Phase polyphenism is an adaptive phenomenon in which some traits vary continuously in response to population densities. In locusts, two extreme phases, solitarious and gregarious, that occur at a low and a high density, respectively, are known and intermediate forms called transient phase also occur in a transition between the two phases or at an intermediate density. Establishment of an albino strain of Locusta migratoria led to the discovery of a neuropeptide, corazonin that is involved in the control of the expression of some phase-related traits in this and another locust, Schistocerca gregaria. This paper describes a summary of phase polyphenism research with a particular emphasis on recent studies about the roles of corazonin in locusts. In L. migratoria, injection of the neuropeptide causes albino nymphs to express various body colors often observed in not only solitarious but also gregarious forms irrespective of the rearing density. Both juvenile hormone and corazonin are necessary to express the green solitarious form normally observed in the field. It has also been suggested that this neuropeptide may be involved in the control of phase-related morphometric ratios of F/C and E/F (F=hind femur length; C=maximum head width; E=elytron length) as well as the development of antennal olfactory sensilla in the two locusts: injection of the peptide mimics crowding effects, thus inducing gregarious characteristics in solitarious (isolated-reared) locusts. Corazonin and related compounds are widespread among insects. Transplantation of the brain and corpora cardiaca from various donors to albino locusts indicates the presence of corazonin or corazonin-like substances in all 18 insect orders so far screened except for the Coleoptera.

View full abstract

The diets of the wolf spiders Pardosa pseudoannulata and Pirata subpiraticus were elucidated by direct observation in paddies from July to September 2000. In July, dipterous insects were the most numerous prey consumed by P. pseudoannulata and the second numerous prey consumed by P. subpiraticus, comprising over 50% and over 20% of their respective diets. In contrast, in August, the proportion of dipterous insects decreased dramatically and hoppers were the most numerous prey, comprising over 60% and over 70% of all insects and spiders consumed by P. pseudoannulata and P. subpiraticus, respectively. In September, predators such as wolf spiders and aquatic Heteroptera were frequently observed in their diets. Overall, the green rice leafhopper, Nephotettix cincticeps, was the most numerous prey consumed by P. pseudoannulata and P. subpiraticus, followed by chironomids.

View full abstract

The insecticidal efficacy of the diatomaceous earth formulation SilicoSec^® (Biofa GmbH) against adults of the rice weevil, Sitophilus oryzae, was evaluated in laboratory experiments on stored wheat. Bioassays were conducted at three temperature levels, 22, 27 and 30°C, two relative humidity (rh) levels, 55 and 65%, and four dose rates, 0.25, 0.5, 1 and 1.5 g of SilicoSec^®/kg of wheat. Three different aged-adult groups, 1, 2 and 7 d-old, were exposed. The mortality of exposed adults increased with the exposure interval and dose rate. Also, the increase of temperature increased S. oryzae mortality in all exposure intervals examined. The increase of rh from 55 to 65% caused a significant decrease in S. oryzae mortality. The age of the exposed individuals did not have a direct effect on SilicoSec^® efficacy.

View full abstract

We investigated the olfactory responses of six strains of the predatory mite Neoseiulus womersleyi Shicha to different amounts of volatiles of Tetranychus urticae Koch-infested kidney bean plants. Four strains of the predators were collected from different sites in Japan (i.e., 4 geographical populations). The other two strains were inbred lines bidirectionally selected from a base population for their olfactory responses. All strains showed significantly higher olfactory preferences for the volatiles of 15 plants than those for 5 plants. We found a significant correlation between preferences for 15 plants and those for 5 plants. The olfactory preferences for spider mite-infested plant volatiles differed significantly among strains. The olfactory preferences of the 2 inbred strains were significantly different. These results suggest that the variation among local populations may result from genetic differences in sensitivity to spider mite-induced plant volatiles.

View full abstract

The cold tolerance of Cylas formicarius from five islands in the southwest of Japan was studied. The thermal threshold of the reproductive activity of adults tended to be lower and the supercooling point of the pupae was a little higher for the Okinawa-Honto population than for the others. The cold tolerance of the adult weevils was slightly accelerated by cold acclimation to 15°C for 4 d. Reproductive diapause induced under 10L : 14D increased cold tolerance significantly. Therefore, the cold tolerance of adult weevils would be accelerated by both cold acclimation at decreasing temperatures from autumn to winter and reproductive diapause induced by short daytime hours. When considering the increased cold-tolerence of C. formicarius through such mechanisms together with the temperature conditions in winter at the northern edge of its distribution area in the USA, C. formicarius probably has the capability to survive in the coastal zone of the Pacific Ocean in southern and central Japan.

