First-principles study of the structural and electronic properties of tetragonal ZrOX (X = S, Se, and Te) monolayers and their vdW heterostructures for applications in optoelectronics and photocatalysis.

Using first-principles calculations, we have studied the structural and electronic properties of ZrOX (X = S, Se, and Te) monolayers and their van der Waals heterostructures in the tetragonal structure. Our results show that these monolayers are dynamically stable and are semiconductors with electronic bandgaps ranging from 1.98 to 3.16 eV as obtained with the GW approximation. By computing their band edges, we show that ZrOS and ZrOSe are of interest for water splitting applications. In addition, the van der Waals heterostructures formed by these monolayers show a type I band alignment for ZrOTe/ZrOSe and a type II alignment for the other two heterostructures, making them potential candidates for certain optoelectronic applications involving electron/hole separation.

Synthetic Co-Attractants of the Aggregation Pheromone of the Date Palm Root Borer Oryctes agamemnon.

Laboratory and field investigations to identify and evaluate plant co-attractants of the aggregation pheromone of the date palm pest Oryctes agamemnon are reported. Volatiles emitted by freshly cut palm core and palm core with feeding males, were collected, analyzed by gas chromatography coupled to mass spectrometry and evaluated in olfactometers alone or combined with synthetic pheromone. A collection of palm odor without male effluvia was attractive alone and enhanced attraction to synthetic pheromone in an olfactometer similar to that to a collection of palm odor emitted with feeding males and containing natural pheromone. Behavioral responses to collections of palm volatiles were correlated to the amount of volatiles material in them. Enhancement of the attractiveness of the pheromone was not correlated to chemicals specific to beetle feeding. The chemicals common to the active collections extracts were benzoate esters, mostly ethyl benzoate, anisole derivatives and sesquiterpenes. Blends of the most abundant components of the extracts were evaluated for enhancement of the attractiveness of pheromone (1 µg) in olfactometers at 1 or 10 µg doses. The mixtures were further evaluated by field trapping in Tunisia at 3-10 mg/day using reference (6 mg/day) or experimental pheromone formulations. A mixture of ethyl benzoate, 4-methylanisole and farnesol (1:1:1 w/w at 6.5 mg/day) enhanced captures in pheromone baited traps in 2014 and 2015 and this mixture was as active as the natural palm bait. The practical prospect of the result for the management for O. agamemnon, and other palm beetles is discussed.

Influence of enhancing electrolytes on the removal efficiency of heavy metals from Gabes marine sediments (Tunisia).

This study focused on the feasibility of the treatment of heavy metals-contaminated sediments from Gabes harbor (Tunisia) using enhanced electrokinetic process. It presented a laboratory short-time electrokinetic experiment. The enhancing agents, as citric, acetic acids and sodium dodecyl sulfate (SDS) were used regarding their low environmental hazard. The electrokinetic cell was specially designed in order to elaborate two experiments at the same time. This paper is composed of three parts. The first part introduces the characterization of Gabes sediments. The second part describes the design of laboratory electrokinetic cell and the followed methods. The third part is dedicated to the results analysis. Treatment efficiency revealed that more than 80% of lead was removed from Gabes marine sediments. The reduction of cooper concentration, in sediments after treatment, ranged from 74 to 87%. Despite, the high removal of cadmium that ranged from 58 to 79%, treated sediments presented Cd concentration above the threshold limit.

Identification of the Aggregation Pheromone of the Date Palm Root Borer Oryctes agamemnon.

Laboratory and field investigations aimed to characterize the chemical communication system of the date palm pest Oryctes agamemnon. Live males or extracts of male effluvia attracted conspecifics in an olfactometer, whereas female effluvia attracted only males. Volatile emissions from adults feeding on sugarcane were sampled and analysed by gas chromatography (GC) and GC/mass spectrometry (GC/MS). Males emitted a blend of 1) ethyl 4-methyloctanoate, 2) 4-methyloctanoic acid, 3) 4-methyloctanyl acetate, and 4) 4-methyloctanol in variable ratio. Single sensillum recordings demonstrated that compounds 1, 2, and 3 are detected by specific olfactory receptor neurons. Olfactometric experiments showed that compounds 1 and 3 attract both sexes of O. agamemnon, but females are more attracted by compound 1 and males by compound 3. Compound 2 was more attractive for females, especially virgin ones. Field experiments confirmed that compound 1 and compound 2 attracted O. agamemnon of both sexes and showed synergy with palm odors. No clear activity of compound 3 was observed. A mix of compounds 1 and 2 with date palm core odor was significantly the most attractive, and captured more females than males. The male aggregation pheromone of O. agamemnon appears therefore to be based on a mixture in contrast to previously identified Oryctes pheromones. Our results provide the basis for developing mass trapping to control this pest.

