Dispersion of Homalodisca coagulata (Hemiptera: Cicadellidae), a vector of Xylella fastidiosa, into vineyards in southern California

Recent epidemics of Pierce's disease of grapevine in California vectored by Homalodisca coagulata (Say), an invasive vector species, have characteristics that differ from epidemics involving native vectors. Among these differences are the longer distances and greater speed that the disease is spread by H. coagulata. In this investigation, we used yellow sticky traps to study the seasonal dispersion activity of H. coagulata in a southern California grape-growing area in which an epidemic of Pierce's disease has caused large losses. For 21 mo, we monitored adult H. coagulata at the edges of vineyards bordering citrus, an important crop host, natural coastal sage scrub vegetation, and natural riparian vegetation. We also monitored H. coagulata dispersion from 0 to 40 m into vineyards. Finally, we examined the vertical dispersion of H. coagulata adults into grapevines through a season. This investigation showed that H. coagulata is associated with citrus, from where it disperses deep into vineyards, and not just the vineyard edge as with Pierce's disease vectors that are native to California. Peak dispersion into vineyards occurred in the summer. Another period of H. coagulata activity occurred in the winter in vineyards bordering citrus. Through the period of peak flight activity, 97% of all H. coagulata adults trapped between 1 and 7 m were caught at an altitude of 5 m or lower, suggesting the potential of a barrier as a management tactic to keep H. coagulata out of vineyards.     

Effect of selected insecticides on Homalodisca coagulata (Homoptera: Cicadellidae) and transmission of oleander leaf scorch in a greenhouse study.

Homalodisca coagulata (Say) is a recent introduction to California. It is known to spread a strain of the bacterium Xylella fastidiosa Wells, Raju, Hung, Weisberg, Mandelco-Paul & Brenner that induces oleander leaf scorch disease in oleander, Nerium oleander L. Oleander leaf scorch is lethal to oleander and threatens to decimate one of the most important landscape shrubs in California. Towards developing a management strategy for H. coagulata-spread oleander leaf scorch, we documented the affects of selected insecticides on H. coagulata mortality, feeding behavior, and disease transmission in a greenhouse study. Oleanders treated with fenpropathrin, fenpropathrin + acephate, and imidacloprid caused significant mortality to caged H. coagulata within 4 h of exposure. Within 24 h, these pesticides caused nearly 100% mortality 3 wk after treatment. In other experiments, acetamiprid and fenpropathrin treatments reduced time spent feeding and total time on plants. H. coagulata on fenpropathrin-, acetamiprid-, and imidacloprid-treated oleander died in less than 13 min on average. Oleander leaf scorch transmission by H. coagulata was blocked by applications of foliar-applied acetamiprid, and soil-applied imidacloprid and thiamethoxam.     

Transmission of Xylella fastidiosa to grapevines by Homalodisca coagulata (Hemiptera: Cicadellidae)

Pierce's disease (PD) of grapevines is caused by a xylem-limited bacterium Xylella fastidiosa (Wells, Raju, Hung, Weisburg, Mandelco-Paul, and Brenner) that is transmitted to plants by xylem sap-feeding insects. The introduction of the sharpshooter leafhopper Homalodisca coagulata (Say) into California has initiated new PD epidemics in southern California. In laboratory experiments, the major characteristics of H. coagulata's transmission of X. fastidiosa to grapevines were the same as reported for other vectors: short or absent latent period; nymphs transmitted but lost infectivity after molting and regained infectivity after feeding on infected plants; and infectivity persisted in adults. Adult H. coagulata acquired and inoculated X. fastidiosa in <1 h of access time on a plant. Inoculation rates increased with access time, but acquisition efficiency (20% per individual) did not increase significantly beyond 6-h access. Estimated inoculation efficiency per individual per day was 19.6, 17.9, and 10.3% for experiments where plant access was 1, 2, and 4 d, respectively. Freshly molted adults and nymphs acquired and transmitted X. fastidiosa more efficiently than did older, field-collected insects. H. coagulata transmitted X. fastidiosa to 2-yr-old woody tissues of grapevines as efficiently as to green shoots. H. coagulata transmitted X. fastidiosa 3.5 mo after acquisition, demonstrating persistence of infectivity in adults. About half (14/29) of the H. coagulata from which we failed to culture X. fostidiosa from homogenized heads (with a detection threshold of 265 CFU/head) transmitted the pathogen to grape, and 17 of 24 from which we cultured X. fastidiosa transmitted.     

