Virus-vector relationships of chickpea chlorotic dwarf geminivirus and the leafhopper Orosius orientalis (Hemiptera: Cicadellidae)

Chickpea chlorotic dwarf geminivirus (CCDV) is one of the viruses associated with chickpea stunt disease. It is transmitted by the leafhopper Orosius orientalis. The minimum acquisition access period (AAPmin) and inoculation access period (IAPmin) were found to be less than 2 min, while the minimum latency period (LPmin) was less than 2 h. The median AAP, IAP and LP were 8.0 h, 2.3 h and 27.7 h, respectively. No difference in transmission rates (proportion of leafhoppers able to transmit) was observed between male and female leafhop-pers. In serial transmission experiments, transmission was shown to be persistent, and after a 2-day AAP about 80% of the leafhoppers transmitted the virus for most of their life. The virus could be detected in individual leafhoppers by DAS-ELISA. It did not multiply in the leafhopper, but, instead, decreased in concentration during leafhopper feeding on a non-host of the virus.     

Chromosomal polymorphism in an Australian leafhopper (Homoptera: Cicadellidae)

Variation in chromosome number from 2n=9 to 2n=7 was found in a species of leafhopper, Alodeltocephalus draba. It is argued that this variation is due to chromosome fusion and that A. draba is presently evolving to a lower number. The process of reduction is more advanced in some populations than in others.Seconded from: Department of Biology, University of Oregon, Eugene, Oregon, U.S.A.     

Behavioral response ofGraminella nigrifrons (Homoptera: Cicadellidae) to experimentally manipulated vibrational signals

Mate recognition for the leafhopper Graminella nigrifrons(Forbes) occurs when a male spontaneously emits a multisectional vibrational calling song to which females respond by emitting simple pulses. Significant differences were found among males in the duration, number of chirps, and chirp rate within sections of the song and the total song. Repeatability (proportion of total variation due to differences among males) of call features ranged from very low (0.04 for total chirps in song) to high (0.67 for section 3 chirp rate). However, song modification and playback experiments revealed that the variation in the measured song features was not important in determining whether a female will respond. Rather, female response depended only on the presence of two of the three types of pulses which comprise a chirp. These essential pulses were found within chirps of all call sections that contain chirps. Manipulation of chirp rates from 0.58 to 2.70 times the normal rate did not affect female response, nor did changing the period of silence between the essential pulse types from 0.25 to 1.75 times the normal period. These results suggest that components of the male calling song function in mate recognition but are not used by females to discriminate among conspecific males.     

Transmission of Spiroplasma citri by the aster leafhopper Macrosteles fascifrons (Homoptera: Cicadellidae)

The aster leafhopper (Macrosteles fascifrons), injected with an isolate of Spiroplasma citri obtained from brittle root-diseased horseradish (Armoracia rusticana), transmitted the spiroplasma to horseradish and China aster (Callistephus chinensis.) After feeding on plants infected with S. citri, M. fascifrons transmitted the spiroplasma from aster to aster and horseradish, from yellow rocket (Barbarea vulgaris) to aster, and from turnip (Brassica rapa) to turnip. Symptoms in infected horseradish were chlorosis and stunting of newly formed leaves, discoloration of root phloem, and reduced plant growth typical of brittle root disease. Chlorosis, stunting, and asymmetry of young leaves occurred in affected aster and turnip. Flowers of infected aster were small and pale in colour and occasionally showed other symptoms including asymmetry, petal distortion, or light green petals. Spiroplasmas were isolated from all plants showing symptoms. Transmission rates by M. fascifrons which acquired S. citri by feeding on infected plants were very low, but injected leafhoppers transmitted more frequently. This is the first report of the transmission of S. citri from diseased to healthy plants by M. fascifrons.     

Fixed precision sampling plans for white apple leafhopper (Homoptera: Cicadellidae) on apple

Constant precision sampling plans for the white apple leafhopper, Typhlocyba pomaria McAtee, were developed so that it could be used as an indicator species for system stability as new integrated pest management programs without broad-spectrum pesticides are developed. Taylor's power law was used to model the relationship between the mean and the variance, and Green's constant precision sequential sample equation was used to develop sampling plans. Bootstrap simulations of the sampling plans showed greater precision (D = 0.25) than the desired precision (Do = 0.3), particularly at low mean population densities. We found that by adjusting the Do value in Green's equation to 0.4, we were able to reduce the average sample number by 25% and provided an average D = 0.31. The sampling plan described allows T. pomaria to be used as reasonable indicator species of agroecosystem stability in Washington apple orchards.     

