Trigonotylus Caelestialium Research Articles

Estimating plant–insect interactions under climate change with limited data

Climate change may disrupt species–species interactions via phenological changes in one or both species. To predict and evaluate the influence of climate change on these interactions, long-term monitoring and sampling over large spatial areas are required; however, funding and labor constraints limit data collection. In this study, we predict and evaluate the plant–insect interactions with limited data sets. We examined plant–insect interaction using observational data for development of the crop plant rice (Oryza sativa) and an effective accumulated temperature (EAT) model of two mirid bugs (Stenotus rubrovittatus and Trigonotylus caelestialium). We combined 11 years of records monitoring rice phenology and the predicted phenology of mirid bugs using spatially–explicit EAT models based on both spatially and temporally high resolutions temperature data sets, then evaluated their accuracy using actual pest damage records. Our results showed that the predicted interactions between rice and mirid bugs explained rice damage to some degree. Our approach may apply predicting changes to plant–insect interactions under climate change. As such, combining plant monitoring records and theoretical predictions of insect phenology may be effective for predicting species–species interactions when available data are limited.

Microhabitat Variation in Egg Diapause Incidence in Summer Within a Local Population: An Adaptation to Decline in Host-Plant Suitability in Trigonotylus caelestialium (Hemiptera: Miridae).

Diapause induction in multivoltine insects is an ecophysiological event that is generally triggered by seasonal cues such as photoperiod and temperature. The rice leaf bug, Trigonotylus caelestialium (Kirkaldy), feeds on various Poaceae grasses and produces several generations a year. Previous studies have shown that adults produce diapause and nondiapause eggs under short-day and long-day conditions, respectively. However, there is a distinct mid-summer peak in diapause incidence before an autumnal increase in diapause incidence in the field, which cannot be explained by the laboratory results. The present study was performed to examine the environmental factors affecting the diapause incidence in mid-summer and the adaptive significance of this phenomenon. Seasonal trends in diapause incidence differed significantly among three sites located 150-400 m apart from each other and with different host plants. The suitability of host plants differs depending on species and seasonally. Therefore, the microhabitat difference in diapause trend is believed to be due to the difference in host plants. When field-collected female adults laying diapause eggs in late June were fed a seasonally deteriorating host (the orange foxtail, Alopecurus aequalis Sobol. [Poales: Poaceae]), they kept laying diapause eggs, whereas when fed a suitable host (the wheat, Triticum aestivum L. [Poales: Poaceae]) for 5 d, they changed oviposition mode to lay nondiapause eggs. These results indicate that host-plant suitability affects the oviposition mode of T. caelestialium. Diapause-egg oviposition in mid-summer in T. caelestialium has adaptive significance as a bet-hedging strategy against unpredictable dietary conditions.

Seasonal Changes and Differences in Vegetation, and Interactions between the Vegetation and Two Mirid Bugs（Hemiptera: Miridae）Causing Pecky Rice in Rice Paddy Levees

We investigated the vegetation management and occurrence of two mirid bugs, Trigonotylus caelestialium（Kirkaldy）（Hemiptera: Miridae）and Stenotus rubrovittatus（Matsumura）（Hemiptera: Miridae）, causing pecky rice, in rice paddy levees over an area measuring 10 ha in Niigata Prefecture, Japan. Mowing and herbicide application were carried out on the levees several times to manage weeds during the growing period of rice. Major poaceous plants on the investigated levees were Poa annua, Alopecurus aequalis, Digitaria ciliaris, and Echinochloa crus-galli. The two mirid bug species existed either separately or together on levees infested with ear-emerged poaceous plants. In July and August, which are important periods for forecasting the two bugs, D. ciliaris was the major plant and occurrence of the two mirid bugs was almost entirely restricted to the levees infested with ear-emerged D. ciliaris. Ears of D. ciliaris vanished after mowing or herbicide application and re-emerged with growth. As a result, the locations of levees infested with ear-emerged D. ciliaris changed over short periods. The observation results were similar over 3 years, and there were no significant changes in weed management, vegetation, and occurrence of the two bugs in the area. In levees infested with ear-emerged D. ciliaris, the spatial distribution pattern of T. caelestialium was aggregated, and that of S. rubrovittatus was even more aggregated. Despite the difference in the distribution, the locations and areas of levees infested with ear-emerged poaceous plants could be used in indices for regionally forecasting the occurrence of the two bugs.

