Competitive habitat utilization in the damselfly,Mnais nawai (Zygoptera: Calopterygidae) coexisting with a related species,Mnais pruinosa

Reproductive behaviors related to habitat utilization were studied in males of the damsefly,Mnais nawai, which has two male forms, territorial orange-winged males (nawai) and non-territorial pale-orange-winged males (sahoi), at the upper part of a mountain stream where they partiallycoexist with a related species,Mnais pruinosa, which also has two male forms, territorial orange-winged males (esakii) and non-territorial hyaline-winged males (strigata). These two species showed parapatric distribution; the lower part of the stream was occupied byM. nawai, and the upper part byM. pruinosa. In the present study, cross-matings occurred between bothMnais species, although normal intraspecific matings occurred more frequently than cross-matings. Territorial males of both species copulated with conspecific females that entered their territory and guarded the ovipositing females, probably to avoid sperm displacement resulting from subsequent copulations. Severe competition for oviposition sites by territorial males even occurred between the two species. On the other hand, non-territorial males of both species have alternative mating strategies (including several tactics such as sneaking, takeover and interception). The possible benefits from conflict among territorial males of both species is discussed.     

Distribution patterns of and sampling plans forTetranychus urticae Koch (Acarina: Tetranychidae) on roses

Summary I sampledTetranychus urticae Koch (Acarina: Tetranychidae) regularly from four rose gardens in Kyoto and Nara Prefectures in 1988–1990. When mite density was low,T. urticae showed an uneven vertical distribution, being more abundant in the lower third and absent from the upper third of the plants. Mite density was less variable within than between plants, suggesting that a sampling plan which includes more leaves from different plants rather than from different levels of a plant is favourable. Spatial distribution ofT. urticae was nonrandom and followed the negative binomial distribution. In addition, both the Taylor’s power law and the Iwao’s patchiness regression described the distribution well. An empty-sample method for estimating mite density from the proportion of empty sampling units was developed. Sampling plans for determining the sample size required to reach a predetermined precision level, based on this method and by directly counting the mites, were designed. The counting method was more accurate than the empty-sample method. However, when the time factor was taken into account, the latter was more favourable, because it was faster than the former at a density range of 1.5–300 mites leaf⁻¹, which was most commonly encountered in the field.     

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.     

Accumulation of phyllodulcin in sweet-leaf plants ofHydrangea serrata and its neutrality in the defence against a specialist leafmining herbivore

Among wild plants ofHydrangea serrata (Hydrangeaceae) in Japan, there are sweet plants whose leave contain a kind of isocoumarin, phyllodulcin, which happens to be 350 times as sweet as sucrose to the human tongue. In a primary beech forest in Ashu, Kyoto, the spatial distribution of sweet plants and temporal and the spatial distribution of phyllodulcin within and among plants were investigated using a high performance liquid chromatograph. The distribution of sweet plants was confined within a valley and was parapatric with non-sweet plants. A plant's characteristic phyllodulcin accumulation did not change, even when transplanted into the different habitats. The phyllodulcin content of the sweet plants varied greatly among plants, and the population mean peaked in July when the plants flowered. Within a plant, phyllodulcin content was elevated by partial defoliation. We examined the possible effect of phyllodulcin on herbivory by a specialist leafmining herbivore,Antispila hydrangifoliella (Lepidoptera: Heliozelidae). We transplanted sweet and nonsweet plants reciprocally between their original habitats, excluded attacks by parasitoids, and compared performance of the leafminer. Leafminer colonization and larval survivorship on transplanted andin situ plants was not significantly different between sites. The fact that accumulation of phyllodulcin did not augment a defensive function, at least against herbivory by the leafminer, and the sporadic distribution of phyllodulcin-accumulating plants, suggest that the genotypes synthesizing phyllodulcin emerged independently at separate localities by mutation, and that the genotypes are almost adaptively neutral in defence against the specialist herbivore.     

Variations in carambola infestation rates byBactrocera carambolae drew and hancock (Diptera: Tephritidae) with fruit availability in a carambola orchard

The relationship between the infestation rate of carambola fruits byBactrocera carambolae Drew and Hancock was investigated in a carambola orchard. Phenology of the fruits was found to influence percentage infestation of fruits byB. carambolae. The proportion of unbagged or susceptible fruits infested varied with time of year and tended to decrease with the increase of unbagged fruits available on the tree. The number of ovipunctures per fruit varied with fruit size and was also found to be indicative of the number of adult insects (B. carambolae and parasitoids) that will emerge from each fruit. Higher number of susceptible fruits available on each tree also decreased both the number of ovipunctures per fruit and the number of eggs laid per fruit, which could possibly be due to the strategy of spreading the risk adopted by the femaleB. carambolae or a result of random selection with more hosts available. The main parasitoids recorded wereBiosteres vandenboschi (Fullaway) andB. arisanus (Sonan). The mean percentage of parasitism was 38.3% and it followed roughly that of infestation of fruits.     