View full abstract

We fed Tyrophagus similis on three organic wastes (cattle feces, sawdust, and rice straw), an organic fertilizer (rapeseed meal), three composts (made from cattle feces, rice husks, and rice straw), three fungi (Fusarium oxysporum, Pythium aphanidermatum, and Rhizoctonia solani) and eight vegetables (lettuce, cucumber, komatsuna, spinach, pak choi, garland chrysanthemum, Welsh onion, and tomato), and determined the materials' suitability as food from the fecundity of females. Rapeseed meal, fungi, and most vegetables were suitable. Organic wastes and composts were unsuitable. These results suggest ways to reduce spinach damage by T. similis: (1) Reduce the use of organic fertilizers such as rapeseed meal during mite season, (2) remove plant residues on the soil before spinach cultivation, and (3) reduce the use of immature organic materials, because they increase fungi that are suitable for T. similis.

View full abstract

To establish a simple method for rearing Propylea japonica (Thunberg), we investigated its larval and pupal development and reproduction when offered Ephestia kuehniella Zeller eggs as an alternative diet. Larvae raised on E. kuehniella eggs matured as well as those raised on Acyrthosiphon pisum (Harris), and could be reared at high densities without cannibalism when a sufficient diet was supplied. Although the mean fertility of the adults reared on E. kuehniella eggs was about one-third of that of the adults reared on A. pisum, 63.7–66.5% of the eggs hatched and the larvae matured normally. These results suggest that E. kuehniella eggs are an available alternative diet for the larval and pupal development and reproduction of P. japonica, and should make it possible to rear successive generations. However, to obtain large amounts of larvae at the same developmental stage and to collect eggs efficiently, the larvae should be reared on E. kuehniella eggs and the adults should be reared on aphids such as A. pisum.

View full abstract

The effect of tomato spotted wilt virus (TSWV) infection on the life span of thelytokous Thrips tabaci, which is known as a TSWV vector with a low transmission rate, was studied in two populations, Shimane (SM) and Iwate (IW). No effects of virus infection were found in the developmental period and mortality of the thrips before adult emergence, but a significant increase was observed in age-specific mortality during the adult lifespan of the TSWV-exposed thrips group when compared with the non-exposed group (mean total longevity of thrips exposed and not exposed to virus was 18.1 and 20.1 d in the SM population and 19.9 and 21.5 d in the IW population). The latent period (LP) was 14.2 d in the SM population and 17.2 d in the IW population, indicating a relatively longer LP than the LPs reported for Frankliniella occidentalis and F. fusca. The potential transmission period (PTP) from the end of the LP to vector death was only 3.3 d in both of the populations. The higher the level of virus infection, the greater the reduction in adult thrips survival. These results suggest that a long LP and TSWV-induced reduction of thrips survival shorten the PTP. This may be responsible for the low transmissibility of TSWV as well as the low transmission rate in thelytokous T. tabaci populations.

View full abstract

Numerous errors and confusion in the literature concerning the genus Trichogramma in Japan have necessitated a formal review of this genus. This review corrects and updates Trichogramma host and distribution records from Hokkaido to the Ryukyu Islands, redescribes and designates a lectotype for T. jezoense Ishii, records two Trichogramma species new to Japan (T. ostriniae Pang and Chen and T. lingulatum Pang and Chen) and describes three new species (T. yabui Honda and Taylor, T. okinawae Honda, and T. aomoriense Honda). Additionally a key to the species is provided for the 14 known Japanese species as are ITS-2 DNA sequences and SEM micrographs of male genital capsules for the majority of the species to aid biocontrol workers in Trichogramma identification.

View full abstract

The mating behavior of the male Gastrophysa atrocyanea, that is, extrusion of the aedeagus, was elicited by the cuticular hydrocarbons on the surface of the female body. Males attempted to mate with a dummy treated with the female equivalent of the female elytra extracts. After fractionation of the elytra extracts by Florisil column chromatography and reverse phase high performance liquid chromatography, two fractions, consisting mainly of methylheptacosanes and methylnonacosanes were found to elicit the male mating behavior. These compounds, synthetic 9-methylheptacosane, 11-methylheptacosane, 9-methylnonacosane and 11-methylnonacosane, were contained in active fractions and showed high pheromonal activity. Therefore, these monomethylalkanes were considered to be contact sex pheromones of this beetle. However, synthetic 13-methylheptacosane, 13-methylnonacosane and 15-methylnonacosane, positional isomers of active monomethylalkanes, also contained in the active fractions, did not have the activity. A mixture of these seven monomethylalkanes at approximately natural concentrations also had enough activity to elicit the male mating behavior. Furthermore, the results of a bioassay using some related structural monomethylalkanes revealed that the length of the carbon backbone and the position of the methyl branch greatly influenced the pheromonal activity of G. atrocyanea.