Seasonal flight activity of two Homalodisca species (Homoptera: Cicadellidae) that spread Xylella fastidiosa in southern California.

Homalodisca coagulata (Say) and Homalodisca lacerta (Fowler) are vectors of a new bacterial disease of oleander in California known as oleander leaf scorch, induced by the bacterium Xylella fastidiosa. H. coagulata also has been implicated in the spread of the strain of X. fastidiosa that induces Pierce's disease of grapevines in California. We monitored the flight activity of H. coagulata and H. lacerta in oleander and citrus by using yellow sticky cards at three southern California locations where outbreaks of oleander leaf scorch have been documented, and where vector compliments are different. Areas sampled included a mesic coastal area (Irvine, CA) that supports predominantly H. coagulata and few H. lacerta, a dry inland location (Palm Desert, CA) that supports predominantly H. lacerta and few H. coagulata, and an intermediate area (Riverside, CA) supporting both Homalodisca species. From November 1996 to October 1999 peak catches of both Homalodisca species occurred during the midsummer at all locations. H. coagulata was trapped in greater numbers in citrus than in oleander at both the Riverside and the Irvine sites. Likewise, H. lacerta in Riverside was more associated with citrus than oleander, yet H. lacerta in Palm Desert was trapped in greater numbers in oleander than citrus.     

Spatial and temporal dynamics of overwintering Homalodisca coagulata (Hemiptera: Cicadellidae)

A 4-yr landscape-scale study was conducted to investigate spatial and temporal dynamics of overwintering Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) in the lower San Joaquin Valley, California. Spatial structures of H. coagulata distributions were characterized with Moran's I index, and spatial associations between H. coagulata and the surrounding environment were investigated with a geographic information system. H. coagulata was caught consistently with sticky traps throughout the winter, and trap catches formed a distinctive peak in December or January, indicating active flight of H. coagulata during the winter. In 2000-2001, the mean +/-SE trap count was 4.8 +/- 1.21 per trap per wk, and H. coagulata trap catches were spatially autocorrelated within approximately 1.3 km. Approximately 49% of H. coagulata were caught in citrus, 23% in stone fruit, and 11% in grape. After a control program began in spring 2001, the mean trap count was considerably lower (0.041 +/- 0.0004 per trap per wk), and no spatial autocorrelations were detected in 2001-2004. H. coagulata trap catch-crop associations also changed after initiation of the control program. Between 25 and 38% of H. coagulata trap catches were from citrus, between 8 and 20% were from stone fruit, and between 11 and 25% were from grape. Potential for winter-season spread and management of Xylella fastidiosa Wells et al., a pathogen causing Pierce's disease, are discussed.     

Evaluation of methods for extracting Xylella fastidiosa DNA from the glassy-winged sharpshooter

The recent spread of the plant pathogenic bacterium Xylclla fastidiosa Wells et al. by an invasive vector species, Homalodisca coagulata Say, in southern California has resulted in new epidemics of Pierce's disease of grapevine. Our goal is to develop an efficient method to detect low titers of X. fastidiosa in H. coagulata that is amenable to large sample sizes for epidemiological studies. Detection of the plant pathogenic bacterium X. fastidiosa in its insect vector is complicated by low titers of bacteria, difficulty in releasing it from the insect mouthparts and foregut, and the presence of substances in the insect that inhibit polymerase chain reaction (PCr). To select the optimal protocol for DNA extraction to be used with PCR, we compared three standard methods and 11 commercially available kits for relative efficiency of X. fastidiosa DNA extraction in the presence of insect tissue. All of the protocols tested were proficient at extracting DNA from pure bacterial culture (1 x 10(5) cells), and all but one protocol successfully extracted sufficient bacterial DNA in the presence of insect tissue. Three DNA extraction techniques, immunomagnetic separation, the DNeasy Tissue kit (Qiagen, Hercules, CA), and Genomic DNA Purification kit (Fermentus, Hanover, MD), were compared more closely using a dilution series of X. fastidiosa (5000-0 cells) with and without insect tissue present. The DNeasy Tissue kit was the best kit tested, allowing detection of 5 x 10(3) X. fastidiosa cells with an insect head background.     

