Pathogenicity of the white muscardine fungus, Beauveria bassiana (BALSAMO) VUILLEMIN, to a coreid bug, Riptortus linearis (F.), a pest of soybean, was investigated in a series of laboratory tests. Beauveria bassiana was pathogenic to 3rd, 4th and 5th stadium nymphs and adults of R. linearis. The 4th and 5th stadium nymphs were more susceptible than adults and 3rd instars. Within the range of 4.5×10³ to 4.5×10⁸ conidia/ml, there was a highly significant linear relationship between the dose of B. bassiana and the mortality of R. linearis. Isolates recovered from cadavers of R. linearis killed by B. bassiana were virulent to R. linearis. At 25°Cand above, pathogenicity of B. bassiana decreased with increases in temperature. This was due to the adverse effect of high temperatures on the germination of conidia. The longer the fungus-treated insects were maintained at high temperatures, the lower the insect mortality. Ultra-violet (UV) irradiation of conidia reduced pathogenicity of B. bassiana to R. linearis.

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The role of predation in regulating a population of the citrus mealybug, Pseudocuccus citriculus, and the effects of ant-attendance on the predator-prey interactions were studied in a pesticide-reduced Satsuma orange orchard in Wakayama Prefecture, Japan. The population of the first generation increased by more than 5 fold when predaceous insects were excluded, whereas it did not show a notable change in size under natural conditions where enemies naturally attacked mealybugs and some mealybugs were well protected by a honey-dew-collecting ant, Lasius niger. The mealybug population showed a drastic decrease by 94% when the attendant ants (L. niger) were excluded. Attending ants (L. niger) were observed to protect P. citriculus by aggressive behaviour towards its natural enemies, the common coccidophagous ladybird beetle Chilocorus kuwanae and a lacewing species (Chrysopidae sp.). Field censuses and laboratory rearing suggested that the two abundant predaceous insects are the effective agents regulating the mealybug population at low density. These result demonstrate that predators regulate the population of P. citriculus and that ant-attedance is indispensable to the persistence of the mealybug population.

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To analyze chromosomal polymorphism in the Chrysolina aurichalcea complex, two new karyotypes were described, and their total complement lengths were compared using their hybrid chromosome. The distribution of the karyotypes, including those studied thus far in the Japanese Archipelago, was surveyed. The new types had chromosome numbers of 2n(♂)=31 and 2n(♂)=41 and were both XO sex-systems. The 31 type differed markedly type was slightly larger than or the same as that of the 41 type. Both types were widely distributed throughout the Japanese Archipelago. The 31 type inhabited most parts of Japan and the 41 type prevailed in Hokkaido, a few islands and mountainous areas in Honshu. Distribution of the two types appeared to be allopatric or parapatric. The geographic distribution of the 41 type is presumed to be a relict type to the 31 type. The relationships between the two types, and between each of the two and the other karyotypes, are discussed in reference to the speed of karyotype differentiation of the two types. It is speculated that karyotype differentiation between the two types may have proceeded at a rather high evolutionary rate.

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When each stage of Histiogaster sp. was a;;lied to a fungal colony of Lentinula edodes (shiitake mushrooms) individually, every larva and protonymph failed to develop and subsequently died. The average survival period of larvae on the fungal colonies was significantly shorter than that on agar mediums, on which most mites were considered to die to starvation. Only 20% of tritonymphs developed into the next stage (adult) on the fungal colonies, while 70% of them succeeded in developing into adults on agar medium. It was suggested that most Histiogaster sp. did not develop on L. edodes due to lack of nutrients. As fecal pellets were not observed on the fungus, it is postulated that they must have failed to feed on hyphae. Addition to this, L. edodes seemed to inhibit mite development because a tendency was observed that often mites became entangled in the hyphae.

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The life cycle of the fall webworm, Hyphantria cunea, has differentiated from bivoltine to trivoltine since the early 1970's in the southwestern areas of Japan. Previous studies showed differentiation in developmental period as well: development was shorter in the trivoltine populations. In the present study, the precise mechanisms of this change were investigated by comparing developmental characteristics between bivoltine (Akita) and trivoltine (Urawa) populations. The theoretical lower threshold temperatures for larval and pupal development were not different between the two populations. The thermal constant for larval development was smaller in the trivoltine population than in the bivoltine population, but that for pupal development was almost identical for the two populations. Most individuals passed six larval instars, and some passed seven in both populations. The incidence of seven-instar larvae was significantly higher in the bivoltine population than in the trivoltine population. The larval period was significantly longer in the seven-instar type than in the six-instar type. Larvae of the six-instar type grew at similar rates in the two populations. Head width of last instar larvae was larger in the seven-instar type than in the six-instar type, but pupal weight was not statistically different between the two types. These results suggest that the reduction in developmental period in the trivoltine population can be attributed to a reduction in the thermal constant, especially than during the larval stage. A lower incidence of seven-instar larvae appears to be the major mechanism for reducing the thermal constant in the trivoltine population.