View full abstract

The influence of food supply on the parasitoid Cotesia plutellae regarding the survival and reproductive potential of a non-target pest, pea leafminer Chromatomyia horticola, was examined in the laboratory. The male longevity of the leafminer dramatically increased when sugar or honey was available. On the other hand, sugar- or honey-fed females lived shorter lives than those fed on the host plant. Lifetime copulation times of the males were increased by their food supply. The lifetime fecundity of a pair significantly increased sugar or honey was supplied. This phenomenon was mainly explained by the positive relationship between the fecundity and the copulation count of females. We discuss the risk of an additional food supply increasing the numbers of non-target pests.

View full abstract

A strain of Beauveria brongniartii PBbr-1 was isolated from infected larvae of Heptophylla picea. This isolated strain attained 100% mortality of H. picea adults at a concentration of 1.0×10⁷ conidia/ml, with a short median lethal time of 8.4 d for females and 7.0 d for males. The number of eggs laid by adults and percent of eggs hatching for females inoculated with PBbr-1 were lower than those by healthy females. However, when PBbr-1 was inoculated directly to the eggs, hatchability was almost the same as that in non-inoculated eggs. Since infected females appeared to lay eggs just before death, the eggs from females infected with PBbr-1 were thought to be unfertilized. Furthermore, PBbr-1 showed a high virulence to the first-stage larvae. PBbr-1 not only had a high virulence to the adults, but also suppressed subsequent generations. PBbr-1 is thus thought to be a very effective control agent for H. picea in combination with Beauveria amorpha HpBa-1.

View full abstract

Cry toxins produced by Bacillus thuringiensis are insecticidal toxins and have been recently introduced to genetically modified (GM) organisms. The toxins are considered harmless to humans and farm animals; however, it remains unclear whether the toxins affect the mammalian intestinal epithelium, the primary portal and absorption site after ingestion. Therefore, we performed immunohistochemical and ligand blot analyses using brush border membrane vesicles to investigate the interaction of Cry1Ab toxin, a popular Cry toxin developed in GM corn, with bovine intestinal epithelium, with special attention to the presence of Cry1Ab toxin-binding proteins of the epithelial cell. We found that Cry1Ab toxin binds to actin, a cytoskeletal protein. However, the toxin did not bind to aminopeptidase N, cadherin, or alkaline phosphatase, all of which are cell membrane receptors or candidate proteins necessary for the development of toxicity in susceptible insect cells. The present results and previous observations that Cry toxins have little acute toxicity on mammalian cells indicate that Cry1Ab toxin is able to bind to cytoskeletal actin, but that the bovine intestinal epithelial cell lacks membrane receptors, which are necessary for the toxin to exert its toxicity on the cell.

View full abstract

The effects of temperature on the larval developmental traits of the fall webworm, Hyphantria cunea (Drury), were investigated at 18, 20, 23, 25 and 27°C. In Japan, this species has two types of larval instars, the six-instar and seven-instar. The proportion of the seven-instar type was significantly higher in females than in males at all temperatures. In females, the proportion of the seven-instar type was high at higher temperatures. However, the effect of temperature on the incidence of larval instar types was not detected in males. The larval developmental time was significantly longer in the seven-instar type than in the six-instar type for both sexes at all temperatures. The difference in the developmental time between the instar types decreased as temperature increased. The pupae of the seven-instar type were heavier than those of the six-instar type at higher temperatures. These results suggest that the fitness advantage of the seven-instar type is greater in females than in males, and is relatively high at higher temperatures because the disadvantage of the long developmental period in the seven-instar type is reduced by higher developmental rates.

View full abstract

We examined whether stimuli among one another are involved in the short-range locations of the Halyomorpha halys adult, which often forms aggregations when overwintering. Ten diapausing adults were released into a clear container at 10°C. After a certain time period, their distribution was compared with a random distribution, and a tendency for a strong concentrated distribution with crowding was observed under both light and dark conditions. However, antennectomy prevented bugs from aggregating and this clarified the role of antenna in short-range locations. This finding suggests that overwintering aggregation in H. halys is guided by a chemical or tactile interaction among individuals, at least within a narrow range. In addition, the relationship between this aggregation habit and temperature was examined. Although temperatures of 15°C and 20°C caused bugs to become active, the habit of settling close to one another was not reduced. Based on these results, we inferred that the aggregation habit of H. halys adults itself is not temperature dependent, and that the overwintering aggregation is caused by an increase in opportunity for contact with each other, such as from a mutual preference for the overwintering environment, and a decrease in behavioral activity resulting from a decrease in temperature.