Diversity and abundance of leafhopper species (Homoptera: Cicadellidae) among red maple clones

A survey was conducted in the 2001 growing season to examine the leafhopper diversity and abundance among trees of 17 red maple (Acer rubrum) clones. Yellow sticky traps were used to qualify and quantify the number of aerial leafhoppers from 1 May 2001 until 4 September 2001. A total of 45 species from eight different leafhopper subfamilies, for a total of 6055 individuals, were considered in this study. The mean number of leafhoppers collected, mean species richness, diversity and evenness were significantly lower on traps of trees for October Glory than for the other clones. Yet, none of the leafhopper species dominated the weekly samples. Species similarity among clones ranged from 56 to 90%. No two clones had complete similarity. Franksred and trees of a controlled cross between October Glory × Autumn Flame shared the highest degree of species similarity, while clones from PA, USA and RI, USA were the least similar. The development of new clones did not create new pest problems, but suppressed populations of damaging pests, and maintained the diversity of low abundance species.     

ATP6蛋白影响异沙叶蝉对小麦蓝矮植 原体的传播效率

【目的】探索异沙叶蝉Psammotettix alienus ATP6蛋白对小麦蓝矮植原体(wheat blue dwarf phytoplasma, WBDp)传播效率的影响。【方法】将异沙叶蝉mRNA反转录合成cDNA,构建分离泛素酵母双杂交膜系统cDNA文库;用WBDp的虫传相关蛋白P2-4为诱饵,从异沙叶蝉cDNA文库杂交筛选互作蛋白;通过RNAi沉默ATP6基因,验证ATP6蛋白对异沙叶蝉3龄若虫传播WBDp的影响。【结果】构建了异沙叶蝉分离泛素酵母双杂交膜系统cDNA文库,用P2-4从cDNA文库中杂交筛选获得了ATP6等多种互作蛋白。RNAi结果发现沉默ATP6基因后异沙叶蝉3龄若虫的WBDp传播率比对照组显著下降了23.33%±3.33%,表明ATP6是异沙叶蝉参与WBDp传播的关键蛋白。【结论】明确了异沙叶蝉ATP6是参与WBDp传播的一个关键蛋白。为进一步探明异沙叶蝉传播WBDp的分子机制和植原体病害的田间防治提供了理论基础。     

Aspects of potato leafhopper (Homoptera: Cicadellidae) biology on Solanum berthaultii and other potato genotypes

Survival of nymphs and adult males and females of potato leafhopper, Empoasca fabae (Harris), on six potato (Solanum spp.) genotypes with varied levels of resistance was evaluated and related to type, density, and droplet/head size of foliar glandular trichomes. Survival was greater on Solanum tuberosum cultivars ('Allegany' and 'Elba') compared with accessions of the wild S. berthaultii (PI 473331 and PI 473334). The barrier provided by glandular trichomes may affect survival of E.fabae by restricting nymph and adult feeding. PI 473331 was the most pubescent host, bearing type A and type B trichomes and the most unsuitable host for E. fabae. Allegany possesses leaflets with low trichome densities and small gland diameter and was the most suitable host for adult E. fabae survival. Females generally had higher survival rates than males. Nymphal and adult leafhoppers differed greatly in their survival rates, particularly on S. tuberosum x S. berthaultii hybrids (Q174-2 and NY123). Interestingly, nymphs had longer (190 d) mean lethal time (LT50) than adults (31 d) when held on Q174-2, and a lower LT50 (19 d) when held on NY123 compared with adults (104 d). Starvation, dehydration, or both were likely associated with mortality of nymphs confined on PI 473331 and PI 473334. Nymphs on these accessions died at a comparable rate to those confined on a starvation treatment and more rapidly than those supplied with water only, sucrose solution or other potato genotypes. Darkened trichome exudates were observed on insects held on PI 473331 and PI 473334, consistent with previous reports that glandular trichomes of S. berthaultii contain phenolic oxidation chemistry. This study aids in the identification of the probable mechanisms of resistance to E. fabae used by S. berthaulti and its hybrids with S. tuberosum.     

