Effect of light colours and weather conditions on captures of Sogatella furcifera (Horváth) and Nilaparvata lugens (Stål)

To study the phototactic responses of white‐backed planthopper, Sogatella furcifera (Horváth) and brown planthopper, Nilaparvata lugens (Stål) to different wavelengths, four colours of light traps (blue, green, yellow and red light‐emitting diodes) were placed in the same rice field along with a traditional black light trap. This study revealed that S. furcifera and N. lugens are more attracted to blue and green lights than that to yellow and red lights. During the 24 nights, compared with the black light trap, the blue LED trap could catch more rice planthoppers at 17 nights. Furthermore, catches of other species (moths and beetles) were substantially reduced in blue LED light traps. Multiple regression models were developed to assess the effect of weather factors on light trap catches of rice planthoppers. Rainfall and mean air temperature at a night mainly affected light trap catches of S. furcifera. Higher rainfall and lower temperature increased light trap catches of S. furcifera. However, wind speed was the main factor affecting the catches of N. lugens, and the lower incidence of catches was found in the night when wind speed exceeded 3.08 m/s. S. furcifera may be flying against wind at light wind nights by 0.3–1.5 m/s, whereas N. lugens may be flying down at strong wind nights by 1.5–3.08 m/s. Relative humidity did not significantly influence on trap catches. Consequently, light wavelengths, precipitation, average temperature and wind should be considered when monitoring rice planthoppers by light traps. Therefore, the blue LED light traps are worth using for monitoring planthoppers.     

Chromosomal‐level genomes of three rice planthoppers provide new insights into sex chromosome evolution

The brown planthopper Nilaparvata lugens, white‐backed planthopper Sogatella furcifera, and small brown planthopper Laodelphax striatellus are three major insect pests of rice. They are genetically close; however, they differ in several ecological traits such as host range, migration capacity, and in their sex chromosomes. Though the draft genome of these three planthoppers have been previously released, the quality of genome assemblies need to be improved. The absence of chromosome‐level genome resources has hindered in‐depth research of these three species. Here, we performed a de novo genome assembly for N. lugens to increase its genome assembly quality with PacBio and Illumina platforms, increasing the contig N50 to 589.46 Kb. Then, with the new N. lugens genome and previously reported S. furcifera and L. striatellus genome assemblies, we generated chromosome‐level scaffold assemblies of these three planthopper species using HiC scaffolding technique. The scaffold N50s significantly increased to 77.63 Mb, 43.36 Mb and 29.24 Mb for N. lugens, S. furcifera and L. striatellus, respectively. To identify sex chromosomes of these three planthopper species, we carried out genome re‐sequencing of males and females and successfully determined the X and Y chromosomes for N. lugens, and X chromosome for S. furcifera and L. striatellus. The gene content of the sex chromosomes showed high diversity among these three planthoppers suggesting the rapid evolution of sex‐linked genes, and all chromosomes showed high synteny. The chromosome‐level genome assemblies of three planthoppers would provide a valuable resource for a broad range of future research in molecular ecology, and subsequently benefits development of modern pest control strategies.     

Direct and feeding‐induced interactions between two rice planthoppers, Sogatella furcifera and Nilaparvata lugens: effects on dispersal capability and performance

Abstract. 1. A series of laboratory experiments was conducted to explore the effects of inter‐specific interactions, both direct interactive effects and those induced through previous feeding, on the dispersal capability (proportion of macropterous adults) and performance (development time and survival) of two wing‐dimorphic planthoppers, the whitebacked planthopper Sogatella furcifera and the brown planthopper Nilaparvata lugens, two pests of rice throughout Asia. 2. An asymmetric effect of inter‐specific crowding on dispersal capability was detected between the two planthoppers. With density controlled, the proportion of macropterous adults in N. lugens was higher when raised in mixed populations with S. furcifera than in pure cultures comprised of conspecifics, suggesting that interspecific effects on dispersal capability are stronger than intraspecific effects. In contrast, interspecific effects on macroptery (%) were weaker than intraspecific impacts for S. furcifera. 3. This trend was parallelled by adverse competitive effects on survival, with interspecific effects stronger than intraspecific impacts for N. lugens and intraspecific effects stronger for S. furcifera. 4. Crowding also affected the incidence of macroptery indirectly through feeding‐induced changes in plant physiology. Rearing N. lugens on plants fed on previously by heterospecifics resulted in a higher incidence of macroptery in females and protracted development than for N. lugens raised on plants fed on previously by conspecifics. By contrast, the intraspecific effect of previous feeding was stronger than the interspecific effect in S. furcifera, with higher macropter production and prolonged development occurring on plants exposed previously to conspecifics. 5. The results suggest that interspecific interactions between herbivorous insects, both direct and via feeding‐induced changes in plant physiology, can have negative consequences for performance and survival and promote the production of flight‐capable adults that can disperse.     

