Bacillus thuringiensis has been used widely as one of representative microbial insecticides against variety of pest. Since the insecticidal principles produced by B. thuringiensis are complex with variety of toxins of different spectrum, spores and soluble substances affecting the biological activity of toxins, the bioassay with insects is requisite and important for comparing the activity among different formulations of B. thuringiensis. However there are several factors affecting the results in the bioassay. Author reviewed and discussed those factors affecting the results in the bioassay with insects using B. thuringiensis formulations at standpoints of species and stage of test insects, procedure for application, test temperatures, kinds of diet used, feeding periods and scoring time, methods for evaluating the biological activity and so on.

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Two isolates of Metarhizium anisopliae were selected based on virulence in order to clarify the relationships between adhesion and virulence of conidia to Thrips palmi. LC₅₀ values (CFUs/ml) of M. anisopliae UZ and OE-2 to adults of T. palmi were 7.5×10⁵ and 2.5×10⁵, respectively. The conidia of M. anisopliae OE-2 bound to the adult cuticles more effectively than conidia of M. anisopliae UZ. This suggests that the virulence of M. anisopliae to T. palmi is correlated with the number of adhereded conidia. The conidial detachment value, conidial germination ratio on the adults and LD₅₀ values (number of conidia/adult) were also compared between the two isolates. These experiments also demonstrated that conidial development after adhesion affected the virulence of M. anisoplae to T. palmi.

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The rice bugs Leptocorisa chinensis Dallas, Lagynotomus elongatus (Dallas), Cletus punctiger (Dallas) and Stenotus rubrovittatus (Matsumura) are serious economic pests of rice crops in Japan. To clarify the ripening stages of spikelets preferentially attacked by these bugs in paddy fields, rice bugs were individually released for three days onto a rice panicle at stages of maturation 7, 14, 21 and 28 days after heading (DAH). The spikelets were classified into three groups according to position in a panicle, which is closely related to the flowering order. Group A contained top spikelets of the primary and secondary branches and bottom spikelets of the primary branches (early flowering). Group B contained spikelets of the primary branches except the top, second and bottom spikelets (mid flowering). Group C contained the other spikelets (late flowering). The bugs chose to feed on the spikelets in Group A and Group B on 7 DAH. At 14 and 21 DAH, however, bugs preferred the spikelets in Group C to those in the other two groups. In L. chinensis, L. elongatus and S. rubrovittatus, the total number of damaged spikelets decreased with maturation of the panicle, whereas there was no remarkable change in the number of spikelets damaged by C. punctiger. These results suggest that all species of rice bugs except C. punctiger selectively damage spikelets of ovaries are developing with lengthwise to sidewise elongation, whereas C. punctiger mainly attacks spikelets of ovaries developing with lengthwise to thickness elongation.

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We studied spontaneous photon emission from kidney bean leaves infested with kanzawa spider mites, Tetranychus kanzawai Kishida (Acari: Tetranychidae). Strong photon radiation was observed from veins strongly infested with spider mites. Temporal changes in the total photon intensity can be described by two different logistic curves: the one was thought to be due to injury caused by the mites and the other due to induced responses. Photon intensity of the wavelength ranging from 500 to 700 nm increased monotonously soon after spider mites attacked. Photon intensity from 300 to 400 nm began to increase about 20 h after infestation and showed two peaks at about 72 and 120 h. The former phenomena may be the result of direct injury (physical stresses) and the latter to physiological (biochemical) actions related to defensive responses. These results suggest that photon measurement is a powerful tool for evaluating plant responses to herbivory.

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Heptophylla picea larvae (Coleoptera: Scarabaeidae) are serious pests of tea fields in Japan. To control H. picea larvae with the entomopathogenic fungus, Beauveria amorpha (Strain: HpBa-1), we studied H. picea larval ecology and properties of HpBa-1 under low temperature conditions. The amount of food consumed by H. picea larvae at 10°C was not significantly different from that at 20°C. Therefore it is necessary to control H. picea larvae before winter (soil temperatures: below 10°C) to suppress damage to tea roots during the winter. The best temperatures for HpBa-1 growth were 20°C and 25°C, but the fungus can grow under 15°C. During October and November (soil temperatures: above 15°C), H. picea larvae moved to the soil surface (0–10 cm) from a depth of 20–30 cm. It is possible to control H. picea larvae by soil surface application of B. amorpha at this time. H. picea larvae seem to be infected and controlled effectively by applying HpBa-1 between October and November.

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Lethal and growth inhibitory activities of a Bacillus thuringiensis formulation containing a delta-endotoxin Cry IC as an active ingredient were investigated in bioassays with different instars of the common cutworm larvae, Spodoptera litura by a leaf dip method using four species of plants (cabbage, tomato, strawberry and perilla). Both the lethal and growth inhibitory activities of B. thuringiensis differed among the larval instars, indicating a lower susceptibility in the larger instars. However the levels of lethal and growth inhibitory activities differed from each other, showing that the differences among instars for growth inhibitory activity were less pronounced than for lethal activity. It is interesting that both activities of B. thuringiensis were markedly influenced by the host plant leaves used for the bioassays. When strawberry or perilla leaves were used for the bioassays, the lethal and growth inhibitory activities of B. thuringiensis decreased 1/3–1/30 and 1/10–1/30, respectively, compared to the activities when cabbage or tomato leaves were used.

