Federico Lessio

Dispersal patterns and chromatic response of Scaphoideus titanus Ball (Homoptera Cicadellidae), vector of the phytoplasma agent of grapevine flavescence dorée

Abstract  1 Scaphoideus titanus Ball, a nearctic leafhopper introduced into Europe in the 1950s, is known to be the vector of the phytoplasma agent of flavescence dorée (FD), a persistent disease of grapevine. Knowledge of its dispersal patterns is thus very important to prevent disease outbreaks.

Relationships between Ostrinia nubilalis (Lepidoptera: Crambidae) feeding activity, crop technique and mycotoxin contamination of corn kernel in northwestern Italy

Abstract The relationships between the feeding activity of Ostrinia nubilalis (Hübner), crop technique (i.e., planting date, nitrogen fertilization, irrigation, and use of deltamethrin), and mycotoxin contamination of kernels were studied in Italian corn crop systems. Field sampling was conducted to determine the incidence of first- and second-generation larvae for each crop technique. At harvest, kernel contamination by fumonisins and zearalenon was measured and related to the number and position of tunnels on corn ears. The number of corn plants injured from second-generation larvae was partially reduced by using deltamethrin (−35%) and by bringing forward planting (−12%), whereas differences in nitrogen and water supply had little effect. The abundance of the first generation was, on average, low. The amount of fumonisin was generally one scale point higher in injured ears, and was positively related to ear tunnelling: tunnels in the apex seem to increase the amount of contamination. No links were detected between O. nubilalis presence and zearalenon contamination.

Seasonal and daily movement of Scaphoideus titanus Ball (Homoptera: Cicadellidae)

Abstract Seasonal and daily flight patterns of Scaphoideus titanus Ball were investigated in northern Italy, throughout a 3-yr period, using yellow sticky traps placed in an experimental vineyard. Capture data were also analyzed in relation to temperature and relative humidity values. The leafhopper was found to be more active from 1800 to 0800 hours, whereas little movement occurred during high light intensity hours. Although the sex ratio was always male biased, no difference in flight periodicity was found between genders. The seasonal flight peak occurred each year in different periods, ranging from the end of June to the beginning of July, depending on mean temperature values. Daily capture increases were correlated with daily minimum and maximum temperatures and were negatively correlated with maximum values of relative humidity. As a result, this species could be crepuscular or nocturnal, and a bimodal flight periodicity is likely.

Spatial Distribution of Nymphs of Scaphoideus titanus (Homoptera: Cicadellidae) in Grapes, and Evaluation of Sequential Sampling Plans

The spatial distribution of the nymphs of Scaphoideus titanus Ball (Homoptera Cicadellidae), the vector of grapevine flavescence dorée (Candidatus Phytoplasma vitis, 16Sr-V), was studied by applying Taylors power law. Studies were conducted from 2002 to 2005, in organic and conventional vineyards of Piedmont, northern Italy. Minimum sample size and fixed precision level stop lines were calculated to develop appropriate sampling plans. Model validation was performed, using independent field data, by means of Resampling Validation of Sample Plans (RVSP) resampling software. The nymphal distribution, analyzed via Taylors power law, was aggregated, with b = 1.49. A sample of 32 plants was adequate at low pest densities with a precision level of D0 = 0.30; but for a more accurate estimate (D0 = 0.10), the required sample size needs to be 292 plants. Greens fixed precision level stop lines seem to be more suitable for field sampling: RVSP simulations of this sampling plan showed precision levels very close to the desired levels. However, at a prefixed precision level of 0.10, sampling would become too time-consuming, whereas a precision level of 0.25 is easily achievable. How these results could influence the correct application of the compulsory control of S. titanus and Flavescence dorée in Italy is discussed.

Seasonal progression of sex ratio and phytoplasma infection in Scaphoideus titanus Ball (Hemiptera: Cicadellidae).

The differences between the seasonal occurrence and likelihood of being infected by FD phytoplasmas, of male and female Scaphoideus titanus Ball, were investigated. Sex ratio (male: female) was calculated by counting males and females sampled by means of yellow sticky traps and sweep-nets and from adults derived from hatched eggs in field-collected grapevine wood. PCR essays were performed to test differences in infection between genders. Overall, the sex ratio on sticky traps was significantly more male biased (1.99:1) if compared to net sweeping (0.62:1) and laboratory rearing (0.60:1). The peak of male presence was recorded in the middle of July in laboratory rearing and sweep net, and in the middle of August on sticky traps; the maximum presence of females was detected at the end of July in laboratory rearing, and at the end of August in sweep net samplings and on sticky traps. The seasonal sex ratio was more male biased at the beginning in laboratory rearing (1.50:1) and sticky traps (9:1), and then decreased in favor of females at the end of the sampling period, both in laboratory rearing (0.17:1) and in sticky traps (0.07:1). This trend was significantly less skewed, although similar, in sweep net samplings that recorded a sex ratio of 1:1 and 0.16:1 at the beginning and at the end of the sampling period, respectively. Concerning phytoplasma detection, an interaction between gender and sampling period was observed, the males showing a peak of infected individuals later in the season (35%). Some possible behavioral explanations of the data obtained are given.

