Masatoshi Hori

Repellency of Rosemary Oil Against Myzus persicae in a Laboratory and in a Screenhouse

The repellencies of 13 labiate essential oils against Myzus persicae were investigated with a linear track olfactometer. Rosemary, thyme, peppermint, lavender, and spearmint oils repelled aphids at a dose of 10 μl. Rosemary and thyme oils repelled at a dose of 1 μl. The repellent actions of 13 components of rosemary oil were also evaluated. Among these components linalool, d,l-camphor, and α-terpineol had repellent action. The repellency of rosemary oil in a screenhouse was investigated. Aphids were released in a screenhouse and allowed to choose between tobacco plants in an area permeated with rosemary oil odor and plants in a control area. The number of aphids in the treatment area was about 70% of that in the control area. These results indicated that the landing of M. persicae on host plants was influenced by odors and that it may be possible to control aphids with repellents.

Determination of iminosugars in mulberry leaves and silkworms using hydrophilic interaction chromatography-tandem mass spectrometry.

Mulberry 1-deoxynojirimycin (DNJ, a potent alpha-glycosidase inhibitor) has been investigated thoroughly for its analytical methods and therapeutic potential against diabetes, whereas little attention has been given to other iminosugars such as 2-O-alpha-D-galactopyranosyl-DNJ (GAL-DNJ) and fagomine. For instance, concentration and composition of these iminosugars in mulberry leaves as well as sericulture products have not been fully characterized due to lack of suitable analytical methods. Here we developed a simultaneous determination method for DNJ, GAL-DNJ, and fagomine using hydrophilic interaction chromatography (HILIC) with tandem mass spectrometry (MS/MS). When mulberry leaf extracts were subjected to HILIC-MS/MS with multiple reaction monitoring (MRM), individual iminosugars could be separated and detected. The developed method is sufficiently sensitive for determining iminosugars in mulberry leaves as well as silkworms, providing new information (e.g., different amounts of iminosugars in mulberry leaf varieties; high DNJ and low GAL-DNJ in the silkworm body, especially in the blood) that is useful for producing iminosugar-rich products for nutraceutical purposes.

Lethal effects of short-wavelength visible light on insects

We investigated the lethal effects of visible light on insects by using light-emitting diodes (LEDs). The toxic effects of ultraviolet (UV) light, particularly shortwave (i.e., UVB and UVC) light, on organisms are well known. However, the effects of irradiation with visible light remain unclear, although shorter wavelengths are known to be more lethal. Irradiation with visible light is not thought to cause mortality in complex animals including insects. Here, however, we found that irradiation with short-wavelength visible (blue) light killed eggs, larvae, pupae, and adults of Drosophila melanogaster. Blue light was also lethal to mosquitoes and flour beetles, but the effective wavelength at which mortality occurred differed among the insect species. Our findings suggest that highly toxic wavelengths of visible light are species-specific in insects, and that shorter wavelengths are not always more toxic. For some animals, such as insects, blue light is more harmful than UV light.

Attractants for Rice Leaf Bug, Trigonotylus caelestialium (Kirkaldy), are Emitted from Flowering Rice Panicles

Volatiles were extracted from rice plants of various growth stages with solid-phase microextraction (SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS) to identify attractants that cause invasion of the rice leaf bug Trigonotylus caelestialium (Kirkaldy) into paddy fields. The composition of volatile blends produced by rice plants changed with rice development. In addition, volatile blend compositions differed between the panicles and the stems and leaves. The relative geranyl acetone content was high in all plant structures analyzed. In volatiles from whole plants in the fourth-leaf stage and panicles in the full-ripe stage, the relative content of green leaf volatiles (GLVs) was higher than that found in other rice plant structures. In contrast, relative terpene levels emitted from whole plants in the panicle-formation stage and by panicles and stems and leaves in the flowering stage were higher than those of other rice plant structures. However, the type of terpenes found differed between the panicles and the stems and leaves. Relative levels of β-caryophyllene in whole plants in the panicle-formation stage and panicles in the flowering stage were much higher than that in stems and leaves in the flowering stage. Our previous studies demonstrated that the odor from whole plants in the panicle-formation stage and panicles in the flowering stage is attractive to rice leaf bugs. Here, the attractiveness of β-caryophyllene to adult bugs was investigated in olfactometer assays. Adult females were attracted to β-caryophyllene at a concentration of 0.001%, which is approximately equivalent to the concentration produced by flowering rice panicles. However, β-caryophyllene also was present in the odor of whole plants in the fourth-leaf stage and in stems and leaves in the flowering stage. Furthermore, the amounts of this compound emitted from these structures were similar. Therefore, we suggest that the relative abundance of this compound in a volatile blend is important for attractance of the bugs.