Pathogenicity and effects on transmission of a mycoplasmalike organism of a transovarially infective bacterium on the leafhopper Euscelidius variegatus (Homoptera: Cicadellidae)

A transovarially transmitted, Gram-negative bacterium (BEV) reduced the median longevity of congenitally infected Euscelidius variegatus 54%, compared to uninfected controls of the same age and bred from the same parental stock. Mean fecundity was reduced over 80%, and nymphal development took almost 50% longer. Infected surviving adults of both sexes, however, weighed significantly more than uninfected controls. Infection of E. variegatus with BEV significantly reduced the transmission of the plant pathogenic mycoplasmalike organism causing X-disease in celery. The pathological effects of the BEV bacterium on its leafhopper host imply that infection by means other than transovarial transmission is necessary for the bacterium to persist in nature.     

Interrelationships between "Candidatus Phytoplasma asteris" and its leafhopper vectors (Homoptera: Cicadellidae)

The titer of chrysanthemum yellows phytoplasma (CYP, "Candidatus Phytoplasma asteris") in the three vector species Euscelis incisus Kirschbaum, Euscelidius variegatus Kirschbaum, and Macrosteles quadripunctulatus Kirschbaum (Homoptera: Cicadellidae) was measured after controlled acquisition from infected Chrysanthemum carinatum (Schousboe) (daisy) plants. Phytoplasma DNA was quantified in relation to insect DNA (genome units [GU] of phytoplasma DNA per ng of insect DNA) by using a quantitative real-time polymerase chain reaction (PCR) procedure. The increase in phytoplasma titer recorded in hoppers after they were transferred to plants that were nonhosts for CYP provides definitive evidence for phytoplasma multiplication in leafhoppers. CYP multiplication over time in M. quadripunctulatus was much faster than in E. incisus and E. variegatus. CYP titer was also highest in M. quadripunctulatus, and this was reflected in the latent period in the insect. The mean latent period of CYP in M. quadripunctulatus was 18 d versus 30 d in E. variegatus. M. quadripunctulatus was the most efficient vector, giving 100% transmission for single insects compared with 75-82% for E. incisus or E. variegatus, respectively. By sequential transmission, we analyzed the time course of transmission: E. variegatus were persistently infective for life or until shortly before death. Occasionally, leafhoppers failed to maintain continuity of infectivity even after completion of the latent period. PCR analysis of transmitter and nontransmitter E. variegatus adults showed that some nontransmitters were CYP positive, whereas others were CYP negative. These findings suggest that both midgut and salivary gland barriers play a role in transmission efficiency.     

Glandular-haired alfalfa resistance to potato leafhopper (Homoptera: Cicadellidae) and hopperburn: development of resistance indices

Eight proprietary genotypes of glandular-haired alfalfa, Medicago sativa L., supplied by two different companies, were compared for the degree and types of resistance to the potato leafhopper, Ernpoasca fabae (Harris), and hopperburn. A tube cage no-choice bioassay was developed to test leafhopper mortality, feeding, settling preferences, severity of hopperburn symptoms (in this case, defined as both yellowing and stem growth reduction), and trichome density and type on feeding sites. Leafhopper mortality was both strongly and significantly associated with feeding and leaf trichome density; decreased hopperburn symptom severity was weakly, although significantly, associated with increased mortality. To quantify hopperburn in terms of both yellowing and stem growth reduction, we developed a ranking system that reduces overall hopperburn expression to a single number that considers the varying responses to both types of symptoms. Great variability in leafhopper settling, leafhopper mortality, and stem glandular trichome density was detected among alfalfa genotypes, suggesting that genotypic differences may be based on the concentration and/or chemical constituency of the trichome exudates. We postulate that, among variably resistant genotypes of glandular-haired alfalfa, differences among leafhopper responses and hopperburn severity are linked to forced movement from the stems to the leaves as refuge feeding sites. Principal component analysis was performed to reduce the 10 variables down to five biologically significant factors. Scores for these factors were then used to develop resistance indices for potato leafhopper resistance, hopperburn resistance, and an overall glandular-haired alfalfa resistance index.     

Potato leafhopper (Homoptera: Cicadellidae) injury disrupts basal transport of 14C-labelled photoassimilates in alfalfa

The potato leafhopper, Empoasca fabae (Harris), is a key pest of alfalfa, Medicago sativa L., in part because of the leafhopper's ability to disrupt upward translocation within phloem tissues. To determine if leafhopper injury also disrupts basal translocation necessary for regrowth and perenniality of alfalfa, we used radiolabeled 14CO2 to measure the basal transport of photoassimilates in injured and healthy plants. In one experiment, less 14C was transported to lower stem tissue of leafhopper-injured plants in comparison to the same tissue of healthy plants in early vegetative and early reproductive stages of alfalfa development. In a second experiment, less 14C was transported to lower stem, crown, and root tissues of injured plants in comparison to the same tissues of healthy, early reproductive plants. The disruption of basal transport caused by potato leafhopper may impact carbon storage and mobilization subsequent to defoliation, winter survival, and nitrogen fixation.     