Feasibility of tracking within-field movements of Homalodisca coagulata (Hemiptera: Cicadellidae) and estimating its densities using fluorescent dusts in mark-release-recapture experiments

A mark-release-recapture technique was developed and tested for use in tracking the field movements of adult glassy-winged sharpshooters, Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), in various agricultural and urban plantings. Greenhouse experiments in which adult H. coagulata were marked with one of five colored fluorescent dusts (Aurora Pink-All, Horizon Blue-A19, Blaze Orange-A15N, Saturn Yellow-A17, and Corona Magenta-A21) and released into cages with citrus seedlings showed that their mortality rates during a 30-d period were statistically similar to that of the undusted controls. Adults marked with a sixth dust color (Signal Green-A18N) suffered higher rates of mortality than did the undusted controls and thus were eliminated from further consideration. Adult H. coagulata marked with one of the five accepted colors of fluorescent dust were able to fly beyond 100 m in a field devoid of vegetation within minutes of their release, and the marking did not affect overall flight behavior significantly compared with that of the undusted controls. However, at wind speeds above 5 m/s, percentage recapture was significantly reduced, which indicates that both dusted and undusted adults were unable to orient their flight. In total, 41,124 marked and unmarked adults were released in the three field experiments in southern California (Riverside and Kern counties) during 2000 and 2001 to evaluate flight dispersal and estimate densities of H. coagulata. The mark-release-recapture and feral data obtained during the June, July, and August 2001 studies, when coupled with the Lincoln index, yielded estimates of adult H. coagulata of 1.2 and 2.2 million per ha, respectively, at a San Joaquin Valley (Kern Co.) and a southern California (Riverside Co.) citrus grove. The use of colored dusts to mark H. coagulata proved to be reliable, cost-effective, and time-efficient for mark-release-recapture studies with this insect within a citrus grove, but they are less likely to be useful for studies of adult H. coagulata movements among plantings.     

Patterns of spread of two non-persistently aphid-borne viruses in lupin stands under four different infection scenarios

Patterns of spread of Bean yellow mosaic virus (necrotic type, BYMV‐N) and Cucumber mosaic virus (CMV) were examined in stands of narrow‐leafed lupin (Lupinus angustifolius) where naturally occurring aphid vectors moved them from external or internal primary virus sources. The lupin stands were: commercial crops near BYMV‐infected clover pasture with or without an intervening non‐host barrier crop; a large rectangular block with BYMV‐N and CMV sources on opposite sides and a narrow, non‐host barrier crop facing the BYMV‐N source; and a plot within which seed‐infected lupin plants acted as internal CMV sources. When BYMV‐N spread into commercial crops in the absence of a non‐host barrier, there was a steep decline in its incidence with distance from the crop edge. However, when a 20 m‐wide perimeter barrier of oats intervened between the two, there was only a shallow decline. When CMV and BYMV‐N spread from opposite directions into a block with a 0.25 m‐wide oat barrier between it and the BYMV‐N source, the BYMV‐N incidence gradient was shallow but in the opposite direction the CMV gradient was steep. When CMV spread from primary sources within a plot, infection was concentrated in large internal patches. Spread of BYMV‐N was more diffuse with more isolated symptomatic plants and small clusters than occurred with CMV, spread of which was more comprehensive, reacting the near monocyclic and polycyclic patterns of spread with BYMV‐N with CMV respectively. Spread of both viruses was greater along than across rows, especially with CMV. With BYMV‐N, three different phased cycles of secondary spread were evident in the individual symptomatic plants within the small clusters that formed away from the edges of lupin stands. These findings help validate inclusion of perimeter non‐host barriers within an integrated disease management strategy for BYMV‐N in lupin.     

