Attempt to practically use a lactic acid bacterial strain, SP 1-3, for making good quality silage in Thailand

Feeding of good quality silage (GQS) throughout the year is a suitable way to stably increase raw milk production in spite of its not being in wide use in Thailand. However, making GQS in Thailand is not always ensured if ensilage depends on natural fermentation. Therefore, lactic acid bacteria (LAB) strains to make GQS were screened, and strain SP 1-3 was selected. 　　For the practical use of this strain, a culture method for harvesting large numbers of LAB cells in a low-cost and convenient way was examined, and a culture medium composed of materials that are readily available in Thailand was designed. The medium designed here consisted of molasses 2.0%, rice bran 0.5%, yeast extract 0.2%, and mineral mixture (pH 6.5), and gave a cell mass of 109 cfu/ml after 24 h culture at 35˚C. The cost of this medium was calculated at about 23 yen/L, about 1/60 of that of MRS broth. A silage inoculant (spray-dried granule) from strain SP 1-3 cultured using this medium was prepared for trial. This granule was stable and kept a living cell count of 108~9 cfu/g under storage at 4˚C for 28 days, as shown in Table 1, and reliably improved the fermentation quality of Napier grass silage prepared beforehand in the laboratory. To use these granules for the preparation of practical-scale silage, a low-cost and convenient method of increasing the cell mass of the LAB strain at farm level was developed using a 5-liter plastic drinking water bottle. LAB cell counts in the water (4.5 L), in which had been suspended 45 mg of granules together with the abovementioned medium, rose to 3.85 x 109 cfu/ml after culturing for 24 h. This LAB liquid (4.5 L) is ideal for preparing 4.5 ton of GQS. The additional cost using this system was calculated to be about 50 yen/ton. 　　Based on these results, Pangola grass and Erianthus silages inoculated with the LAB liquid were prepared on a practical scale. After being kept at 30~35˚C for 90 days, the silage pH, the organic acids and volatile basic nitrogen (VBN) content and microbial cell counts were examined. The results are shown in Table 2. Compared with silage without inoculation of LAB, the fermentation quality of silage inoculated with LAB liquid was improved as shown as pH reduced to below 4, increased lactic acid content, and reduced VBN content. These improvements were particularly notable in Erianthus silage. However, the yeast cell count was not reduced by inoculation with LAB. Abundant yeast cells in silage prepared in Thailand were hitherto known, and this trend was marked in the case of Pangola grass silage in this experiment. Abundant yeast cells in silage leads to the outbreak of aerobic deterioration after opening the silo. However, silage pH 48 h after opening the silo rose to almost neutral while the pH was about 3.5 on initial opening. 　　In addition, the palatability of silage inoculated with LAB was compared with non-inoculated silage by the cafeteria method using Brahman steers and native Thai steers. However, no significant difference in intake amount was seen between both types of silage (data not shown). (S. Ohmomo)

Table 1.  Variation in the survival of the cells in granules prepared from strain SP 1-3. Table 2.  Fermentation quality of practical-use silage inoculated with LAB strain SP 1-3.

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The impacts of climate change on the world food market: Mid-term analysis using International Food and Agricultural Policy Simulation Model (IFPSIM)