Host effects of glandular-haired alfalfa on alfalfa weevil (Coleoptera: Curculionidae) and potato leafhopper (Homoptera: Cicadellidae) populations in Virginia

Cultivars of glandular-haired alfalfa, Medicago sativa L., such as '54H69', are currently available and marketed as being resistant to potato leafhopper, Empoasca fabae (Harris). Between 2000 and 2002, studies were conducted to compare the effects of '54H69' and a standard, nonglandular-haired alfalfa cultivar, 'Choice', on alfalfa weevil, Hypera postica (Gyllenhal), and potato leafhopper populations at Campbell and Montgomery counties, Virginia. '54H69' had no effect on alfalfa weevil populations. At each location, densities of alfalfa weevil in '54H69' and 'Choice' were similar, but pest pressure was higher at Campbell Co. than at Montgomery Co. and always exceeded the economic threshold before insecticide was applied. Densities of potato leafhopper also did not differ between '54H69' and 'Choice' in any year at the two locations. Insecticide treatment effectively reduced potato leafhopper densities in the two cultivars, although populations were below the economic threshold at both locations when the insecticides were applied. Overall, postinsecticide treatment comparisons showed that the densities of alfalfa weevil and potato leafhoppers were similar or higher in untreated '54H69' compared with insecticide-treated 'Choice'. In addition, there were no differences in seasonal dry yields between '54H69' and 'Choice' in any year at either location. Our results indicate that the glandular-haired alfalfa '54H69' does not provide acceptable resistance to potato leafhopper and also does not offer a yield advantage to growers in Virginia.     

Within-field manipulation of potato leafhopper (Homoptera: Cicadellidae) and insect predator populations using an uncut alfalfa strip

The effects of a 3-m wide uncut alfalfa strip on the within field distribution of Empoasca fabae (Harris) (Homoptera: Cicadellidae) and several species of insect predators were examined for 3 yr (1998-2000). The objectives were to determine whether this uncut strip would serve as a trap crop for E. fabae and a refuge for insect predators at first harvest. Empoasca fabae and insect predators in the families Coccinellidae, Nabidae, Anthocoridae, Chrysopidae, and Hemerobiidae were collected weekly using sweep samples and sticky traps from the uncut strips and up to 40 m into the alfalfa regrowth. For 2 yr, both small- (0.34 ha) and large-scale (approximately 11.3 ha) field trials showed higher numbers of E. fabae in 73% of the uncut strips for 2-3 wk after harvest. Similarly, the number of insect predators found within <50% of the uncut strips was also higher during the first or second week after harvest. In 1999, however, we did not observe higher numbers of E. fabae in the uncut strips. Differences may be because of higher E. fabae population numbers in 1999 compared with 1998 and 2000. This research provides alfalfa growers a potential cultural management technique for E. fabae while conserving predatory insects.     

Management of corn leafhopper (Homoptera: Cicadellidae) and corn stunt disease in sweet corn using reflective mulch

Plastic reflective mulches significantly reduced populations of corn leafhopper, Dalbulus maidis (DeLong & Wolcott), adults and the incidence of corn stunt disease caused by Spiroplasma kunkelii (CSS) in late planted sweet corn (Zea mays L.). The reflective mulches were more effective than were either foliar or soil applied insecticides in managing both the leafhopper and the pathogen it transmits. Yields of marketable ears were 1.5 to 2 times greater in reflective mulch plots than from fallow plots. This was due to larger ears (individual ear weight and length) rather than an increase in the number of ears. The use of reflective mulches provides an alternative strategy to insecticides in the management of both D. maidis and corn stunt disease. Such a strategy may prove useful to growers in Latin America and to limited resource growers and organic growers in the United States who wish to grow corn without the use of insecticides.     

Conversion of spheroplast symbiotes in a leafhopper, Helochara communis Fitch (Cicadellidae: Homoptera).

In mycetomes of leafhoppers, Helochara communis, ultrastructural and histochemical studies revealed that spheroplast symbiotes (t-symbiotes) were converted to 'a-symbiotes' (so-called), with apparent loss of DNA--a phenomenon reminiscent of rhizobium-bacteroid conversion in certain legume nodules. Additional t-symbiotes were incorporated into the substance of these 'a-symbiotes'.