Laboratory experiments were designed to determine the effects of four constant temperatures (15, 20, 25, and 30°C) on immature development of the gregarious larval parasitoid, Bessa parallela, using Pieris rapae crucivora as a host. The developmental rate from oviposition to adult emergence increased with increasing temperature. The lower developmental threshold from oviposition to adult emergence was 8.0°C for females and 7.5°C for males. The total effective temperature from oviposition to adult emergence was 333.3 degree-days for females and 250.0 degree-days for males. We estimated that B. parallela could have nine generations at most per year in Fukuoka City. Immature survival was not influenced by temperature, but the adults emerged at 30°C tended to have smaller body size than those at the lower temperatures.

View full abstract

Experiments evaluating the bio-control of the cabbage root maggot, Delia radicum, with entomopathogenic nematodes were conducted in the greenhouse and in the field. In the greenhouse better control was obtained with Steinernema feltiae than with S. arenarium, S. carpocapsae, Heterorhabditis megidis, and H. bacteriophora. Increasing doses of S. feltiae improved insect control; the best results were obtained with applications of 4,000 or 8,000 infective juveniles per plant. Applying S. feltiae eight days earlier or eight days later than the inoculation of insect eggs or applying both at the same time did not give significant differences in D. radicum control. Field control of D. radicum with S. feltiae was not successful in early spring but improved in summer. The number of surviving insects and the cabbage damage were significantly reduced after applying S. feltiae in summer.

View full abstract

To clarify assemblage patterns of overwintering ground beetles (Coleoptera: Carabidae) and other insect predators in farmland habitats for the purpose of proper land management to enhance beneficial predators, we collected carabid and other insect predators at eight plots including arable and fallow rice and vegetable fields and a bank of an adjacent irrigation pond in central Japan. In total, 159 adults and 268 larvae of 33 carabid species, and 178 individuals of at least 17 species of other insect predators were collected by the quadrat sampling method. In rice fields, both the number of species and no. of individuals of overwintering carabid beetles increased as the soil became dry and vegetational succession proceeded, whereas in fallow vegetable fields carabids decreased according to succession. Similar trends were confirmed in other insect predators. Variations of carabid species richness and abundances among the plots might be attributed to soil water content, vegetation and prey availability. In early-successional fallow vegetable fields, the larvae of the carabid genus Harpalus overwintered with high density; this appeared to be because the fingergrass Digitaria ciliaris (Poaceae), whose seeds were a potential food for Harpalus, were densely vegetated there. In a dry fallow rice field and early-successional vegetable fields, beneficial predators such as Dolichus halensis (Coleoptera: Carabidae), Agrypnus binodulus (Coleoptera: Elateridae), and soldier beetle (Coleoptera: Cantharidae) larvae hibernated with high densities. For proper farmland management to augment insect predators, it is desirable to maintain fallow rice and vegetable fields as relatively dry habitats and at early successional stages. Ploughing fallow fields in winter may reduce overwintering predacious insect larvae.

View full abstract

We used a baiting method to isolate 65 entomopathogenic fungi with pathogenicity to the chestnut weevil larva from soil samples. Metarhizium anisopliae strain HF293 showed the highest pathogenicity. Under laboratory conditions, the LD₅₀ value of strain HF293 on the 10th day after treatment of newly emerged larvae was 9.9×10³ conidia/larva, and the mortality rate of larvae reached 56% at five weeks after treatment with a conidial dose of 2.0×10²/larva. Susceptibility of the larvae that had been stored at 6°C to strain HF293 gradually decreased over the first three months of storage but stabilized by the fourth month. The results of a field study of larvae in flowerpots indicated that the survival rate of larvae decreased with increasing doses of conidia of M. anisopliae strain HF293.

