flies at least about 1.3 m between successive abdominal bending behaviors, irrespective of the plant density, when the plant density is sufficiently high. Received: October 23, 1998 / Accepted: February 15, 1999     

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.     

Seasonal life cycle and autogeny in the mosquitoAedes togoi in northern Kyushu, Japan, with experimental analysis of the effects of temperature, photoperiod and food on life-history traits

We studied seasonal changes in the larval population structure, adult size, and autogeny (egg production without a bloodmeal) of the mosquitoAedes togoi on the seacoast of northern Kyushu, Japan. The effects of temperature, photoperiod and food conditions on larval development, adult size and autogeny were studied in the laboratory.Aedes togoi overwintered in both the egg and larval stages and was multivoltine. Adult size was greater in spring and autumn and smaller in summer. Autogeny occurred in spring and autumn but not in summer. Autogenous females were larger than anautogenous females, and larger autogenous females produced more eggs. Laboratory experiments showed that autogeny was promoted under low temperature and short-day conditions which corresponded with spring/autumn conditions in the field. Experimental food limitation in the larval stage greatly reduced adult size and autogenous egg production. In the field, large inter-pool variations in adult size and autogeny rate probably resulted from variations in nutrient and crowding conditions. Seasonal autogeny ofAedes togoi was discussed in terms of life-history strategy under fluctuating environmental conditions where relative advantages of autogenous and anautogenous reproduction alternate seasonally.     

One-host one-parasitoid system: Population dynamics of a zygaenid mothPryeria sinica Moore in an undisturbed habitat

Summary The population dynamics ofPryeria sinica was investigated in an undisturbed area in 1976–1979. We analyzed the process stabilizing the local population by the life table approach for immature stages and the mark-recapture method for the adult stage. Females usually layed about 130 eggs in an egg-mass. The shape of the survivorship curve was convex and was characterized by a relatively low mortality in the egg and larval stages and by a relatively high mortality in the prepupal and pupal stages. The low mortality in the early stage seemed to be not only due to the peculiar life cycle of this species (larvae develop in early spring when natural enemies are not active) but due to their protective nest-webs, larval warning coloration and repellent smell. The high mortality after cocooning was caused by severe parasitization byAgrothereutes minousubae. The number of adult in the population varied by 2.10-fold, which was less than that of other gregarious moths. The life table data and field observations suggest that adult female dispersal would have acted as a stabilizing factor, andA. minousubae as a conditioning factor on the dynamics of the moth population.     

Effects of host and parasitoid age on search behaviour and oviposition rates inLariophagus distinguendusF?rster (Hymenoptera: Pteromalidae)

Summary Oviposition rates and related behaviours were quantified forLariophagus distinguendus F?rster attackingCalosobruchus chinensis (L.) andC. maculatus (F.). Oviposition rates varied with parasitoid age; parasitoids aged 1–7 days laid approximately twice as many eggs per day as those aged 8–14 days. Similar differences were noted in search rates and handling times; younger parasitoids had higher attack rates and lower handling times than older parasitoids. Search rates and handling times also varied with the host stage available for attack. Search rates were higher and handling times were lower on larger stages. The results are discussed with reference to their impact on the dynamical behavior of insect parasitoid-host populations.     

Survivorship and fertility schedules of two Sumatran tortoise beetles,Aspidomorpha miliaris andA. sanctaecrucis (Coleoptera: Chrysomelidae) under laboratory conditions