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The distribution of root-knot nematodes was surveyed in tobacco fields of Japan. In 1992 and 1994, 219 populations of root-knot nematodes in tobacco fields covering the northern most area of Honshu to the Ryukyu Is. were identified on isozyme patterns of esterase and malate dehydrogenase. In this work, four Maloidogyne species, M. incognita, M. arenaria, M. hapla and M. javanica, were found. In M. arenaria, two distinct esterase phenotypes, one (A-1) and two (A-2) band types, were found. Meloidogyne incognita was widely found from southern Tohoku to the Shinetsu districts and southward to the Ryukyu Is. This species was recorded for the first time in Gifu, Nagano, Fukushima, Yamagata and Miyagi Prefs. Meloidogyne arenaria (A-2) was widely found from the Ryukyu Is. to Akita and Iwate Prefs., however, its distribution in Kyushu and the Ryukyu Is. was patchy. This species was found for the first time in Akita and Iwate Prefs. Meloidogyne arenaria (A-1) was mainly concentrated in Kyushu and the Ryukyu Is., and was found in one locality in Shikoku. Meloidogyne hapla was distributed from Shinetsu to the Kanto distinct northward to Aomori Pref. Meloidogyne javanica was found only in the Ryukyu Is. In areas where the distribution of these species overlapped, two or three species were often found in a single field.

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Copulation and post-copulatory mounting behaviors of Atractomorpha lata MOTSCHULSKY were observed and described under laboratory conditions. Copulatory behavior was initiated by a male approaching a stationary or feeding female without any courtship behavior. Pair formation involved mounting of the female without genital contact followed by a brief period of genitalia probing. Copulation, which is frequently linked with post-copulatory mounting, was determined in 2:5, 3:3 and 5:2 (female:male) sex ratio groups. The results show that the frequency of copulation and post-copulatory mounting were significantly higher in the 2:5 group than in the other two groups. Age difference did not affect the frequency of copulation but more copulations were followed by post-copulatory mounting in 30 d old females paired with 10 d old males than in 10 d old females paired with 30 d old males. These results suggest than post-copulatory mounting functions as a post-copulatory mate guarding behavior.

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Susceptibility of Pseudaletia separata larvae parasitized by Cotesia kariyai to an entomopoxvirus of P. separata (PsEPV) was compared to that of nonparasitized larvae under laboratory condition. Prasitized larvae were more susceptible than nonparasitized larvae when fourth-instar larvae were perorally inoculated with Ps EPV and then parasitized at 3 days later. The LD₅₀ values for parasitized and nonparasitized larvae were 6.9×10³ and 2.4×10⁴ spheroids/ insect respectively and were significantly different as indicated by lack of overlap of their 95% fiducial limits. The presence of the wasp greatly enhanced the susceptibility of Pseudaletia separata larvae to the virus infection.

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To determine whether the honeybee queen has the potential ability to decide the sex ratio of the eggs that are to be laid, experiments were carried out with special frames. The results showed that the queens selected either worker or drone cells and laid most eggs in worker cells, when queens were provided with both worker and drone cells, while the worker unpreferentially stayed on and prepared worker or drone cells by cleaning for the queen's oviposition. The queens were also observed changing the sex ratio of the eggs in drone and worker cells, with the ratio depending on the season. More eggs were laid in drone cells during the swarming season. The cues that queens use to determine the ratio of eggs in drone and worker cells are discussed.

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Courtship-like signals produced by males during mating behavior were recognized for the first time in whiteflies. Synchronous audio-video recordings ascertained that sexually matured males of Trialeurodes vaporariorum (WESTWOOD) produced substrate-borne vibrations by rapidly oscillating their abdomens in a stereotyped rhythm accompanied with a short moving action around the female. Signals were consisted of a sequence of discrete bouts of sounds, and were named "chirps." A chirp was composed of a series of sinusoidal waves divided into several sections called "pulses." A chirp was composed of a series of sinusoidal waves divided into several sections called "pulses." A pulse was defined as having a bimodal phase. Pulse intervals varied from 19.9 to 25.8 ms distinguished by small waves of low amplitude. A chirp was composed of 10-20 pulses, varying in number in the courtship progress. Chirp durations varied from 0.62 to 1.44 ms in proportion to the pulse number. Chirp intervals showed no periodicity, varying from 2.45 to 14.4 s. At the final male courting behavior, a persistent, periodically placed wing flicking was substituted for the train of chirps. Prolonged courtship behavior might be due to the necessity of sexual stimulation for female by repeated emission of the male acoustic signals as well as his persistent wing flicking.

