The subject of this study was to examine biological aspects and predatory abilities of predatory bugs that prey on stored-product insects. Biological controls in stored products are being regarded with increasing interest since they are nontoxic and do not damage human health or the environment. Several species of predatory bugs have been studied as biological control agents. Specifically, Xylocoris flavipes (Reuter) is the most studied candidate biological control agent among predatory bugs. X. flavipes is advantageous because it has a high population increase capacity and wide distribution. X. flavipes has been reported to suppress populations of small insects, but it can not predate large insects and internal grain feeding insects. As Amphibolus venator (Klug), Peregrinator biannulipes (Montrouzier & Signoret) and Joppeicus paradoxus Puton can attack large insects, more research should be carried out on the suppression effects of these bugs. A combination of several biological control agents that can attack different types of insects will be needed to control whole pest complexes in various stored environments.
Biological soil disinfestation (BSD) is one of the methods for soil disinfestation recently developed and consists of organic amendment, irrigation, and covering the soil surface with plastic film. BSD trials with artificially infested soils effectively killed Fusarium oxysporum f. sp. lycopersici and Ralstonia solanacearum. F. oxysporum f. sp. lycopersici was not detected 9 days after treatment. Application of BSD to R. solanacearum-infested soil decreased disease severity 4 weeks after transplantation. Reduction in soil pH and Eh was observed in the BSD-treated soil. HPLC analysis revealed the accumulation of acetic acid and butyric acid in the soil and the disinfestation effect of BSD was almost reproduced by mixing these organic acids with the infested soil. Volatile compound(s) evolved in the BSD-treated soil was also suggested to contribute to disinfestation. PCR-DGGE (PCR-denaturing gradient gel electrophoresis) analysis revealed the increase in the abundance of several bacteria in the BSD-treated soil, and two of them had 100% similarity with potential organic acid producers, Clostridium sp. and Enterobacter sp.
Rice production is one of the major non-point sources of pesticide pollution in Japan. Monitoring of pesticide concentrations in river systems detected a number of herbicides commonly used in paddy fields, and these concentrations may appear to have adverse effects on the aquatic ecosystem. In this paper, two mathematical models developed in Japan, the PADDY and PCPF models for simulating the fate and transport of pesticides in a paddy environment are introduced. These models have been validated with observed data from laboratory experiments and field monitoring studies. In addition, the application of a mathematical model (RICEWQ) modified in Europe for high tier risk assessment in paddies is provided. We applied the PADDY and PCPF models to controlling pesticide runoff losses from paddy fields and to ecological risk assessment in the aquatic environment. The recommendation from model simulations for reducing pesticide runoff from paddy fields are 1) application of an intermittent irrigation scheme with a high drainage gate and 2) application of a longer water holding period after pesticide application. In order to establish a realistic assessment and management procedure for environmentally-friendly rice production, it is important to develop and validate mathematical models adapted to paddies in the Asian region.
A total of 119 blast (Magnaporthe grisea (Hebert) Barr.) isolates collected from the Philippines, were characterized for their pathogenicities using 19 rice (Oryza sativa L.) differential varieties (DVs) targeting for 18 resistance genes. These isolates were classified into 31 groups based on the reaction patterns to 9 DVs for targeting 9 resistance genes, Pia, Pib, Pii, Pit, Pita, Pish, Piz-t, Pi3, and Piz-5, at first, and then further divided into 70 pathotypes considering the reaction pattern of the other 9 DVs for the other resistance genes, Pik, Pik-h, Pik-m, Pik-p, Pik-s, Pita-2, Piz, Pi1, and Pi20(t). Twenty isolates that have differentiating ability, stable reactions and good sporulating ability were selected. The reactions of these isolates were confirmed using the monogenic lines as a set of DVs for targeting 24 resistance genes, Pia, Pib, Pii, Pik, Pik-h, Pik-m, Pik-p,Pik-s, Pish, Pit, Pita, Pita-2, Piz, Piz-t, Piz-5, Pi1, Pi3, Pi5(t), Pi7(t), Pi9(t), Pi11(t), Pi12(t), Pi19(t), and Pi20(t). Several resistance alleles of Pik locus, Pik, Pik-h, Pik-m, and Pik-p, and Pi1 had the same reaction patterns and could not be differentiated by these selected blast isolates. No avirulent isolate for Pit and Pi19 was found. The three genes, Pish, Piz-5, and Piz, showed a wide spectrum of moderate resistances to these isolates. These findings suggested the existence of a wide variation of blast pathogens in the Philippines. This information on pathogenicity of blast isolates from the Philippines will be also useful to understand the differentiation and relationship between blast races and resistance genes. The monogenic lines as the DVs and the selected 20 blast isolates can be used as the first differential system, which can characterize the resistances of rice varieties and pathogenicities of blast isolates in the tropics.
Rice in storage in Thailand is often infested with stored insect pests. Local rice milling factories in this region are unwalled employing a traditional open-air ventilation system and therefore insect pests easily attack the stored rice. The factories keep the rice for a few months to a year and do not usually clean the premises after the milling operation. The unclean environment becomes a suitable habitat for reproduction of insect pests, and consequently insect infestations on rice increase during storage. We set up two rooms (cleaned and uncleaned) to examine the effect of cleaning on stored rice grains. Bags of paddy, brown and milled rice were placed in the two kinds of rooms for one year to observe population dynamics of the insects and infestations caused by the pests on the rice. We found fewer insects in the milled rice than in paddy and brown rice but suggest that cleaning of the storage premises may decrease grain losses on all the types of rice.
