In bioassays for quality control of Bacillus thuringiensis formulations, the silkworm, Bombyx mori, has been generally used as a test insect in Japan. The median lethal concentration (LC50) of a test sample to the 3rd instar silkworm is usually calculated based on mortality at 5 days after treatment and is compared with that of a standard sample. In the present study, the total weight of 2nd or 3rd instar silkworm survivors at 48 h after treatment was measured instead of mortality and per cent growth reduction was obtained by comparison of larval weight gains in treatments against those of controls. Relationships between logalistic concentrations of test sample and per cent growth reduction by probit showed a straight line and the median growth reductive concentrations (EC50) were calculated by probit analysis. EC50 values of test samples between the 2nd and 3rd instar silkworms at 25°C were similar of about 10 times lower than the LC50 values. EC50's in the 2nd instar silkworms at 20 and 25°C were similar. The present study demonstrated that the bioassay based on growth reduction in the 2nd instar silkworm was more sensitive and speedy than one based on mortality for the quality control of B. thuringiensis formulations, reducing the test period from 5 to 2 days at 25°C.
Relationships between seasonal fluctuations in pheromone trap catches of Spodoptera litura F. (Lepidoptera: Noctuidae) and the number of soybean leaves newly injured by young larvae of this species were examined in soybean fields from 1999 to 2002 in Saga Pref., Japan. In soybean fields sown in July, a small peak of injured leaves occurred in mid to late August and a large peak occurred in mid to late September. In most cases, the pheromone trap catches and occurrence of injured leaves exhibited similar trends with both peaks occurring almost simultaneously (±3 days) in mid to late September. This suggests that not only a prominent increase in soybean leaves injured by young larvae, but also a prominent increase in pheromone trap catches are useful information to determine a precise timing of control. On the other hand, the timing of control seems to be difficult to predict using the effective accumulative temperature of this species.
The developmental period, reproductive potential, and adult longevities of Liriomyza sativae Blanchard, L. trifolii (Burgess), and L. bryoniae (Kaltenbach) were examined on kidney beans. The total developmental period (oviposition to adult emergence) decreased with increasing temperature between 15°C and 30°C in L. sativae and L. trifolii, and between 15°C and 25°C in L. bryoniae with a 15L–9D photoperiod. A significantly longer developmental period was found in each species with 10L–14D than with 15L–9D photoperiods at 18°C. The developmental zeros for total development of L. sativae, L. trifolii, and L. bryoniae were 10.7, 9.8, and 8.1°C, respectively. The effective accumulative temperatures of L. sativae, L. trifolii, and L. bryoniae were 248.1, 251.3, and 316.5 day-degrees, respectively. The adult emergence rates for all three species were highest at 25°C. The total fecundity was highest for L. sativae among the three Liriomyza species. Adults of L. sativae lived significantly longer than those of L. trifolii and L. bryoniae. The intrinsic rates of natural increase for L. sativae, L. trifolii, and L. bryoniae were 0.21, 0.17, and 0.12, respectively.
In order to find alternative diets for Amblyseius cucumeris, eleven pollen species and three high protein powders were tested. Females laid numerous eggs when fed on pollen from tea, craple myrtle, fragrant olive, persimmon and Japanese pear, but few eggs on pollen from chrysanthemum, tall goldenrod, Asiatic lily, cistus and orange. They also laid few eggs when fed on soybean flour, casein powder and defatted Deccan glass powder. Survival rates on the first five pollen species were not significantly different from the mold mite controls, indicating these pollen species are suitable as food sources. A. cucumeris showed an escaping behavior to pollen of Lycoris radiata and died within 4 days. Toxic compounds may be contained in pollen of this species. There was no correlation between pollen size and oviposition rates. Suitability of pollen species as a diet appears to be related to taxa of the plants.
The brown winged green bug, Plautia crossota stali Scott (PCS), is a serious pest in major fruits orchards in Japan. To test the feasibility of controlling PCS with an entomopathogenic fungus, in 2000 and 2001, we set up 29 and 20 inoculum stations, respectively, in an 650-ha pilot area. The average mortality rates of PSC collected from 5 pheromone traps in the area were 28% and 35% in 2000 and 2001, respectively. Broad-leaved trees were used for the inoculum stations. Five or 10 lures containing synthesized aggregation pheromone and 20 non-woven fabric sheets containing the entomopathogenic fungus Beauveria bassiana E-9102 were attached to each tree. Both males and females of PCS were attracted to the station and were infected with conidia dispersed from the sheets. The average mortality rates of PCS adults collected from the inoculum stations were consistently between 75% and 70% in 2000 and 2001, respectively, until about 30 days after the inoculum station was installed. It has been suggested that the stink bug trap consists of aggregation pheromone and B. bassiana E-9102 seems promising for the control of PCS in Japan.
Eighteen species and cultivars of warm-season and 14 of cool-season turfgrasses were evaluated for resistance to lawn cutworm, Spodoptera depravata (Butler) (Lepidoptera: Noctuidae), larvae in the laboratory. Larvae fed on cool-season turfgrass leaves showed higher survival rates than those fed on warm-season turfgrass leaves. All larvae fed on leaves of Eremochloa ophiuroides and Zoysiagrass ‘Emerald’ died within 6 and 8th days, respectively. All larvae fed on warm-season turfgrass leaves exhibited lower weights (19.9–101.2 mg) as compared to those fed on cool-season turfgrass leaves (193.6–273.6 mg) during a 10 day evaluation. Larval development period was longer when fed on warm-season turfgrass leaves (21.5–31.9 days) than on cool-season turfgrass leaves (17.0–19.5 days). Extended developmental periods were observed in cutworm larvae especially on leaves of Hybrid Zoysia ‘Miyako’, Z. japonica ‘Himeno’, native, Z. matrella, Cynodon dactylon ‘Sahara’, and Stenotaphrum secundatum.