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Since the 2000's in Korea, the regional hotspots of rice stripe virus (genus Tenuivirus, RSV), transmitted by small brown planthopper (Laodelphax striatellus (Fallen), SBPH), have changed from the southeastern to the western coastal regions. The reasons for this are as yet unknown, but recent changes in temperatures in spring, the time at which the vectors migrate from overwintering sites to rice fields, are thought to be an important factor. In this study, we investigated the differences in the development of RSV-infected and RSV-free SBPH populations and further investigated how spring temperatures affect RSV transmission to rice (Oryza sativa). Two temperature conditions (15 and 20 °C) were chosen based on the average temperature in April–May and May–June in Korea, respectively, at which the SBPHs begin to migrate from Gramineae weeds to rice during the spring season. The nymphal developmental period in the RSV-infected SBPH was significantly shorter than that in the RSV-free SBPH. The body weight of males was significantly higher in the RSV-infected SBPH than in the RSV-free SBPH at early nymphal stage (1st day of 5th instar). The transmission of RSV to the rice seedlings was higher at 20 °C than at 15 °C. Rapid nymphal development of the RSV-infected SBPH with higher RSV transmission rate at high temperature is considered to be related to the geographical shift of RSV hotspots from the southeastern to the western coastal regions of Korea.

Pupation site selection behavior of Plodia interpunctella (Hubner) in response to its larval parasitoid, Bracon hebetor Say, was evaluated. Under the presence of the parasitoid, more moth larvae pupated in a layer deeper than 5 mm. Because the parasitoid searched for the host mostly in the surface layer (< 5 mm), larvae in deeper layers were able to successfully escape attack by the parasitoid. However, this behavior did not affect the numerical response of the parasitoid. The parasitoid laid more eggs per host larvae when the number of attacked larvae decreased.

In this study, we determined the effect of controlling rice weevils on the mycoflora of stored brown rice by using Anisopteromalus calandrae (Howard), a parasite of the rice weevil. The mycoflora in brown rice with the parasitoid was similar to that without the parasitoid; however, the dominant mold species differed. Without the parasitoid, Aspergillus candidus Link and Penicillium islandicum Sopp were the dominant species, whereas Aspergillus penicilloides Speg. and P. islandicum were dominant when the parasitoid was present. The difference appeared to be due mainly to the difference in the grain moisture content with and without the parasitoid. A. candidus was the dominant species in the communities without the parasitoid and was not observed when the weevils were suppressed. P. islandicum dominated or co-dominated regardless of the presence of the parasitoid which suggested that P. islandicum is tolerant to low grain moisture content or is positively affected by the presence of the rice weevil.

A representative isolate KU53 of the predominant Penicillium species was obtained from rice samples from rice processing complexes of National Agricultural Cooperative Federation in Korea. In this study, isolate KU53 was identified by its morphological and molecular characteristics. The macro- and microscopic characteristics of isolate KU53 were compared with the P. fellutanum reference isolate KCTC16913 on different media; isolate KU53 was generally identical to those of the reference isolate KCTC16913. In a molecular-based identification, the β-tubulin and translation elongation factor 1-alpha sequences of isolate KU53 was most closely related to those of P. fellutanum. Thus, isolate KU53 from stored rice could be identified as P. fellutanum, some isolates of which are known to produce mycotoxin-related metabolites. To our knowledge, this is the first detection of P. fellutanum from stored rice in Korea.

Climate change induces an alteration in the life cycle of many poikilothermic organisms, resulting in changes in the structure and function of communities. Changes in voltinism in the pine moth Dendrolimus spectabilis (Butler), which is known to be univoltine in South Korea, were studied to elucidate the effects of climate change on their voltinism. The developmental stages of the pine moth were evaluated through field surveys, and the developmental rate was estimated at five different temperatures: 17, 20, 25, 28, and 32°C. Field surveys showed that the moths completed two generations per year, indicating that the phenology of the pine moth in this area had changed from univoltinism to bivoltinism. Laboratory experiments showed that increasing the temperature could induce a change in voltinism in the pine moth population. Generations of the bivoltine population displayed phenotypic plasticity: the fitness of the first generation was greater than that of the second generation with regard to size and fecundity. The difference in fitness between the first and second generations could be due to the influence of factors such as low food quality and heat stress on the second generation. Therefore, changes in thermal conditions due to climate change have offered this species the chance to develop a bivoltine population, but they have also exerted ecological costs, especially for the second generation of the pine moth.

