Identification and Synthesis of a Male-Produced Pheromone for the Neotropical Root Weevil Diaprepes abbreviatus

An unsaturated hydroxy-ester pheromone was isolated from the headspace and feces of male Diaprepes abbreviatus, identified, and synthesized. The pheromone, methyl (E)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate, was discovered by gas chromatography-coupled electroantennogram detection (GC-EAD), and identified by gas chromatography–mass spectrometry (GC-MS) and nuclear magnetic resonance spectroscopy (NMR). The synthesis yielded an 86:14 mixture of methyl (E)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate (active) and methyl (Z)-3-(2-hydroxyethyl)-4-methyl-2-pentenoate (inactive), along with a lactone breakdown product. The activity of the synthetic E-isomer was confirmed by GC-EAD, GC-MS, NMR, and bioassays. No antennal response was observed to the Z-isomer or the lactone. In a two-choice olfactometer bioassay, female D. abbreviatus moved upwind towards the synthetic pheromone or natural pheromone more often compared with clean air. Males showed no clear preference for the synthetic pheromone. This pheromone, alone or in combination with plant volatiles, may play a role in the location of males by female D. abbreviatus

Potential Geographic Distribution of Brown Marmorated Stink Bug Invasion (Halyomorpha halys)

BACKGROUND: The Brown Marmorated Stink Bug (BMSB), Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), native to Asia, is becoming an invasive species with a rapidly expanding range in North America and Europe. In the US, it is a household pest and also caused unprecedented damage to agriculture crops. Exploring its climatic limits and estimating its potential geographic distribution can provide critical information for management strategies. METHODOLOGY/PRINCIPALS: We used direct climate comparisons to explore the climatic niche occupied by native and invasive populations of BMSB. Ecological niche modelings based on the native range were used to anticipate the potential distribution of BMSB worldwide. Conversely, niche models based on the introduced range were used to locate the original invasive propagates in Asia. Areas with high invasion potential were identified by two niche modeling algorithms (i.e., Maxent and GARP). CONCLUSIONS/SIGNIFICANCE: Reduced dimensionality of environmental space improves native model transferability in the invade area. Projecting models from invasive population back to native distributional areas offers valuable information on the potential source regions of the invasive populations. Our models anticipated successfully the current disjunct distribution of BMSB in the US. The original propagates are hypothesized to have come from northern Japan or western Korea. High climate suitable areas at risk of invasion include latitudes between 30°-50° including northern Europe, northeastern North America, southern Australia and the North Island of New Zealand. Angola in Africa and Uruguay in South America also showed high climate suitability

Nano-Crystalline &Amorphous Silicon PhotoTransistor Performance Analysis

In this thesis, we compared electrical performance and stability of a novel nanocrystalline Si (nc-Si) thin film phototransistor (TFT) phototransistor and a regular amorphous silicon (a-Si:H) TFT phototransistor for large area imaging applications. The electrical performance parameters of nc-Si TFT phototransistor were extracted from the electrical (current-voltage) testing in dark and under illumination. The field-effect mobility is found to be around 1.2 cm2V-1s-1, the threshold voltage around 3.9V and the sub-threshold voltage slope around 0.47V/Dec. Optical properties of nc-Si TFT phototransistor have been evaluated under the green light illumination in the range of 1014 – 1017 lum, and the photocurrent gain and the external quantum efficiency were extracted from the experimental results. By comparing the results with those for a-Si:H TFTs measured under the same conditions, we found that nc-Si TFT has higher photo current gain under low illumination intensity, 5 ×1014 to 7 ×1015 lum. This thesis shows the relations bewteen the photo current gain, the external quantum efficiency, TFT drain and TFT gate bias; the photo current gain and the external quantum efficiency can be controlled by the Vds and the Vgs

Behavioural responses of diapausing Halyomorpha halys (Hemiptera: Pentatomidae) to conspecific volatile organic compounds

The brown marmorated stink bug, Halyomorpha halys Stål (Hemiptera: Pentatomidae), is an invasive pest in America, Europe and Asia and causes serious economic loss to crops, and nuisance problems during overwintering. Uninvaded southern hemisphere countries, such as New Zealand and Australia, see an increase in H. halys border interceptions during the northern hemisphere populations’ overwintering period as large aggregations of H. halys can settle to diapause in items for export, e.g. vehicles, containers, etc. Here, we explored aspects of diapausing H. halys behaviour relative to release and perception of defensive odour compounds. First, to determine whether group size and agitation affect the release of defensive odours, diapausing H. halys were confined in glass tubes as individuals or in varying group sizes and mechanically agitated or remained stationary and the presence or absence of defensive odours was recorded. Using gas chromatography-mass spectrometry, we also established if exposure to individual defensive odour components (tridecane, (E)-2-decenal, 4-oxo-(E)-2-hexenal, and dodecane) induced individuals to release defensive compounds. Additionally, H. halys dispersal was measured in the laboratory following exposure to individual components of their defensive odour or their natural blend. We found that agitating individual bugs did not induce the release of defensive odours. The release of human-detectable odours was only found in groups of mechanically agitated H. halys, whereas non-agitated bugs did not emit odour. Exposure to 4-oxo-(E)-2-hexenal was the only odour component that resulted in individual H. halys releasing defensive compounds. Diapausing H. halys exposure to the natural blend of defensive compounds resulted in increased horizontal distance moved and velocity, while tridecane exposure increased distance moved, velocity and angular velocity, and (E)-2-decenal exposure increased distance moved. Our behavioural and chemical data suggest that defensive compounds released by diapausing H. halys act as an alarm pheromone, particularly when adults are in aggregations