Susceptibility of source plants to Sugarcane Fiji disease virus influences the acquisition and transmission of the virus by the planthopper vector Perkinsiella saccharicida

Abstract:  Fiji leaf gall (FLG) caused by Sugarcane Fiji disease virus (SCFDV) is transmitted by the planthopper Perkinsiella saccharicida . FLG is managed through the identification and exploitation of plant resistance. The glasshouse-based resistance screening produced inconsistent transmission results and the factors responsible for that are not known. A series of glasshouse trials conducted over a 2-year period was compared to identify the factors responsible for the erratic transmission results. SCFDV transmission was greater when the virus was acquired by the vector from a cultivar that was susceptible to the virus than when the virus was acquired from a resistant cultivar. Virus acquisition by the vector was also greater when the vector was exposed to the susceptible cultivars than when exposed to the resistant cultivar. Results suggest that the variation in transmission levels is due to variation in susceptibility of sugarcane cultivars to SCFDV used for virus acquisition by the vector.     

Hybridization studies in the planthopper genus Ribautodelphax (Homoptera,Delphacidae)

Seven known Ribautodelphax species and four recently discovered taxa were crossed. Forty-three percent of the interspecific crosses were successful. Interspecific crosses generally resulted in low numbers of hybrids. In some combinations prolonged larval development of the hybrid males was observed. Backcrosses showed that both male and female hybrids were fertile. Reproductive isolation was mainly maintained by premating barriers. Insemination tests revealed that prolonged confinement of males and females lowered mating thresholds. The taxonomic status of the known species and new taxa was shown to be in need of revision. No indications for a hybrid origin of the pseudogamous triploid Ribautodelphax females were found.     

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.

     

Host plant relations in the planthopper genus Ribautodelphax (Homoptera, Delphacidae)

ABSTRACT. 1. Host plant relations of closely related species and pseudogamous triploid forms of the planthopper genus Ribautodelphax were studied.
2. From field data and experimental results it is concluded that eleven European Ribautodelphax species and undescribed taxa are monophagous or oligophagous on different grass species. Only two Ribautodelphax species are found on the same grass species in the field.
3. Differential host plant relations indicate that four recently discovered taxa are probably true species.
4. Ribautodelphax species show a more restricted host plant range in choice experiments compared with breeding tests.
5. Choice experiments indicate no differences in host plant preference between males and females of two Ribautodelphax species.
6. No differences are found in host plant relations between bisexual species and associated pseudogamous triploid forms.     

Alary polymorphism in the small brown planthopper Laodelphax striatellus (Homoptera: Delphacidae)

Environmental and genetic factors which influence alary polymorphism in Laodelphax striatellus (Fallén) were studied. It has been found that alary polymorphism in L. striatellus is determined by quality and quantity of food, and crowding. There is also a clear genetic basis for polymorphism.

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Zusammenfassung In dieser Studie werden einige Umweltfaktoren und genetische Faktoren untersucht, welche den Flügelpolymorphismus bei Laodelphax striatellus (Fallén) beeinflussen. Es wurde festgestellt, dass verschiedene Umweltfaktoren wie Qualität und Quantität des Futters und Crowding bestimmend wirken. Es besteht auch eine klare genetische Basis für Polymorphismus.

     

Genetic diversity of Costa Rican populations of the rice planthopper Tagosodes orizicolus (Homoptera: Delphacidae)

Tagosodes orizicolus (Homoptera: Delphacidae) is one of the main constraints of the rice production in the Neotropics. This planthopper produces severe damages as a phloem feeder, causes mechanical injury during oviposition and vectors the rice hoja blanca virus (RHBV). The main objective of this study was to determine the genetic diversity of T. orizicolus populations from three rice growing regions of Costa Rica, using RAPDs. Individuals from Guanacaste, Parrita, San Carlos and Cali-Colombia, as outgroup, were analyzed using the random primers. Phenetic relationships revealed that the Costa Rican populations were clearly separated from Cali-Colombia, sharing less than 25% similarity. Costa Rican populations were divided into two main branches separated at 30% similarity. The first branch included Guanacaste and San Carlos and the second displayed Parrita. In relation to similarity indexes within groups, the Guanacaste cluster showed the highest (over 50%) and Cali-Colombia was the most diverse (28%). The correspondence analysis confirmed the clusters of the phenogram and showed close interactions between the Parrita and San Carlos populations. The genetic separation observed could be the result of the geographic isolation among populations, but it could also be explained by the infection with the rickettsia Wolbachia pipientis. This bacterium causes cytoplasmic incompatibility in its host, which results in non-viable progeny when infected males mate with non-infected females, or when insects hosting different strains of Wolbachia mate. Then, a search for Wolbachia in previously described populations of T orizicolus was initiated. The presence of the bacteria was analyzed by PCR with 16S rDNA-specific primers for Wolbachia. The PCR analyses revealed infections of 86% in the population of San Carlos, 96% in Guanacaste, 37% in Parrita and 100% in Cali-Colombia. Crosses between individuals of T. orizicolus from Parrita and Guanacaste were performed for testing cytoplasmic incompatibility. When infected males were crossed with non-infected females within the same population, a significant reduction in progeny number was obtained as well as when crosses between infected individuals belonging to different populations were performed. These experiments showed cytoplasmic incompatibility not only caused by the presence of Wolbachia within the population, but also by the presence of different strains of the bacteria between populations.     