Geographical variation in population dynamics of a species offers an opportunity to understand the factors determining observed patterns of spatial dynamics. We evaluated the spatial variation in the population dynamics of the pine needle gall midge (PNGM), Thecodiplosis japonensis, which is a severe insect pest in pine forests in Korea, and studied the influences of weather factors that could affect its population dynamics. Results revealed that PNGM population dynamics were classified into five clusters based on the analysis of autocorrelation function and self-organizing map, which is an artificial neural network. We also quantified spatial synchrony in the population dynamics of PNGM using the nonparametric covariance function. Variation in spatial synchrony was strongly related to differences in maximum temperature and precipitation in Random Forest analysis, suggesting that the synchrony in PNGM population dynamics is largely the result of the Moran effect. In addition, spatial differences in population dynamics could be influenced by transient process of synchronization following invasion. Finally, the present results indicate that differences in population dynamics can be induced by interactions among several factors such as maximum temperature, precipitation, and invasion history of species.

We evaluated microbial populations and aflatoxin production in unhulled and white rice from rice processing complexes of the National Agricultural Cooperative Federation in five regions in Korea and identified three predominant Aspergillus species. Fungal and bacterial populations in rice samples were significantly different between regions in 2007. Aflatoxins were also detected and varied at the levels of 2.45 - 3.43 ng per g unhulled rice grain and 1.29 - 2.09 ng per g white rice grain. Unhulled rice generally detected higher level of aflatoxins than white rice regardless of sampling regions; however, no significant differences were found in Anseong and Cheonan in 2005 and Cheonan and Gimpo in 2007. Aflatoxin production between sampling regions was not different regardless of rice type and sampling year. Although the fungal diversity was highly distinct from region to region, three Aspergillus isolates were predominant in the rice samples; thus, representative isolates AC317, AF57, and AF8 were selected and identified based on their morphological and molecular characteristics. Consequently, isolates AC317, AF57, and AF8 were identified as A. candidus, A. flavus, and A. fumigatus, respectively. These fungi can produce mycotoxins that are harmful for consumers and thus it is important to detect and reduce the population of storage fungi in rice.

This paper presents sequential sampling plans for evaluating the pest density based on complete counts from probe in a rice storage warehouse. Both maize weevil and Indian meal moth population showed negative binomial dispersion patterns in brown rice storage. For cost-effective monitoring and action decision making system, sequential sampling plans by using the sequential probability ratio test (SPRT) were developed for the maize weevil and Indian meal moth in warehouses with 0.8 M/T storage bags. The action threshold for the two insect pests was estimated to 5 insects per kg, which was projected by a matrix model. The results show that, using SPRT methods, managers can make decisions using only 20 probe with a minimum risk of incorrect assessment.

In this study, we assessed the interaction occurring between the rice weevil and two storage molds (Aspergillus candidus Link and Aspergillus niger Van Tiegem) that prefer different moisture regimens under rice storage conditions. Rice weevil induced rapid population growth in both of the storage molds. The colony forming units (CFUs) of A. candidus and A. niger peaked at 10(9.00 +/- 0.02) and 10(7.72 +/- 0.03)/g, respectively. All of the rice grains were infested with the molds and eventually deteriorated; in the jars infested with A. candidus, no living weevils were found after 135 d. Suppression of the rice weevil by its larval parasitoid, Anisopteromalus calandrae (Howard), significantly retarded the growth of A. candidus but completely halted the growth of A. niger, which was replaced by xerophyllic molds including Aspergillus penicilloides Spegazzini and Wallemia sebi (Fries). Regression analyses showed that the total number of weevils was a significant factor explaining grain moisture content, which was in turn a significant factor in the growth of both mold species. The growth of A. niger was dependent on the grain moisture content (r2 = 0.52), thereby suggesting that the growth of A. niger was caused primarily by activity of the rice weevil and the resulting increased grain moisture content. However, 27% of the growth of A. candidus was explained by grain moisture contents, suggesting that a factor other than the grain moisture content may also affect its growth. Suppression of rice weevil by A. calandrae could induce an A. candidus-dominant molds community, which would be a factor for consideration in biological control program.

We have previously obtained a representative isolate KU101 of the predominant Penicillium species from rice under indoor storage conditions. In this study we attempted to characterize isolate KU101 using its morphological and molecular characteristics. When the micro- and macroscopic characteristics of isolate KU101 were compared with the P. islandicum reference isolate KCCM 34763, isolate KU101 was generally identical to those of isolate KCCM 34763, however, isolate KU101 grew faster and produced more orange to red pigments than isolate KCCM 34763. In a molecular-based identification, the nuclear sequence of the ITS1-5.8S-ITS2 region of isolate KU101 was most closely related to that of P. islandicum. Therefore, these results indicated that isolate KU101 from stored rice could be identified as P. islandicum, some isolates of which are known to produce mycotoxins.

