134 research outputs found
Donor/Acceptor Heterojunction Organic Solar Cells
The operation and the design of organic solar cells with donor/acceptor heterojunction structure and exciton blocking layer is outlined and results of their initial development and assessment are reported. Under halogen lamp illumination with 100 mW/cm2 incident optical power density, the devices exhibits an open circuit voltage VOC = 0.45 V, a short circuit current density JSC between 2 and 2.5 mA/cm2 with a fill factor FF â 50%, an external quantum efficiency (electrons/s over incident photons/s) EQE â 5% and a power conversion efficiency of about 0.5%. Measurements of the photoelectrical characteristics with time are also reported, confirming that non encapsulated organic solar cells have limited stability in ambient atmosphere
Indagini sulle infestazioni di Aphis gossypii Glover su melone invernale (Cucumis melo Var. Helios) in aziende a conduzione biologica della Sicilia occidentale.
Investigations on the aphid infestation occurring on winter melon crops (Cucumis melo var. Helios) in organic
farms of western Sicily
The winter melon (Cucumis melo L.) is an important crop in Sicily. Previous studies carried out in western Sicily have shown
that the aphid species Aphis gossipii is the key pest of winter melon crops.A. gossypii is a cosmopolitan species with very polyphagous
habits; this phytophagous insect is capable of serious economic damage due to direct feeding of the sap plant and due to the honeydew
secretion and the consequent presence of sooty mold and due to the possible transmission of viruses.
The aim of this work was to investigate the levels of aphid infestation in two different organic winter melon fields located
in western Sicily by monitoring the dynamic of population of A. gossypii and the complex of natural enemies associated
with the pest. In addition the possible influence of mulching as aphid repellent has been evaluated.
In one location we monitored the aphid infestation through direct observation of the plants that have been carried out
weekly from transplant to harvest of the product. In the other location, we investigated the dynamics of population and levels
of adult infestation, evaluating also the possible influence of mulching, using chromotropic traps, consisting in yellow
adhesive plates placed horizontally in mulched rows, on the plastic film, and alleyways, on the ground. In addition, surveys
were carried out by comparing mulched plots and not mulched plots.
Our results showed that, in both locations, the population density of A. gossypii was low and no serious damage has been
inflicted to the crop: this is probably related to the abundant presence of natural enemies of the pest and to the repellent action
of mulching
Indagine su Raphidopalpa foveicollis (Lucas) nella coltura del melone biologico della Sicilia occidentale.
Investigations on Raphidopalpa foveicollis (Lucas) in an organic cultivation of winter melon in western Sicily
Red pumpkin beetle (Raphidopalpa foveicollis), is a Chrysomelidae beetle that lives on various species of cucurbits with greater preference for Cucumis sp. Both larval and adult stages are injurious to the crops. The former feeds on roots and stems of the plants, while the latter feeds on foliage, petals and fruits. In Sicily, this insect has occurred in the past as a secondary pest on the winter melon, but sometimes it reaches levels of infestation to arouse considerable concern among farmers. In order to implement economic methods of pest control a study on organic cultivation of winter melon was conducted in Camporeale (500 meters a.s.l.) (Palermo).
Particularly, the dynamics of population and infestation levels have been investigated, taking into account also the possible influence of mulching, using chromotropic traps. Such traps consisted of yellow adhesive plates placed horizontally in mulched rows, on the plastic film, and between the rows, on the ground. In addition, surveys were carried out by comparing mulched plots and not mulched ones.
Results showed that the peak catches (47.4 adults / trap) occurred in mid-June and the greater number of catches was found in the traps placed between the rows, with significant difference. A greater number of individuals has been detected on plants of the not mulched plots than that of the mulched plots, even though no statistically significant difference was found. The percentage of plants with damaged leaves ranged from 68.7% to 100% on mulched plots and 93.3% to 100% on not mulched plots with no significant differences. The presence of adults has also been observed on fruits but without signs of trophic activity. In addition, young stages were not detected in the plants examined.
