Three bacteria, Alcaligenes faecalis , Flavobacterium sp., and Providencia vermicola , were isolated from dauer juveniles of Rhabditis blumi . The pathogenic effects of the bacteria against 4th instar larvae of Galleria mellonella were investigated. Providencia vermicola and Flavobacterium sp. showed 100% mortality at 48 h after haemocoelic injection, whereas A. faecalis showed less than 30% mortality. Dauer juveniles showed 100% mortality against G. mellonella larvae, whereas axenic juveniles, which do not harbor associated bacteria, exhibited little mortality. All of the associated bacteria were used as a food source for nematode growth, and nematode yield differed with bacterial species. Among the bacterial species, P. vermicola was most valued for nematode yield, showing the highest yield of 5.2 × 10(4) nematodes/mL in the plate. In bacterial cocultures using two of the three associated bacteria, one kind stimulated the other. The highest total bacterial yield of 12.6 g/L was obtained when the inoculum ratio of P. vermicola to A. faecalis was 10:1. In air-lift bioreactors, the nematode growth rate increased with an increasing level of dissolved oxygen. The maximum nematode yield of 1.75 × 10(5) nematodes/mL was obtained at 192 h with an aeration rate of 6 vvm.

A recently introduced fungus gnat, Bradysia agrestis, has caused serious problems in Korean propagation houses where vegetable seedlings are produced for transplant into the fields. Although chemical insecticides are available against this pest, alternate control measures are needed. A Korean isolate of the entomopathogenic nematode, Steinernema carpocapsae Pocheon strain, was tested against this insect in the laboratory and propagation house. In the laboratory, S. carpocapsae affected oviposition, with the untreated females laying an average of 1219/25 eggs, whereas the treated females averaged 79/2 eggs. The infectivity of S. carpocapsae to the fungus gnat was affected by the developmental stage and temperature, with highest mortality observed with the third and fourth instars and pupal stage. Nematode mortality in the second instar fungus gnat ranged between 23 and 35%, but showed no significant differences among the temperatures tested. The egg and first instar were not infected by the nematode. In nematode dispersal studies, adult female fungus gnats alone dispersed S. carpocapsae from the nematode-treated area to the control area at a higher rate than male and female gnats or male gnats alone. In the propagation house experiments with watermelon seedlings, no significant difference was observed in fungus gnat larval reduction at S. carpocapsae concentrations of 5, 10, or 20 infective juveniles (IJs)/g of soil at 7, 14, and 21 days after treatment. In comparison with the control, the S. carpocapsae treatments significantly reduced B. agrestis larval numbers. When the watermelon seed was treated with S. carpocapsae at sowing, the larval density of B. agrestis was significantly reduced, that is, the number of B. agrestis larvae ranged from four to eight and from five to eight in the nematodetreated plots compared with 26 and 30 in the control plots on the 17th and 34th day posttreatment, respectively. In the chemical insecticide treatments, diflubenzuron and chlorpyrifos were significantly more effective than S. carpocapsae and diazinon in reducing larval populations of the fungus gnat. Our data show that, although some of the chemical insecticides were more effective than S. carpocapsae Pocheon strain, the nematode was still an effective tool for management of the fungus gnat larvae and in protecting seedlings from damage in propagation houses.

This study was conducted to investigate the characteristics of oviposition and the effect of density suppression by yellow-colored sticky trap on Ricania shantungensis in blueberry. The occurrence of an egg mass of R. shantungensis in the upper, middle and lower region were 56.6~60.2%, 23.8~28.1% and 11.7~19.7%, respectively. The number of egg masses in the branch was investigated. Percentage of the branch with one egg mass was greatest (50.9%) than with two (20.5%), three (14.6%) and over four (14.0%). The effect of yellow-colored sticky trap to reduce the number of R. shantungensis egg masses in blueberry was also investigated. In a month after yellow sticky trap installation, 17.1 adults of R. shantungensis were attracted per trap. Moreover, the number of egg masses on a tree in yellow-colored sticky trap plot was much lower (0.4) than control (1.3). Consequently, this result shows that use of yellow-colored sticky trap may contribute to decrease ovipisotion rate of R. shantungensis in blueberry.

No abstract

Oxalic acid has potent nematicidal activity against the root-knot nematode Meloidogyne incognita. In this study, fermentation parameters for oxalic acid production in submerged culture of Aspergillus niger F22 at 23, 25, and 30 °C were optimized in 5-L jar fermenters. The viscosity of the culture broth increased with increasing temperature. There was a negative correlation between oxalic acid production and the apparent viscosity; high volumetric productivity of oxalic acid was obtained at low apparent viscosity (less than 1000 cP), with a productivity of more than 100 mg/L h. When the apparent viscosity was over 2500 cP, the volumetric productivity decreased below 50 mg/L h. In addition, the volumetric mass transfer coefficient, K a, positively correlated with volumetric productivity. When the K a value increased from 0.0 to 0.017 /s, the volumetric productivity proportionally increased up to 176 mg/L h. When the temperature decreased, K a increased due to the decrease in viscosity, leading to increased volumetric productivity. The highest productivity of 7453.3 mg/L was obtained at the lowest temperature, i.e., 23 °C. The nematicidal activity of culture filtrate was proportional to the content of oxalic acid. Based on a constant impeller tip speed, oxalic acid production was successfully scaled up to a 500-L pilot vessel, producing a final concentration comparable to that in the 5-L jar.