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.     

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'.     

The distribution of a typhlocybine leafhopper, Ribautiana ulmi (Homoptera: Cicadellidae) on a specimen wych elm tree

ABSTRACT.

• 1 Higher numbers of feeding and resting Ribautiana ulmi (L.) were found on the more highly illuminated areas of the canopy of a wych elm tree, Ulmus glabra Huds. cv. Camperdownii.
• 2 Higher numbers were also found on the basal leaves of each branch when compared with the distal leaves, and on exposed areas of individual leaves when compared with the shaded areas which they overlapped.
• 3 Leaf thickness, tannin concentrations and leaf toughness were greater, and water content lower, in leaves from exposed areas of the canopy than from shaded ones.
• 4 R.ulmi feeds selectively on the contents of the palisade mesophyll cells, and therefore was assumed to ingest the highest available levels of tannins.

     

Role of the glandular trichomes in resistance of perennial alfalfa to the potato leafhopper (Homoptera: Cicadellidae)

Experiments were performed to elucidate resistance of glandular-haired alfalfa, Medicago sativa L., to the potato leafhopper, Empoasca fabae (Harris). The primary objective was to examine the potential role of the glandular trichomes and stem lignification for imparting resistance to this pest. During free-choice foliar discoloration experiments, the resistant alfalfa clone FGplh13 expressed lower levels of injury than the susceptible P5373 after 13 d. No-choice tests performed using nymphal potato leafhoppers showed higher levels of mortality associated with the resistant glandular-haired clone FGplh13, and no nymphs survived after 48 h. Additional no-choice experiments using FGplh13 and P5373 alfalfa with the glandular and nonglandular trichomes intact or removed show that mortality of nymphs and adults decreased after removal of the glandular trichomes from FGplh13. Nymphal and adult mortality and nymphal development time did not differ on FGplh13 with the trichomes removed and P5373 with the trichomes intact or removed. Firstinstar, and possibly second-instar, potato leafhoppers were entrapped by an exudate produced by the glandular trichomes on the FGplh13 alfalfa. Stem lignification and the number of vascular bundles did not differ between FGplh13 and P5373 alfalfas. The glandular trichomes on FGplh13 alfalfa appeared to provide the major host resistance factor, with resistance to adults being chemically based and resistance to nymphs being chemically and mechanically based. To maintain levels of potato leafhopper resistance, breeders would appear to benefit by continuing to select for the expression of the glandular trichome phenotype.     

Typhlocybinae of New Zealand (Homoptera: Cicadellidae)

Two tribes of the subfamily Typhlocybinae are represented in New Zealand, as follows. Erythroneurini: the cosmopolitan genus Zygina is represented by 4 endemic species—toetoe, ramsayi n.sp., dumbletoni, and agni n.sp.—plus zealandica, which occurs in Australia also. Typhlocybini: Typhlocyba froggatti, T. lethierryi, Ribautiana tenerrima, Eupteryx melissae, Kybos smaragdula, and K. betulicola are introduced Northern Hemisphere elements; Matatua montivaga n.gen.&sp. is endemic; M. maorica (formerly Dikraneura maorica), also endemic, is of uncertain identity in the absence of male specimens. Keys are given for the separation of all taxa, the genera and species are described, and all species except Matatua maorica are figured.     

Estimating the potato leafhopper Empoasca fabae (Homoptera: Cicadellidae) overwintering range and spring premigrant development by using geographic information system

The potato leafhopper, Empoasca fabae (Harris), is a circular migratory pest of many crops in the United States that overwinters in the southern states. Northward migrant population arrival to the northern states occurs earlier in the north central states compared with northeastern states. Migrant leafhopper arrival to the north varies from year to year depending on factors influencing the development of spring migrants in the overwintering areas and on timing of weather systems capable of transporting the migrants northward. An estimate of the potato leafhopper minimum temperature survival, the geographic limits of the potato leafhopper overwintering range, leafhopper spring development in the overwintering areas, and the identification of the spring migration initiation northwards can help to predict the leafhopper arrival time in the northern states. In the current study, geographic information system (GIS) was used to estimate the potato leafhopper minimum temperature survival and premigrant development. The minimum winter temperature was estimated by overlaying minimum temperature isolines with potato leafhopper collection data taken during the winter, The geographic limits of the overwintering range were estimated using the minimum temperature survival to create a condition-based model by using ArcMap-GIS 8.2. The estimated overwintering range was larger and covered areas further north than previously estimated and included Missouri, Kansas, Kentucky, Virginia, and Maryland. The use of degree-day accumulation to estimate days of first adult emergence in the overwintering areas resulted in earliest adult emergence in the south central region. First adult emergence in south central and southeastern areas occurred before the detection of potato leafhoppers in the north central United States. These data suggested that the difference in population arrival between the north central states and the northeastern states was more dependent on factors affecting the migration and weather conditions encountered along the migration pathway.     

Deltocephalinae of New Zealand (Homoptera: Cicadellidae)

The subfamily Deltocephalinae is represented in New Zealand by 3 tribes, 9 genera, and 20 species, of which 3 genera and 13 species are new to science. All taxa are described, and keys are given for their separation. Three of the genera are endemic, 3 are Australian, 2 are Holarctic, and 1 is cosmopolitan. Nesoclutha and Macrosteles are recorded in New Zealand for the first time, and the presence of Deltocephalus is authenticated. Fourteen species are endemic, 4 are Australian, 1 is widespread in the Pacific area, and 1 is Holarctic. Nesoclutha pallida, Macrosteles fieberi, and Deltocephalus hospes are recorded in New Zealand for the first time.     

Amino acids as determinants of host preference for the xylem feeding leafhopper,Homalodisca coagulata (Homoptera: Cicadellidae)

Summary Homalodisca coagulata is a highly polyphagous xylem feeder with distinct seasonal patterns in it's selection of host plants. These patterns were examined in relation to the amino acid content of the xylem for four common host species; Lagerstroemia indica, Baccharis halimifolia, Prunus persica, and Prunus salicina. Xylem fluid was collected from each host species at times when numbers of feeding leafhoppers were both low and high. In each case, concentrations of amino acids were greatest when numbers were high. Similarly, comparisons between host species at given times showed that concentrations of amino acids were positively correlated with host selection. In a second study, amino acids of xylem were manipulated by budding scions of a non-preferred host (P. persica) on rootstocks of preferred (P. salinica) and non-preferred (P. persica) hosts. Morphology and phenology of the budded trees were similar to that of the scion species yet the xylem composition of amino acids was primarily dependent on the rootstock. Concentrations of amino acids and the preference of leafhoppers were roughly two-fold greater for scions of the preferred than the non-preferred rootstock. In both studies, amides (glutamine plus asparagine) were the amino acids most highly correlated with host selection. These compounds are the predominant amino acids in xylem fluid, have high nitrogen to carbon ratios, and account for a high percentage of the caloric value in xylem fluid. Many of the less abundant amino acids were positively correlated with host preference, but the correlations were less consistent and correlation coefficients were generally lower.Florida Agricultural Experiment Station Journal Series No. 9672