Feeding behaviors of rice-ear bugs, Trigonotylus caelestialium and Stenotus rubrovittatus (Hemiptera: Miridae), in response to starch and its related substances

We investigated the feeding behavior-stimulating properties of starch and related substances, namely, rice starch, soluble starch, amylopectin, and d-glucose, in the mirid bugs Trigonotylus caelestialium (Kirkaldy) and Stenotus rubrovittatus (Matsumura). Using an electrical penetration graph, feeding behaviors were roughly categorized into three distinct processes: test probing, ingestion, and resting. Rice starch strongly stimulated the feeding behavior of S. rubrovittatus at all concentrations tested (10–50%), prompting an increase in ingestion behavior and a decrease in resting behavior. Rice starch stimulated the feeding behavior of T. caelestialium at a concentration of 10%. Soluble starch also elicited feeding-stimulant activity in S. rubrovittatus at all concentrations tested (10–30%), but did not stimulate feeding behavior at any concentration tested in T. caelestialium. Amylopectin, a main component of rice starch, showed feeding-stimulant activity in S. rubrovittatus only at a concentration of 10%. In T. caelestialium, amylopectin did not stimulate ingestion, but did decrease resting behavior. d-Glucose, the building block of amylopectin, stimulated feeding behavior in S. rubrovittatus, leading to an increase in the duration and frequency of ingestion at concentrations of 10% and 10–20%, respectively. These findings indicate that starch is one of the main feeding stimulants for rice-ear bugs, particularly S. rubrovittatus.

Oxidative enzymes activity during abiotic and biotic stresses in Zea mays leaves and roots exposed to Cu, methyl jasmonate and Trigonotylus caelestialium.

The activities of antioxidative enzymes, i.e. superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX), in the leaves and roots of Zea mays L. plants exposed to abiotic (methyl jasmonate, MJ, or/and copper, Cu) and biotic (Trigonotylus caelestialium) factors were examined. The contribution of MJ as a signal molecule in the defense mechanism against abiotic and biotic stresses was studied. All plants were cultivated hydroponically and divided into three groups: not treated by abiotic factors (control), treated by MJ only (MJ) and by MJ and Cu (MJ+Cu) and in each group half of the plants were exposed to T. caelestialium attack. The enzymatic activities of SOD, CAT, APX, and GPX in the leaves were higher in the insect-treated than non-insect-treated control plants, but lower in both MJ+Cu- or MJ- and insect-treated plants. In the roots, the enzyme activities were elevated in all insect-treated plants with the highest rise in MJ+Cu, in comparison with the MJ-treated plants. The results showed that MJ and MJ+Cu were efficient in reducing the activity of the antioxidative enzymes in the leaves under the insect influence by elevating enzyme activity in the roots.

Molecular Cloning and the Expression Profile of Vitellogenin in Relation to Tissue and Food Source inApolygus lucorum(Hemiptera: Miridae)