Evaluation and modeling of synergy to pheromone and plant kairomone in American palm weevil.

BACKGROUND: Many behavioral responses to odors are synergistic, particularly in insects. In beetles, synergy often involves a pheromone and a plant odor, and pest management relies on them for the use of combined lures. To investigate olfactory synergy mechanisms, we need to distinguish synergistic effects from additive ones, when all components of the mixture are active. RESULTS: As versatile tools and procedures were not available, we developed a bioassay, and a mathematical model to evaluate synergy between aggregation pheromone (P) and host plant odors (kairomone: K) in the American palm weevil, a pest insect showing enhanced responses to P+K mixtures. Responses to synthetic P and natural K were obtained using a 4-arm olfactometer coupled to a controlled volatile delivery system. We showed that: (1) Response thresholds were ca. 10 and 100 pg/s respectively for P and K. (2) Both stimuli induced similar maximum response. (3) Increasing the dose decreased the response for P to the point of repellence and maintained a maximum response for K. (4) P and K were synergistic over a 100-fold range of doses with experimental responses to P+K mixtures greater than the ones predicted assuming additive effects. Responses close to maximum were associated with the mixture amounts below the response threshold for both P and K. CONCLUSION: These results confirm the role of olfactory synergy in optimizing active host-plant localization by phytophagous insects. Our evaluation procedure can be generalized to test synergistic or inhibitory integrated responses of various odor mixtures for various insects.

Perception of cuticular hydrocarbons by the olfactory organs in Periplaneta americana (L.) (Insecta: Dictyoptera).

Despite the importance of cuticular hydrocarbons (CHs) in insect chemical communication, direct proof that they are detected and recognized by insects by contact or by olfactory receptors are rare. In Periplaneta americana, CHs induce aggregation. The aim of our study was to investigate how CHs are detected by P. americana antennae. Using solid phase microextraction and gas chromatography, the three main CHs of the species profile were identified in the volatiles emitted by these insects. Gas chromatography coupled to electroantennography recordings demonstrated that the antennae responded to these three CHs. Furthermore, CHs had an attraction effect in Y-olfactometer bioassays when presented at high concentrations. As CHs can be perceived by P. americana, at least from a short distance, they could play a role in attracting conspecifics during aggregation processes, in addition to inducing aggregation when direct contact is possible.

Cuticular hydrocarbon profiles and aggregation in four Periplaneta species (Insecta: Dictyoptera).

Cuticular hydrocarbon (CH) profiles of four Periplaneta species were compared and their role in aggregation and interspecific recognition was evaluated. CH profiles are species specific and include from 19 to 25 hydrocarbons. P. brunnea, P. fuliginosa and P. australasiae have more CH components in common with one another than with P. americana. P. americana hydrocarbons include components from 24 to 43 carbon atoms but hydrocarbons for the three other species range from 21 to 41 atoms. The major compound in CH profiles in P. americana is 6,9-heptacosadiene that is absent from the three other species. The major compound in CH profiles of P. Brunnea and P. fuliginosa is 13-methyl pentacosane that is not found in the CH profile of P. americana. Major compounds in P. australasiae species are tricosene and 13-methyl pentacosane, respectively, in males and females. Binary choice tests demonstrated that specific CH extracts induced aggregation in the four species. High CH amounts were required to induce aggregation of P. americana and P. brunnea on conditioned sites, whereas low amounts were sufficient to induce aggregation of P. fuliginosa and P. australasiae. These results suggest that CHs are involved in aggregation and interspecific recognition.

Structure and function of the antennal sensilla of the palm weevil Rhynchophorus palmarum (Coleoptera, Curculionidae).

The distribution, fine structure and function of the sensilla present on the antennal club of Rhynchophorus palmarum were studied. No sex dimorphism was observed. Scanning and transmission electron microscopy showed five types of hair-like structures, four of which were evenly distributed on the antennal club. Two types of hair (IV and V) showed wall pores, a characteristic of olfactory sensilla. The antenna numbers 11,190 +/- 3040 type IV and 7360 +/- 1500 type V hairs. Using single sensillum recording, we identified 17 types of olfactory receptor neurons (ORNs) on the basis of their responses to pheromone and host plant odors, triggering synergic behavioral responses. We characterized highly specific and sensitive ORNs tuned to the aggregation pheromone (18% ORNs; 0.01-1 ng response threshold) and to host plant odors such as ethyl acetate, ethanol, acetoin and guaiacol (10% ORNs; 1-10 ng response threshold). Eleven percent of the ORNs were more generalist, responding to several odors with low sensitivity. Nine percent of the ORNs showed a complex pattern of responses, being co-activated by the pheromone and plant odors. This suggests an interaction at the sensory neuron level between pheromone and plant odors, triggering synergic behavioral responses.