Host-size related feeding and oviposition behaviour, and allocation of progeny sex by Anisopteromalus calandrae (Howard) were tested on Sitophilus oryzae L. The parasitoid showed a host-size-dependent partition of feeding and oviposition behaviour, preferring small hosts for feeding, but large hosts for oviposition. Neither the mutual interference nor the host density showed any effect on the behaviour of the parasitoid. Allocation of progeny sex by the female parasitoid appeared to be based more likely on absolute than on relative host size encountered. A model for the progeny sex ratio was constructed based on: (1) ovipositional preference of the parasitoid on large hosts; (2) feeding preferentially on small hosts; and (3) host-size-related regulation of progeny sex ratio. The progeny sex ratio of the parasitoid predicted by the model was in close agreement with the observed value.

This research was conducted to evaluate fungal and bacterial populations in unhulled and brown rice under indoor storage conditions, and to examine the relationship between microbial populations and environmental conditions such as temperature and relative humidity. The temperature and relative humidity of the storage room ranged from and 23.3% to 44.2%, respectively. Total fungal and bacterial populations remained relatively stable over the storage period. Predominant fungi included Aspergillus candidus, A. flavus, A. fumigatus, and Penicillium spp.; the predominant bacteria were Bacillus, Microbacterium, Sphingomonas, and Methylobacterium spp. Total fungi and bacteria were not significantly correlated with either unhulled (r

The biology of indian meal moth and maize weevil on the trehalose gene introduced rice (var `Nakdong`) (T-Nakdong) was compared to that on the rice without gene introduction (Nakdong) at . Development of the both two insects was significantly delayed; on T-Nakdong, the developmental periods of female moth and weevil were , respectively. Whereas those on Nakdong were , respectively. Net reproduction rate of Indian meal moth on T-Nakdong was significantly lower than that on Nakdong , due to the lower emergence rate . The life table statistics of maize weevil on T-Nakdong was estimated to be similar to those on Nakdong. The delayed development of T-Nakdong suggested that the factor for development of the insects could be changed by the introduction of trehalose gene into the rice variety.

The demography of Paronychiurus kimi , a dominant collembolan in paddy fields of Korea, was quantified for four treatments of the herbicide paraquat (0, 1.6, 16, 160 and 1600 μg/cm 2 ) in a controlled environment using plaster-of-Paris as the test substrate. The survival rate of adults and the reproductive fitness of P. kimi were not affected by paraquat except at the highest dosage (1600 μg/cm 2 ), when fed baker's yeast and reared on plaster–charcoal substrate. However, results of life-history experiments suggest that fitness was maintained by a tradeoff between fecundity and reproductive period. It is suggested that these are potential life-history tradeoffs of Collembola that were exposed to the manufacturer's recommended concentration of paraquat (16 μg/cm 2 ).

Functional Analyses of Three Gα and One Gβ Subunits in Gibberella zeaeComparison between Wild Strains of Pitoporus betulinus Collected from a Single TreeEcological Study of Sparassis crispa in Gwan...

The heterogeneous physico-chemical properties of soil make it difficult to normalize the toxicological effects of metals in the Collembolan species Paronychiurus kimi (Lee). Furthermore, the physico-chemical properties of soil themselves can function as limiting factors that affect population fitness. In this study, the effects of soil organic matter (OM) and pH on the biological performance of P. kimi were assessed, and the influence of these properties on cadmium toxicity to P. kimi was also assessed at the individual and population levels. The OM and pH were found to significantly influence offspring production. All toxicological values of cadmium to P. kimi showed consistent patterns of increase with increasing OM and pH values, implying a decreased toxicity. The 28-d LC50 values varied from 34.9 to 115.9 mg/kg, and the 28-d EC50 and 28-d ri=0 also varied depending on the OM and pH values. These findings indicate that the OM and pH values themselves are important factors in determining not only the biological performance of P. kimi but also the toxicity of cadmium to P. kimi on the individual and population levels. Therefore, when ecological risk assessments are conducted for a certain soil, pre-examinations of the effects of abiotic factors and the selection of an appropriate endpoint must be accomplished before establishing levels of chemicals of concern (COC) for a certain species.

