Pecky Rice Research Articles

Current Status of Breeding of Rice Cultivars with Resistance to Pecky Rice Incidence Caused by the Stink Bugs

Current Status of Breeding of Rice Cultivars with Resistance to Pecky Rice Incidence Caused by the Stink Bugs

Egg parasitoid wasps of the rice bug, <i>Leptocorisa chinensis</i> (Hemiptera: Alydidae) in the southern part of Shiga Prefecture

The rice bug, Leptocorisa chinensis (Hemiptera: Alydidae) is a pest insect that feeds on rice ears, resulting in pecky rice. We collected the eggs of rice bugs in grassland overgrown with gramineous plants on July 17 and 24, 2018, in the southern part of Shiga Prefecture, and then investigated the species of egg parasitoids. Four species of egg parasitoids, Hadronotus japonicus and H. nigricornis (Hymenoptera: Scelionidae) and Ooencyrtus nezarae and O. acastus (Hymenoptera: Encyrtidae), emerged from the eggs of rice bugs. Two species of wasps considered to be dominant, namely, H. japonicus and O. nezarae, exhibited high percentages of parasitism. Our study also recorded O. acastus parasitizing L. chinensis eggs for the first time in the literature.

Resistance factors of pecky rice incidence caused by the rice stink bugs (Leptocorisa chinensis, Nezara viridula) in rice line CRR-99-95W

ABSTRACT Pecky rice incidence caused by rice stink bugs greatly decreases the quality of rice grain and has come a big problem not only in Japan but also many other rice producing countries recently. In this study, antixenosis and tolerance were examined as the factors of resistance to rice stink bugs attack of rice line CRR-99-95 W. Two experiments were conducted to determine a possibility of antixenosis involvement as a factor of the resistance in CRR-99-95 W. The results showed no correlation between the number of Leptocorisa chinensis parasites and pecky rice incidence. Furthermore, no significant difference was found between the sucking frequency of Nezara viridula on mature husks of CRR-99-95 W and that on the check genotypes. These results suggest that CRR-99-95 W does not exhibit antixenosis effect against rice stink bugs. Then, to examine the tolerance factor involved in the resistance mechanism, the husks structures were analyzed. The results showed that the packing ratio of cell wall of the sclerenchyma fibers in the palea tended to be higher in CRR-99-95-W compared to the check genotype. In addition, the width of the hook openness of the palea of CRR-99-95 W was narrower than that of the check genotype. Such morphological characteristic of CRR-99-95 W may play an important role in its resistance against stink bug attack.

Intraspecific variations in life history traits of two pecky rice bug species from Japan: Mapping emergence dates and number of annual generations.

The mirid bugs Stenotus rubrovittatus and Trigonotylus caelestialium, which cause pecky rice, have become a threat to rice cultivation in Asia. Damage caused by these pests has rapidly become frequent since around 2000 in Japan. Their expansion pattern is not simple, and predicting their future spread remains challenging. Some insects with wide ranges have locally adapted variations in life‐history traits. We performed laboratory rearing experiments to assess the geographical scale of intraspecific variations in life‐history traits of S. rubrovittatus and T. caelestialium. The experiments were aimed at increasing the accuracy of occurrence estimates and the number of generations per year. These results were compared with previous research, and differences in development rates were observed between populations of different latitudes, but not of the same latitude. Finally, plotting the timing of adult emergence and the potential number of generations per year on maps with a 5‐km grid revealed that they differed greatly locally at the same latitude. These maps can be used for developing more efficient methods of managing mirid bugs in integrated pest management.

Indirect effects of weeds on rice plants via shared heteropteran herbivores

AbstractIn agricultural ecosystems, weeds indirectly affect crops via phytophagous insects that feed on both weeds and crops. In paddy fields, heteropteran insects are among the most serious pests of rice plants. In some heteropterans, the proboscis is used to suck rice ears, inducing black spots on the grains (i.e., pecky rice). Even a low proportion of pecky rice (>0.1%) significantly decreases the market price of rice; in Japan, this problem has led to severe economic losses. Because heteropterans feed on the reproductive organs of weeds as well as rice plants, various weeds that grow around paddy fields may increase the populations of heteropterans that cause pecky rice. To clarify which types of weeds can be used by heteropterans causing pecky rice, we investigated the interactions between plants (including rice plants) and heteropterans in an agricultural landscape in Hyogo, Japan. We observed 833 individuals of 27 heteropteran species (13 families) feeding on the reproductive organs of 35 plant species (Poales: three families) including rice plants from June to October 2019. All heteropteran species were native, whereas six of 35 plant species were non‐native. We found 12 heteropteran species on rice plants; nine of the 12 heteropteran species fed on weeds (a total of 32 species) as well as rice plants, whereas the other three species fed exclusively on rice plants. Heteropterans fed on native weeds throughout the growing seasons (June–October), but on non‐native weeds only before rice plants bloomed (June–July). Therefore, diverse weed species that grow around paddy fields are food resources for heteropteran insects and they might indirectly increase the incidence of pecky rice.