Global warming caused by concentration of carbon dioxide in the atmosphere will be a major issue in world food markets over the next century. Agricultural production will be affected by climate change, such as rising temperatures or droughts, mainly through changes in crop yields. Environmental changes in a particular country or region will affect agricultural production in other countries or regions indirectly through the trade of food products. Thus, it is likely that climate changes, such as global warming, will cause drastic changes in agricultural markets. This research examines the possible impacts of global warming on world agricultural product markets using IFPSIM, the world food model of JIRCAS. 　　Rainfall and temperature affect crop production. It is assumed that only yield is affected by these climatic variables. The following double-log form yield function is estimated as lnYH t = a + b 1T + b 2 ln PRC t + b3lnTMPt , where YH is yield, T is the time trend, PRC is rainfall measured in millimeters, and TMP is temperature measured in degrees Celsius. The difference function is estimated if the probability that the yield data is non-stationary is higher than ten percent. 　　The rainfall and temperature data are the average values from the Global Historical Climatology Network (GHCN). The climate variables are based on monthly data on the flowering or silking season of each crop. The year term of the estimation period is from 1961 to 2000. Large countries are divided into regions based on the cropping map. The crops in the model are wheat, maize, other coarse grains, rice, and soybeans. The other coarse grains include barley, rye, oats, millet, and sorghum. The yield and production data for each crop is that of Food and Agriculture Organization of the United Nations (FAO)-STAT. The base year of the simulation is 1998 and the term of the projection is from the base year to 2025. 　　The assumptions of the simulation are as follows: (1) the cropping calendar is fixed, (2) the area available for cropping is fixed, (3) the climatic variables directly affect only yields, (4) the temperature measured in degrees Celsius of all countries and regions increases 0.05% per year, and (5) all other parameters are fixed. 　　Table 1 shows the results of the estimation. The parameters are the elasticities of yield for rainfall and temperature. The results show that rainfall has a significantly positive effect on the production of maize and other coarse grains. On the other hand, higher temperatures have a negative effect on the production of most crops except for rice. Figs. 1 and 2 show that the growth rates of production in different countries between 2005 and 2025. Wheat production in the USA will increase due to falling production in other countries. The production of rice in the USA will sharply decrease while that in Japan, South Korea, and many developing countries will increase. Fig. 2 shows that the world production of most farm commodities will not be severely affected by high temperatures, even though each country will be affected by climate change. This is because the sign of elasticity is different for each country, as seen in Table 1. Rice production, however, will be significantly affected by climate change, largely because of the sharp drop in rice yields and production in the USA and South Asian countries. 　　While the scenario is fairly simple (temperature increases 0.05% per year for all countries, or about 0.2 ˚C over the next twenty years), drastic changes in crop production are seen in some countries. Countries that suffer severe damage due to higher temperatures may need to consider changes in cropping patterns and practices.          (J. Furuya)

Table 1. Elasticity of yields for climatic variables. Fig. 1. Growth rate of production in the USA. Fig. 2. World growth rate of production.

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Utilization of sugarcane silage as feed for beef cattle in Northeast Thailand

　　Northeastern Thailand is the biggest region of beef cattle production in Thailand. Most beef cattle are raised on small mixed farms. It is generally recognized that the shortage of forage in the dry season is the chief factor limiting beef cattle production in the region. Additionally, hay and silage preservation is not easy, because of frequently unsuitable weather for forage drying during the rainy season and low fermentable substrate content in tropical grasses for silage fermentation. Sugarcane, which is planted widely in this region, has high amounts of fermentable substrates, i.e., sugars, and gives high yields. Therefore, there is the potential for preparing reliable and high-quality silage that will provide a steady supply of food throughout the year. This study aimed to make and evaluate sugarcane silage, and to investigate the effect of sugarcane feeding on growth performance in beef cattle.

　　 Pangola grass (Digitaria eriantha), which was cut at early bloom, and sugarcane, which was harvested at around six months after regrowth, were chopped and ensiled in plastic bags, then evaluated for their chemical components and quality six months later. Crude protein content in sugarcane silage was lower than that in pangola grass silage (Table 1). On the other hand, the lactic acid content was higher for sugarcane silage than pangola grass silage, and pH and spoilage ratios due to molds were lower for sugarcane silage than pangola grass silage. These results show that the fermentation quality of sugarcane silage was higher than that of pangola grass. Total digestible nutrient content, digestible energy content and metabolizable energy content of the sugarcane silage were respectively 49.6% DM, 9.7 MJ/kgDM and 7.8 MJ/kgDM. A feeding experiment with the beef cattle diet was conducted at a beef cattle raising farm in Khonkaen District. Six American Brahman crossbred bulls (around 18 months old) were separated into two groups, one of which was fed Ruzi grass (Brachiaria ruziziensis) hay with concentrate and the other sugarcane silage with concentrate. Both groups were fed the same roughage-to-concentrate ratio (38:62) for three months. The results showed that an average daily gain of 0.9 kg/day could be achieved with sugarcane silage during the feeding period (Table 2). 