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Twelve artificial diets were tested for suitability in the laboratory rearing of legume pod borer larvae, Maruca vitrata, under 25°C and 14L10D conditions. The larval developmental periods were significantly longer in all artificial diet regimes and pupal weight was heavier than in the natural diet regime. The survival rates to adult emergence on 30–50% cowpea and 10–70% azuki artificial diets were not significantly different from those of the natural diet. One female laid about 500 eggs on 30%, 70% cowpea artificial diets and 30–70% azuki artificial diets and can develop by mass-rearing in the laboratory. All 12 artificial diet regimes allowed the insects to complete their development. The 30–50% cowpea diets and 30–70% azuki diets were the most suitable for mass-rearing, because the daily reproductive rates (fecundity×emergence rate×copulation rate/(developmental duration+duration for a maximum oviposition day)) were the highest (5.2–6.6 eggs/day/female).

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In general, plusiine moths actively begin flying from dusk and feeding and calling activities have been clearly discussed in many reports. We examined daily behaviors, specifically, flight, feeding and calling activities of the plusiine moths, Autographa nigrisigna, Thysanoplusia intermixta, Ctenoplusia agnata and Chrysodeixis eriosoma, which are major pests of various commercial crops in the Kanto region of Japan. Daily flight activities were tested with an actograph system in the laboratory. The insects showed pronounced flight activity soon after the lights were turned off, during darkness and after the lights were turned on. Of specific interest is that during darkness, C. eriosoma showed high flight activity earlier than the other three species. We also observed daily feeding and calling activities, and found these two activities were synchronized with flight activity. We conclude that patterns of calling and associated flights are not the same for all plusiine species although most adults of the Plusiinae fly actively during darkness.

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The purpose of this study was to investigate the effects of calcium carbonate and saccharides on the feeding behavior of newly hatched larvae of the silkworm, Bombyx mori L. Japanese strains, “Hi”, “KAI”, “Ryo” and “Yo”, and Chinese strains, “Kai”, “Bono”, “Kenpaku” and “Tsukuba”, were used for the experiments. Calcium carbonate (CaCO₃) and sucrose were added to the basal diet, consisting of cellulose powder, agar and distilled water. This was fed to the larvae immediately after they hatched. It was found that the feeding of any variety of silkworm was improved by the synergetic effects of CaCO₃ and sucrose. The amount of feeding for “Kai” and “Bono”, however, were notably less than those of the other varieties. Next, diets containing CaCO₃ and two kinds of saccharides were fed to both the “Kai” and “Bono”. The amount of diet consumed by “Kai” and “Bono” remarkably increased when CaCO₃ was used together with sucrose and myo-inositol, and CaCO₃ together with glucose and myo-inositol, respectively. The above results indicated that CaCO₃ combined with sucrose or other saccharides synergistically stimulated larval appetite. Also it was found that CaCO₃ could restrict larval movement to the area immediately surrounding the diet.

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During the period from 1986 to 2004, the susceptibility to insecticides of the diamondback moth (DBM) in Iwaoka, Kobe City, Hyogo Prefecture, was determined using 3rd-instar larvae by the leaf dipping method. Moths were collected from a cabbage field every year in Iwaoka. The efficacy of the field's insecticides in that area was also evaluated every year. According to the leaf dipping test results, before 1995, DBM's susceptibility was remarkably low to acephate, phethoate, permethrin, chlorfluazuron, cartap and BT kurstaki. After 1996, the activity of all these insecticides against DBM seemed to improve, however, in the meantime, some newer insecticides marketed after 1996, such as chlorfenapyr, emamectin-benzoate, spinosad and BT aizawai, have remained highly active in laboratory tests throughout the monitoring period. According to the field test results in 2003 and 2004, phethoate, cartap and BT kurstaki showed good efficacy against DBM. The field efficacy of acephate and chlorfluazuron seemed to improve but they are still insufficient to control DBM at present. The field efficacy of permethrin, however, has continued to be low. On the other hand, some insecticides marketed after 1996 such as chlorfenapyr, emamectin-benzoate, spinosad and BT aizawai, has remained excellent throughout the monitoring period. Upon reviewing prior research, it appears that most insecticides introduced before 1994 lost their practical efficacy within a few years of being placed on the market. However, to dates, insecticides newly marketed after 1996 do not seem to have apparent resistance problem. Therefore, we can surmise that before 1995 and after 1996, a dramatic change has occurred in the area of insecticide resistance problems.

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The attractiveness of synthetic sex pheromones of the rice leaf bug, Trigonotylus caelestialium (Kirkaldy), was evaluated in the field. The rubber septum was soaked in synthetic sex pheromone, mixture of n-hexyl n-hexanoate, (E)-2-hexenyl n-hexanoate, n-octyl n-butyrate in ratios of 100 : 40 : 3. The rubber septum was used as a lure and was hung on a water pan trap about 10 cm above the water surface. The attractiveness of the synthetic pheromone at 0.001 mg and 0.01 mg per rubber septum to males was equal to that of 10 virgin females. The rubber septum impregnated with 0.01 mg synthetic pheromone remained attractive to males for one month.

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The rice leaf bug, Trigonotylus caelestialium (Kirkaldy), is an important species of stink bugs causing pecky rice. Control of this bug with fenitrothion is insufficient in paddy fields of Niigata Prefecture. Therefore, susceptibility to fenitrothion was assayed in populations sampled from seven regions of Niigata Prefecture in 2001 and 2002. LD₅₀ values of five populations ranged from 50.6 to 146.2 μg/g, and these values were remarkably higher than 18.8 μg/g of the most susceptible population tested. I concluded that resistance to fenitrothion developed with continuous applications of fenitrothion.

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