Establishment of baseline susceptibility data to various insecticides for Homalodisca coagulata (Homoptera: Cicadellidae) by comparative bioassay techniques

Homalodisca coagulata Say, adults from three locations in California were subjected to insecticide bioassays to establish baseline toxicity. Initially, two bioassay techniques, petri dish and leaf dip, were compared to determine the most useful method to establish baseline susceptibility data under laboratory and greenhouse conditions. Comparative dose-response data were determined by both techniques to endosulfan, dimethoate, cyfluthrin, and acetamiprid. Toxic values were similar to some insecticides with both techniques but not for all insecticides, revealing susceptibility differences among the three populations of H. coagulata. In subsequent tests, the petri dish technique was selected to establish baseline susceptibility data to various contact insecticides. A systemic uptake bioassay was adapted to estimate dose-mortality responses to a systemic insecticide, imidacloprid. A 2-yr comparison of toxicological responses showed all three populations of H. coagulata to be highly susceptible to 10 insecticides, including chlorpyrifos, dimethoate, endosulfan, bifenthrin, cyfluthrin, esfenvalerate, fenpropathrin, acetamiprid, imidacloprid, and thiamethoxam. In general, two pyrethroids, bifenthrin and esfenvalerate, were the most toxic compounds, followed by two neonicotinoids, acetamiprid and imidacloprid. The LC50 values for all insecticides tested were lower than concentrations used as recommended field rates. Baseline data varied for the three geographically distinct H. coagulata populations with the petri dish technique. Adult H. coagulata collected from San Bernardino County were significantly more susceptible to select pyrethroids compared with adults from Riverside or Kern counties. Adults from San Bernardino County also were more sensitive to two neonicotinoids, acetamiprid and imidacloprid. The highest LC50 values were to endosulfan, which nonetheless proved highly toxic to H. coagulata from all three regions. In the majority of the tests, mortality increased over time resulting in increased susceptibility at 48 h compared with 24 h. These results indicate a wide selection of highly effective insecticides that could aid in managing H. coagulata populations in California.     

Impact of duration versus frequency of probing by Homalodisca vitripennis (Hemiptera: Cicadellidae) on inoculation of Xylella fastidiosa

Successful infection of the plant pathogenic bacterium Xylella fastidiosa (Wells) from an infected plant to a new host involves three main steps: 1) acquisition of the bacterium by a vector; 2) inoculation of a noninfected host plant by the vector; and 3) establishment of sufficient titers of X. fastidiosa in the host plant to sustain a chronic infection. Understanding the basic biology of the transmission process is a key to limiting the spread of plant diseases induced by X. fasdidiosa and reducing agricultural losses, especially those experienced in California since the introduction of a new vector, Homalodisca vitripennis (Germar) (Hemiptera, Cicadellidae) (formerly H. coagulata Say), the glassy-winged sharpshooter. In this study, H. vitripennis adults that acquired X. fastidiosa were allowed access to chrysanthemum plant cuttings for 30, 60, 90, or 120 min. The numbers of X. fastidiosa acquired (i.e., cells present in the insect foregut) and the number inoculated to the plant cuttings were separately determined using quantitative real-time polymerase chain reaction (PCR). In addition, the number of times glassy-winged sharpshooter stylets probed plant cuttings and the amount of time glassy-winged sharpshooter spent actively ingesting were monitored using video surveillance. Linear regression did not indicate a relationship between the number of X. fastidiosa cells inoculated into the plant cutting and either the titer of pathogen present in the insect or amount of time spent ingesting per probe. However, the number of probes significantly influenced the number of X. fastidiosa cells inoculated. Due to the highly variable nature of transmission, our model could not account for all observed variation as indicated by low R2 values. However, our results suggest that the mechanism of transmission is dependent on probing behaviors more than ingestion duration.     

Avoidance and rheotropic responses in phycomyces. Evidence for an 'avoidance gas" mechanism

If a mature sporangiophore is placed next to a barrier that is moving in a clockwise direction, it grows both away from the barrier and into the wind; the wind is generated by the moving barrier itself. When the barrier is moving in a counterclockwise direction, the sporangiophore grows towards both the barrier and the wind. The net direction of growth appears to be the vector sum of the rheotropic response and the avoidance aiming error and does not involve the classic stationary- barrier avoidance response. Our experiments all support the suggestion that the avoidance response, the rheotropic response and the variety of reported wind responses can be explained by the presence of a self- emitted, growth-simulating avoidance gas. We present data that suggest that it is the direction of the net flux (mass transfer) of this gas that determines both the direction and the magnitude of the sporangiophore growth. We further suggest that the region of the cell wall showing maximum mass transfer will show a minimum growth rate, i.e., the direction of growth will always be in the direction of maximum transfer. If water is the avoidance gas, then it would follow that the total hydration of the cell wall in an aqueous salt solution should result in cell wall softening; cell wall softening has been correlated directly to cell wall growth. Using the Instron technique, we now show that submerging the entire sporangiophore in an aqueous salt solution for 4 min causes an increase in cell wall extensibility.     