The invertebrate springtail species Paronychiurus kimi (Lee) was selected for use in toxicity testing because it is more ecologically relevant to Korean soils than Folsomia candida Willem, which is the standard animal for toxicity tests. Responses of P. kimi to cadmium, mercury and lead were evaluated in artificial soils following the standardized ISO protocol. Although, reproduction of P. kimi was not as high as that of F. candida , 30 adults produced at least 200 juveniles over 28 days. For each of the three heavy metals, LC 50 and EC 50 for reproduction and NOEC and LOEC for the effect on reproduction and instantaneous rate of population increase ( r i ) were also estimated. The 7 days LC 50 was 532, 3.9 and 1322 mg/kg dry soil for cadmium, mercury and lead, respectively. As exposure time increased from 7 to 28 days, the LC 50 values decreased for cadmium but not or only slightly for mercury and lead. The 28 days EC 50 was 60.0 for cadmium, 0.23 for mercury and 428 mg/kg for lead. Significant changes in r i of P. kimi were closely followed by the changes in the sublethal endpoint measured (reproduction) and populations were heading toward extinction ( r i = 0) at concentration of 129, 2.0 and 1312 mg/kg dry soil for cadmium, mercury and lead, respectively. P. kimi was found to be more sensitive to all heavy metals tested than F. candida , confirming its suitability as a bioindicator species for soil toxicological testing in Korea.

Notes on Three Species of the Genus Euphoriomyces (Laboulbeniales) from KoreaTaxonomic Studies on Myelochroa from KoreaMolecular Analysis of Korean Anzia opuntiella (Lichenized Ascomycota) Based on...

Stored cereal crops form the major component of the world's food supply. It is well known that post-harvest crop losses, due to insects and microbes, cause significant economic waste in both developed and developing countries. In general, the environment in storage facilities is prone to rapid pest development, leading to significant grain losses. Rice weevil (Sitophilus oryzae L.) is one pest of cereal crops that deposits its eggs on or in a seed. To detect rice weevil in stored rice, we developed PCR-based molecular markers of Sitophilus oryzae. Several sets of PCR primers from the ‘internal transcribed spacer 2’ gene of S. oryzae were analyzed to identify molecular markers that are specific to the S. oryzae genome. Among six sets of molecular markers identified, three were found to be useful for identifying rice weevil. Our results demonstrate that a PCR marker system permits rapid and reliable identification of weevil in stored grain. Furthermore, this PCR assay would expand the choice of too...

The effect of soil moisture on population dynamics of Paronychiurus kimi (Collembola) was examined by combining an empirical soil moisture model with a temperature-sensitive, stage-structured population model. Field observations of soil temperature were used to drive the population model, and simulations were compared to field observations of juvenile and adult densities. Simulations without soil moisture effects produced stable, interyear population dynamics and a significant correlation between simulations and observations (n=12, r 2=0.40, P

The ability of Bracon hebetor Say, a larval parasitoid of certain stored product moths, to suppress a Plodia interpunctella (Hlibner) population was studied in differing rice products. The larvae of P. interpunctella gathered on the topmost layer of the experiment cages filled with rice product (less than 3 cm in depth), and were rarely observed in deeper depths (deeper than 3 cm). Without P. interpunctella, B. he-etor did not show a preference for any of the three types of milled rice products used. In rice flour, the searching behavior of B. hebetor for P. interpunctella was limited, apparently due to the thick webbing pro-uced by the moth larvae. B. hebetor suppressed P. interpunctella population successfully in cracked rice kernels, but failed to suppress the moth population in rice flour. In whole rice kernels, B. hebetor suppressed the moth population only when the volume of rice in the cage was large enough to support a high population density of P. interpunctella (2.4 kg/cage). Success and failure of B. hebetor to suppress the moth population in the three different rice products are discussed in relation to the larval webbing and intraspecific com-etition of P. interpunctella larvae.