View full abstract

The behavioral responses of the female cigarette beetle to 57 plant essential oils commonly used for the flavoring of foods and cosmetics, were investigated with an olfactometer. Forty-eight of these essential oils exhibited repellency and only patchouli oil exhibited attractiveness at a dose of 1 μl. The repellency of the 28 essential oils that strongly repelled the beetles at this dose were furthermore evaluated at a dose of 0.1 μl. Six plant oils (shiso, savory, cassia, thyme, peppermint and Litsea cubeba oils) strongly repelled the beetles at this dose. Then, the dose-responses of these six oils on repellency against the beetles were investigated. These oils exhibited attractiveness at lower doses than each threshold except shiso oil, which did not attract the beetles at any doses tested. The first major components of these six oils repelled the beetles at a dose of 1 μl or 1 mg. However the repellency of these components was less than that of each essential oil. The repellency of shiso oil in the presence of cured tobacco odor, which attracted the beetles, was further evaluated. Shiso oil repelled the beetles at a dose of 10 μl even in the presence of the tobacco odor.

View full abstract

We suggest here easy-to-use equations for population estimation for a single mark-release experiment in which individuals are captured at two points in time without being re-released. Two models are considered. Both models adopt an assumption that the survival rate of marked individuals is constant. In Model A, the total number of individuals including marked and non-marked individuals is assumed to be constant. The proportion of captured individuals need not be constant in this model. In Model B, the probability that an individual is captured is assumed to be constant. The total number of individuals need not be constant in this model. Maximum likelihood estimates and the unbiased estimates are derived in explicit form for both Model A and Model B. The relation with classical methods, such as Jackson's positive method and Itô's modified positive method, is examined. Numerical simulation indicates that the unbiased estimates work better than do other methods in both Model A and Model B.

View full abstract

The parameters in the law of total effective temperature, the developmental zero temperature (t) and the effective cumulative temperature (k), were estimated in several species or strains of the family Tenebrionidae. It was shown that the relationship between t and k is linear; k decreases with increasing t. Similar relationships were noted among members of the genus Periplaneta in the family Blattidae, the genus Aedes in the family Culicidae, the family Pyralidae, the family Aphididae and the family Tetranychidae. Based on analysis among groups of orders or higher categories, several researchers have found a similar relationship. The current study on a family or a genus revealed a more rigorous linearity. However, the focus of this study was the linear relationship itself and it was discovered that the t-k relationships of members within each taxonomic group of arthropods determines a common temperature (Tc) and a common duration of development (Dc). This phenomenon was mathematically deducible as a consequence of the t-k linear relation. Biologically, Tc and Dc are probably the optimum temperature and duration of development, respectively, that a group of organisms possess in common.

View full abstract

In a population of the gall midge Asteralobia sasakii, we discovered individuals that entered a prolonged diapause. To interpret the adaptive significance of this prolonged diapause, the life history of A. sasakii was investigated in relation to parasitoid attacks. The survey was conducted on two host plants, Ilex crenata and I. integra in central Honshu, Japan. The majority of midges were univoltine and spent only one winter as mature larvae. On I. integra, some individuals diapaused in the first stadium and spent two or more winters, so that the total emergence pattern was a polymodal pattern. The advantage of the prolonged diapause was unclear. Allochronic isolation was found between the two host-associated populations of A. sasakii in the field. The two populations of midges also differed in the species composition of parasitoids. Our results suggest that the two populations of A. sasakii belong to two distinct biological species.

View full abstract

We assessed potential adult longevity and male choice for a mate in two populations of Asteralobia sasakii associated with Ilex crenata and I. integra to test the hypothesis that interbreeding between these populations is prevented by the difference in emergence timing in the field. A previous study showed that the last day of adult emergence on I. integra and the first day of adult emergence on I. crenata were separated by six to 11 days. When adults were maintained in the laboratory with restricted flying, mating and oviposition, adults from both populations survived for four to five days, suggesting that the period when adults were active did not overlap between the two populations in the field. The mate choice test showed that males clearly approached females of the same host origin. These results suggest that the two populations have little chance of interbreeding even when they occur sympatrically. Other life history parameters such as the number of eggs in the ovary, daily emergence pattern, sex ratio and the duration of copulation also varied between the two populations. Our overall results strongly suggest that the two populations on different host plants can be referred to as distinct species.