Effects of insecticides on the five species of rice bugs causing pecky rice in Shiga Prefecture

Effects of insecticides on the five species of rice bugs causing pecky rice in Shiga Prefecture

Effects of Pecky Rice Bugs in a Forage Rice Field on the Adjacent Staple Rice Field

Effects of Pecky Rice Bugs in a Forage Rice Field on the Adjacent Staple Rice Field

The Effect of Several Insecticides on Pecky Rice Bugs

The Effect of Several Insecticides on Pecky Rice Bugs

The role of Oryza sativa L. 'Milyang 44' husks on the resistance to two rice stink bugs.

To elucidate the resistance mechanisms of the rice (Oryza sativa L.) cultivar ‘Milyang 44’ against rice stink bugs, we compared the number of stylet sheaths, husk perforations, and feeding marks on the surface of the grains caused by Leptocorisa chinensis and Cletus punctiger on Milyang 44 and the control cultivar, i.e., ‘Aichinokaori SBL’. We also examined the cross-sectional structure of the rice husks. We found that the number of stylet sheaths per panicle was higher in Milyang 44 than in Aichinokaori SBL for both rice stink bug species, except in one test involving C. punctiger. However, Milyang 44 had significantly less damage per number of stylet sheaths than Aichinokaori SBL, resulting in a lower percentage rates of pecky rice grains in Milyang 44. Interestingly, there was no difference in the percentage rates of pecky rice between the two cultivars after removing one third of the husks. Histological analysis showed that the sclerenchymatous cell wall containing lignin of husk was thicker in Milyang 44 than in Aichinokaori SBL, suggesting that the husk of Milyang 44 plays an important role in its resistance to these two rice stink bug species.

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.

Is Halyomorpha halys (Hemiptera: Pentatomidae) a threat to California rice?

The brown marmorated stink bug Halyomorpha halys (Stål), is an invasive pest in California that represents a potential threat to California rice (Oryza sativa L.) production. Populations of H. halys can be found in the rice production regions of California but have not been detected in rice fields. We conducted greenhouse trials to determine if H. halys injures and potentially reduces yields in rice. We observed a 42% reduction in kernel weights during the milk stage in cages with H. halys adults in 2014. We observed a 30% increase in empty kernels in rice infested with H. halys and a 10–20% increase in pecky rice across various rice maturation stages in 2016. The results suggest that yield reductions in rice could occur if H. halys establishes on rice as a host plant in the United States. This is the first reported case of H. halys being able to feed on rice in North America.

Temperature-dependent development and oviposition models of Leptocorisa chinensis Dallas (Hemiptera: Alydidae)

Leptocorisa chinensis Dallas (Hemiptera: Alydidae) is known to cause pecky rice by sucking panicles of milk stage of rice. Based on its continuous spread and expanded damage area in Asian countries such as Japan with high reproduction potential, it is highly likely that L. chinensis will become an important rice pest in the near future. However, limited information is available to predict its distribution and occurrence. Thus, the objective of this study was to develop models for their development and oviposition. We investigated the development of L. chinensis immatures (from egg to adult) at 11 constant temperatures ranging from 16.2 to 35.3°C and the oviposition of female adults at five constant temperatures ranging from 22.3 to 35.3°C in this study. For L. chinensis immatures, the lower developmental threshold temperature, optimal developmental temperature, upper developmental threshold temperature were 12.7, 32.3, and 37.6°C, respectively. The highest survival rate of immatures was observed at temperature of 25.2°C and the highest mean total fecundity was 585.8 at 28.0°C. This study provides basic information for the ecology of L. chinensis. It is applicable to forecast the phenology of its populations in the fields and to predict its future distribution under global warming.