Photosynthesis and translocation of assimilates in rice plants following phloem feeding by the planthopper Nilaparvata lugens (Homoptera: Delphacidae)

Experiments were conducted to measure the effect of feeding by the planthopper Nilaparvata lugens (St?l) on photosynthesis and the translocation of assimilates in rice plants, Oryza sativa L. We used mature japonica rice plants and applied the 13CO2 feeding method to evaluate those physiological effects. The photosynthetic rate was suppressed by N. lugens infestation, especially at the lower leaf position, with rates 30% lower than that of control plants at the booting stage. Leaf nitrogen concentration in infested plants was also lower than that in control plants. After flowering, the chlorophyll content and total plant dry weight were reduced by N. lugens. Stem and sheath dry weights were significantly reduced by N. lugens infestation, whereas panicle dry weight was not affected. Little effect was found on disruption in translocation of assimilates, even when 13CO2 was supplied to the infested leaves. Results suggested that removal of assimilates and reduction in photosynthesis by N. lugens have the greatest effect on growth and yield of rice plants as compared with the disruption in the translocation of assimilates. Plant death can occur by N. lugens infestation if the amount of energy supplied is less than that required for tissue maintenance.     

Oxalic acid as a sucking inhibitor of the brown planthopper in rice (Delphacidae, Homoptera)

Oxalic acid, isolated from leaf sheath extract of rice, has been identified as a potent sucking inhibitor against the brown planthopper. Potassium and sodium oxalate at concentrations of 0.1%–0.2% completely inhibited sucking on a 15% sucrose solution. Of twelve aliphatic acids commonly present in plants, only oxalic, maleic, andtrans-aconitic acids at 0.1%, significantly reduced sucking activity while Krebs cycle acids, such as citric, malic, and succinic, did not have any inhibitory effect.

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Résumé L'acide oxalique, isolé des gaines foliaires du riz, a été identifie comme un puissant inhibiteur de la succion deNilaparvata lugens. Les oxalates de potassium et de sodium aux concentrations de 0,1% et 0,2% inhibent complètement la succion d'une solution de sucrose à 15%. Parmi les douze acides aliphatiques généralement présents dans la plante, seuls les acides oxalique, maleique et trans-aconique réduisent significativement à 0,1% l'activité de succion, tandis que les acides cycliques comme les acides citrique, malique et succinique n'ont pas d'effet inhibiteur.

     

The variability of mating signals and preferences in the brown planthopper,Nilaparvata lugens (Homoptera: Delphacidae)

Male and female brown planthoppers, Nilaparvata lugens(Stål) (Homoptera: Delphacidae), exchange substrate-transmitted signals prior to mating. The pulse repetition frequency of the male song is known to be involved in mate recognition and also to vary among geographical populations. Here the variability of male signals, female signals, and female preferences has been examined within a population. Female preference variation has been partitioned into variation in mean preference and variation in the window of preference of individuals. The genetic component of variation has been examined using isofemale lines. Male signal variation was limited (CV=8%) and was mainly within individuals. Female signal variation was greater (CV=15%). Female mean preference varied little (CV=10%) and was closely matched to the male signal mean, but the preference window was wide (> 4 male signal standard deviations on average) and variable (CV=56%). There was evidence for genetic variation only for preference window. These results are discussed in relation to theories of signal system evolution.     

Repeated copulation in the brown planthopper, Nilaparvata lugens Stál (Homoptera; Delphacidae)

Abstract. 1. Mating of the brown planthopper, Nilaparvata lugens , was investigated in relation to oviposition. Females became unreceptive immediately after mating and showed various types of repelling behaviour to courting males. As a result, females usually did not mate repeatedly in quick succession, but after ceasing to lay fertilized eggs they behaved as virgins and mated again before producing more fertilized eggs.
2. Copulation, followed by deposition of fertilized eggs, occurred twice, or in a few cases three times, throughout the adult stage. Copulation lasted about 2 min at the first mating and about 1 min at the second or third mating.
3. When the number of fertilized eggs began to decrease rapidly, oviposition rate also decreased, but it increased again immediately after re-mating. Repeated copulation was also related to the potential rate of population increase. In the present experiments, the estimates of net reproductive rate ( R ₀) in brachypterous females was 287.7 (first mating), 88.3 (second mating) and 7.2 (third mating) and in macropterous females 286.8, 120.6 and 3.6 respectively.
4. In a patchy environment, repeated copulation following an invasion may contribute to the increase of a population.     