View full abstract

The development of 4th stadium Psacothea hilaris larvae under various feeding and starving regimens was investigated to determine whether there is a threshold weight for metamorphosis. In larvae fed ad libitum, 56% of individuals spent a mean of 13 d in the 4th stadium and 18 d in the 5th stadium before pupation, whereas the rest remained in the 4th stadium for 24 d and pupated. When starved upon ecdysis to the 4th stadium, no larvae molted to the 5th stadium and most eventually died without pupation. In contrast, when larvae were fed for 1 d and then starved, 47% prematurely metamorphosed into small pupae after a mean of 18 d in the 4th stadium. Pupation success from the 4th stadium increased as the feeding period was extended, reaching 97% in the larvae that had fed for four days. All these pupae gave rise to small but morphologically normal adults. The relationships between the weight changes of experimental larvae during starvation and their pupation success suggested the threshold weight for metamorphosis to be 180 mg. The adaptive significance of premature pupation in starved P. hilaris is discussed as a life history strategy under unpredictable food conditions for larval growth.

View full abstract

Acetamiprid resistance in the diamondback moth (DBM) Plutella xylostella (L.) from cabbage fields of Iwaoka-cho, Kobe City, where acetamiprid is the primary insecticide for DBM control, was monitored from 1999–2001. The results showed only a slight change in the susceptibility of the population over the monitoring period, considering the LC₅₀ values and their corresponding resistance ratios (RRs). However, the LC₉₅ values showed a significant shift towards acetamiprid resistance, suggesting that the population could develop higher levels of resistance to the insecticide in the future. To retard the progress of acetamiprid resistance, growers rotate acetamiprid with other insecticides. We thus evaluated the efficacy of five other insecticides to identify efficacious products to be used with acetamiprid. Results indicated that the population was moderately resistant to esfenvalerate and phenthoate, and tolerant to cartap. The population was, however, susceptible to chlorfluazuron and a preparation of Bacillus thuringiensis (btk). Incorporating chlorfluazuron and btk into the resistance management tactic adopted in Iwaoka-cho is thus a sound option.

View full abstract

In the summer of 1997, larvae of the oriental beetle, Blitopertha orientalis, with milky disease were collected from a turf field in Chiba Prefecture, Japan. Characteristic footprint-shaped sporangia containing a spore and a parasporal body were isolated from the larval hemolymph. Examination of the bacteriological characteristics of this strain revealed that it was unable to grow in 2% NaCl, was susceptible to vancomycin, and had two plasmids, of about 9.8 and 5.5 kb. The sequence of the 16S ribosomal RNA gene (16S rDNA) of this strain was more homologous with that of Paenibacillus (Bacillus) lentimorbus ATCC 14707^T than those of the most famous, traditional American culture, Paenibacillus (Bacillus) popilliae ATCC 14706^T and NRRL B-4081. From homology of the 16S rDNA, this strain was identified as P. lentimorbus, and named strain ‘Semadara’. The sequence of strain Semadara was highly homologous with those of three Japanese isolates of B. popilliae. Strain Semadara also infected four other scarabaeids: Anomala cuprea, Anomala rufocuprea, Phyllopertha diversa, and Popillia japonica. When second or third stadium larvae of each of the four scarabaeids were inoculated with sporangia of strain Semadara at a concentration of 1.5×10⁸ sporangia/cup, most of the larvae died 2–4 weeks after inoculation.

View full abstract

Ostrinia ovalipennis has been recorded only in Shigakogen, a highland area in Honshu. Here, we report the occurrence of the species in Hokkaido. Since Ostrinia latipennis, a close relative of O. ovalipennis, is distributed widely in northeastern Japan, these two species occur sympatrically at some localities. The two species can be diagnosed based on the wing morphology. Another diagnostic character useful for distinguishing the Shigakogen population of O. ovalipennis from O. latipennis, i.e., the sacculus length (SL) of male genitalia, could not distinguish some individuals of the Hokkaido population of O. ovalipennis from O. latipennis. To revise the species diagnosis of the two species in terms of male morphometric traits, and to compare the degree of geographic differentiation in morphology between the two species, we analyzed 10 morphological traits. A linear discriminant analysis showed that O. ovalipennis could be distinguished from O. latipennis by a combination of two traits, SL and mid femur length. Morphological differentiation was greater between the Shigakogen and Hokkaido populations of O. ovalipennis than between the same local populations of O. latipennis. We suggest that the difference in the degree of geographic differentiation between the two species has been caused by the difference in their distribution patterns.