　　It is possible to supply silage which of good and reliable quality using sugarcane, and to raise beef cattle using sugarcane silage as the basic diet. However, sugarcane silage needs to be consumed as soon as possible after opening due to its low aerobic stability.

(T. Suzuki)

Table 1.  Chemical components and fermentation quality of pangola grass silage and sugarcane silage.

Table 2. Feed chemical components and performance of beef cattle fed Ruzi grass hay or sugarcane silage with concentrate†

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Piperine, a component of long pepper, suppresses insect pests of rice storag

　　Under the JIRCAS international research project entitled "Development of low-input technology for reducing postharvest losses of staples in Southeast Asia," the research team studied the growth-inhibitory effect against stored-product insect pests of various botanicals. The target insect pests were the rice weevil (Sitophilus oryzae), maize weevil (S. zeamais), red flour beetles (Tribolium castameum) and rice moth (Corcyra cephalonica), which are commonly found in stored rice worldwide. The project team found a strong growth-inhibitory effect of a spice plant, long pepper (Fig. 1, Piper retrofractum) against weevils and the beetle. Long pepper is a vine in the family Piperaceae; the fruit has a hot taste similar to black pepper. It is widely used in many types of food and medicines in tropical and subtropical regions. In the experiment, dried and powdered long pepper fruits were mixed into feed and its effect against insect pests was examined. Long pepper completely suppressed adult emergence from eggs of weevils at a dose of 0.5% (w/w), and the growth of 1–7-day-old red flour beetle larvae by approximately 90% at a dose of 5% (w/w). 

In addition, long pepper showed a definite suppressive effect against red flour beetles in the model experiment using imitation warehouse-like boxes in which brown rice and starch powder mixed with long pepper powder were separately placed. Long pepper also inhibited the development of another important insect pest, the rice moth (Corcyra cephalonica), but the effect was not as strong as against Coleoptera. The growth-inhibitory component of long pepper was then isolated by activity-guided fractionation using weevils. The obtained pale yellow crystals of the active principle were identified as piperine by mass and nuclear magnetic resonance (NMR) spectrometry. Piperine is an alkaloid found in the black pepper seed that has a hot flavor. Purified piperine substantially suppressed the adult emergence of weevils by 50% (ED50) at a dose of approximately 50 ppm (Fig. 2). The risk of long pepper extract or piperine to human health is likely to be much lower than most other synthetic insecticides, since it has a long history of use as a spice. We therefore believe that long pepper has the potential to provide a safe alternative to synthetic insecticides. The project team is currently studying how to apply long pepper or piperine extracts on an individual scale in rice storage. 

(G. Trakoontivakorn, R. Juntarawimoon, Y. Hanboonsong and K. Nakahara)

Fig. 1. Long pepper (Piper retrofractum), fresh fruit and leaves (left bottom); dried fruits (top right).

Fig. 2. Growth- inhibitory effect of piperine against weevils.

Eggs of weevils were reared in the feed pellet containing purified piperine at the indicated doses. Emerged adult weevils during 8 weeks were counted. The chemical structure of piperine is shown in the panel.

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Arachidonic Acid can Help the Aquaculture Industry to Take off in Developing Countries “Hatcheries in the Tropics require arachidonic acid for stable fry production”

　　Aquaculture contributes significantly to food production, incomes and jobs in developing regions. However, the persistent constraint in aquaculture development is presently the supply of good quality seeds (fry) in quantity. Hatcheries are expected to provide stable fry supply for farmers, but fry production is often highly variable due to low survival rates. During the period 2002–2005, the Southeast Asian Fisheries Development Center - Aquaculture Department (SEAFDEC/AQD, Iloilo, Philippines) and JIRCAS have collaborated on studies aimed at developing advanced diets to improve the quality and production of eggs, larvae and seedstock for tropical marine fish species.
　　

The most striking difference between cold water fish species and tropical fish species is that arachidonic acid, which is found in only minor quantities in cold water fish species with their high EPA levels, is one of the major essential fatty acids in the ovaries, testes, eggs and muscles of tropical fish species from mangrove areas or coral reefs in the Philippines, Malaysia and Ishigaki, Japan. It is notable that the major essential fatty acids in tropical fish species are DHA and arachidonic acid (not EPA) at a ratio of about 2:1. This result suggests that a dietary ratio of DHA/arachidonic acid (not EPA) of about 2 or greater can be recommended as an ideal regimen for broodstock of tropical fish species.