Effect of acetone solution in a topical application method on mortality of rice planthoppers, Nilaparvata lugens, Sogatella furcifera, and Laodelphax striatellus (Homoptera: Delphacidae)

The effect of acetone solution on the mortality of rice planthoppers, Nilaparvata lugens (St?l), Sogatella furcifera (Horváth), and Laodelphax striatellus (Fallén), was examined, as it is widely used as a solvent solution in a topical application method for monitoring insecticide susceptibility. The mortality of N. lugens and S. furcifera was significantly higher at 0.32 and 0.28 μl or more acetone droplets per insect than in the control treatment (without acetone), respectively. The mortality of L. striatellus was significantly higher at 0.24 μl or more acetone droplets per insect than in the control treatment. Another commonly used solvent solution, methanol, had a similar effect on L. striatellus. The most standard topical application method uses a hand-operated micro-applicator (Burkard Manufacturing Co., Ltd., UK) equipped with a 50-μl micro-syringe, which can deliver a very small amount of droplets of insecticide/acetone solution per insect, 0.08 μl, so there is no effect of acetone solution on the mortality of N. lugens, S. furcifera, and L. striatellus. However, other equipment for topical application, a repeating dispenser (Hamilton Co., USA) attached with a 10-μl micro-syringe, can deliver a 0.24-μl droplet at a minimum. This equipment can be used for N. lugens and S. furcifera, but not for L. striatellus. It is necessary to choose appropriate equipment for each rice planthopper so that they are not affected by the solvent solution.     

The strepsipteran parasite <Emphasis Type="Italic">Elenchus japonicus</Emphasis> (Strepsiptera,Elenchidae) of planthoppers consists of three genotypes

The twisted-wing parasite Elenchus japonicus is a major parasitoid of rice planthoppers (Hemiptera: Delphacidae), including the brown planthopper Nilaparvata lugens, the white-backed planthopper Sogatella furcifera, and the small brown planthopper Laodelphax striatellus. Another Elenchus species, E. yasumatsui, which is considered to be synonymous with E. japonicus, has also been described in southern Asia. However, limited biological and molecular data on this important parasitoid of rice planthoppers are available. In this study, E. japonicas-stylopized planthoppers were obtained from various regions in Asia and Japan. Sequences of the nuclear 18S ribosomal RNA gene and the mitochondrial cytochrome oxidase I gene of the strepsipterans were analyzed from 40 samples of E. japonicus: 14 from N. lugens, 6 from S. furcifera and 20 from L. striatellus. Sequence analysis of these samples revealed three genotypes of E. japonicus. Of the three types of E. japonicus, one was isolated only from L. striatellus from northern Japan. The other two types were found in all three rice planthopper species collected from a wide area in Asia. These results suggest that the three different genotypes of Elenchus can be associated with a particular geographical region and/or planthopper species. The relationship between two previously described Elenchus species and the present three genotypes needs to be elucidated.     

Induction of P450 genes in Nilaparvata lugens and Sogatella furcifera by two neonicotinoid insecticides

