Green Rice Leafhopper Research Articles

Electrically Recorded Feeding Behavior of Nephotettix cincticeps

Feeding activities of the green rice leafhopper (GRL), Nephotettix cincticeps, on rice plants were electrically monitored with a high impedance D.C. pre-amplifier, specifically to avoid any external currents during the preparation. Behaviors of the insect were also monitored with a video camera fitted with a macro lens and honeydew excretion was recorded. When freed to choose feeding sites, GRLs fed mainly on the leaf blade although some feeding took place on the leaf sheath (80% : 20% of time spent feeding, respectively). On the leaf blade, GRLs fed mainly on the adaxial surface and their probing was distributed evenly throughout the entire surface of the leaf, veins being penetrated directly. On the leaf sheath, GRLs mainly probed on the adaxial protoderm (31%) and at the borders of vascular bundle (41%). Direct injection of a stylet into veins rarely took place and vascular bundles were approached indirectly. Microsections of leaf blades and sheaths were analyzed in order to correlate the electrical penetration graphs (EPGs) recorded with the insect's stylet probing. Waveforms corresponding to stylet probing in the epidermis and parenchyma (type S), and in the lacuna and all other areas outside the vascular bundle (type O) were identified on the leaf sheath and blade. On the leaf sheath, waveforms corresponding to probing in the xylem (type X) and phloem (type Ph) were found. On the leaf blade, where sections showed that GRLs were probing in very small vascular bundles in many cases, one pattern, corresponding to vascular bundle probing (type XP) was found and distinct patterns corresponding to stylet positions in either phloem or xylem were not found. Electrical monitoring showed that the GRLs spend most of their time probing in vascular bundles (84% blade, 81% sheath) and, on the sheath, more time is spent in the phloem bundle sheath (55%). When feeding on the leaf blade, GRLs spend 12% of their time probing in the parenchymatous tissue, although relatively less time is spent doing this on the sheath. When EPG recording was combined with monitoring honeydew excretion, an extremely high rate of excretion was discovered where xylem probing in the sheath is accompanied.

Possible difference in the structure of acetylcholinesterase between insecticide susceptible and resistant strains of Culex tritaeniorhynchus resulted from structure-activity relationship of 3-alkylsulfonylphenyl methanesulfonates

Acetylcholinesterase (AChE) inhibiting activity of eight 3-alkylsulfonylphenyl methanesulfonates was measured and its relationship with the structure of substituted alkyl moieties was analyzed in susceptible and resistant strains of Culex tritaeniorhynchus. The activity of the compounds was not so potent as that for the green rice leafhopper, Nephotettix cincticeps, previously reported. However, a parabolic relationship of the activity was detected with the distance between the S atom and the distal C atom of the alkyl moiety. The shape of the parabolic curve and the optimum distance were the same in susceptible and resistant strains, but the activity was about 100 times higher for AChE of the susceptible strain than for that of the resistant strain. No significant relationship was detected with the steric constant. An activity structure relationship was, however, detected with the steric constant in N. cincticeps, but not with the distance S-C, based on the previous results. Considering that the sulfone moiety of methanesulfonates conjugates with the esteratic subsite of the AChE active site to inhibit its activity, a structural change apparently occurred in the esteratic subsite of AChE in the resistant strain of C. tritaeniorhynchus, and was different from that of N. cincticeps.

Response of Green Rice Leafhoppers to Rice-Planting Practices in Northern Thailand

Recent changes in rice-seeding practices in Thailand have altered the traditional density and spatial dispersion of rice plants in a field. Typical transplanted fields have a low density of uniformly spaced plants, whereas broadcast or direct-seeded fields have a high density of irregularly dispersed plants. Effects of these variations in plant texture on the abundance and movement of important rice pests, the green rice leafhoppers, Nephotettix virescens and N. nigropictus, were examined in controlled field experiments in Chiang Mai, Thailand, in 1989 and 1991. Nephotettix colonized broadcast fields more quickly than transplanted fields and peaked in both types of fields when rice plants reached panicle initiation, suggesting phenological synchrony with crop development. Although leafhoppers did not respond consistently to treatment changes in plant or tiller density, leafhopper load per plant was highest in transplanted rice fields of low plant density and uniform dispersion. Visual stimuli during colonization and subsequent phenological changes in plant quality appeared to influence seasonal patterns of leafhopper abundance. Nephotettix movement was greater in uniform transplanted fields than in irregular broadcast fields throughout most of the crop season, regardless of plant density. Eggs were more evenly distributed in transplanted fields than in broadcast fields, where they were more frequently found in border plants. Results suggest that, despite the delayed establishment of Nephotettix populations in transplanted fields, the combination of higher leafhopper load per plant and more frequent within-field movement could lead to greater incidence of leafhopper-transmitted pathogens in transplanted than in broadcast rice. The greater risk of crop loss to leafhopper-transmitted viruses would be influenced by the amount of viral inoculum in surrounding areas and possibly partially offset by higher yields in transplanted rice. Factors associated with seeding practice, rather than plant or tiller density per se, most influenced the leafhoppers’ abundance and movement patterns.