Vitellogenin proteins (Vgs) are precursors of the major egg yolk proteins in many oviparous vertebrates and invertebrates. Here we cloned the full-length cDNA of the Vg gene of Apolygus lucorum , an omnivorous mirid bug that feeds on various agricultural crops and small insects. The gene has 6,131 base pairs (bp) with an open reading frame (ORF) of 5,988 bp, encoding a protein with 1,996 amino acids, with molecular mass 218.3 kDa and isoelectric point 9.02. Phylogenetic analysis showed that Vg gene has a high similarity with that in Hemiptera insects and was most closely related to the rice leaf bug, Trigonotylus caelestialium . The expression of Vg gene was significantly higher in the fat body than in other tissues in females (ovary, hemolymph, gut, and malpighian tubule). Vg gene expression was extremely low in newly emerged adult females and increased with age. The effect of different food sources on the expression level of Vg in adult females was investigated after they were fed on green bean pods (Gb), H. armigera eggs (He), or a combination of green bean pods and H. armigera eggs (GbHe). The results showed that transcript level of Vg gene in females was significantly higher on the GbHe diet than on Gb or He. Our results demonstrate that A. lucorum can acquire nutrients from both plant and animal origin food sources, and the combined food sources significantly facilitated Vg synthesis.

Effects of converted grassland on Hemiptera assemblages in surrounding rice fields

AbstractEstablishment of pastures for cattle grazing adjacent to rice crops may increase the abundance of rice pests, because some cultivated grass species are host plants to these insects. In this study, we investigated assemblages of Hemiptera potentially causing pecky rice in paddy fields in Japan, and the effects of converted grasslands on surrounding rice fields. We systematically sampled Hemiptera in five land‐use types, comprising riverside vegetation, rice fields, forage rice paddies, fallow fields and pasture in a fine‐scale agricultural mosaic. We also examined the abundance of the two main rice bug species, in relation to the proportion of pecky rice and distance to pasture. Converted pastures that contained cultivated bahia grass (Paspalum notatum Flügge) and Italian ryegrass (Lolium multiflorum Lam.), had the greatest abundance of three rice bug species; Stenotus rubrovittatus (Matsumura), Trigonotylus caelestialium (Kirkaldy) and Cletus punctiger (Dallas). The percentage of damaged pecky grains was significantly greater in rice fields near pasture (within 200 m) than in those farther away. Our study provides evidence that the main source of rice bugs in agricultural croplands was pasture; and suggests that managing food sources for these insect pests in pastures close to rice paddies could help reduce their detrimental impact on rice crops.

The effects of mating status and time since mating on female sex pheromone levels in the rice leaf bug, Trigonotylus caelestialium

Although mating status affects future mating opportunities, the biochemical changes that occur in response to mating are not well understood. This study investigated the effects of mating status on the quantities of sex pheromone components found in whole-body extracts and volatile emissions of females of the rice leaf bug, Trigonotylus caelestialium. When sampled at one of four time points within a 4-day postmating period, females that had copulated with a male had greater whole-body quantities of sex pheromone components than those of virgin females sampled at the same times. The quantities of sex pheromone components emitted by virgin females over a 24-h period were initially high but then steadily decreased, whereas 24-h emissions were persistently low among mated females when measured at three time points within the 4 days after mating. As a result, soon after mating, the mated females emitted less sex pheromones than virgin females, but there were no significant differences between mated and virgin females at the end of the experiment. Thus, postmating reduction in the rate of emission of sex pheromones could explain previously observed changes in female attractiveness to male T. caelestialium.Electronic supplementary materialThe online version of this article (doi:10.1007/s00114-013-1141-3) contains supplementary material, which is available to authorized users.

アカヒゲホソミドリカスミカメに対するLED光の誘引性

In the laboratory, the adult rice leaf bug, Trigonotylus caelestialium (Kirkaldy), most preferred 375 nm light-emitting diodes (LED) among lights of four wavelengths ranging from 375 to 450 nm with constant light intensity. Under a rated output current condition, short-wavelength range LEDs (375 nm, 400 nm) attracted more bugs than long-wavelength range LEDs (505–600 nm). In the field, the prototype LED (375 or 400 nm) trap caught few adult bugs of the overwintering generation in the spring (April to mid-June), while it caught adult bugs continuously during the summer (late June to September). Many adult bugs of the presumed second generation, which is considered to be especially related to pecky rice damage, were caught in the trap from late July to mid-August. Thus, LED traps might be useful tools to monitor T. carestialium under field conditions.