The influence of aphids and honeydew on the leaving rate of searching aphid parasitoids from wheat plants

Dispersal cages were used to investigate the effects of aphids and treatment with artificial honeydew on the leaving rate of searching females of the parasitoid Aphidius rhopalosiphi from groups of wheat plants. Parasitoids which flew away from groups of plants placed in the centre of a cage were trapped on the sides and roof of the cage and thus were prevented from returning to the plants. The positions of trapped parasitoids suggested their direction of flight when dispersing from the plants. Parasitoids increased their residence times on groups of plants in the presence of aphids and of artificial honeydew, but the rate of parasitism of the host Sitobion avenae was not raised by the presence of artificial honeydew under the experimental conditions used. The direction of flight taken by the majority of parasitoids suggested that they were leaving the plants in order to locate further plants nearby to continue searching rather than to terminate searching and disperse away from the area. The need to consider plant patch size in studies of parasitoid searching behaviour is stressed.     

Evaluation of barrier plants for the cultural control of tomato yellow leaf curl disease

Barrier cropping plays an essential role in controlling insect pests and insect-transmitted diseases in cultural control. It has been proven efficient in suppressing the spread of nonpersistently transmitted viruses. For suppressing the spread of persistently transmitted viruses, barrier cropping is not considered an effective control strategy because barrier plants cannot act as a virus sink to purge the virus in the vector. However, few successful cases of barrier cropping suppressing the spread of persistently transmitted viruses have been reported. The objectives of the present study were to screen candidates (cucumber, okra, Chinese kale, soybean, and corn) for potential barrier plants to control tomato yellow leaf curl Thailand virus (TYLCTHV) and examine whether prefeeding on these plants can reduce the virus titer in its vector, Bemisia tabaci, thus reducing TYLCTHV transmission. The results revealed that nonviruliferous whiteflies preferred cucumber and okra to tomato, whereas viruliferous whiteflies preferred cucumber to tomato. Although prefeeding on cucumber, okra, and Chinese kale did not reduce the titer of TYLCTHV in viruliferous whiteflies, the vector transmission rate decreased after the whiteflies fed on Chinese kale. It implies that planting Chinese kale as a barrier plant for tomato cultivation may reduce the incidence of TYLCTHV. In addition, the preference to cucumber plants may reduce the incidence of whiteflies acquiring TYLCTHV from virus-infected tomato plants and of viruliferous whiteflies inoculating the virus into healthy tomato plants, thereby reducing the disease incidence. Further field trials of barrier cropping using the candidate plants are warranted.     

Flight of Heliothis virescens males in the field in response to sex pheromone

Abstract. The behaviour of Heliothis virescens males flying upwind in the field in a sex pheromone plume was videorecorded and analysed. Males flew faster and straighter, with less counterturning, and heading more directly into the wind when they were 9-11m away from the odour source than when they were 1–3 m away. Regardless of their distance from the source or the windspeed, they maintained an average groundspeed of c. 200 cm s^_1, except when they arrived within 1 m of the source, when their groundspeed slowed significantly. Two or more males flying in the plume at the same instant often exhibited either extremely straight and directly upwind tracks or else zigzagging tracks with significant counterturning (as did males flying through the field of view of the cameras at slighdy different times). The males' position, either in the centre of the plume's axis or along one side, might explain these differences in track straightness, which previous studies with H.virescens have shown to be caused by higher frequencies of contact with plume filaments. When a significant shift in wind direction occurred, males tended to make an initial movement in the direction of the shift, perhaps due to latencies of response in both the olfactory and visual systems associated with flying into clean air. The males' behaviour in the field overall was similar to that observed in the wind tunnel, except that their airspeeds and groundspeeds were significantly higher than those observed in the laboratory. The fact that they flew faster in the field can be explained both by the significandy higher windspeeds that males need to compensate for in the field to attain a preferred velocity of image motion, as well as by a higher height of flight over the ground in die field causing a slower apparent motion of images at a given groundspeed compared with the laboratory.     