RESPONSE OF GREEN RICE LEAFHOPPERS TO RICE-PLANTING PRACTICES IN NORTHERN THAILAND

Recent changes in rice-seeding practices in Thailand have altered the traditional density and spatial dispersion of rice plants in a field. Typical transplanted fields have a low density of uniformly spaced plants, whereas broadcast or direct-seeded fields have a high density of irregularly dispersed plants. Effects of these variations in plant texture on the abundance and movement of important rice pests, the green rice leafhoppers, Nephotettix virescens and N. nigropictus, were examined in controlled field experiments in Chiang Mai, Thailand, in 1989 and 1991. Nephotettix colonized broadcast fields more quickly than transplanted fields and peaked in both types of fields when rice plants reached panicle initiation, suggesting phenological synchrony with crop development. Although leafhoppers did not respond consistently to treatment changes in plant or tiller density, leafhopper load per plant was highest in transplanted rice fields of low plant density and uniform dispersion. Visual stimuli during colon...

Graphical genotypes of rice parental lines for resistance to green rice leafhopper

Graphical genotypes of rice parental lines for resistance to green rice leafhopper

Purification and Characterization of Carboxylesterases of a Rice Green LeafhopperNephotettix cincticepsUhler

More than four carboxylesterase isozymes in the homogenate of a rice green leafhopper,Nephotettix cincticepsUhler, could be resolved by isoelectric focusing electrophoresis. A combination of ammonium sulfate fractionation, gel filtration, and chromatofocusing chromatography was used to isolate and purify these isozymes. Four fractions, i.e., E1, E2, E3, and E4, with pI's ranging from 5.1 to 4.85, were obtained. The most abundant E3 had a molecular mass of 58.6 kDa and appeared electrophoretically homogeneous on SDS–PAGE. [1,3-3H]Diisopropyl fluorophosphate-labeling experiment revealed that the proteins of 58.6 kDa, a minor component of E2 and the major component of E4, were the carboxylesterase isozymes sought. A protein of the same molecular weight which existed in a very minute amount in E1 and was barely detectable on SDS–PAGE by Coomassie blue staining was actually the carboxylesterase isozyme of pI5.1. All four fractions exhibited significant activity toward several model substrates with α-naphthyl butyrate being the most preferred. Their activity toward malathion, permethrin, and cypermethrin was ca. 106-fold lower than their activity toward the model substrates. The pyrethroids were hydrolyzed more readily than malathion by these hydrolases, andcis-permethrin was more preferred than thetrans-isomer. E4 was the only fraction that cross-reacted with the antiserum against carboxylesterases of a rice brown planthopper,Nilaparvata lugens.Among the four isozyme fractions, E3, the most abundant, showed surprisingly low activity toward all four insecticides and was actually the least active fraction towardcis-permethrin and cypermethrin. A field strain ofN. cincticepshad 26- to 37-fold higher carboxylesterase activity toward the model substrates than a susceptible strain. Yet, little, if any, difference in the hydrolysis of malathion, permethrin, and cypermethrin was observed between these two strains. The field strain produced at least eight times more carboxylesterases than the susceptible strain.