Reduction of Female Mating Receptivity after Injection of Male-Derived Extracts inTrigonotylus caelestialium(Heteroptera: Miridae)

AbstractThe effects of male-derived extracts on female receptivity to remating were investigated in Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae). The aqueous extracts of male reproductive tracts were observed to reduce receptivity both at 3 h and at 1 d after injection into the abdomens of females. Next, ultrafiltration was used to divide the aqueous extracts of the male reproductive tracts into three molecular-weight (MW) fractions: <3.5 kDa, 3.5–14 kDa, and >14 kDa. The filtrate containing the MW substances <3.5 kDa reduced female receptivity 3 h after injection, whereas the fraction containing MW substances >14 kDa inhibited receptivity at 1 and 2 d after injection. Finally, the male reproductive tract organs were divided into the accessory glands, testes, and the remaining reproductive organs, including the seminal vesicles. Aqueous extracts of the accessory glands reduced the receptivity of females both at 3 h and 2 d after injection, whereas those of the testes decreased the receptivity of females at 3 h after injection. Together, the results indicate that more than one mechanism may be involved in the effects of male-derived substances on female receptivity in T. caelestialium. The findings suggest that low-MW male-derived substances in the accessory glands and testes cause short-term inhibition and that the high-MW substances in the accessory gland inhibit female mating at a later period.

フェロモントラップの開口部の広さとアカヒゲホソミドリカスミカメ誘殺数との関係

The SE trap® is considered unsuitable for monitoring the rice leaf bug, Trigonotylus caelestialium, because of its low capture efficiency. One of the reasons for this low efficiency is that the opening size of this trap is assumed to be too small for the males to reach the sticky plate. We therefore improved the SE trap to widen the openings. Specifically, a pillar was placed at each corner between the roof and the bottom plate, and the entrance area was varied through the length of the pillar (i.e., 5 cm, 10 cm, and 15 cm). In paddy fields, the average number of males captured per trap increased with the length of the pillar. The average number of males captured in traps with pillars 10 cm or 15 cm long was not significantly different from with a vertical sticky trap, which is generally used as a pheromone trap for this bug. The results suggest that these improved traps may be a useful alternative to the vertical sticky trap.

Attractiveness of synthetic volatile blends of flowering rice panicles to Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae)

AbstractThe attractiveness of 22 synthetic volatile blends or seven individual chemicals emitted from flowering rice panicles to a rice leaf bug, Trigonotylus caelestialium (Kirkaldy), were investigated with an olfactometer to identify the active compounds responsible for the invasion of the bugs into paddy fields. n‐Decanal attracted only male bugs, whereas β‐caryophyllene attracted only females. β‐Elemene repelled males and methyl benzoate marginally repelled females. The other chemicals did not attract or repel male and female bugs at all. Two‐, 3‐, 4‐ and 5‐component blends of β‐caryophyllene, n‐decanal, n‐tridecene, methyl salicylate and geranyl acetone were attractive to neither females nor males. Two‐component blends comprised of β‐caryophyllene and methyl salicylate, or n‐decanal and methyl salicylate, marginally repelled females. The three‐component blend comprised of β‐caryophyllene, n‐decanal and geranyl acetone marginally repelled females. The five‐component blend comprised of β‐caryophyllene, n‐decanal, n‐tridecene, methyl salicylate and geranyl acetone repelled males. The seven‐component blend comprised of β‐caryophyllene, n‐decanal, n‐tridecene, methyl salicylate, geranyl acetone, methyl benzoate and β‐elemene attracted female bugs and marginally attracted male bugs. Six‐component blends without any one of these seven components were not attractive to the bugs although the six‐component blend without n‐decanal was marginally attractive to females. The six‐component blend without n‐tridecene repelled males. These findings suggest that mixtures of these seven compounds play an important role in the attractiveness of flowering rice panicles to both sexes of the bugs, although the attractiveness of individual compounds differs between sexes.