The host quality model for explaining the sex ratio of progeny of hymenopterous parasitoids was tested with Anisopteromalus calandrae (Howard) parasitizing Sitophilus oryzae (L.). The life span of females and males did not show any influence of body size: 15.3 ± 6.14 and 15.9 ± 4.16 d for females of small and large size, and 5.4 ± 1.90 and 6.0 ± 2.30 for males. However the reproduction rate of large females was twice as high as for small females (80.9 ± 5.78 versus 37.4 ± 3.16). Large males mated with twice as many females as did small males (19.2 ± 3.8 versus 8.1 ± 3.8), suggesting that females do not gain greater fitness by being large than males. In a system in which the parasitoid was permitted to search among randomly dispersed host patches, large females showed a higher net reproduction rate than small females. This was not influenced by the size of male the females mated with: 132.8 ± 9.81 and 132.5 ± 7.41 for large females mated with large and small males, respectively, and 70.4 ± 13.72 and 54.07 ± 6.17 for small females mated with large and small males. The size-dependent dispersal ability among host patches of females, which is the active dispersal sex, is another factor that influenced oviposition behavior of A. calandrae, which assigns daughters on large hosts and sons on small hosts.

A matrix model for the population dynamics of Paronychiurus kimi in the field, based on life table statistics of P. kimi in a laboratory at constant temperature under optimum environmental conditions is described. The temperature-dependent development and fertility schedule of P. kimi were estimated in terms of degree-days (for temperatures ≥ 7.83 ◦ C). The model simulates reasonably accurately the seasonal fluctuation of P. kimi in Ichon, Korea. It predicted a significantly higher density than that observed in the field between mid April and early June, when the soil moisture content was lowest and with high variance. Our results suggest that soil moisture content is the limiting factor suppressing the population below the density level predicted. The validity of the model as a standard phenology of P. kimi in the field is discussed, including the capability to account for factors other than temperature. © 2002 Elsevier Science B.V. All rights reserved.

Egg dispersion and the sex ratio of progeny were studied in relation to the host density of the parasitoid, Bracon hebetor Say, infesting larvae of Plodia interpunctella (Hubner). Females appeared to allocate eggs in relation to host density to avoid laying more eggs than could complete development on a host. The dispersion pattern of the parasitoid ovipositions among hosts was influenced by host density. Multiple visitations and ovipositions by females on hosts caused a highly aggregated pattern at low-host densities. Hatch rate of eggs decreased as the number of eggs on a host increased. Females seemed to regulate progeny sex ratio (male/total) based on the number of eggs on the hosts and the clutch size of the hosts they encountered. However, the overall progeny sex ratio remained at approximately 0.5 regardless of host density, probably because the allocation of eggs was related to host density.

Regulation of progeny sex by Anisopteromalus calandrae (Howard) in relation to host preference, host vulnerability and host size was studied with two host species, Sitophilus oryzae (L.) and Callosobruchus chinensis L. A. calandrae preferred S. oryzae to C. chinensis (preference index = 0.87). The progeny sex ratio (females/total) was significantly higher on C. chinensis, the less preferred host, than on S. oryzae regardless of the instar age of the two host species. A. calandrae could locate only a few young larvae of C. chinensis (≤third instar), which could be apparently due to the low vulnerability of the young larvae locating deeper in the adzuki bean kernels. The larval instar age of Sitophilus oryzae affect the progeny sex ratio of A. calandrae, but that of Callosobruchus chinensis did not except invulnerable ones. The progeny sex ratio of A. calandrae produced from C. chinensis, ranged from 0.66±0.05 to 0.82±0.02. The invulnerability of the young larval instar of C. chinensis and regulation of the progeny sex ratio by A. calandrae based on host size in a manner of absolute rule could explain the higher sex ratio on the young larval instar of C. chinensis, less preferred and less vulnerable host, than the old larval instar of S. oryzae, highly preferred host. The differences in host vulnerability could be another factor for A. calandrae assigning progeny sex ratio.

Summary We studied the influence of temperature, soil moisture content, and nutrition level on the biology of Paronychiurus kimi (Lee). The hatchability and juvenile survival rate were not related to temperature in the range tested from 17 °C to 28 °C. The juvenile developmental rate increased linearly as the temperature increased up to 28 °C, and the lower threshold temperature for development of P. kimi was estimated to be 8.6 °C. The intrinsic rate of natural increase ( r m ) increased with increasing temperature up to 25 °C, but reduced beyond that temperature. An empirical nonlinear model describing the relation between temperature and r m suggests that a P. kimi population is able to develop in the temperature range of 7.9 °C – 30.3 °C, with an optimum at 25 °C. The soil moisture content and nutrition level significantly affect the reproduction of P. kimi . The P. kimi population is unable to increase at 10% soil moisture content except when the springtail is provided with large amounts of yeast. This suggests greater tolerance of well-fed springtails to low soil moisture. Based on this study, we discuss the seasonal fluctuation of the P. kimi population in a rice paddy field.

