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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.

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.

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.

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.

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.

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.

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.