A method to estimate meteorological factors on a 250 m square grid using real-time data from a local weather station network was developed. The method had better precision than an existing one. The 250 m square grid meteorological information was created to cover Memuro City, Hokkaido. The information was used with a wheat developmental model to predict the distribution of wheat maturity days in the city, which had 6, 170 ha of wheat fields and 50 combine harvesters, to support decisions for the best management of the harvesters to avoid damage by preharvest sprouting.
In this study the processes of dissolved organic matter (DOM) adsorption by charcoals and activated carbon were quantitatively evaluated by the adsorption rate model. Five types of charcoal and a commercial granular activated carbon (GAC) were used to remove DOM eluted from rice-straw in an adsorption test. The adsorption rate model was considered as the adsorption process in the early steps which showed significant adsorption changes. The results of the adsorption test indicated that the DOM adsorption rate and volume treated by charcoals carbonized at high temperature (group-2) showed significantly higher levels than those of charcoals carbonized at low temperature (group-1). Although group-2 adsorbed less DOM than GAC after 6 hours, the adsorption rate and adsorbed volume of group-2 were greater than those of GAC under 6 hours. The results of the evaluation by the adsorption rate model showed that the calculated value agreed well with the measurements obtained from the adsorption test. It was suggested that DOM could move to the adsorption surface of group-2 more rapidly than that of the GAC in the early adsorption process. In the latter process the volume of DOM adsorption from sample water treated by group-2 was exceeded by that of the GAC which has a large specific surface area. The DOM adsorption processes depended on the specific surface area of charcoals/GAC as well as the DOM transfer rate and desorption.
To recover fish habitats and restore rich biota in rural areas, we evaluated the habitat potential for field gudgeon Gnathopogon elongatus elongatus, a representative species in rural areas, in non-improved drainage canals with soil and improved drainage canals having concrete walls but with a soil bottom in Yatsu paddy fields of the Shitada-gawa River basin, Chiba Prefecture, Japan, using habitat suitability indexes (SI). SI relations for water depth, water velocity, water width, substrate, and vegetation covering for life stages of the fish were developed using field research data collected from July 2002 to June 2004. The composite suitability indexes SIdepth × SIsubstrate × SIwidth (larvae), SIdepth × SIvelocity × SIwidth (juvenile) and SIdepth × SIsubstrate × SIvegetation (adult) were adopted statistically for calculation of the habitat potential (HP), expressed by a dimensionless weighted usable area. The values of HP varied monthly, but did not show significant differences between non-improved and improved canals for all life stages. This result showed that the improved canals were not inferior in producing fish habitats when compared with the non-improved canals. Also, it was clarified that the improved canals could even be used as alternative habitats to give temporary refuge to the fish, when a canal in this basin was being modified.
Radon-222 (222Rn) concentration in surface water is a useful indicator for groundwater seepage. However, the natural concentration of 222Rn in surface water is too low to measure. It is therefore necessary to concentrate 222Rn content in water samples before analysis. This is a difficult operation requiring specialized equipment. We developed a method of measurement of 222Rn concentration in surface water (a method to concentrate radon by air-circulation) and applied it to detect groundwater seepage in the Ban Phai subwatershed, northeast Thailand. We also measured electric conductivity to determine whether dissolved ions in water were brought by groundwater. In areas of high-elevation (>180 m above sea level), 222Rn concentration in surface water was low, indicating that the velocity of subsurface water flow was slow even in the rainy season. This result supported a flow velocity previously calculated from the permeability of surface soil and the hydraulic gradient. Our measurements of 222Rn concentrations revealed that groundwater can be obtained by digging to a depth of about 1 m in the river bed in some areas. In areas of low-elevation (<160 m above sea level), electric conductivity increased markedly in the dry season. This was attributed to evaporation, rather than the effect of groundwater seepage, because the 222Rn concentration was low, suggesting little influence of groundwater.
We studied the soil water dynamics of the humid tropics at a 1.6-ha Acacia mangium stand in Sabah State, northern Borneo, to quantify the effect of landscape position and vegetation on soil water conditions. We monitored the volumetric soil water content (VSW) at a depth of 30 cm at 12 locations in the research plot, every 30 min for 1 year using ADR theta probes. To analyze the drying process, twelve events were selected in the course of the research period when comparatively long intervals without rainfall occurred. The decline in soil water during the drying periods fit linear regressions well when we excluded the data from the first 24 h after the last rain event. The absolute value of the slope of the regression was termed the drying rate (DR). Topographic index, described as ln(α/tanβ) (α = upslope contributing area per unit contour; tanβ = local slope angle) was also determined. The range of the VSW in bottomland was smaller than for other landscape positions, but no significant relationship was observed between the topographic index and the VSW. The median DR was significantly correlated with tree density, and with the topographic index. During a drying period, evapotranspiration was the major factor controlling the soil water regime in this stand. The normalized DR according to tree density was significantly lower in the bottomlands, and described the wet gleyic characteristics of the bottomland well. The DR appeared to be a good indicator for detecting the effects of vegetation and topography on soil water conditions in the humid tropics.