Intraspecific competition among larvae of the indianmeal moth suggested a scramble-like competition. The number of female moth progeny was inversely proportional to the female moth introduced. When the moth occurred together with the rice weevil, significantly more female progenies were produced, suggesting that severity of the larval competition be reduced by the rice weevil. The impacts of the rice weevil on the moth population were discussed briefly in the context of interspecific competition between the adult rice weevil and young moth larvae.

A phenology model of Indianmeal moth, Plodia interpunctella (Hubner), was constructed to predict the moth emergence in stored product storage. The moth emergence curve based on the physiological time (summation of developmental rate per day) could be well described by both Weibull function and Stinner function. The phenology on the basis of the models showed that the moth could have five to six generations per year, which agreed to the trends of the moth catch in the warehouses in Ansung and Taegu. The phenology model on the basis of Weibull function predicted generations with no overlap except of the first and second generations, whereas Stinner model showed generations with overlap. Although the moth generations overlapped, the peak time of the moth catch in the pheromone traps coincided with that predicted by the model on the basis of Weibull function. The results showed a possibility that continuous monitoring of temperature in a storage and prophylactic control of the moth on the basis of the phenology model could be a base of successful eradication of moth from stored food materials.

Life history of Bracon hebetor Say was studied on Plodia interpunctella Hubner. The life span of female (mean±s.e.) was estimated to be 20.88±0.97 days. The females laid eggs from the first day on after emergence and the oviposition period ranged from 11 to 27 days. But 65% of the total eggs were laid in the first 10 days. The progeny sex ratio (female/total) in the first 15 days was female-bias ranged from 0.51±0.08 to 0.88±0.02, but changed into male-bias ranged from 0.14±0.04 to 0.34±0.12. The overall sex ratio of progeny produced per female was estimated to be 0.66. Total number of progeny per female and net reproduction rate were estimated to be 205.17±13.03 and 136.21, respectively. Other life table statistics were presented.

Stored rice was collected from rice processing complexes of National Agricultural Cooperative Federation of 11 regions in Korea to evaluate the occurrence of fungi and bacteria and to identify the predominant fungi and bacteria to the genus levels. Most rice samples generally produced the higher levels of fungi and bacteria than white rice. The occurrence of fungi and bacteria varied in various locations of Korea. Among fungi observed, Aspergillus spp. and Penicillium spp. were dominant in the samples and Aspergillus spp. were observed more frequently than Penicillium spp. Predominant bacteria from rice and white rice samples tentatively belonged to the Genus Bacillus, Pectobacterium, Pantoea, and Microbacterium according to BIOLOG and FAME analyses. The results of this study showed that rice in Korea was contaminated in a relatively high level by two dominant storage fungi such as Aspergillus spp. and Penicillium spp. In addition, occurrence of mycotoxins in rice by the fungi could be possible and thus it is necessary to control the storage fungi.

Influences of the spatial distribution of resource patches on the host-parasitoid system (brown rice patch - rice weevil - Anisopteromalus calandrae ) dynamics and stability in patchy environment were studied with a biological model system. When the 40 resource patches (each containing 5 g of brown rice) were contagiously distributed among 453 empty patches, the host population increased logistically and then fluctuated at an equilibrium level about 5,000. However, when the resource patches were randomly distributed, the host population showed a cyclical fluctuations in the range from 532 to 7089 with significant delayed density-dependence. Distribution of resource patches affected the distribution of hosts among resource patches, which could be a reason for the different features of population dynamics in the two system. In both resource patch distribution systems, the interactions between host and parasitoid populations could be persistent and maintained at an equilibrium level with oscillatory damping. The equilibrium level in each system was far below than that in the system without parasitoid, suggesting that the parasitoid did regulate the host population. However, overall mortality of host due to the parasitism was host density-independent in the contagious system or inversely host density-dependent in the random system. Therefore, the regulation seemed due not to overall host density-dependent parasitism, but rather to the indirect effect of the parasitoid leading the host population to be highly aggregating to some resource patches, which, in turn, resulted in stronger intraspecific competition. The key factor in regulation of the host population was estimated to be intraspecific competition in the contagious resource patch system, whereas it was parasitism in the random patch system. The persistence and stability of host-parasitoid population interaction, the role of parasitoid in the interaction and the resulting equilibrium level were discussed with reference to the resource patch distribution.