Summary Two species of tortoise beetles,Aspidomorpha miliaris (AM) andA. sanctaecrucis (AS) feeding on a shrub-like morning glory,Ipomoea carnea, were reared under laboratory conditions to study their survivorship and fertility schedules. AM and AS required 34–39 days and 30–37, respectively, for the development of the immature stages. The mean longevity of the males was 88.4 days in AM and 63.8 in AS, and that of females was 87.9 days in AM and 83.3 in AS. The mean length of the pre-reproductive period (27.2 days in AM and 33.8 in AS) was much longer than that of the post-reproductive period (10.9 days in AM and 14.3 in AS). Females laid eggs at a nearly constant rate throughout their reproductive period. The reproductive valueV _x /V ₀ of the two species remained high for most of their adult life, as a result of prolonged survivorship and fertility periods. The total number of eggs produced per female was 442.9 (AM) and 80.1 (AS). The intrinsic rate of natural increaser was 0.070 (AM) and 0.044 (AS) per capita per day. The prolonged reproductive schedules, coupled with strong dispersal power, of these species no doubt have an adaptive value for living in highly disturbed tropical environments, where rainfall is ample but unpredictable and food resources are available throughout the year in a wide area, but distributed in widely flung patches. Contributions to the knowledge of population dynamics of tortoise beetles in Sumatra 3. Contribution No. 33 of Sumatra Nature Study (Entomology). Partly supported by Grants from Japan Society for Promotion of Science for JSPS-DGHE Scientific Cooperation (1980, 1982) and Grants-in-Aid for Overseas Scientific Survey from Ministry of Education, Science and Culture of Japan (Nos. 56041027 and 58041030).     

Adult population parameters and life tables of an epilachnine beetle (Coleoptera: Coccinellidae) feeding on bitter cucumber in Sumatra

Summary The population dynamics of an epilachnine beetle, which is closely related toEpilachna sparsa Dieke (henceforth called “sp. C”) and feeds on bitter cucumberMomordica charantia, was studied by mark-recapture of adults and the construction of life tables. The study was repeated three times, i.e., March–May, July–September and October–December in 1982, in Padang, Sumatra, Indonesia. After the establishment of the host plants, adults of “sp. C” soon colonized, and each study period ended in the death of the plants due to defoliation by the larvae and adults. The estimated mean length of residence of adults ranged from 6–11 days, but this was probably much shorter than the actual longevity, because the adults were so active that they flew away, or dropped off the plants, when they were approached or slightly disturbed. Life tables indicated that egg mortality ranged from 17.8–53.9%, and a parasitic waspTetrastichus sp. B made up 41.1–64.2% of egg mortality. Two wasps,Tetrastichus sp. C andPediobius foveolatus killed 1.2–19.4% (7.6–100%)^* of 4th instars and only the latter species attacked the pupae, killing 24.6–59.1% (45.1–72.4%). Parasitism and starvation by overcrowding contributed most to the total mortality from egg to adult emergence, which ranged from 89.4–99.5%. “Sp. C” had a higher diversity and level of parasitism than the Japanese species,E. vigintioctopunctata. The high dispersal power of “sp. C”, coupled with the prolongedl _x−m_x schedules shown under laboratory conditions, was advantageous for exploiting the food plant which was available throughout the year, but was rather patchily distributed in space.     

Analysis of contagiousness in the action of mortality factors on the western tent caterpillar population by using the \mathop m* - m\mathop m\limits^* - m relationshiprelationship

Summary The contagiousness in the operation of mortality processes on the colonies of the western tent caterpillar,Malacosoma californicum pluviale, was analyzed from two different aspects: successive changes in the frequency distribution of the number of surviving individuals per colony in the course of development, and the distribution pattern of the individuals killed by some biotic mortality factors. Also, for a tachinid parasite,Tachinomyia similis, the analysis was made on the egg-laying pattern on colonies as well as on individual larvae. The methods of these analyses were all based on the relation of mean crowding (m) on mean . A braconid parasite,Rogas sp., tended to kill few individuals together once it attacked a colony, but its effect on host colonies was rather equivalent to the random removal of individuals from all the colonies. Diseases in the late-stage larvae before cocooning was contagious in their action. Nuclear polyhedrosis virus seemed to have no basic contagiousness in its action, but it caused highly contagious distribution of deaths among the colonies when its average incidence was high. A spore-formingBacillus had a tendency to kill several individuals once it appeared in a colony, but the distribution of its incidence (no. of times it appeared per colony) was considered to be nearly at random. The female ofTachinomyia tended to lay more than one egg successively on the same colony. It also attacked individual larvae with a definite tendency for aggregation, which seemed to be resulted from the parasite’s preference to large hosts. When the number of eggs laid on prefered hosts exceeded a certain threshold, however, the fly seemed to change its attention to less attractive, smaller individuals.