Onion aphid (Neotoxoptera formosana) attractants, in the headspace of Allium fistulosum and A. tuberosum leaves

Abstract:  Attractancy of Allium fistulosum L. and Allium tuberosum Rottl. to adult apterae of the onion aphid, Neotoxoptera formosana (Takahashi), an oligophagous aphid pest of Allium crops, was investigated with a Y‐tube olfactometer. The aphids were significantly attracted to both A. fistulosum and A. tuberosum. The headspace components of both plants were extracted with solid‐phase microextraction (SPME) and analysed by gas chromatography‐mass spectrometry (GC‐MS). The main volatile components of A. fistulosum were dipropyl disulphide (relative contents: 67%), 1‐propenyl propyl disulphide (23%) and dipropyl trisulphide (6%). In the headspace of A. tuberosum, diallyl disulphide was detected as the main component (58%). Attractancy of dipropyl disulphide, dipropyl trisulphide and diallyl disulphide to the aphids was examined with the Y‐tube olfactometer. The aphids were significantly attracted to dipropyl trisulphide and diallyl disulphide at a concentration of 0.01%. Dipropyl disulphide did not significantly attract the aphids at any concentrations tested. It was revealed that attractancy of A. fistulosum and A. tuberosum was caused by dipropyl trisulphide and diallyl disulphide, respectively. The findings suggest that N. formosana uses these sulphur compounds, characteristic components of Allium plants, as olfactory cues to find the host plants.

Chemicals affecting the feeding preference of the Solanaceae-feeding lady beetle Henosepilachna vigintioctomaculata (Coleoptera: Coccinellidae)

The phytophagous lady beetle, Henosepilachna vigintioctomaculata, feeds mainly on potato, tomato, and eggplant leaves. The methanol extracts of tomato and eggplant leaves stimulated feeding activity in the adult beetles. The feeding stimulants from the lipid‐soluble fractions of tomato and eggplant leaves were found to be same compounds, identified as methyl linoleate and methyl linolenate. The feeding stimulants in the aqueous fractions of tomato leaves were identified as three sugars – fructose, glucose, and sucrose – and in eggplant leaves, the feeding stimulant was one sugar, sucrose. Although methyl linoleate and methyl linolenate were inactive without sugars, they acted synergistically with sugars, and the amounts of methyl linoleate, methyl linolenate, and sugars contained in tomato and eggplant leaves were adequate to stimulate feeding activity in the beetles. It is suggested that the synergisms of methyl esters of unsaturated fatty acid and sugars play important roles in host selection of this insect. Solanaceae species are often rich in alkaloids, which act as feeding deterrents for many insect species. Leaves of potato, Chinese wolfberry, and black nightshade, which are suitable hosts of H. vigintioctomaculata, contain α‐solanine and α‐chaconine as the main alkaloids. A mixture of α‐solanine and α‐chaconine showed neither feeding stimulant nor inhibitory activity at a concentration of 1 g leaf equivalents of the above plants. α‐Solanine and tomatine contained in tomato did not inhibit the beetle’s feeding at a concentration of 0.5%. On the contrary, nicotine and capsaicin contained in non‐hosts (tobacco and red pepper, respectively) showed feeding deterrent activities at a concentration of 0.1%. It is thought that adaptation of the beetles to alkaloids contained in solanaceous hosts also plays an important role in their host selection.

Olfactory response of Trigonotylus caelestialium (Het.: Miridae) to rice plant and gramineous weeds

Abstract:  The olfactory response of Trigonotylus caelestialium, to rice, Oryza sativa L., and two species of gramineous weeds, Poa annua and Digitaria ciliaris, was investigated with an olfactometer to clarify the role of host‐plant odours as olfactory cues in their host‐finding behaviour. Third‐instar nymphs and adult males were significantly attracted to whole plants (above ground parts) of P. annua. However, adult females were not significantly attracted to whole plants of P. annua. Attractancy of rice to T. caelestialium differed with the growth stage and part of the plant. Adult females were significantly attracted to stems and leaves in the panicle‐formation stage, and panicles in the flowering stage. They were not attracted to stems and leaves in the fourth‐leaf stage and flowering stage, or to panicles in the milk‐and full‐ripe stages. Although adult males were significantly attracted to stems and leaves in the panicle‐formation stage, they were not attracted to the other rice structures tested. Both females and males were significantly attracted to stems and leaves, as well as panicles of D. ciliaris in the flowering stage. The findings suggest that T. caelestialium use host‐plant volatiles as olfactory cues to find their host plants and their invasion to paddy fields were caused by olfactory responses to rice plant.