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.     

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.     

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.     

Genetic estimations for body size characters, development period and development rate in a coccinelid beetle,Harmonia axyridis

Heritabilities and genetic correlations for body size characters and development period in a coccinellid beetle,Harmonia axyridis were estimated by a sib-analysis experiment. Positive genetic correlations were detected between size characters and development rate. If this is upheld in the field, genetic variation would be eliminated, as the loci affecting the characters are supposed to be fixed. However, the results indicated moderate heritabilities for all characters. Possible explanations for the results are discussed.     

Life tables and population parameters of the green leafhopper,Nephotettix cincticeps (Uhler), in the southwestern district of Japan with special reference to the first generation on foxtail grass

Summary The three year (1988–1990) life tables ofNephotettix cincticeps were constructed, and the daily survival rate and longevity of female adults were estimated by Hokyo and Kiritani’s (1967) method for the overwintering and the first-generations on the foxtail grass in Okayama, southwestern Japan. The life tables and the population parameter values estimated were compared with those in the other generations on rice. The FARMCOP suction sampler was employed to survey the population density. The durations of pre-ovarial maturation of female adults of the 1st generation on foxtail grass and rice seedling were similar. Longevity of adults of the overwintering and the first generations which emerged on the wild host was longer than that of the other generations (2nd and 3rd generations) on the rice plants. Fecundity of females decreased successively as the generation proceeded and it became lowest in the final 3rd generation. Only about 3.5 percent of first-instar nymphs of the 1st generation emerged as adults in the fallow field. The survival rate of nymphs on foxtail grass was always lower in comparison with that on rice plants. However, the survival rates of nymphs on foxtail grass and rice seedling were not significantly different from each other under laboratory conditions. In the fields, senescence of foxtail grass occurred in the midst of nymphal period of the 1st generation. The survival rate of nymphs on foxtail grass decreased with the increasing in the nymphal density. Abundance of spiders during the 1st generation was higher than that in the early stage of rice plants.     

Age distribution, sex ratio and mortality of the red foxVulpes vulpes in Tochigi, central Japan: an estimation using a museum collection

One hundred and thirty carcasses of the red fox were collected in Tochigi Prefecture, by the Tochigi Prefectural Museum, from 1981 to 1991. The young/adult ratio of the sample was 1.60, which suggests that the hunting pressure has been relatively low in this area. Six percent of the animals were 5 years or older which compares to those taken in Hokkaido, but is higher than those in Europe and North America. The sex ratio for all specimens had a tendency towards male bias (0.587), but this bias was higher for the adult (0.605) than for the young (0.576). Among young (0 year-old) foxes, more individuals were killed on roads than by trapping or shooting (P<0.02, chisquare test). This mortality pattern was caused by high mortality of young males (P<0.02). The proportions of adults killed by the three mortality factors were similar, though only one of the 14 foxes older than 4 years old was shot, probably due to age-linked activity patterns. Most road-kills of young foxes occurred in May when juveniles began exploiting and in November when sub-adults began dispersal. The ratios of road-kills for the whole sample and for adults alone were 42% and 34%, respectively. These high rates of road-kills suggest that the mortality pattern in Tochigi has been affected by factors characteristic of urban environments.     

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.     

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.     

Population dynamics of the whitebacked planthopper,Sogatella furcifera (Hemiptera: Delphacidae) with special reference to the relationship between its population growth and the growth stage of rice plants

A population census was conducted to describe the effects of the growth stage of rice on the population dynamics ofS. furcifera, in particular, on immigration, seasonal abundance, population growth rate, and wing-form expression. The number of immigrants was highest on rice plants 17 to 30 days after transplanting (DAT), which suggested that immigrants prefer to settle or remain more on rice plants at the tillering stage (approximately 20–30 DAT). Population growth rate from immigration to the 1st generation decreased with an increase in rice plant age. In contrast, population growth rate from the 1st to 2nd generation was not influenced by rice plant age and was negatively density-dependent. The percentage of macropters (flyers) was positively related to the growth stage of rice when rice was in the vegetative or early part of the reproductive stage, and reached 100% at about 10 days before heading (booting stage). Threafter, most adult females molted into macropters regardless of population density. The roles of host plant age and crowding effect on the population dynamics ofS. furcifera are discussed.