We studied intra- and interspecific competition among 2 parasitoids [ Anisopteromalus calandrae (Howard) and Lariophagus distinguendus (Forster) (Hymenoptera: Pteromalidae)], which attack the rice weevil, Sitophilus oryZae (L.). As the intraspecific density of the parasitoids increased, the search rate per female and rate of population increase of A. calandrae decreased curvilinearly, suggesting a type of contest-like intraspecific competition. The other parasitoid, L. distinguendus , seemed to exhibit a type of scramble-like intraspecific competition; as long as the number of hosts available was not severely limiting, the search rate and rate of population increase of the parasitoid were not related to the intraspecific density of parasitoids. Statistics estimated for the interspecific competition model suggested that A. calandrae was the dominant competitor and could displace L. distinguendus . However, under conditions of interspecific competition, the 2 species of parasitoids coexisted until the rice weevil population was completely suppressed. This apparent coexistence seemed to be possible because of the differences in the type of intraspecific competition exhibited by the 2 parasitoids.

Biological control of rice weevil, Sitophilus oryzae (L.), and Indianmeal moth, Plodia interpunctella (Hubner), by their parasitoids Anisopteromalus calandrae (Howard) and Bracon hebetor Say was examined while considering the intraspecific competition pattern of the pests. In both experimental and simulation studies, A. calandrae was shown to suppress the rice weevil population, a contest type competitor, regardless of the parasitoid/weevil ratios tested. In contrast, B. hebetor only significantly suppressed the Indianmeal moth, a scramble type competitor, when the parasitoid/moth ratio was >0.05. At ratios lower than 0.05, the role of B. hebetor was negligible, and the correlation coefficients between the number of moths that had emerged and the parasitoid/moth ratio was estimated to be 0.07. The control efficiency of the two parasitoids with respect to the parasitoid/host ratio was estimated using a ratio-response model. To suppress the weevil density to a level that was only 10% of the current density, the ratio was estimated to be 0.02, whereas this value was 0.14 for the Indianmeal moth. However, for the continuous suppression of the Indianmeal moth, periodic and iterative introduction of B. hebetor was required.

The effects of oviposition behavior of Callosobruchus chinensis (L.) on life table statistics of progeny and on attack by the larval ectoparasitoid Anisopteromalus calandrae (Howard) were studied. As the number of eggs per seed increased, larval development time and survival rate decreased. Differences in mortality between treatments was caused largely by competition in the late instars. Life table statistics showed an inverse linear relationship to the number of eggs per seed. Depositing one egg per seed increased progeny production by ≈56% compared with six eggs per seed. The functional response of A. calandrae showed a linear relationship with host density in the range of 1–64 per 100 seeds. The parasitoid searched for its hosts more efficiently when the number of eggs per seed increased from one to four; search rate of the parasitoid based on random search increased from 0.045 ± 0.013 (mean ± SEM) to 0.154 ± 0.025. The results indicate that ovipositing fewer eggs per seed is also a good defense tactic for the weevil against the parasitoids. Whether parasitoids or larval competition selected the oviposition behavior is not yet clear. However, the influence of natural enemies should be studied further to understand the evolutionary process of the weevil's oviposition behavior more precisely.

In four mixed media composed of (1) brown and polished rice, Oryza sativa L., (2) brown and rough rice, (3) polished and rough rice, and (4) brown, polished, and rough rice, feeding and oviposition of the rice weevil, Sitophilus oryzae (L.), were observed. In all media, the weevil rarely exploited rough rice. The rice weevil fed on brown rice more frequently than on polished rice, but did not concentrate on brown rice in the media containing both brown and polished rice. The feeding preference index for brown rice over polished rice was ≍1.9. Females laid more eggs on brown rice than on polished rice. In the media containing both brown and polished rice, females laid eggs exclusively on brown rice; the preference index for brown rice over polished rice was ≍19.3. Mortality of the weevil during development in the medium without brown rice was significantly higher than in the media with brown rice. Life table statistics for the weevil in the four media showed that brown rice was the critical factor determining population development. Thus, the weevil's strong oviposition preference for brown rice allows it to maximize its fitness when feed with a variety of resources of different qualities. The relative impact of oviposition versus feeding preferences of the weevil on its reproductive success is discussed.