Karyotypic variation in bisexual species and pseudogamous forms of the planthopper genus Ribautodelphax (Homoptera,Delphacidae)

Chromosome numbers of Ribautodelphax collinus. R. angulosus, R. pungens, R. imitans, R. fanari, R. pallens, R. albostriatus, and of four undescribed species, provisionally indicated as Taxon 1 to 4, were determined. The chromosome number of all species was found to be 2n=30 (14II+XX-XO); however, in several species some females with 2n=31 or 32 also occurred. One female of R. collinus and one of Taxon 1 possessed eggs with 16 bivalents and one egg with 32 bivalents. One female of R. pungens contained only tetraploid eggs. Pseudogamous triploid females occurred in populations of R. pungens and Taxon 4. Their chromosome numbers ranged from 3n=40 to 46 in R. pungens and 3n=41 to 45 in Taxon 4. In several pseudogamous females from two R. pungens populations, eggs with 45 univalents and with various numbers of univalents, bivalents and trivalents were found. The mode of origin of pseudogamous triploid females is discussed and it is concluded that karyotypic data are consistent with an autopolyploid origin.     

Probing stimulants from the rice plant towards the smaller brown planthopper, Laodelphax striatellus (FALLEN) (Homoptera: Delphacidae)

When adult males of the smaller brown planthopper, Laodelphax striatellus were fed on 2% crude rice (leaf and stem) extract containing 15% sucrose there were characteristic stylet sheaths deposited on parafilm membrane. Further bioassays with the butanol-soluble fr. of the extract revealed that it is highly effective for the insects. When the butanol fr. was charged on an ODS open column and eluted in sequence with 20, 40 and 100% methanol in water, the ODS-40% methanol fr. was shown as the most effective one. Further separation of the ODS-40% methanol fr. resulted in six effective components. These components acted to stimulate very high probing response on L. striatellus only when they are combined. This activity was found to be similar to those of the ODS-40% methanol fr. and the original crude rice plant extract. Two of the active components were identified as tricin 5-O-glucoside and tricin 7-O-glucoside, respectively, through spectroscopic analyses.     

Determination and distribution of a female-specific protein in the brown planthopper, Nilaparvata lugens Stal (Homoptera: Delphacidae)

Electrophoretic analyses of hemolymph and body or ovary homogenates from reproducing females, males, and 5th instar nymphs of the brown planthopper, Nilaparvata lugens Stal, revealed a protein band of 175 kDa in females. An immunoblot test using antibody against this protein showed a positive reaction with a 175 kDa protein from female body or ovary homogenates. It is likely that this protein in hemolymph is vitellogenin (Vg). Distribution of Vg was determined by immunofluorescence and immunogold labeling techniques. The results showed that the positive immunofluorescence reactions were present in yolk particles, the intercellular space of follicle cells, hemolymph, and the epithelial plug of ovarioles. In addition, the yeast-like symbiotes (YLS) in mycetocytes of adults and various nymphal instars as well as those free in hemolymph or entering oocytes also exhibited a positive reaction. Electron micrographs showed that immunogold particles were found most in yolk mass and YLS over other tissues. Especially the YLS in various developmental stages all contained immunogold particles, implying that the symbiote is somewhat related with production of the female-specific protein.     

Host plant interactions of the corn planthopper, Peregrinus maidis Ashm. (Homoptera: Delphacidae) in maize and sorghum agroecosystems

The corn planthopper, Peregrinus maidis (Ashmead) (Homoptera: Delphacidae) causes serious economic losses in corn and sorghum. The insect occurs mostly at humid low elevations in the tropics and coastal areas of subtropical and temperate regions of all continents, the Caribbean Islands, and islands in the Atlantic, Indian, and Pacific Oceans. This review provides a detailed compilation on the chronological progress made in basic and strategic aspects of research on the interactions between P. maidis and various host plants. The nature of damage by P. maidis and its economic impact, ecobiology in relation to host diversity, abiotic, and seasonal interactions; and life tables and alary polymorphism are discussed. Host plant resistance studies indicate that very few sources of resistance to P. maidis have been identified in maize, sorghum, or pearl millet, warranting a need to standardize rapid and reliable screening methods. The behavioral responses vis-à-vis mechanisms of resistance show the predominance of antixenosis for colonization and/or oviposition with variable degrees of antibiosis affecting life cycle parameters of P. maidis on maize and sorghum. The role of morphological traits, physiological mechanisms, and biochemical factors governing resistance are described. Population dynamics based on density-dependent and density-independent interactions are also discussed. In addition, aspects of P. maidis on chemical control, biological control, and trophobiosis interactions are listed. Future thrusts on research approaches are also discussed. Genetic engineering techniques involving lectin genes in the development of transgenic plants, and the molecular mapping of genes conferring resistance to both P. maidis and its transmitted virus diseases may stimulate further research and lead to better understanding of P. maidis—host plant interactions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Differences in preference for species-specific female calls between acoustically experienced and acoustically naive maleRibautodelphax planthoppers (Homoptera: Delphacidae)