Predicting potential rice damage by insect pests using land use data: A 3-year study for area-wide pest management

Abstract To mitigate crop damage by insect pests, it is important to determine priority areas for the allocation of available pest management resources, which are usually limited. We tested whether the occurrence of pecky rice damage caused by the sorghum plant bug Stenotus rubrovittatus (Hemiptera: Miridae), a major rice pest in Japan, could be predicted using a spatial model based on land use data. Using a data from a 3-year field study, we examined the relationships among the land use of the area within a 300-m radius around each focal paddy field, the abundance of S. rubrovittatus, and level of pecky rice damage in the Maesawa region of northern Honshu Island, Japan. We also used mapping to visualize potential priority areas using a model and GIS software. From a linear mixed model analysis and model selection by Akaike’s information criterion values, areas of source habitats, soybean fields and rice paddies were selected for the best model, but the abundance of S. rubrovittatus was not. Based on the model’s evaluation, the predicted value of pecky rice damage, when compared with the observed value, was not sensitive enough for a quantitative prediction. However, the model was accurate enough to predict whether the brown rice was first grade, which is of greatest importance to local farmers. Therefore, it is possible that potential pecky rice damage by S. rubrovittatus could be predicted when the spatial arrangement of arable fields in a certain year is determined. Our results will be useful to support decision-making that involves insecticide applications to mitigate pecky rice damage.

斑点米カメムシ抵抗性系統 「CRR-99-95W」 の斑点米低減要因

斑点米カメムシ抵抗性系統 「CRR-99-95W」 の斑点米低減要因

Reducing Effect of Isoprothiolane on the Number of Cracked Hull Grains and the Pecky Rice

Reducing Effect of Isoprothiolane on the Number of Cracked Hull Grains and the Pecky Rice

Risk Factor Analysis for Injuries at Sutures of Pecky Rice Grains in Iwate Prefecture, Japan

Risk Factor Analysis for Injuries at Sutures of Pecky Rice Grains in Iwate Prefecture, Japan

Food Preference of Pecky Rice Bugs Is Influenced by Experience

This study investigated whether prior experience influences the plant food preference of Trigonotylus caelestialium and Stenotus rubrovittatus which cause pecky rice grain, by using rice plants and 2 poaceous weeds. In a choice experiment between Digitaria ciliaris and the rice plants, both T. caelestialium and S. rubrovittatus adults that were reared on D. ciliaris plants showed significant initial preference for D. ciliaris over rice. In a choice experiment between Echinochloa crus-galli var. aristata and rice plants, T. caelestialium adults reared on E. crus-galli var. aristata strongly preferred E. crus-galli var. aristata over rice throughout the experiment. However, at and after 24 h, T. caelestialium adults reared on rice showed no food preference, although T. caelestialium initially preferred E. crus-galli var. aristata. In contrast, S. rubrovittatus adults reared on rice showed no preference between E. crus-galli var. aristata and rice. However, S. rubrovittatus reared on E. crus-galli var. aristata initially preferred E. crus-galli var. aristata to rice, with this preference waning with time. The same results were obtained for both sexes. Although the effect of experience differed with food source and the species of mirid bug, prior experience initially had a noticeable effect, which disappeared with time (1 d).

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.

A pecky rice-causing stink bug Leptocorisa chinensis escapes from volatiles emitted by excited conspecifics

The stink bug Leptocorisa chinensis (Hemiptera: Alydidae), which causes pecky rice grains, emits pungent volatiles when disturbed. To study ecological functions of the volatiles, we investigated the responses of adult L. chinensis in a small observation arena. When an undisturbed individual of the same gender was introduced into the arena, the initially occupying L. chinensis did not show any behavioural responses. However, when a disturbed conspecific of the same gender was introduced, the initial occupant was excited immediately and escaped from the arena through the hole, suggesting that the pungent volatiles from a disturbed conspecific caused excitement/escape behaviour. Chemical analyses using a gas chromatograph–mass spectrometer showed that disturbed adults of both sexes emitted octanal, (E)-2-octenal, octanol, hexyl acetate, (Z)-3-octenyl acetate, octyl acetate and (E)-2-octenyl acetate. (E)-2-Octenal was the major compound. When exposed to (E)-2-octenal and to (E)-2-octenyl acetate, undisturbed females were excited and escaped from the observation arena with a similar proportional response as to disturbed females. Males and females escaped from (E)-2-octenal at ca. 2–10 ppbV in a mesh cage. The possible use of the volatile compounds eliciting excitement/escape behaviour in L. chinensis for control of this species in paddy fields is discussed.

Control of Sorghum Plant Bug, Stenotus rubrovittatus Causing Pecky Rice by Mowing Paddy Levees after Insecticide Application at the Late Ripening Stage of Rice Plants

Control of Sorghum Plant Bug, <i>Stenotus rubrovittatus </i>Causing Pecky Rice by Mowing Paddy Levees after Insecticide Application at the Late Ripening Stage of Rice Plants