Glutathione-Dependent <i>O</i>-Alkyl and <i>O</i>-Aryl Conjugations for Dicapthon and Fenitrothion in Several Insects

Glutathione-dependent O-alkyl and O-aryl conjugations for 24 C-dicapthon (O, O-dimethyl O-2-chloro-4-nitrophenyl phosphorothionate) and 14 C-fenitrothion (O, O-dimethyl O-3-methyl-4-nitrophenyl phosphorothionate) were studied in the each cytosolic fraction prepared from the whole bodies of the azuki bean beetle, Callosobruchus chinensis, the chestnut weevil, Curculio dentipes, the green rice leafhopper, Nephotettix cincticeps, the almond moth, Ephestia cautella, the yellow peach moth, Conogethes punctiferalis, and the rice stem borer, Chilo suppressalis. Fenitrothion was degraded almost by O-alkyl conjugation, whereas relatively high ratio of O-aryl conjugation was observed for dicapthon degradation. Particularly in the azuki bean beetle, the green rice leafhopper and the almond moth, O-aryl conjugation was dominant (60- 80%). This result is the first evidence that O-aryl conjugation is preferentially occurred for O, O-dimethyl O-aryl phosphorothionates in insects. Malpighian tubes, fat body and midgut prepared from the common cutworm, Spodoptera litura, were also assayed with 14 C-dicapthon. Interestingly, the ratios of O-alkyl and O-aryl conjugation were clearly different among the three tissues.

Relationship between Outbreaks of the Green Rice Leafhopper, Nephotettix cincticeps (Uhler), and Hot Summer in Miyagi Prefecture, 1994

Relationship between Outbreaks of the Green Rice Leafhopper, <I>Nephotettix cincticeps</I> (Uhler), and Hot Summer in Miyagi Prefecture, 1994

The outbreak mechanisms of the green rice leafhopper, Nephotettix cincticeps Uhler, in northern Japan

Intraspecific regulatory processes keep the population ofNephotettix cincticeps stable at a low density in southern Japan. In northern Japan, however, the yearly population density of the insect fluctuates violently, and large outbreaks occasionally take place. To clarify the difference in the population dynamics between the two regions, we analyzed light-trap and sweep-net sampling records from prefectural and national agricultural experimental stations. The survival rate of the overwintering population decreased with increases in the period of continuous snow cover (PCSC) in the north, and initial population densities in the years of long PCSC were too low for populations to reach equilibrium density by the end of the active breeding season. This made yearly population fluctuations in the north much larger than in the south. The equilibrium density in the north was higher than in the south. The higher equilibrium density presumably permits the higher population density and larger yearly population fluctuations in the north. A major factor responsible for the difference in equilibrium densities between the two regions is the difference in heading dates of the host plant (rice). Qualitative differences among rice plant varieties, and among biotypes ofN. cincticeps, may also be important.

Multiplication and Distribution of Rice Yellow Dwarf Phytoplasma in Infected Tissues of Rice and Green Rice Leafhopper Nephotettix cincticeps.

Multiplication and distribution of rice yellow dwarf phytoplasma in infected tissues of rice and the vector, green rice leafhopper (Nephotettix cincticeps), were demonstrated by dot hybridization using DNA probes for phytoplasma DNA. Phytoplasma DNA was first detected in rice plants at 20 days after the termination of a 3-day inoculation feeding of phytoplasma-exposed insect vectors. The amount of DNA in infected rice tissues started to increase rapidly at 30 days after the feeding, leveled off by 40 days, and remained at the same high level for up to 80 days. In RYD-infected rice tissues, the amount of phytoplasma does not correlate to the severity in chlorosis. In insects, phytoplasma DNA was detected at 10 days after the termination of a 3-day acquisition access feeding on RYD-infected plants, and the amount increased rapidly at 30-40 days after the feeding. Phytoplasma DNA was detected mainly in the abdomen and thorax at 25 days after the feeding, but mainly in the head at 50 days.

Mortality and Honeydew Profiles of Nephotettix cincticeps UHLER (Homoptera: Cicadellidae) Supplied with a Leafhopper-Resistant Rice Variety

Almost all the green rice leafhopper Nephotettix cincticeps UHLER placed on seedlings of Norin-PL6, a newly established leafhopper-resistant rice variety, died within 6 days. About 90% of nymphs placed on a related variety, Toyonishiki, survived and molted to further nymphal instars. Daily mortalities on Norin-PL6 seedlings were completely cancelled if the survived nymphs were transferred to Toyonishiki seedlings. A large amount of amino acids and sugars (mainly sucrose, glucose and fructose) were found in honeydew of adult males fed on Toyonishiki, but non-detectable or only faint levels were in those from Norin-PL6.