Patterns of spread of Tomato spotted wilt virus in field crops of lettuce and pepper: spatial dynamics and validation of control measures

Patterns of spread of Tomato spotted wilt virus (TSWV) were examined in lettuce and pepper plantings into which thrips vectors spread the virus from external virus sources. These plantings were: 1) seven separate field trials into which TSWV ‘infector’ plants of tomato were introduced alongside or near to plantings of lettuce or pepper, and 2) three commercial lettuce plantings into which spread from nearby external infection sources was occurring naturally. The vector thrips species were Frankliniella occidentalis, F. schnitzel and Thrips tabaci, at least two of which were always present. Spatial data for plants with TSWV infection collected at different stages in the growing period were assessed by plotting gradients of infection, and using Spatial Analysis by Distance IndicEs (SADIE) and maps of spatial pattern. Despite the persistent nature of TSWV transmission by thrips vectors, in both lettuce and pepper plantings there was a steep decline in TSWV incidence with distance from external infection sources that were alongside them. The extent of clustering increased over time and was greatest closest to the source. The relationship between percentage infection and assessment date suggested that spread was predominantly monocyclic with only limited polycyclic spread. Development of isolated clusters of infected plants distant from TSWV sources within both crops was consistent with only limited polycyclic spread. Spread to lettuce was greater downwind than upwind of virus source, with magnitude and proximity of source determining the amount of spread. When 15 m wide fallow or non-host (cabbage) barriers separated TSWV sources from lettuce plantings, spread was slower and there was much less clustering with the latter. In commercial lettuce plantings, spread was favoured by TSWV movement within successive side-by-side plantings. The spatial data from the diverse scenarios examined enabled recommendations to be made over ‘safe’ planting distances between external infection sources of different magnitudes and susceptible crops that were short-lived (e.g. lettuce) or long-lived (e.g. pepper). They also helped validate the inclusion of isolation and ‘safe’ planting distances, planting upwind, prompt removal of virus sources, avoidance of side-by-side plantings, and deploying intervening non-host barrier crops as control measures within an integrated disease management strategy for TSWV in field vegetable crops.     

Fate of a genetically modified bacterium in foregut of glassy-winged sharpshooter (Hemiptera: Cicadellidae)

Symbiotic control is a new strategy being investigated to prevent the spread of insect-transmitted pathogens by reducing vector competence. We are developing this strategy to reduce the spread of Xylella fastidiosa by Homalodisca vitripennis (Germar) [formerly Homalodisca coagulata (Say)] (Hemiptera: Cicadellidae), the glassy-winged sharpshooter. In this study, the fate of a transformed symbiotic bacterium, Alcaligenes xylosoxidans variety denitriicans (S1Axd), in the foregut of glassy-winged sharpshooter when fed on citrus (Citrus spp.) and grape (Vitris spp.) was assessed. TaqMan-based quantitative real-time polymerase chain reaction (PCR) was used to detect and quantify bacterial cells remaining in the foregut at 0, 2, 4, 9, and 12 d after acquisition. S1Axd titer dropped rapidly by 2 d after acquisition, but in spite of this, at end of the 12-d experimental period, 45 and 38% of the glassy-winged sharpshooters retained the transformed bacteria, when fed on grape and citrus, respectively.     

Impact of population age structure on Wolbachia transgene driver efficacy: ecologically complex factors and release of genetically modified mosquitoes

Wolbachia symbionts hold theoretical promise as a way to drive transgenes into insect vector populations for disease prevention. For simplicity, current models of Wolbachia dynamics and spread ignore ecologically complex factors such as the age structure of vector populations and overlapping vector generations. We developed a model including these factors to assess their impact on the process of Wolbachia spread into populations of three mosquito species (Anopheles gambiae, Aedes aegypti and Culex pipiens). Depending on the mosquito species, Wolbachia parameters, released mosquito life stage and initial age structure of the target population, the number of Wolbachia-infected mosquitoes that we predict would need to be released ranged from less than the threshold calculated by the simple model to a 10-30-fold increase. Transgenic releases into age-structured populations, which is an expectation for wild mosquitoes, will be difficult and depending on the circumstances may not be economically or logistically feasible due to the large number of infected mosquitoes that must be released. Our results support the perspective that understanding ecological factors is critical for designing transgenic vector-borne disease control strategies.     