　　Thus, arachidonic acid is a major fatty acid widely distributed in tropical marine fish species and is likely to be important to reproduction and larval/fry performance. However, most studies on essential fatty acids in relation to fry production have been focused on EPA and DHA, and the potential value of arachidonic acid has not been applied to fry production technologies for tropical and subtropical fish species.

　　In the mangrove red snapper, total egg production and total number of spawn can be clearly improved providing a formulated diet containing arachidonic acid at 5 g/kg. Moreover, this diet can increase the percentage of normal larvae and boosts the cumulative survival rate to more than twice the level of those on diets without arachidonic acid. Rabbitfish fry, when fed rotifers or brine shrimps enriched with a combination of DHA and arachidonic acid, always showed the best survival rate. We conclude that adding arachidonic acid to broodstock diets or larval feeds dramatically improves seed production. Improved hatchery production of seedstocks can thereby help aquaculture take off in the developing tropical countries.

(H. Ogata)

Fig.1 Arachidonic acid levels are higher in tropical fishes than in cold water fishes. Fig.2 Dietary arachidonicacid improves egg production. Total egg production (x106) Fig.3 Arachidonic acid improves survival of rabbitfish fry. Survival (%)

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Recycling-oriented aquaculture system utilizing natural ecological functions

　　Coastal aquaculture in mangrove swamp areas has rapidly developed and expanded since the middle of the 1980s, and the production of cultured prawns has greatly increased. During the 25 years from 1975 to 2000, shrimp farming areas increased more than sixfold, from 129 km² to 811 km². However, excessively intensive utilization of brackish water areas has resulted in the destruction of many mangrove ecosystems and water pollution affecting the culture ponds and adjacent coastal areas. Recovery of mangrove ecosystems is of utmost importance for restoring the productivity of coastal aquaculture and fisheries. To develop a rational and sustainable utilization strategy for mangrove ecosystems, it is necessary to carry out studies relating to the practical use of coastal aquaculture systems that are compatible with the preservation of the environment.

　　To investigate rational and sustainable utilization of benthic organisms for prawn aquaculture, the community structure of macrobenthic organisms was examined in Samut Songkhram aquaculture ponds in the innermost part of the Gulf of Thailand. A total of 84 species/taxa of macrobenthos were identified, in which 42 species/taxa were found in the six experimental ponds: four ponds used for prawn culture and two ponds planted with mangrove stands. The dominant species belong to three taxonomic categories; that is, (1) sedentary, tube-dwelling spionids, Polydora sp., free-living nereids, Perinereis sp. and some other polychaetes (Annelida); (2) gastropods such as Cerithidea cingulata, Cerithium coralium, Thiara riqueti, and Stenothyra ovalis, which live on the surface or in the shallow layers of the substratum (Mollusca); and (3) barnacles, Balanus sp., and some small crustaceans such as ostracods, copepods, harpacticoids, amphipods and dipterans (Arthropoda). Population density, biomass and species diversity in the mangrove planted ponds were higher than those in the prawn culture ponds, and depending on their behavioral traits, the depth of sediment utilized.

　　Model experiments of a recycling-oriented prawn aquaculture that exploited the natural purification capacity of the mangrove ecosystem and the productivity of the macrobenthic community were carried out in the experimental ponds in Samut Songkhram. The survival rate and average weight of prawns in the water-circulated culture systems were higher than those in the closed culture system. When prawns were cultured under semi-intensive conditions in mangrove planted ponds, their average size increased about by 25%, and artificial feed could be reduced about by 19% compared to the intensive culture system. Diversity and biomass of the macrobenthos decreased during the culture experiments in the prawn culture ponds, while they increased in the mangrove ponds, indicating the possibility that the prawns fed on the small macrobenthos such as polychaetes and juvenile gastropods as a natural food source under aquaculture conditions. The results of feed preference experiments in the laboratory demonstrated that prawns significantly selected polychaetes and crustaceans over commercially sold pellet feed. It was concluded that macrobenthic invertebrates are an important natural feed for prawn aquaculture and may participate closely in the transfer of energy from the producer organisms to the cultured prawns.