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Oviposition and host-feeding behaviors of Aphelinus gossypii were examined, with the aid of a video-recorder, and compared. A total of 139 encounters between female wasps and second- to fourth-instar larvae of Aphis gossypii were observed. Of these encounters 53 led to oviposition and 20 to host-feeding. In ovipositional attacks wasps examined aphids with the wasp inserted the ovipositor more deeply than in ovipositional attacks, kept the hind legs on the aphid and repeatedly inserted and withdrew the ovipositor. Then the wasp turned forward, searched the ovipositor wound and fed on the body fluids of the aphid. On 36 occasions wasps failed in ovipositing due to defence reactions by the aphids. Sometimes an egg was deposited but it was not completely placed into the aphid body and shrivelled soon afterward. On 19 occasions wasps were not able to locate the ovipositor wound after turning forward. Two of these wasps attacked the same aphids again but 17 retreated. The mean duration from encounter with an aphid to retreat was 347 s (5.8 min) for oviposition and 1, 798 s (27.7 min) for host-feeding.

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Cotesia kariyai first recognized a host habitat through antennal perception of volatile substances from the plant fed on by host larvae, and examined the feeding traces by antennal contact with the plant. The characteristic arrestment behavior was also elicited when the wasp found exuviae and fecal pellets of host larvae. The arrestant was confirmed to be a mixture of 2, 5-dialkyltetrahydrofurans which was bioassayed using a filter paper disc. When the arrestant was applied to a small glass rod, C. kariyai responded with ovipositor stabbing. A similar composition of 2, 5-dialkyltetrahydrofurans to those in extracts of the feces and exuviae was confirmed in extracts from cuticular wax of Pseudaletia separata larvae. A mixture of hydrocarbons was the major component of the cuticular wax, and results of the bioassay showed a similar oviposition stimulant activity. The same compounds from different sources acting as an arrestant and as an oviposition stimulant were identified using different materials as the substrates for the bioassay.

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Cotesia kariyai first recognized a host habitat through antennal perception of volatile substances from the plant fed on by host larvae, and examined the feeding traces by antennal contact with the plant. The characteristic arrestment behavior was also elicited when the wasp found exuviae and fecal pellets of host larvae. The arrestant was confirmed to be a mixture of 2, 5-dialkyltetrahydrofurans which was bioassayed using a filter paper disc. When the arrestant was applied to a small glass rod, C. kariyai responded with ovipositor stabbing. A similar composition of 2, 5-dialkyltetrahydrofurans to those in extracts of the feces and exuviae was confirmed in extracts from cuticular wax of Pseudaletia separata larvae. A mixture of hydrocarbons was the major component of the cuticular wax, and results of the bioassay showed a similar oviposition stimulant activity. The same compounds from different sources acting as an arrestant and as an oviposition stimulant were identified using different materials as the substrates for the bioassay.

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Growth of Beauveria bassiana at various pHs was investigated an the fungus was found to be able to grow well at high pHs of more than 10. The fungus was also resistant to CuCl₂ and to low sugar content. New selective media for the isolation of B. bassiana were developed by integrating CuCl₂, low sugar, and either crystal violet or brilliant green in the media. Beauveria bassiana was isolated from soil samples using the developed media, and isolation efficiency was found to be higher using one of our newly developed media than by using that of VEEN and FERRON which has commonly been used for the selective isolation of B. bassiana.

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During coevolution of plants and herbivores, natural selection is assumed to increase preference-performance covariance, but some recent studies put that assumption in doubt. Our study of a gall aphid Neothoracaphis yanonis demonstrated that the stem mothers produce galls more abundantly on the leaves at the lowest position on a shoot, and on the basal intermediate part (B-part) of a leaf blade. The leaf position was determined by the synchronization between the appearance of stem mothers and the leaf opening phenology, but the leaf part was chosen by preference of the stem mothers. On this leaf position and leaf part, aphids produced larger galls containing more abundant alates. Thus, our observations support the preference-performance hypothesis. As gall density increased, gall size declined, the percentage of indehiscent galls increased, and the relative abundance of upper-type galls increased. The density effect resulted in promoting the dispersal of stem mothers and reducing fitness of aphids which located on less favorable sites.

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