View full abstract

The attraction of Urocerus japonicus to volatile chemicals, which discolors the wood of conifers, was examined in the field. Attracting effects of α-pinene and ethanol that were suggested to be effective as attractants were compared to U. japonicus with Hodoron^®, which has been used as an attractant for woodwasps. Adults of U. japonicus were captured in chemically treated adhesive traps, which were set up in a hinoki Cypress Chamaecyparis obtusa plantation. More female adults of U. japonicus were captured in traps with α-pinene or Hodoron^® than in those without chemicals. There was no significant difference between the number of captured females in traps with α-pinene and those with Hodoron^®. There were also no significant differences in the number of captured males among treatments. Traps with ethanol did not attract either sex of U. japonicus. It was indicated that both α-pinene and Hodoron^® have attracting effects on female U. japonicus.

View full abstract

To investigate the process of template renewal in the European honeybee, we collected workers showing nestmate discrimination ability and exposed them to unfamiliar colony environments by keeping them with non-nestmates in a small box or by fostering them in an unrelated colony. Bees exposed to non-nestmates for 25 min showed more tolerance, than bees not exposed, to members of the colony to which they had been exposed, but were still aggressive to bees from other colonies. However, this treatment did not affect their response to nestmates. In the fostering experiment, although fostered bees became significantly more tolerant to bees from the fostering colony after 24 h, their response to former nestmates changed little until 96 h after fostering started. These results suggest that European honeybees change their template rapidly by referring to the inner-colony environment but retain the old template temporally in the early phase of template renewal. This is probably appropriate for accepting nestmates who have not yet acquired the new recognition cue when the colony odor changes.

View full abstract

Corazonin (Crz) is a neuropeptide with a conserved structure and distribution pattern in the central nervous system (CNS) of many insects. We cloned the Crz gene from brains of the honey bee workers (Apis mellifera L., Apime). The ApimeCrz cDNA comprises 502 base pairs and encodes a new form of corazonin displaying Thr⁴ substitution of [His⁷]-corazonin. In workers of A. mellifera, corazonin immunoreactivity was found in a group of four to five lateral neurosecretory cells (LNSC) in each hemisphere of the protocerebrum and in lateral paired neurons segmentally distributed in the ventral ganglia. However, the ApimeCrz mRNA was transcribed only in the LNSC. The Crz LNSC projected into the ipsilateral corpus cardiacum. The pattern of distribution of corazonin immunoreactive material in the CNS suggests that Apime-corazonin plays roles as a neurohormone as well as a neurotransmitter or neuromodulator. The effects of this neuropeptide on the induction of dark color in albino nymphs of Locusta migratoria and spinning rate in spinning larvae of Bombyx mori were assayed. The results indicate that Apime-corazonin shows biological activities comparable to those for [Arg⁷]- and [His⁷]-corazonins.

View full abstract

Some cry genes from Bacillus thuringiensis Berliner (Bt) have been transferred into rice plants for resistance to lepidopterans. The ecological risks of Bt rice, especially the non-target effects of Bt rice pollen on the domestic silkworm, Bombyx mori Linnaeus in mulberry-rice mixed cropping area should be clarified cautiously. In light of B. mori fully domesticated and not surviving independently in the field, a series of laboratory bioassays were conducted to evaluate the effect of the pollen from an indica transgenic rice line, TT9-3 with a fused cry1Ab/cry1Ac gene on B. mori based on the investigation of rice pollen deposition under normal field conditions and the quantitation of the fused insecticidal protein expression in the pollen. No significant adverse effects were observed on the survival, growth and development of B. mori young larvae, even after the neonates had been exposed to Bt pollen at the highest density of 3,395.0 grains/cm² for 48 h which the pollen density is far higher than the highest pollen density on mulberry leaf, 1,635.9 grains/cm², naturally occurred in the field. According to these results and considering the extensive biotic and non-biotic factors such as the type of Bt genes used and expressed in Bt rice line TT9-3 which are safe to B. mori, the relatively low exposure amount of insecticidal protein in the Bt pollen, and other conditions which influence the silkworm's exposure to Bt pollens, it suggests that the pollen from Bt rice line, TT9-3 poses little effect on silkworm rearing in natural settings.