　　On the basis of the results of the present study, we constructed a model of a recycling-oriented aquaculture system by utilizing the natural ecological functions of benthic and planktonic organisms, mangrove stands and seaweeds. 

(Y. Fujioka)

A model of recycling-oriented aquaculture system utilizing natural ecological functions of benthic and planktonic organisms, mangrove stands and seaweeds. 

Overview of recycling-oriented aquaculture system of Samut Songkhram.

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Co-culture of Black tiger shrimp (Penaeus monodon) and Sea grapes (Caulerpa lentillifera)

　　We are attempting to develop co-culture in shrimp farming intended to improve the environment within shrimp ponds by using biofilters. Caulerpa lentillifera, a species of edible seaweed, was chosen for co-culture with Penaeus monodon.
　　It became obvious that C. lentillifera has high water purification abilities (dissolved nutrient uptake and physical filtration) and it also offers a hiding place for the shrimp.
On the other hand, C. lentillifera is expected to guarantee an alternative income in the event that the P. monodon perish in large numbers, making it possible to prevent the abandonment or neglect of shrimp culture ponds.

　　The co-culture of P. monodon and C. lentillifera markedly decreased the ammonia nitrogen (by up to approximately 50%), which exerts the most adverse effect on the cultivation of underwater shrimp. We discovered that favorable water quality could be easily maintained over the long term by co-culture with seaweed, since seaweed grows more steadily than phytoplankton. As a result of C. lentillifera utilizing the nutrients dissolving from leftover shrimp feed, chemical fertilizers are not needed for growth of C. lentillifera. The growth of seaweed by this system showed an almost identical value to that grown independently using chemical fertilizers.

　　Caulerpa lentillifera has the ability to adapt to environments with a salinity of approximately 25~35% and water temperatures between approximately 23~33 ˚C. It was thus thought that C. lentillifera would be a suitable species for shrimp culture ponds where temperature and salinity can readily change. The growth of shrimp is not obstructed by co-cultivation with the C. lentillifera.
　　

Using this co-culture system, the number of bacteria adhering to the gills of the shrimp decreased, and the biomass of bacteria in the water stabilized. It is possible to prevent total annihilation of the shrimp from the normally inescapable yellow head virus (YHV), since 1% of shrimps infected with YHV in several earthen shrimp ponds were observed to survive due to co-culture with C. 

　　When a taste test targeting Thai people was conducted, the unexpected flavor and fragrance of this species of C. lentillifera presented no problems, and the texture was particularly popular. It has the potential to become a popular food throughout Bangkok and subsequently Thailand, and may have a bright future as a secondary means generating income for small-scale shrimp culture farmers.
　　We believe that seaweed has a potentially large market in Thailand, since it can be utilized as human food, in cosmetic and pharmaceutical products, and for animal feed. Our experiments indicate that some seaweeds are effective in improving the aquatic environment. A further series of experiments will be necessary to choose other organisms, like shellfish, to act as effective biofilters in an integrated system.

(K. Hamano)

Changes in ammonia (NH3), nitrite (NO2) and nitrate (NO3) concentration in the water of monoculture and co-culture tanks. Error bars indicate standard deviation with n = 4.

A Black Tiger Shrimp that survived mass death by YHV disease in a culture pond where Caulerpa lentillifera grows abundantly.

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Effect of shuttle breeding by taking advantage of the wide latitude in Japan for heading traits of wheat

　　Usually it takes many years to breed wheat cultivars. Rapid generation advancement is, therefore, one of the more important techniques for shortening the process. On the other hand, photoperiod response (photoperiod-sensitive or insensitive) and vernalization response (winter or spring growth habit), which are controlled by Ppd and Vrn genes, respectively, are particularly important physiological characters, since they are responsible for earliness of heading and are thus closely related to regional adaptability. If the desirable Ppd and Vrn genotypes can be selected by natural and artificial selection during rapid generation advancement, its system should be very efficient. In this study, to establish an efficient method of rapid generation advancement applicable to spring wheat breeding programmes, the impact of shuttle breeding through fall-sown cultivation on Ishigaki (24˚N), Okinawa, in the southernmost part of Japan, followed by the spring-sown cultivation at Memuro (42˚N), Hokkaido in the northernmost part of Japan on the fluctuation in the frequency of the Ppd and Vrn genotypes was investigated.