View full abstract

I examined parasitism of two grasshopper species, Parapodisma tanbaensis and P. subastris, by the flesh fly, Blaesoxipha japonensis, the genus of which includes important parasitoids of grasshoppers and locusts. I collected adult grasshoppers in the northern suburbs of Kyoto from late July to late October 2001 and reared them in the laboratory to investigate parasitism. The parasitism rates were greater for P. tanbaensis than for P. subastris, except for those in Kurama, where no parasitism was observed. The puparial weight decreased as the larval density within the host increased. This tendency was significant only for female hosts, since more puparia often egressed from female hosts than from male hosts. Male puparia were generally heavier than female puparia; this was more evident in female hosts with fewer than three fly larvae. In contrast, puparial weight did not differ by sex when puparia egressed from male hosts. These tendencies were also confirmed in the laboratory experiments. These results suggest that female hosts provide potentially greater resources for fly larvae than male hosts, and that male larvae develop considerably larger at low larval density.

View full abstract

Overwintered adults of the rice water weevil, Lissorhoptrus oryzophilus Kuschel, were used to examine the impacts of nitrogen (N) fertilization on their feeding, oviposition and survival. Rice plants (cultivar Shanyou 63) were fertilized with urea at 20 days after sowing at rates 0, 30, 60, 90, and 120 kgN/ha, respectively. Plants were initially used the day after fertilization to determine adult performance, and used at 3, 9 and 16 days after transplantation (23, 29 and 36 days old, respectively) to test adult feeding and oviposition preference. Feeding, oviposition period, fecundity and survival duration increased significantly as fertilization increased from 30 to 60 kgN/ha, and from 60 to 90 kgN/ha (except for fecundity), while they no longer increased significantly as fertilization increased further to 120 kgN/ha. When provided with 29-d-old plants, adults preferred to feed on the plants fertilized at 60 kgN/ha rather than on those fertilized at higher levels, while for 36-d-old plants, the results were strikingly reversed. On 23-d-old plants, adults preferred to deposit eggs on those fertilized at 60 kgN/ha; on 29- and 36-d-old plants, however, plants fertilized at 90 and 120 kgN/ha were significantly more preferred for oviposition.

View full abstract

Isolates of the entomopathogenic fungus Beauveria brongniartii differ in the shape of the conidia and the amount of red pigment production, which are associated with the host insects they were obtained from. We investigated intraspecific polymorphisms among 38 isolates of B. brongniartii by using restriction fragment length polymorphisms (RFLP) of the internal transcribed spacer regions (ITS1 and ITS2), 5.8S rDNA, and small portions of the 18S and 28S rDNAs. Based on the RFLP patterns, the isolates were divided into two distinct groups. One group was composed mainly of isolates from longicorn beetles (Coleoptera: Cerambycidae), whereas the other group mainly contained isolates from scarab beetles (Coleoptera: Scarabaeidae). The DNA sequences of the amplified regions showed high homology between the groups, with only 7 substitutions in 852 nucleotides, and just 1 of the 7 substitutions accounted for the difference in the RFLP patterns between the two groups. Furthermore, RFLP successfully distinguished all of the B. brongniartii isolates from the 5 tested isolates of B. bassiana and the 1 of B. amorpha.