In this study, we assessed the interaction occurring between the rice weevil and two storage molds (Aspergillus candidus Link and Aspergillus niger Van Tiegem) that prefer different moisture regimens under rice storage conditions. Rice weevil induced rapid population growth in both of the storage molds. The colony forming units (CFUs) of A. candidus and A. niger peaked at 10(9.00 +/- 0.02) and 10(7.72 +/- 0.03)/g, respectively. All of the rice grains were infested with the molds and eventually deteriorated; in the jars infested with A. candidus, no living weevils were found after 135 d. Suppression of the rice weevil by its larval parasitoid, Anisopteromalus calandrae (Howard), significantly retarded the growth of A. candidus but completely halted the growth of A. niger, which was replaced by xerophyllic molds including Aspergillus penicilloides Spegazzini and Wallemia sebi (Fries). Regression analyses showed that the total number of weevils was a significant factor explaining grain moisture content, which was in turn a significant factor in the growth of both mold species. The growth of A. niger was dependent on the grain moisture content (r2 = 0.52), thereby suggesting that the growth of A. niger was caused primarily by activity of the rice weevil and the resulting increased grain moisture content. However, 27% of the growth of A. candidus was explained by grain moisture contents, suggesting that a factor other than the grain moisture content may also affect its growth. Suppression of rice weevil by A. calandrae could induce an A. candidus-dominant molds community, which would be a factor for consideration in biological control program.

Development of lariophagus distinguendus (Forster) parasitizing fourth instars of Sitophilus oryzae (L.) was studied in relation to temperature. As the temperature increased from 20 o to 32 o C, total developmental period of the female and male parasitoids decreased from 31.0±1.02 to 14.2±0.7 d and from 28.0±1.0 to 13.8±0.8 d, respectively. The developmental period at 34 o C was similar to that at 32 o C. Complete development at 18 o C was significantly inhibited. Males developed faster than females. the relationship was described fairly well by a combination model ; lower and upper thresholds for complete development of female and male were estimated to be 15.1 o and 37.2 o C, and 15.2 o and 38.7 o C respectively

The functional and numerical response of Lartophagus distinguendus (Forster) to various densities of its host (fourth instar Sitophilus oryzae [L.]) were examined under five temperature conditions (20, 25, 28, 30°C, and room temperature). Temperature significantly influenced the relationship between host density and the number of hosts attacked: as temperature increased from 20 to 30°C, the coefficients of determination of the estimated curves increased from 0.26 to 0.65. The relationship between host density and the number of female L. distinguendus emerging was also influenced by temperature; the coefficients of determination of the curves increased from 0.19 at 20°C to 0.70 at 30°C. Search efficiency of female parasitoids seemed unrelated to temperature, but handling time became significantly shorter with increasing temperature from 20 to 28°C and remained at a similar level at 30°C. Results suggested that regulation of rice weevil density by L. distinguendus could be possible in the optimal temperature range (28-30°C) for the development of both insects.

A second-order central composite design was employed to investigate the effect of organic matter (OM) content and soil acidity (pH) on the cadmium toxicity to Paronychiurus kimi (Lee), a collembolan species native to Korea. Two independent variables, OM and pH, were adjusted from 0 to 10% (in total dry wt) and 4.5 to 7.0, respectively. Cadmium concentrations tested were 10, 20, 40, 80, and 160 mg/kg dry soil. The toxic effects that cadmium exerted on P. kimi (28-day median lethal concentration (LC50s)) varied significantly with different combinations of OM content and pH. The second-order response surface model was appropriate for describing combined effects of OM and pH on the cadmium toxicity to P. kimi. Linear effects (OM and pH) were predominant contributors accounting for ≈70% of the total variance of cadmium toxicity to P. kimi. No significant quadratic (pH × pH) and interaction (OM × pH) effects were observed; therefore, the final second-order response surface model could be reduced as follows: 28-day LC50 of cadmium (mg/kg) = –94.87 + 26.69 × OM + 16.64 × pH – 1.82 × OM2. Validation of the developed response surface model using 4 soil media with different OM content and pH resulted in a significant correlation coefficient (R2 = 0.97) between predicted and observed 28-day LC50. Based on physico-chemical properties of the test media, developed models can be used to explain the variation of cadmium toxicities at various environmental conditions and may improve current environmental risk assessment procedures of metals.

The development of Sitophilus oryzae (L.) in relation to temperature was studied on rice. The total developmental periods on rice were similar to those reported on wheat. A model constructed by combinging those of Logan et al. (1976) and Wollkind et al. (1978) provided a good description of this weevil's development throughout the range of lower and upper threshold temperatures. The lower and upper threshold temperatures for overall development of the weevil were estimated to be 15.0° and 34.1°C.

The basic components of the predation ofPhytoseiulus persimilisAthias-Henriot feeding upon eggs ofTetranychus urticaeKoch were studied in an open system where the predator could disperse freely.