　　Analysis of heading date in characteristic wheat cultivars and the F2 populations indicated that the earliness of heading in Okinawa and Hokkaido was closely related to both Ppd and Vrngenotypes and the Vrn genotype, respectively. The two hybrid populations segregating for Ppd or Vrn genes, ‘Saitama 27’ (Ppd-S, Vrn-A1) × ‘Haruhikari’ (no Ppd genes, Vrn-A1 Vrn-B1) and ‘Saitama 27’ × ‘Norin 59’ (Ppd-S, no Vrn genes), were treated using rapid generation advancement (F2: Okinawa, F3: Hokkaido). As a control, the same cross combinations were also treated using the single seed descent method in F2 - F3 generations. The analysis of their photoperiod and vernalization responses showed that plants with photoperiod-sensitivity and winter growth habit were eliminated in Okinawa and those with winter growth habit were eliminated in Hokkaido (Table).

　　The present study proved this system of rapid generation advancement to be effective in eliminating the photoperiod-sensitive and winter types, therefore making it useful for photoperiod-insensitive spring wheat breeding. In addition, it was considered that, in a cross combination between distantly related parents, the following shuttle breeding system scheme would be appropriate, taking the degree of fixation into account: 1st year (F2: Okinawa, F3: Hokkaido) and 2nd year (F4: Okinawa, F5: Hokkaido). On the other hand, for photoperiod-sensitive spring wheat breeding, a long-day treatment is necessary to avoid eliminating photoperiod-sensitive types in fall-sown cultivation in Okinawa.

(M. Tanio, K. Kato, N. Ishikawa, T. Tabiki, Z. Nishio, K. Nakamichi,
Y. Tamura, M. Sato, H. Takagi and M. Matsuoka)

Table1. Fluctuation in photoperiod response (A) and vernalization response (B) with rapid generation advancement (RGA) or single seed descent (SSD) in two wheat hybrid populations

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Evaluation of functional components in passionfruit cultivated under drip-fertigation and light culture

　　Passionfruit is produced from South Kyushu to Okinawa in Japan and is consumed as a table fruit or as juice. The flavor is appealing and the taste is subacid to acid. Passionfruit contains many functional components such as carotenoids and ascorbic acid. In open field culture, passionfruit is harvested only in summer and winter. However, it is possible to harvest it in autumn as well by using drip-fertigation and light culture, which comprises drip-fertigation culture that allows optimum control of fertilizer application and ground temperature, and light culture using energy-efficient red LEDs that induce flower bud formation (Fig. 1). We attempt to identify contained in passionfruit and examine the influence of harvesting season on the quantity of the functional components under drip-fertigation and light culture.

　　‘Summer Queen’ passionfruit used in this study was collected from the Kagoshima Fruit Tree Experimental Station. As a result of analyzing the juice of the passionfruit using HPLC, it was found from the absorption spectrum that the main carotenoid in the passionfruit was z- carotene (Fig. 2). The UV-visible spectrum of z-carotene showed lmax at 379, 400 and 425, with high spectral fine structure (%III/II 93). After filtering the passionfruit juice on a Sep-Pak C18 cartridge, the concentration of ascorbic acid was rapidly and simply determined using the Reflectoquant Ascorbic Acid Test (Merck Ltd., Japan) without the need to use HPLC. The quantities of z-carotene and ascorbic acid in the passionfruit juice varied significantly according to harvesting season (Fig. 3). The concentrations of z-carotene and ascorbic acid were significantly higher in fruits harvested in autumn than in summer and winter. There was a direct correlation between z-carotene and ascorbic acid content (Fig. 4) that was not influenced by harvesting season, making it possible to estimate the concentration of z-carotene by measuring the concentration of ascorbic acid using the Reflectoquant Ascorbic Acid Test.