Nilaparvata lugens and Sogatella furcifera are two primary planthoppers on rice throughout Asian countries and areas. Neonicotinoid insecticides, such as imidacloprid (IMI), have been extensively used to control rice planthoppers and IMI resistance consequently occurred with an important mechanism from the over‐expression of P450 genes. The induction of P450 genes by IMI may increase the ability to metabolize this insecticide in planthoppers and increase the resistance risk. In this study, the induction of P450 genes was compared in S. furcifera treated with IMI and nitromethyleneimidazole (NMI), in two planthopper species by IMI lethal dose that kills 85% of the population (LD₈₅), and in N. lugens among three IMI doses (LD₁₅, LD₅₀ and LD₈₅). When IMI and NMI at the LD₈₅ dose were applied to S. furcifera, the expression changes in most P450 genes were similar, including the up‐regulation of nine genes and down‐regulation of three genes. In terms of the expression changes in 12 homologous P450 genes between N. lugens and S. furcifera treated with IMI at the LD₈₅ dose, 10 genes had very similar patterns, such as up‐regulation in seven genes, down‐regulation in one gene and no significant changes in two genes. When three different IMI doses were applied to N. lugens, the changes in P450 gene expression were much different, such as up‐regulation in four genes at all doses and dose‐dependent regulation of the other nine genes. For example, CYP6AY1 could be induced by all IMI doses, while CYP6ER1 was only up‐regulated by the LD₅₀ dose, although both genes were reported important in IMI resistance. In conclusion, P450 genes in two planthopper species showed similar regulation patterns in responding to IMI, and the two neonicotinoid insecticides had similar effects on P450 gene expression, although the regulation was often dose‐dependent.     

Susceptibility and tolerance in hybrid and pure‐line rice varieties to herbivore attack: biomass partitioning and resource‐based compensation in response to damage

Hybrid rice has been noted for its susceptibility to insects and diseases compared to pure‐line (conventional) rice varieties. We investigated herbivory by Nilaparvata lugens, Sogatella furcifera and Scirpophaga incertulas on replicated three‐line hybrid sets (parental and hybrid lines) in field and greenhouse experiments. In a field experiment, caterpillar densities and stemborer damage was similar among hybrid and parental lines. In field and greenhouse experiments, the cytoplasmic male sterile (CMS)‐lines and maintainer lines had higher densities of planthoppers (including N. lugens and S. furcifera) than restorer or hybrid lines likely because of their wild abortive CMS‐lineage. High nitrogen levels increased plant mortality due to N. lugens, but often reduced mortality from S. furcifera and S. incertulas: this was similar between hybrid and pure‐line varieties. The hybrids were generally more tolerant of herbivory (lower biomass reductions per unit weight of insect) than the inbred parental lines. The addition of nitrogen to both the hybrid and pure‐line varieties had contrasting effects on tolerance depending on the nature of the attacking insect: fertiliser increased tolerance to S. furcifera (lower losses of yield and shoot biomass per mg insect) and S. incertulas (lower yield, shoot and root biomass loss) but fertiliser reduced tolerance to N. lugens (higher loss of root biomass and no effects on yield and shoot biomass loss). Our results indicate that hybrid rice is not physiologically more susceptible to herbivores than are pure‐line varieties even under high nitrogen conditions, but does have higher tolerance to insect damage.     

Occurrence and short-distance migration of Nilaparvata lugens (Hemiptera: Delphacidae) in the Vietnamese Mekong Delta

In migration analysis of the brown planthopper, Nilaparvata lugens (Stål), in a tropical region, it is difficult to know the arrival timing of the immigrants because rice plants in different growth stages are simultaneously cultivated, and local insects may already occur in destination areas. Due to this analytical difficulty, additional information is necessary to discriminate between immigrants and locally originated individuals in the light trap catch. This study applied rice phenology maps retrieved from satellite images to analysis of N. lugens’s migration in the Vietnamese Mekong Delta. The analysis also employed occurrence data by dense light traps and trajectory analysis. The result showed that the occurrence of N. lugens peaked periodically at an interval of 27.2–30 days, changing in association with the rice cropping area in the harvesting stage. For an N. lugens occurrence in late July 2009 in the delta, the rice phenology suggested catch increases in light traps in a destination area could likely be attributed to immigrants from outside the area. Therefore, the migration analysis suggested that N. lugens that emigrated from paddy fields in An Giang and Kien Giang provinces possibly moved to east-neighboring provinces. The migration distance was estimated to be about 100 km at a maximum.     