Spatial patterns of Scaphoideus titanus (Hemiptera: Cicadellidae): a geostatistical and neural network approach

The spatial distribution of the leafhopper Scaphoideus titanus Ball, the vector of the pathogen Flavescence dorée of grapevine, was studied in the Asti Province (Piedmont) Italy. Field sampling of adults was carried out using yellow sticky traps both in vineyards subjected to different pest management regimes, and in woods containing American grapevines. The spatial correlation of S. titanus captures was studied using geostatistical analyses. An artificial neural network (ANN) was designed to operate as a spatial predictor driven by external factors (elevation, slope, height above channel, agricultural communities, perimeter-to-area ratio, potential solar radiation, and pest management) for estimating the population density of the leafhopper. The captures were spatially related up to 210 m: the variogram fitting was significant, but resulted in low R 2 values. The ANN achieved a significant generalization of the infestation levels of S. titanus, permitting prediction maps based upon simulated pest management scenarios to be obtained. The most important factors affecting S. titanus population density were pest management, and secondarily agricultural communities.

Insect vectors of plant pathogenic Mollicutes in the Euro-Mediterranean region

This paper embeds a review of insect vectors of Mollicutes plant pathogens in Europe and Middle East. A dissertation on systematic and phylogeny introduces the two groups of vectors: Auchenorrhyncha and Sternorrhyncha (Psyllidae). Aspects involving the differences in the transmission process of pathogens and the relationships of insect vectors and host plants have been considered. From an environmental point of view, flight activity, dispersal and spatial distribution have been dealt with in relationship with plant disease epidemiology. Finally, the main control and monitoring strategies have been discussed, along with the problem concerning alien species and quarantine regulations.

Influence of temperature on the embryonic and post-embryonic development of Scaphoideus titanus (Hemiptera: Cicadellidae), vector of grapevine Flavescence dorée

The embryonic and post-embryonic development of Scaphoideus titanus, the main vector of grapevine Flavescence dorée, was studied under laboratory conditions, at constant temperatures (T = 15, 18, 20, 22, 24, 27, and 29 °C). The data obtained were fitted to the equation of Brière, and the model was validated against independent field data. The minimum cardinal temperature for eggs ranged from 18 to 20 °C, the duration of egg hatching was minimum at T = 24 °C, egg hatchability was optimum at 22 °C, and very few eggs hatched at T ≥ 27 °C. The duration of post-embryonic development clearly shortened as the temperature increased, both overall and within the same life stage, almost half-reducing itself from 18 to 29 °C. Within the same temperature tested, the early instars took less time to moult compared to the late ones. The data obtained provided a significant fit with the equation of Brière. Validation was satisfactory, particularly concerning third instar nymphs and adults, which are the key life instars for targeting integrated pest management (IPM) strategies. The model proposed could be used to predict the development of S. titanus in north-western Italy for IPM purposes.

New insights in phytoplasma-vector interaction: acquisition and inoculation of flavescence dorée phytoplasma by Scaphoideus titanus adults in a short window of time: Phytoplasma acquisition and transmission by Scaphoideus titanus adults

The leafhopper Scaphoideus titanus is able to transmit 16SrV phytoplasmas agents of grapevine’s flavescence dorée (FD) within 30–45 days, following an acquisition access period (AAP) of a few days feeding on infected plants as a nymph, a latency period (LP) of 3–5 weeks becoming meanwhile an adult, and an inoculation access period (IAP) of a few days on healthy plants. However, several aspects of FD epidemiology suggest how the whole transmission process may take less time, and may start directly with adults of the insect vector. Transmission experiments have been set up under lab condition. Phytoplasma-free S. titanus adults were placed on broad bean (BB) plants (Vicia faba) infected by FD-C (16SrV-C) phytoplasmas for an AAP=7 days. Afterwards, they were immediately moved onto healthy BB for IAP, which were changed every 7 days, obtaining three timings of inoculation: IAP 1, IAP 2 and IAP 3, lasting 7, 14 and 21 days from the end of AAP, respectively. DNA was extracted from plants and insects, and PCR tests were performed to identify FD phytoplasmas. Insects were dissected and fluorescence in situ hybridisation was made to detect the presence of phytoplasmas in midguts and salivary glands. The rate of infection in insects ranged 46–68% without significant differences among IAPs. Inoculation in plants succeeded in all IAPs, at a rate of 16–23% (no significant differences). Phytoplasma load was significantly higher in IAP 3 than IAP 1–2 for both plants and insects. Phytoplasmas were identified both in midgut and salivary glands of S. titanus at all IAP times. The possible implications of these results in the epidemiology of flavescence dorée are discussed.