Suitability of poaceous plants for nymphal growth of the pecky rice bugs Trigonotylus caelestialium and Stenotus rubrovittatus (Hemiptera: Miridae) in Niigata, Japan

Under laboratory conditions, we investigated the host suitability of 24 poaceous plants for Trigonotylus caelestialium (Kirkaldy) and Stenotus rubrovittatus (Matsumura). More than 50 % of the nymphs of both bugs reached the adult stage on Poa annua L., Alopecurus aequalis Sobol. var. amurensis (Komar.), Poa sphondylodes Trin., Hordeum murinum L., Agrostis clavata Trin. ssp. matsumurae (Hack. ex Honda), and Lolium multiflorum Lam. In addition, a similar number of S. rubrovittatus nymphs reached the adult stage on Dactylis glomerata L. and Digitaria violascens Link. However, a high percentage of T. caelestialium adults emerged on both spikelets and leaves of the host plants, whereas a lower percentage of S. rubrovittatus adults emerged on leaves than on spikelets. While the numbers of T. caelestialium adults that emerged on spikelets and leaves were similar, those reared on spikelets had a shorter developmental period and longer forewings than those reared on leaves, indicating that spikelets were more suitable for growth. In addition, more adults of both species emerged on plants with ears that arise during the spring and early summer than on plants with ears that arise during the summer and fall. Therefore, the development of these bugs is dependent on the season of ear emergence.

Host plant use for oviposition by Trigonotylus caelestialium (Hemiptera: Miridae) and Stenotus rubrovittatus (Hemiptera: Miridae)

The main hosts and sites of oviposition for the two bugs, Trigonotylus caelestialium (Kirkaldy) (Hemiptera: Miridae) and Stenotus rubrovittatus (Matsumura) (Hemiptera: Miridae), that cause pecky rice were investigated in 24 poaceous plants. Nymphs of T. caelestialium emerged from both spikelets and leaf sheaths, while nymphs of S. rubrovittatus emerged almost exclusively from spikelets. Suitable plants for oviposition by T. caelestialium are Lolium multiflorum, Digitaria violascens and Hordeum murinum, while Poa annua, Anthoxanthum odoratum, Alopecurus aequalis and D. violascens were preferentially used by S. rubrovittatus. There was a greater difference in the number of nymphs emerging from different plants for S. rubrovittatus than for T. caelestialium. This difference may be because T. caelestialium can oviposit on leaf sheaths if the spikelets are not suitable for oviposition, whereas S. rubrovittatus only oviposits on spikelets. Although both bugs oviposited on spikelets, the internal oviposition sites were different. In D. ciliaris, T. caelestialium laid all eggs between the lemma of the first floret and the second floret, whereas S. rubrovittatus laid eggs almost exclusively inside the second floret. In contrast, in P. annua, T. caelestialium laid all eggs inside the florets, whereas S. rubrovittatus laid eggs both between and inside the florets.

Reduction of mating receptivity and changes in longevity of rice leaf bug, Trigonotylus caelestialium (Heteroptera: Miridae), females after mating

To develop new and improved pest management strategies against Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae), a major pest of rice in Japan, it is important to understand the mating behavior of this species. In this study, we examined the effect of mating on subsequent mating receptivity and longevity in female T. caelestialium. After mating, females temporarily exhibited decreased mating receptivity. In addition, the cumulative remating frequency of females that mated with a male that had just mated with another female was higher than that of females who mated with virgin males. As a result, we hypothesized that the male ejaculate reduces female mating receptivity. Furthermore, mated females survived longer without food and water than virgin females; on the other hand, the life span of mated females with access to food and water was less than that for virgin females.