Evidence of sibling species between two host-associated populations of brown planthopper, N. lugens (stål) (Homoptera: Delphacidea) complex based on morphology and host–plant relationship studies

Morphological and host–plant relationship studies were conducted to differentiate two sympatric populations of brown planthopper (BPH), Nilaparvata lugens, one from rice (Oryza sativa) and the other from Leersia hexandra, a weed grass. In morphometric studies based on esterase activities, an UPGMA dendrogram using 17 quantitative morphological characters, including stridulatory organs (courtship signal-producing organs) between two sympatric populations of N. lugens, one from rice and the other from L. hexandra, a weed grass revealed that both populations were separated from each other. An out-group, N. bakeri, was found to be completely different from the two sympatric populations of N. lugens. Rice plants were best suited for the establishment of the rice-infesting population, and L. hexandra was a favourable host for the Leersia-infesting population. The individuals derived from one host did not thrive on the other host, as shown by a significant reduction in survival and nymphal development, ovipositional preferences, ovipositional response, and egg hatchability. Therefore, morphological and host–plant relationship studies indicate that rice-associated population with high esterase activities and L. heaxandra-associated population with low esterase activities are two closely related sibling species.     

Accumulation of salicylic acid,jasmonic acid and phytoalexins in rice, <Emphasis Type="Italic">Oryza sativa</Emphasis>, infested by the white-backed planthopper, <Emphasis Type="Italic">Sogatella furcifera</Emphasis> (Hemiptera: Delphacidae)

In order to clarify the mechanism of induced resistance to blast disease in rice, Oryza sativa, that had been previously infested by the white-backed planthopper, Sogatella furcifera Horváth, we first investigated the accumulation of salicylic acid (SA) and jasmonic acid (JA) in rice plants infested by the planthopper. The results confirmed that infestation of S. furcifera strongly stimulates the production of SA and JA in rice. These results indicate that both salicylate- and jasmonate-mediated pathways (SA and JA pathways), which are involved in the general defense system in plants, were activated in rice infested by S. furcifera. Further results confirmed that S. furcifera infestation induces accumulation of a major rice diterpenoid phytoalexin, momilactone A, and a flavonoid phytoalexin, sakuranetin, which are well known as antimicrobial chemicals, particularly in blast disease caused by the blast fungus, Magnaporthe oryzae B. Couch. All these results strongly suggest the following hypothetical mechanism of induced-resistance to M. oryzae in rice infested by S. furcifera. First, S. furcifera releases some elicitor-active compounds, which might be produced in the salivary glands, into the rice plant during feeding. Next, the defense signal systems, SA- and JA-mediated pathways, are activated by the elicitor. Finally, phytoalexins are induced in rice as antimicrobial compounds mainly through activation of the JA-mediated pathway.     

Flight duration of the brown planthopper, Nilaparvata lugens (Homoptera: Delphacidae)

ABSTRACT.

• 1 The brown planthopper, Nilaparvata lugens (Stål), is a major pest of rice in Asia. It is known to make wind-assisted migratory flights each year to colonize the summer rice growing areas of China, Japan and Korea.
• 2 Modelling windborne displacements between rice growing areas in Asia requires migratory behaviour and flight duration to be established for this insect.
• 3 Field and laboratory observations suggest that N. lugens take-off at dusk and that some continue flying for up to 24–26 h if the temperature is ≥ 17°C.
• 4 Trajectories for 10 m above ground level and 1.5 km above mean sea level are used to identify possible sources and, hence, to estimate the flight times of N.lugens caught in nets on ships on the East China Sea in 1973 and 1981.
• 5 Estimated flight times between the sources and the ships ranged from about 9 to 30 h.
• 6 Results suggest that long-distance migration can occur in surface winds, when they are strong, but that long-distance migration is more likely at 1.5 km.
• 7 When simulating windborne displacements of N.lugens, it can be assumed that in areas and at heights where the temperature is ≥ 17°C, some migrants will fly downwind for up to 30 h after a dusk take-off. Others will fly for shorter periods, giving the population as a whole the opportunity to colonize all the rice crops flown over.