View full abstract

The species composition and seasonal dynamics of predatory phytoseiid mites on magnolia, Magnolia hypoleuca, were investigated for 4 y to determine whether M. hypoleuca may act as a source of natural enemies for tetranychid and eriophyid mites on apples. Euseius finlandicus was the most dominant species and formed more than 70% of the mite specimens collected during each year. Amblyseius orientalis was also found consistently as the second dominant species. E. finlandicus was found in low numbers in spring, and its density increased gradually to more than 10 adult females per leaf in autumn. Although the seasonal dynamics of A. orientalis showed some variation depending on the survey years and sites, A. orientalis showed a good predatory ability on Panonychus ulmi, and it developed and reproduced well on this prey in the laboratory.

View full abstract

The strawberry leaf beetle, Galerucella vittaticollis Baly, is an oligophagous insect that feeds on strawberry and polygonaceous plants. Behavioral responses of G. vittaticollis to host and non-host plant volatiles were investigated. Beetles were attracted to the odors of their host, rosaceous plant, Fragaria ananassa Duchn., and polygonaceous plants, Rumex obtusifolius L., Fagopyrum esculentum Moench, Polygonum thunbergii Sieb. et Zucc., P. cuspidatum Sieb. et Zucc. and P. blumei Meisn. They were not attracted to non-host plants, Raphanus sativus L. (Brassicaceae), Lycium chinense Mill. (Solanaceae), Artemisia princeps Pampan. (Compositae) and Triticum aestivum L. (Gramineae). The main component of the headspace of all host plants tested was one of the green leaf volatiles, cis-3-hexenyl acetate. This compound was detected also in the non-host plants except T. aestivum. However, its relative content in A. princeps or L. chinense was different from that in host plants. The headspace of R. sativus contained one of the isothiocyanates, characteristic components of brassicaceous plants, in addition to cis-3-hexenyl acetate. The attractancy of cis-3-hexenyl acetate and two other typical green leaf volatiles, cis-3-hexen-1-ol and trans-2-hexenal, to the beetles was examined. The beetles were significantly attracted to only cis-3-hexenyl acetate. The findings suggest that G. vittaticollis uses cis-3-hexenyl acetate as an olfactory cue to find the host plants, strawberry and polygonaceous plants.

View full abstract

The biology of the tachinid fly, Drino inconspicuoides, a gregarious ovolarviparous parasitoid of some lepidopteran pests, was studied in the laboratory at 25°C, 60–70% RH and a 16L : 8D photoperiod in the host Mythimna separata. The duration of mating averaged 79.4±9.2 min (mean±SE). After mating, the parasitoid had a pre-oviposition (gestation) period of 6.3±0.3 d. Females of D. inconspicuoides had a daily oviposition rate of 11.6 eggs and a mean fecundity of 163.6±13.4 eggs during a mean oviposition period of 14.8±1.3 d. Total lifetime fecundity per female varied from 57 to 271 eggs. The mean longevity of mated females provided with hosts, including the pre-oviposition period was 21.1±1.5 d. Mated female parasitoids deprived of hosts lived an average of 29.3±2.9 d, which was significantly longer than that of their un-deprived counterparts. Unmated males lived an average of 15.5±1.9 d. When one egg was laid per host, the larval period averaged 7.9±0.4 d for males and 8.3±0.3 d for females, and the puparial period averaged 10.5±0.2 d for males and 11.4±0.2 d for females. The mean total developmental period for males and females was 18.5±0.4 and 19.7±0.4 d, respectively.

View full abstract

To examine the effects of tillage practices on spider assemblages in rice paddy fields, we investigated the abundance and biomass of spiders in untilled and tilled paddy fields over three cropping seasons (from 1999 to 2001). In total, we collected 6,829 spiders, consisting of 13 species in seven families. The family Lycosidae was the most abundant, followed by Tetragnathidae, Linyphiidae, and Salticidae. Spider abundance and biomass were greater in untilled than in tilled paddies during each cropping season. Although we detected no significant effect of tillage on spider abundance, we did observe a significant effect of tillage on spider biomass in 2000 and 2001. No differences were found in the abundance and biomass of tetragnathid and linyphiid spiders during the cropping season. In contrast, the abundance and biomass of lycosid or salticid spiders tended to be larger in untilled paddies than in tilled paddies, especially later in the cropping season.

View full abstract