View full abstract

The effect of leaf condition on the diapause induction of Tetranychus kanzawai Kishida was investigated. Two leaf-condition treatments were prepared under a constant short daylength of 9L : 15D. In the “refreshed” treatment, dietary bean leaves were renewed twice at the deutonymphal (pre-imaginal) and adult stages, while leaves were not renewed in the “non-refreshed” treatment. At the population level most females entered diapause at 15°C and 18°C under both leaf conditions, while a significantly lower proportion of females entered diapause at 20°C under both leaf conditions. The diapause incidence was consistently lower in the “refreshed” treatment, though the difference was not significant. When comparing each lineage initiated from one fertilized female at 20°C/9L : 15D, lower diapause incidence was consistently found in the “refreshed” treatment than in the “non-refreshed” one. ANOVA showed a significant interaction between lineage and leaf condition. These results suggest that under moderate temperatures leaf condition acts as a secondary factor to enhance the primary diapause-inducing effects of short-day and temperature.

View full abstract

The pinewood nematode, Bursaphelenchus xylophilus, is the causative agent of pine wilt disease. The virulence of nematodes significantly varies among pine trees, but does not vary within a single pine. To elucidate the reason for no variation in virulence within a single pine, a technique to investigate the population structure of nematodes of different virulence is needed. In this study, the demonstration of interbreeding between virulent and avirulent populations of B. xylophilus in vitro was attempted using PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) method. Ribosomal DNA containing the 5.8S gene, the internal transcribed spacer regions 1 and 2, and partial regions of 18S and 28S genes were used for analysis. First, PCR-RFLP patterns of offspring produced by interbreeding between two individuals of virulent and avirulent isolates were analyzed. The offspring from a single-pair interbreeding showed 3-digested fragment patterns with the restriction enzyme HhaI, patterns the same as the virulent isolate, the avirulent isolate and a hybrid pattern containing both fragments of the virulent and avirulent isolates. The virulent population was mixed with the avirulent one in vitro and propagated nematodes were individually analyzed by PCR-RFLP method. The nematodes showed the same 3 PCR-RFLP patterns as the offspring from a single-pair interbreeding. The detection of nematodes with a hybrid pattern demonstrates the occurrence of interbreeding between virulent and avirulent populations of B. xylophilus.

View full abstract

Insects visiting lettuce flowers were investigated under field and enclosure conditions. In a 4-year field survey, visitors of 11 species belonging to 3 orders were observed. Most species visiting the flowers were sweat bees (Hymenoptera; Halictidae). The frequency (total days of visitation to lettuce flower/total days of flight by the insect) of visitations by the sweat bee Lasioglossum villosulum trichopse was obviously higher at 65.5% than those of other insects. Honeybees were not observed on the lettuce flowers. In a 5-year survey under enclosure conditions, 10 of 17 bee species reared and a hoverfly were observed to visit the lettuce flowers. The highest frequency of visitation was shown by L. villosulum trichopse (59.4%), followed by Andrena knuthi (19.2%) and Osmia cornifrons (8.6%). Most visitors were one-day foragers and classified as temporary nectar foragers and continual pollen (and nectar) gatherers. Continual nectar foraging was observed in only 3 species, L. villosulum trichopse, An. knuthi and Ceratina boninensis. Daily flight activities of L. villosulum trichopse and the Lactuceae oligolectic bee An. knuthi corresponded to the morning blooming time of lettuce. The sweat bee L. villosulum trichopse may be a pollinator for hybrid seed production of lettuce.

View full abstract

We examined the effect of an insulin-related peptide, bombyxin-II, on the mitotic division of Bombyx mori hemocytes in vitro. Hemocytes isolated from larval hemolymph (day 1 of 4th instar) were cultured singly in MGM-450 medium. Some cultured prohemocytes (11.1%), plasmatocytes (2.6%), granulocytes (8.5%) and spherulocytes (10.8%) underwent mitotic division in the medium. Synthetic bombyxin-II added to the medium together with 10% larval hemolymph notably increased the ratio of dividing granulocytes to 45.5%, while no effect was evident on the other types of hemocytes. Bombyxin-II or hemolymph alone failed to stimulate the division of granulocytes. These results suggest that bombyxin-II acts cooperatively with hemolymph factor(s) to stimulate mitotic division of granulocytes. Bovine pancreas insulin was also active and could substitute for bombyxin.

View full abstract