     

Functional significance of Micraspis discolor (F.) (Coccinellidae: Coleoptera) in rice ecosystem

Coccinellids are key predators that are conserved and augmented in agricultural ecosystems, to achieve biological control of pests. Actual quantification of field predation has not been attempted for many of the beneficial coccinellids. Numerous reports show coccinellids as opportunistic, feeding on a variety of food material in addition to their preferred prey. Micraspis discolor is the most abundant species of coccinellid in rice ecosystems and touted as a biocontrol option for brown planthopper (BPH), Nilaparvata lugens (Stal), a key pest of rice. However, it has been reported as both entomophagous and phytophagous. Native polyacrylamide gel electrophoresis (PAGE) was used to separate esterases from whole‐body homogenates of Micraspis and its prey viz., green leafhopper (GLH) Nephotettix virescens (Distant), BPH N. lugens, whitebacked planthopper (WBPH) Sogatella furcifera (Horvath), aphid Rhopalosiphum padi L., thrips, Haplothrips sp., and pollen. Field‐collected beetles showed a range of bands, some corresponding with pollen and GLH, while others were different from prey offered, indicating a wider range of prey spectrum than envisaged. Feeding preference studies confirmed a preference for pollen and GLH in no‐choice (H = 20.724; P = 0.001) and multiple‐choice tests (H = 20.52; P < 0.001) and a significant preference for pollen over all insects offered in the paired‐choice test (t = 5.099; P = 0.007). The abundance of adult M. discolor in rice at flowering phase does not correspond to prey abundance in the field but rather reflects an inclination to pollen feeding more than entomophagy.     

Host-recognition kairomone from Sogatella furcifera for the parasitoid Anagrus nilaparvatae

A kairomone produced by the rice white-backed planthopper Sogatella furcifera (Horvath) for the mymarid egg parasitoid Anagrus nilaparvatae Pang et Wang was investigated. Eggs, female and male adults, nymphs, exuvia, honeydew, nymph-damaged plants and plants with S. furcifera eggs all elicited searching behavior in the parasitoid. Eggs, female adults and plants with eggs were the most attractive, while exuvia and honeydew evoked the weakest responses. The active compound(s) from S. furcifera female adults, nymphs and plants with eggs could be effectively extracted with methanol, acetone, n-hexane, ethyl ether and dichloromethane. Isolation of the active chemical(s) in three solvent extracts, the acetone and n-hexane extracts of S. furcifera female adults, and the acetone extract of S. furcifera nymphs, was accomplished by thin-layer chromatography. Only one fraction was active and had the same chemical properties in the three solvent extracts. Infra-red analysis of this fraction revealed a kind of ester with saturated and unsaturated fatty acids, which was previously found to be active in the same compound as the extracts from the nymphs and female adults of the rice brown planthopper, Nilaparvata lugens (Stål), and identified as palm oil. The results are discussed in relation to host location by A. nilaparvatae.     

水稻褐飞虱内生共生细菌Arsenophonus的鉴定和系统分析

利用16S rDNA通用引物扩增了水稻褐飞虱Nilaparvata lugens（Stål）体内共生细菌的序列,经克隆、测序和NCBI数据库比对,发现褐飞虱体内存在杀雄菌属Arsenophonus类共生细菌,系统发育上与粉虱科和木虱科体内的Arsenophonus属亲源关系较近。在褐飞虱体内该共生细菌具有两种长度不同的16S rDNA序列,分别为1 504 bp和547 bp,其中后者为前者中间缺失了957 bp,其余序列相同。通过重新设计两对引物进行扩增,进一步确认不同褐飞虱地理种群及寄主种群均存在两种片段。Arsenophonus特异的 23S rDNA引物的扩增结果表明,Arsenophonus存在于所有检测的褐飞虱种群中,但不存在于水稻寄主中。荧光定量PCR检测发现3个褐飞虱室内寄主种群Arsenophonus属共生细菌含量不同,其中TN1种群明显高于Mudgo种群和ASD7种群。此为水稻褐飞虱体内存在Arsenophonus属共生细菌的首次报道。     

Biochar amendment to soils impairs developmental and reproductive performances of a major rice pest Nilaparvata lugens (Homopera: Delphacidae)

Biochar amendments to soils had aroused much interest for having potential for greenhouse gas mitigation, soil improvement and increased crop productivity. However, little attention had been focused on the influence of biochar amendments on herbivorous insect pests. This study investigated whether a biochar amendment affected developmental and reproductive performances of the rice brown planthopper (Nilaparvata lugens) feeding on rice plants. The biochar from the pyrolysis of wheat straw was used for treatments of soils (from a fallow rice field), and the treated soils were applied to grow rice seedlings in small vials, in which N. lugens life history was observed. The nymphal development time was delayed and nymph‐to‐adult survival decreased with a high level of 200 g/kg biochar application. Herbivore lifetime fecundity decreased with increasing amounts of biochar, from 256 eggs under the control down to 69 eggs under the high level (200 g/kg) of biochar application. Egg‐hatching rate significantly decreased at the highest biochar level (200 g/kg), compared to the other lower biochar levels. Our results suggest that biochar amendment to rice fields may have negative impacts on the rice brown planthoppers when applied at level of 200 g/kg of soil.     