Purification and characterization of carboxylesterases of a rice brown planthopper, Nilaparvata lugens Stål

More than 10 molecular forms of carboxylesterases were observed with α-naphthyl acetate as substrate in a rice brown planthopper (BPH), Nilaparvata lugens Stål, using isoelectric focusing. The three most active ones, E 1, E 2 and E 3, purified with gel permeation/chromatofocusing chromatography were characterized. Their subunit molecular mass varied between 62 and 64 kDa and the pI ranged from c.4.7 to 4.9. They were immunologically related and showed no difference in sensitivity toward the inhibition of paraoxon, methyl paraoxon, and malaoxon. E 1 consistently exhibited much higher activity than the other two isozymes toward some model substrates, i.e. α-naphthyl acetate and butyrate, β-naphthyl acetate, and 4-nitrophenyl acetate as well as some insecticides. While malathion and trans-permethrin were readily hydrolyzed by these isozymes, very limited or no degradation of cypermethrin and cis-permethrin was detected. The carboxylesterases of BPH, being unable to hydrolyze parathion, could bind strongly the potent anticholinesterase paraoxon and oxons of several organophosphorus insecticides, rendering them nontoxic. Resistant BPH had higher activity and quantity of carboxylesterases (notably E 1) than susceptible BPH. Protein subunits immunologically related to E 1 of BPH were detected in two other rice planthoppers ( Laodelphax striatellus and Sogatella furcifera) and two aphids ( Myzus persicae and Aphis gossypii), but not in the green rice leafhopper ( Nephotettix cincticeps) and southern house mosquito ( Culex quinquefasciatus).

レンゲ圃場におけるツマグロヨコバイの発生消長

レンゲ圃場におけるツマグロヨコバイの発生消長

箱処理剤連用地域におけるツマグロヨコバイのカーバメート系薬剤に対する抵抗性発達とマラソン剤との交差抵抗性

Populations of the green rice leafhopper, Nephotettix cincticeps, sampled from five regions in Miyagi Prefecture in 1988 and 1989 were less susceptible to malathion, fenobucarb, carbaryl and propoxure than populations collected in 1971. The population at Rokugou, Sendai sampled in 1989 was 161-times less sensitive to malathion than the 1971 population. Despite fewer insecticide applications, susceptibility to malathion, fenobucarb and carbaryl decreased in populations of two regions. Resistance to these insecticides may be related to the extent of control by propoxure and carbosulfan used as systemic insecticides.

Antimetabolic effects of plant lectins and plant and fungal enzymes on the nymphal stages of two important rice pests, Nilaparvata lugens and Nephotettix cinciteps

AbstractInsect feeding trials were carried out to determine the effects of incorporating a range of plant derived proteins into artificial diets fed to leafhopper and planthopper pests of rice. The lectins Galanthus nivalis agglutinin (GNA) and wheat germ agglutinin (WGA), and the enzyme soy bean lipoxygenase (LPO) were shown to exhibit significant antimetabolic effects towards first and third instar nymphs of rice brown planthopper (Nilaparvata lugens Stål) when incorporated into artificial diet at 0.1% (w/v), 0.1% (w/v) and 0.08% (w/v) levels respectively. The lectin GNA was also shown to exhibit a significant antimetabolic effect towards third instar nymphs of the rice green leafhopper (Nephotettix cinciteps Uhler). A number of inert proteins, lectins, protein inhibitors and enzymes also tested showed relatively little or no effect towards both insects.

Negatively correlated cross resistance: Combinations of N‐methylcarbamate with N‐propylcarbamate or oxadiazolone for green rice leafhopper

AbstractThe use of insecticide mixtures is generally considered to result in the simultaneous development of resistance to the components. However, experiences with leaf and planthoppers do not necessarily support this opinion and indicate that the N‐methylcarbamate/N‐propylcarbamate combination can overcome the resistance of the green rice leafhopper (GRLH) by synergism between the two components. It was found that the N‐methylcarbamate/oxadiazolone combination gave a similar but more remarkable synergism than the former combination. The mechanism of synergism was studied by the analysis of acetylcholinesterase (AChE) inhibition using the log v‐t plot. AChE from the resistant population is provided with two active sites, one being sensitive to N‐methylcarbamate and oxadiazolone compounds and the other being insensitive to N‐methylcarbamates but highly sensitive to oxadiazolones. The overall results indicate that the biochemical mechanism of action of the N‐methylcarbamat/oxadiazolone combination is essentially the same as that of the N‐methylcarbamate/N‐propylcarbamate combination. Selection of susceptible GRLH by a N‐methylcarbamate developed the cross‐resistance to the whole N‐methylcarbamate group; but the population became more susceptible to N‐propylcarbamates. When further selected by the N‐methylcarbamate/N‐propylcarbamate combination, no further resistance developed to the combination or its components. Thus, certain combinations of insecticides may be useful in resistance management. © 1993 Wiley‐Liss, Inc.