In conclusion, the combined effect of mulching, at least until the vegetation does not cover the plastic film, and sticky traps, placed mostly between the rows, plays a synergistic action to the pest control. Considering the low cost of such technique, it may be a potential tool for managing this pest using mass trapping method
First report of Melittobia australica Girault in Europe and new record of M. acasta (Walker) for Italy
Melittobia acasta and M. australica are newly recorded from Sicily, Italy, and the second species is reported in Europe for the first time. A short historical background about Melittobia parasitoid wasps, their hosts, and distribution, with emphasis in those two species is presented together with illustrations to facilitate their identification. Brief discussion about the presence and possible distribution of the species in Sicily is also included
Prospects of herbivore egg-killing plant defenses for sustainable crop protection
Due to a growing demand of food production worldwide, new strategies are suggested to allow for sustainable production of food with minimal effects on natural resources. A promising alternative to the application of chemical pesticides is the implementation of crops resistant to insect pests. Plants produce compounds that are harmful to a wide range of attackers, including insect pests; thus, exploitation of their natural defense system can be the key for the development of pest-resistant crops. Interestingly, some plants possess a unique first line of defense that eliminates the enemy before it becomes destructive: egg-killing. Insect eggs can trigger (1) direct defenses, mostly including plant cell tissue growth or cell death that lead to eggs desiccating, being crushed or falling off the plant or (2) indirect defenses, plant chemical cues recruiting natural enemies that kill the egg or hatching larvae (parasitoids). The consequences of plant responses to eggs are that insect larvae do not hatch or that they are impeded in development, and damage to the plant is reduced. Here, we provide an overview on the ubiquity and evolutionary history of egg-killing traits within the plant kingdom including crops. Up to now, little is known on the mechanisms and on the genetic basis of egg-killing traits. Making use of egg-killing defense traits in crops is a promising new way to sustainably reduce losses of crop yield. We provide suggestions for new breeding strategies to grow egg-killing crops and improve biological control
Indagine su Henosepilachna elaterii (Rossi) (=Epilachna chrysomelina (F.)) e Raphidopalpa foveicollis (Lucas) in meloneti biologici della Sicilia occidentale.
Investigations on Henosepilachna elaterii (Rossi) and Raphidopalpa foveicollis (Lucas) in an organic cultivation
of winter melon in western Sicily.
A study on H. elaterii and R. Foveicollis, serious pests of winter melon, was conducted in two organic melon fields of
the western Sicily. Dynamics of population and infestation levels were investigated. In addition, the possible influence of
mulching on R. Foveicollis infestation has been taken into account.
Our results showed that H. elaterii occurred only in one field from the beginning of June and it infested 60% of the
plants in the mid-July, then the pest population density dropped to about 10%. R. foveicollis occurred in both locations
from the beginning of June and reached high levels of population density around the mid-June; then the pest density rapidly
decreased in the two following weeks. Adults were found in the traps and the peak catches occurred in mid-June. A
greater number of catches was found in the traps placed between the rows and the greater number of individuals has been
detected on plants of the not mulched plots.