QUANTIFYING PREDATION BY UMMELIATA INSEC-TICEPS BOES. ET STR. (ARANEAE: LINYPHIIDAE) ON RICE PLANTHOPPERS USING ELISA*

Abstract An enzyme-linked immunosorbent assay (ELISA) has been developed to quantify predation by Ummeliata insecticeps Boes. et Str. on rice planthoppers in paddy fields in Dasha Township, Guangdong Province. The assay was completely specific for rice planthopper materials. The detection periods for antigens after an adult of U. insecticeps had fed on three 3–5th instar nymphs of white-back planthopper (WBPH), Sogatella furcifera (Horvath), and brown planthopper (BPH), Nilaparvata lugens (Stal), at room temperature were 96 h and 120 h, respectively. The proportion of individual species of predators scoring positive ranged from 19. 05% to 47. 34% for WBPH, and from 9. 25% to 66. 67% for BPH in the early rice season. Although the numbers of the rice planthoppers consumed by U. insecticeps increased with increasing prey densities, the predation rates declined. When rice planthopper densities were low, the predation rates were relatively high. This kind of predation can explain why the rice planthoppers have never reached outbreak levels in rice fields in Dasha Township since 1973.     

Elicitor(s) in Sogatella furcifera (Horváth) Causing the Japanese Rice Plant (Oryza sativa L.) to Induce the Ovicidal Substance,Benzyl Benzoate

We elucidate the mechanism for inducing the production of ovicidal benzyl benzoate by Japonica rice varieties to kill eggs of the whitebacked planthopper, Sogatella furcifera (Horváth), lying in the rice plant. Even when subjected to physical damage by a needle or damage with water, the rice plant produced no benzyl benzoate. However, significant benzyl benzoate was produced when the plant was damaged with a methanol extract or homogenate of S. furcifera. The extract of the male did not induce the production of benzyl benzoate, but that of the female did. We concluded from these results that benzyl benzoate was induced by some elicitor(s) in the female of S. furcifera.     

Prey preference of the wolf spider,Pardosa pseudoannulata (Boesenberg et Strand)

Functional responses of the wolf spider, Pardosa pseudoannulata (Boesenberg et Strand) attacking the rice brown planthopper, Nilaparvata lugens (Stål.), and the mirid predator Cyrtorhinus lividipennis Reuter were both those of Holling Type II. The attack rate was higher and handling time lower for C. lividipennis. However, when caged with the two prey, the wolf spider showed a significant preference for N. lugens at a lower prey proportion. Proportions of prey attacked were significantly different from the expected ratios of prey available as well as from the predicted preferences derived from the functional response parameters. As proportions of N. lugens attacked changed from greater to less than expected as the proportions of N. lugens available increased, a “reverse switch” behaviour seems to be evident.     

基于rDNA ITS1和ITS2序列的褐飞虱、白背飞虱和灰飞虱的分子鉴定

本研究测定了褐飞虱Nilaparvata lugens、白背飞虱Sogatella furcifera和灰飞虱Laodelphax striatellus的rDNA ITS1和ITS2的序列, 以探讨这3种稻飞虱的分子鉴定方法。3种飞虱的ITS1和ITS2侧翼区（18S, 5.8S和28S）序列相对稳定, 但ITS1和ITS2序列在3种飞虱中变异较大。 ITS1在所分析的438个位点中可变位点达294个, ITS2在分析的403个位点中可变位点为177个。根据3种飞虱rDNA的ITS1和ITS2序列设计了特异性引物, 应用特异性引物对样品进行了PCR扩增, 分析发现3种飞虱ITS1区的特异性引物扩增效果不理想, 而ITS2区的特异性引物可以稳定地扩增出明显的目的DNA条带. 因此, 采用ITS2区的特异性引物可以对3种飞虱进行快速的分子鉴定。