Factors Responsible for the Difference in Densities between Southwestern and Northern Japanese Populations of the Green Rice Leafhopper, Nephotettix cincticeps(UHLER)(Hemiptera:Deltocephalidae), in Their Later Generations : I. Effects of the Heading Time of Rice Varieties on the Oviposition and Propagation of the Second Generation

Factors Responsible for the Difference in Densities between Southwestern and Northern Japanese Populations of the Green Rice Leafhopper, Nephotettix cincticeps(UHLER)(Hemiptera:Deltocephalidae), in Their Later Generations : I. Effects of the Heading Time of Rice Varieties on the Oviposition and Propagation of the Second Generation

Effects of Ploughing of Fallow Paddy Fields on the Population Density of the Green Rice Leafhopper, Nephotettix cincticeps(UHLER)(Hemiptera:Cicadellidae)

The green rice leafhopper, Nephotettix cincticeps, is an important vector of rice dwarf virus disease in southwestern Japan. The nymphs and adults of the overwintering generation as well as the first generation inhabit Alopecurus aequalis (SOBOL) in fallow paddy fields. The effects of ploughing fallow paddy fields on the population density of the first generation were investigated and compared to an unploughed field in Okayama, western Japan. Three treatments were used: ploughing once before the emergence of overwintering adults, ploughing once at the peak oviposition period of overwintering females, and ploughing at the times of both emergence and oviposition peaks. The density of eggs, immature stages and adults was significantly lower in the last two fields, although the density of all stages of the leafhopper between the two fields was not significantly different. Therefore, ploughing once at peak oviposition of the females is the most effective strategy to reduce density of the first generation.

Studies on Novel 3(2H)-pyridazinone Derivatives with Juvenile Hormone-Like Activity

In the course of studies on 3(2H)-pyridazinone derivatives, the authors found that some compounds substituted with phenyl group at 2-position showed distinct JH-like activity (metamorphosis-inhibiting activity) on the green rice leafhopper, Nephotettix cincticeps. Following elaborate investigations of structure-activity relationships among the related compounds, NC-170 [4-chloro-5-(6-chloro-3-pyridylmethoxy)-2-(3, 4-dichlorophenyl)-pyridazin-3(2H)-one] was discovered as the most potent candidate, which strongly inhibited the metamorphosis in leafhoppers and planthoppers, but not in any other insects at all. Further studies showed that the substituent at the 2-position on the pyridazinone ring played an important role on this strict selectivity and that the introduction of halogenated alkyl groups into the position drastically expanded the biological spectrum. NC-184 [4-chloro-2-(2-chloro-2-methylpropyl)-5-{(6-iodo-3-pyridyl)methoxy}-pyridazin-3(2H)-one], one of the most potent compounds among 2-halogenated alkyl derivatives, exhibited JH-like activity not only in hoppers but in various species over 11 orders. In the field trials against the brown planthopper, Nilaparvata lugens, a single treatment of NC-184 in late-July suppressed the population growth during summer and prevented the ‘hopper-burn’ in autumn. The results suggested that these novel JH mimics are promising agents for future hopper-control programs in paddy fields.

Cloning and Detection of Chromosomal and Extrachromosomal DNA from Mycoplasmalike Organisms That Cause Yellow Dwarf Disease of Rice

DNA was extracted from rice plants infected with mycoplasmalike organisms (MLOs) causing yellow dwarf disease. DNA of the causal agent was separated from the host DNA by repeated bisbenzimide-CsCl equilibrium density gradient centrifugations. MLO DNA cut by HindIII was ligated into plasmid Bluescript II and cloned in Escherichia coli NM522. The DNA inserts were labeled with peroxidase and employed as probes in hybridization. Southern analysis revealed that the insert in pRYD-12 consisted of one, presumably chromosomal, piece of MLO DNA, whereas the insert in pRYD-19, another recombinant plasmid, consisted of one, presumably extrachromosomal, piece of MLO DNA. Cloned DNA probes were successfully applied in dot blot hybridization for the detection of rice yellow dwarf disease MLOs in rice plants and in an insect vector, the green rice leafhopper (Nephotettix cincticeps).