The percentage of plants with damaged leaves ranged from 68.7% to 100% on mulched plots and 93.3% to 100% on
not mulched plots. In conclusion, the damages inflicted by R. foveicollis are counterbalanced by the rapid growing rate
of the plant occurring during June. Hence, this pest may cause serious injuries only in case of heavy infestation on winter
melon seedlings. Similarly, the damage caused by H. elaterii is usually not heavy even if presence of high levels of infestation
Thermal stress affects patch time allocation by preventing forgetting in a parasitoid wasp
Learning and memory allow animals to adjust their foraging strategies through experience. Despite the known impact of temperature on many aspects of the behavioral ecology of animals, memory retention in the face of realistic thermal stress has seldom been assessed. In the laboratory, we studied the behavioral expression of an egg parasitoid's (Trissolcus basalis) memory when exposed to thermal stress that could be encountered in nature. We hypothesized that thermal stress would disrupt memory consolidation and/or modify the optimality of memory retention, thus affecting patch time allocation strategies. Memory consolidation was resilient to 1h of thermal stress following an unrewarded experience (learning) on a patch of host-associated infochemicals. Neither high (40 °C) or low (10 °C) thermal stress changed the intensity of the experienced wasps' behavioral response relative to those held at a moderate temperature (25 °C). Next, we investigated how temperature stress could affect the parasitoids' memory retention ("forgetting"). When kept at a constant moderate temperature after learning, residence times of wasps retested on host cues increased relative to controls (naive wasps) over a period of 4 days as they presumably "forgot." However, both hot and cool daily temperature cycles prevented forgetting; the residence times of retested experienced wasps in these treatments did not change relative to controls over time. We discuss to what extent this may be an adaptive response by the parasitoids versus a physiological constraint imposed by temperature. Our findings contribute to an understanding of the impact of thermal stress on foraging strategies that involve learning and memory
The response of an egg parasitoid to substrate-borne semiochemicals is affected by previous experience
Animals can adjust their behaviour according to previous experience gained during foraging. In parasitoids, experience plays a key role in host location, a hierarchical process in which air-borne and substrate-borne semiochemicals are used to find hosts. In nature, chemical traces deposited by herbivore hosts when walking on the plant are adsorbed by leaf surfaces and perceived as substrate-borne semiochemicals by parasitoids. Chemical traces left on cabbage leaves by adults of the harlequin bug (Murgantia histrionica) induce an innate arrestment response in the egg parasitoid Trissolcus brochymenae characterized by an intense searching behaviour on host-contaminated areas. Here we investigated whether the T. brochymenae response to host walking traces left on leaf surfaces is affected by previous experience in the context of parasitoid foraging behaviour. We found that: 1) an unrewarded experience (successive encounters with host-contaminated areas without successful oviposition) decreased the intensity of the parasitoid response; 2) a rewarded experience (successful oviposition) acted as a reinforcing stimulus; 3) the elapsed time between two consecutive unrewarded events affected the parasitoid response in a host-gender specific manner. The ecological role of these results to the host location process of egg parasitoids is discussed
Disk precession to explain the super-orbital modulation of LMC X-4: results from the Swift monitoring campaign
We studied the spectral changes of the high-mass X-ray binary system LMC X-4
to understand the origin and mechanisms beyond its super-orbital modulation
(30.4 days). To this aim, we obtained a monitoring campaign with Swift/XRT
(0.3-10 keV) and complemented these data with the years-long Swift/BAT survey
data (15-60 keV). We found a self-consistent, physically motivated, description
of the broadband X-ray spectrum using a Swift/XRT and a NuSTAR observation at
the epoch of maximum flux. We decomposed the spectrum into the sum of a
bulk+thermal Comptonization, a disk-reflection component and a soft
contribution from a standard Shakura-Sunyaev accretion disk. We applied this
model to 20 phase-selected Swift spectra along the super-orbital period. We
found a phase-dependent flux ratio of the different components, whereas the
absorption column does not significantly vary. The disk emission is decoupled
with respect to the hard flux. We interpret this as a geometrical effect in
which the inner parts of the disk are tilted with respect to the obscuring
outer regions.Comment: 14 pages, 15 figures, Accepted for publication in MNRA
Spectral and timing characterization of the X-ray source 1RXS J194211.9+255552
We report on the first spectral and timing characterization of the transient X-ray source 1RXS J194211.9+255552 using all available data from the Swift X-ray satellite. We used 10 years of hard X-ray data from the Burst Alert Telescope (BAT) to characterize its long-term behaviour and to search for long periodicities, finding evidence for a periodic modulation at 166.5 ± 0.5 d, that we interpret as the orbital period of the source. The folded light curve reveals that the X-ray emission is mostly concentrated in a restricted phase-interval and we propose to associate 1RXS J194211.9+255552 to the class of the Be X-ray binaries. This is also supported by the results of the spectral analysis, where we used the BAT data and three pointed Swift/XRT observations to characterize the X-ray broad-band spectral shape. We found mild spectral variability in soft X-rays that can be accounted for by a varying local neutral absorber, while the intrinsic emission is consistent with a hard power law multiplied by a high-energy exponential cut-off as typically observed in this class of systems
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