Comparison of the effects of landscape composition on two mirid species in Japanese rice paddies

Two rice bug species, Stenotus rubrovittatus (Matsumura) and Trigonotylus caelestialium (Kirkaldy) (Hemiptera: Miridae), are major rice pests in Japan. The populations of these insects are maintained by widely distributed host plants and by a broad range of movements among resource patches. To develop an effective pest management strategy for a region where two rice bug species coexist, the impacts of the surrounding landscape and of weed-infested field boundaries on the field abundances of the two rice bug species were compared. Field abundances of the two species were estimated using the sweep-netting technique. The number of weed-infested field boundaries was also counted within a 100 m radius around 14 study paddies at three sites in Japan. The distinctive features of the surrounding landscape furnished the best predictor at a spatial scale radius of 300 m for S. rubrovittatus and at 200–300 m for T. caelestialium. The abundances of both species increased as the amounts of weed-infested area and reclaimed land increased. The size and number of sources also affected the two rice bug species. These results emphasize that adequate field boundary management can reduce the risk of high pest abundance in the fields, even when an extensive weed-infested area exists within the functional scale of the species.

Evaluating the fungal endophyte Neotyphodium occultans for resistance to the rice leaf bug, Trigonotylus caelestialium, in Italian ryegrass, Lolium multiflorum

Fungal endophytes of the genus Neotyphodium (Ascomycota: Clavicipitaceae) form symbiotic associations with many grass species of the subfamily Pooideae, including some important forage and turf grasses from the genus Lolium. Some Neotyphodium-infected grasses have enhanced resistance to the rice leaf bug, Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae), one of the major pests in rice production in Japan. The insects can grow on Lolium grasses and thus cause a conflict of interest between production of forage and rice. Endophyte-mediated resistance to T. caelestialium is likely to be conferred by N-formylloline, one of the major loline alkaloids (saturated 1-aminopyrrolizidines) observed in some grass–Neotyphodium associations. We checked the feasibility of using Neotyphodium occultans, the native endophyte of Italian ryegrass (Lolium multiflorum Lam.), to reduce T. caelestialium, as this endophyte produces N-formylloline, but no known mammalian toxins. To this end, we conducted choice and no-choice feeding assays using T. caelestialium first instars and 35 N. occultans-infected Italian ryegrass plants with different in planta N-formylloline concentration. Some N. occultans-infected ryegrass showed significant resistance to T. caelestialium. The preference and the survival of this insect were considerably lower on infected plants, and the higher the in planta N-formylloline concentration, the greater the adverse effects on the insect. The incremental risk of death of the insect was assumed to be due to intake of the chemical, and in addition, to the decreased amount of feeding caused by its insect-deterrent effect. These results indicated that the use of the N. occultans–grass associations has potential to reduce T. caelestialium propagation in ryegrass crops. The breeding of N. occultans-infected Italian ryegrass cultivars with high N-formylloline concentrations should be an effective way to develop pasture grasses with a greater protective effect against T. caelestialium.

The systematic position of the tribe Stenodemini (Heteroptera: Cimicomorpha: Miridae: Mirinae) in the light of the male internal reproductive system

The study focuses on the morphology and ultrastructure of the male reproductive system of 13 Hemiptera species representing the tribes Stenodemini and Pithanini: Acetropis carinata, Dolichomiris linearis, Leptopterna dolabrata, L. ferrugata, Megaloceroea recticornis, Notostira elongata, N. erratica, Stenodema (Brachystira) calcarata, Stenodema (Stenodema) holsata, S. (S.) laevigata, Trigonotylus caelestialium, T. pulchellus and Myrmecoris gracilis. The study also embraces three species which belong to the tribe Mirini, and play the role of an out-group in the conducted analyses. These species are: Adelphocoris seticornis, Calocoris affinis and Lygus rugulipennis. On the basis of total preparations, cross and longitudinal sections, we have studied the number of testicular follicles, their dimensions, types of connections between follicles and vas deferens, the structure of vasa deferentia, as well as the number, structure and origin of accessory glands. The above-listed features have provided complementary information, alongside morphological features, helpful in verifying the taxonomic position of the tribe Stenodemini.

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.

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

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. 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. 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 bug's 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.