Influence of host plant odours on invasion of the rice leaf bug Trigonotylus caelestialium into paddy fields

1 The host‐odour preferences of the rice leaf bug Trigonotylus caelestialium between the rice plant Oryza sativa L. and four species of graminaceous weeds, Poa annua, Alopecurus aequalis, Digitaria ciliaris and Eleusine indica, were investigated with an olfactometer aiming to clarify the influence of these odours on invasion of the bug to paddy fields at the flowering stage of rice. 2 Both female and male adults significantly preferred the graminaceous weed A. aequalis in the flowering stage to rice in the fifth‐leaf stage. The bugs also significantly preferred flowering P. annua and A. aequalis to rice in the panicle‐formation stage. However, the bugs showed no preferences between rice in the flowering and grain‐filling stages and the flowering graminaceous weeds P. annua, D. ciliaris and E. indica. 3 The preference of the rice leaf bug for the flowering graminaceous weeds before rice flowering coincides with the fact that these bugs mainly live on these weeds before rice flowering. It is considered that the bugs similar preference for flowering rice panicles as the flowering graminaceous weeds causes the intense invasion of the bug into paddy fields at this rice developmental stage.

Olfactory response of Stenotus rubrovittatus to rice and paddy weed, Scirpus juncoides.

The olfactory response of the sorghum plant bug, Stenotus rubrovittatus (Matsumura) (Het., Miridae), to rice, Oryza sativa L., and paddy weed, Scirpus juncoides Roxb. var. ohwianus T. Koyama, was investigated with an olfactometer to clarify the mechanism of the invasion of the bugs in paddy fields. Both adult females and males were significantly attracted to panicles of rice in the flowering and full‐ripe stages. Whole plants (aboveground parts) of rice in the panicle‐formation stage, and stems and leaves of rice in the flowering stage significantly attracted only adult females. Other rice structures tested did not attract males or females. Both males and females were attracted to the flowering spikelets of S. juncoides. Although females showed no olfactory response to stems of S. juncoides in the flowering stage, males were repelled by them. Only females were attracted to whole plants of flowering S. juncoides. Whole plants of S. juncoides in the spikelet‐formation stage significantly attracted only females. The findings suggest that the invasions of S. rubrovittatus into paddy fields are caused by their olfactory responses to the volatiles emitted from rice and some paddy weeds such as S. juncoides.

Host plant volatiles responsible for the invasion of Stenotus rubrovittatus (Heteroptera: Miridae) into paddy fields

We investigated the attractiveness of synthetic volatile blends or individual volatiles of flowering rice panicles or flowering Scirpus juncoides spikelets to the sorghum plant bug Stenotus rubrovittatus (Matsumura). None of the individual chemicals tested attracted either sex of the bug. Synthetic volatile blends of flowering rice panicles composed of geranyl acetone, β‐caryophyllene, n‐decanal, methyl salicylate, β‐elemene and n‐tridecene attracted females. The synthetic blend of volatiles was just as attractive as natural flowering rice panicles to females. Other synthetic blends did not attract the bug. We sampled headspace volatiles from flowering S. juncoides spikelets with solid‐phase microextraction and analysed them using gas chromatography–mass spectrometry. The main volatile emitted from S. juncoides was β‐caryophyllene, one of the major volatile components of flowering rice panicles. β‐Elemene was a common volatile found in flowering rice panicles and flowering S. juncoides spikelets. Therefore, we investigated the attractiveness of synthetic blends of flowering rice panicles and S. juncoides spikelets composed of β‐caryophyllene and β‐elemene. The synthetic blend of flowering S. juncoides spikelets significantly attracted males but not females. The synthetic blend of flowering rice panicles composed of β‐caryophyllene and β‐elemene did not attract either sex. These results suggest that β‐caryophyllene and β‐elemene are common active compounds responsible for attractiveness of flowering rice panicles and S. juncoides spikelets although some of the other volatile components act synergistically with these two compounds in natural plant odours.