　　These results indicate that drip-fertigation and light culture is useful for harvesting autumn fruit that contains numerous functional contents.

(H. Kato)

Fig. 1. Light culture by red LEDs (A) and drip-fertigation (B) of passionfruit. Fig. 2. UV-visible spectrum of major carotenoid fraction (retention time = 59.29 min). The conditions were as follows: column, YMC carotenoid S5 µm (4.6 x 250 mm); temperature, 40 ˚C; flow rate, 1.0 mL/min; mobile phase, A: 20% (v/v) MeOH in H2O, B: MTBE: MeOH (9:1); gradient, 26% B hold for 15 min, to 34% B in 25 min, to 44% B in 10 min, to 56% B in 15 min, hold for 10 min, then back to 26% in 5 min. The structural formula of z-carotene is illustrated. Fig. 3. Concentration of z-carotene (A) and ascorbic acid (B) in the juice of ‘Summer Queen’ passionfrui The concentration of z-carotene is *measured as b-carotene corresponding. Vertical bars indicate SE (n = 4-15). Different letters are significant at P < 0.05 according to the Tukey-Kramer HSD test. Fig. 4. Relationship between contents of ζ-carotene and ascorbic acid in juice of ‘Summer Queen’ harvested in summer (●), autumn (▲) and winter (□). *** Significant at the 0.1% level.

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Moving distance a day of the released citrus psyllid, Diaphorina citri using a newly developed marking method

　　The Asian citrus psyllid, Diaphorina citri Kuwayama, is a vector of Asian Citrus Greening Disease which is spreading in Asia, including Japan, North and South America. Citrus greening disease or Huanglongbing (HLB) is the most destructive disease affecting citrus production. However, although knowledge of its vector ecology, especially dispersal studies, is needed for its control, data regarding the movement of this psyllid is minimal or entirely lacking. We have recently developed an effective marking method for this psyllid using fluorescent powder. We investigated the moving ability of the psyllids using this newly developed marking method and took into account moving characteristics as related to weather factors in the field.

　　First, we prepared 20,000 marked psyllids (Fig. 1) in a release experiment, reared for mass propagation in a glasshouse on orange jasmine. The reared psyllids used in this experiment were CG-free, since the CG bacterium does not propagate in orange jasmine. These marked psyllids were monitored at 65 points which comprised four orange jasmine trees per point, located concentrically at 50-m intervals up to 350 m from the release point (the center of our station) after one day (Fig. 2). Release experiments were conducted twice, in May and October 2005, at our station on Ishigaki Island, southwest of Japan.

　　The first experiment was conducted on March 21, 2005. The daily mean wind speed and daily mean wind direction at our station were 2.2 m/s and SSW, respectively, on the day of release. One day later, 516 psyllids had taken up residence on the orange jasmine plants at the monitoring points. Of those, 79.5% were observed on the north side and on the leeward of the release point. (Fig. 2).
　　The second experiment was conducted on October 15, 2005. The daily mean wind speed and daily mean wind direction at our station were 5.8 m/s and NNE, respectively, on the day of release. One day later, 118 psyllids were observed on the orange jasmine plants at the monitoring points. Of these, 96.6% were observed on the south side, on the leeward of the release point. The maximal distance traveled after a day of these marked psyllids was measured as 200 m and the mean moving distance was estimated at 66.9 m.

　　These results indicate that the marked vector psyllids moved to the leeward of the release point, and the maximal distance traveled after a day of these marked psyllids was measured as 350 m. The mean distance traveled in the two field experiments was estimated at 73.4 m. Since the psyllids moved 350 m in the first release experiment, some may have father migrated to the leeward side, exceeding the monitoring limit. These results will contribute to basic knowledge of the control strategy of this insect. 

(T. Nakata)

Fig. 1. Large amount of marked psyllids on orange jasmine for release experiments.

Fig. 2. The movement of marked psyllids in a day from a release point.

20,000 marked psyllids were released in the field on March 21, 2005, and a day later the number of psyllids was monitored visually on the orange jasmines. The intervals of the concentric circle were 50 m and the maximum range was up to 350 m.

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