Seasonal phenology of Aphis glycines (Hemiptera: Aphididae) and other aphid species in cultivated bean and noncrop habitats in Wisconsin

The occurrence of aphid-transmitted viruses in agricultural crops of the Midwest and northeastern United States has become more frequent since the arrival and establishment of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae). A. glycines is a competent vector of plant viruses and may be responsible for recent virus epidemics in Wisconsin snap bean, Phaseolus vulgaris L., fields. To determine whether vegetation surrounding crop fields could serve as sources of virus inocula, we examined the settling activity ofA. glycines and other aphid species in agricultural crops and noncrop field margins adjacent to snap bean fields. Noncrop field margins were made up of numerous virus-susceptible plant species within 10 m from snap bean field edges. During summers 2006 and 2007, horizontal pan traps were placed in commercial soybean [Glycine max (L.) Merr.], snap bean, and surrounding field margins to characterize aphid flight activity patterns in the different habitat types. Alate abundance and peak occurrence across years varied between crop and noncrop field margins and differed among patches of plants in field margins. Overall aphid activity peaked late in the season (21 August in 2006 and 28 July in 2007); with the majority (52%) of total aphids trapped in all habitats being A. glycines. Susceptibility to viral infection and confirmed visitation of A. glycines to these forage plants suggests the importance ofnoncrop habitats as potential sources of primary virus inoculum. Viral disease onset followed peak aphid flights and further implicates A. glycines as a likely vector of viruses in commercial bean and other crops in Wisconsin.     

The laboratory epidemiological study of the joint circulation of the influenza virus A subtypes A/H1N1/ and A/H3N2/ in Bulgaria]

The National Influenza Center of Bulgaria made the epidemiological analysis of the spread of influenza virus, type A, for the period of 11 years on the basis of mass laboratory investigations. Subtype A (H1N1) was found to be the main factor of epidemics in 1978 and 1982, while the epidemics of 1980, 1983, 1985, 1986, 1987 and 1988 were mainly caused by subtype A (H3N2). The data of laboratory and epidemiological studies indicated that after 20-year absence influenza virus A, subtype A (H1N1), was found again to circulate among the population of Bulgaria, and in 1978-1988 circulated simultaneously with the previous subtype A (H3N2). The simultaneous circulation of two subtypes of influenza virus was of great importance for the frequency, spread and duration of influenza epidemics.     

Age Distribution of Influenza Like Illness Cases during Post-Pandemic A(H3N2): Comparison with the Twelve Previous Seasons,in France

In France, the 2011–2012 influenza epidemic was characterized by the circulation of antigenically drifted influenza A(H3N2) viruses and by an increased disease severity and mortality among the elderly, with respect to the A(H1N1)pdm09 pandemic and post-pandemic outbreaks. Whether the epidemiology of influenza in France differed between the 2011–2012 epidemic and the previous outbreaks is unclear. Here, we analyse the age distribution of influenza like illness (ILI) cases attended in general practice during the 2011–2012 epidemic, and compare it with that of the twelve previous epidemic seasons. Influenza like illness data were obtained through a nationwide surveillance system based on sentinel general practitioners. Vaccine effectiveness was also estimated. The estimated number of ILI cases attended in general practice during the 2011–2012 was lower than that of the past twelve epidemics. The age distribution was characteristic of previous A(H3N2)-dominated outbreaks: school-age children were relatively spared compared to epidemics (co-)dominated by A(H1N1) and/or B viruses (including the 2009 pandemic and post-pandemic outbreaks), while the proportion of adults over 30 year-old was higher. The estimated vaccine effectiveness (54%, 95% CI (48, 60)) was in the lower range for A(H3N2) epidemics. In conclusion, the age distribution of ILI cases attended in general practice seems to be not different between the A(H3N2) pre-pandemic and post-pandemic epidemics. Future researches including a more important number of ILI epidemics and confirmed virological data of influenza and other respiratory pathogens are necessary to confirm these results.