Males of the planthopper Ribautodelphax imitanswere exposed to playbacks of either conspecific or heterospecific (R. imitantoides)female calls during their development from egg to adult, and thereafter these, as well as naive males,were offered a two- way choice between these calls. Males of all treatments approached the conspecific call significantly more often. However, males primed by the conspecific call chose the heterospecific call almost four times less often than did males primed by heterospecific calls or naive males, thus showing that the preference for conspecific calls can be partly learned. Males primed by heterospecific calls performed very similarly to completely naive males, suggesting that the signal recognition mechanism is much less sensitive to heterospecific calls than to conspecific calls. Males with experience of the conspecific female call tended to take more time to reach the call source in the trials than both other types of males. The evolutionary implications of these findings are discussed.     

Electroantennogram responses of Nilaparvata lugens (Homoptera: Delphacidae) to plant volatile compounds

Electroantennogram (EAG) recordings were made from the plaque organ receptors of the rice brown plant hopper, Nilaparvata lugens (St?l). The receptors of the distal plaque organ of both male and female hoppers responded to the air from above chopped rice plants, and those of females gave a larger response. Female hoppers, tested with 27 plant volatiles, gave dose-related responses to 16 of the compounds, including a range of green leaf volatiles. The aliphatic aldehydes hexanal and (E)-2-hexenal elicited a larger response than a range of green leaf alcohols. Of the remaining compounds, acetophenone, benzaldehyde, ethyl and methyl benzoate, and amyl and isoamyl acetate were among the most effective in eliciting responses. Receptor recovery times showed some variation between compounds. A comparison of the dose-related response of 16 compounds in paraffin oil and in pentane showed that considerably larger responses were recorded when the highly volatile solvent pentane was used.     

Changes of zeatin riboside content in rice plants due to infestation by Nilaparvata lugens (Homoptera: Delphacidae)

The effect of Nilaparvata lugens (St?l) (Homoptera: Delphacidae), infestation on the content of zeatin ribosides (ZR) in rice plants was investigated with enzyme-linked immunosorbent assay. Hydroponics experiments were conducted on 'Zhendao 2' rice, in which plants were subjected to N. lugens infestation at three nonhopperburn-causing densities (15, 30, and 60 nymphs per hill) for 2, 4, 6, and 8 d and at one hopperburn-causing density (240 nymphs per hill) for 2, 4, and 6 d, respectively. When rice plants were infested at the nonhopperburn-causing densities, ZR content in leaves varied significantly with the infestation density. Compared with the control plants, ZR content in rice leaves decreased significantly after infestation by 60 nymphs per hill for 2 d, but it tended to increase due to prolonged infestation at all the nonhopperburn-causing densities. In contrast, ZR content in rice roots significantly reduced after the plants being infested at the density of 15 nymphs for 2 d and at all densities for prolonged duration, except for the plants infested by 60 nymphs for 6 and 8 d, in which the ZR content increased or did not change significantly. However, infestation at the hopperburn-causing density caused significant reduction in ZR content in rice roots, regardless of infestation duration, and in rice leaves from the plants subjected to 2-d infestation. These results are discussed in relation to the possible physiological reaction of rice plants to N. lugens infestation and the resultant severe damage or hopperburn.     

Genetic control and evolution of acoustic signals in planthoppers (Homoptera: Delphacidae)

Acoustic signals are part of the specific mate recognition system of planthoppers. The genetic control of acoustic signal characters was studied in the planthopperRibautodelphax imitans. Artificial selection for interpulse interval in the female call revealed a large additive genetic component for this polygenic character. Other female call characters showed a correlated response. Some male call characters also appeared to be genetically correlated with the female character selected for, despite the rather different structure of male and female calls. Parent-offspring regression provided significant heritability estimates for those male call characters that also responded to artificial selection in the female call, one of which appeared to be influenced by sex-linked genes. It is argued that the differentiation of this mate recognition system in planthopper populations and species could be the result of founder effects, enabled by the genetic plasticity of the call characters and the existence of a wing length dimorphism in these animals.