Development of Melaleuca oils as effective natural-based personal insect repellents

For many decades effective insect repellents have relied on synthetic actives such as N,N -diethyl- meta -toluamide. Increasingly, consumers are seeking natural-based alternatives to many everyday products including insect repellents. While many studies have been published detailing the potential of essential oils to act as insect repellents, few oils have been identified as viable alternatives to synthetic actives. This study details the process involved in the selection of Australian essential oils effective as repellents and the subsequent testing of natural-based insect repellents using the selected oils. Using a combination of laboratory-based and field-based testing, oil from Melaleuca ericifolia was identified as being an effective insect repellent. When formulated into three different bases: an alcohol-based spray, an emulsion and a gel, these Melaleuca -based repellents were shown to be as effective at repelling mosquitoes Aedes vigilax (Skuse) (Diptera: Culicidae) and Verrallina carmenti (Edwards) (Diptera: Culicidae), the bush fly Musca vetustissima (Walker) (Diptera: Muscidae), and biting midges Culicoides ornatus (Taylor) (Diptera: Ceratopogonidae) and Culicoides immaculatus (Lee & Reye) (Diptera: Ceratopogonidae) as a synthetic-based commercial repellent. This study has shown that effective insect repellents based on natural active ingredients can deliver repellency on par with synthetic actives in the field. Three Melaleuca -based formulations have been registered as repellents and are now commercially available.     

The most effective pollinator revisited: pollen dynamics in a spring-flowering herb

Most flowers are visited by a wide range of potential pollinators. However, their efficiency in pollen removal and deposition, and other behavioural factors affecting pollination effectiveness may greatly differ among taxa, and even individuals. Fritillary (Fritillaria meleagris L., Liliaceae) is a spring-flowering, critically endangered plant in the Polish flora, red-listed in most of the European countries of its range. Based on indirect evidence, that is, body pollen loads, visitation frequency and seasonal abundance, it is estimated that its key pollinators are queen bumblebees, but, as shown in the literature, the largest Fritillaria pollen loads are carried by solitary bees. To study pollinator effectiveness for floral visitors to F. meleagris, we performed a garden experiment, where we analysed pollen deposition and assessed pollen removal per single flower-visit in the plant. Similarly to field conditions reported in the literature, our experimental plants were serviced by nectar-seeking bumblebee queens and two taxa of solitary bees, small pollen-collecting Andrena and large, nectar-seeking Anthophora males. When “quality” component was addressed, despite the character of visits, insects from all groups deposited more pollen than was found on unvisited flowers, but they did not differ significantly from each other in pollen deposition on virgin stigmas. We also found some differences in pollen removal both within- and among-visitor species and control flowers, unfortunately due to extremely high variation of the results they were all statistically insignificant. However, when “quantity” component of insect performance was concerned, we observed that over 81 % of visits were by bumblebees. Bombus queens stayed on flowers significantly less time than small Andrena individuals (13 % of recorded visits) and equally long as Anthophora males (only 6 % of visits). We conclude that although all the visitor groups can pollinate the flowers of F. meleagris, bumblebee queens indeed proved to be the most effective pollinators of the plant, when both quality and quantity components of pollination are concerned.     

白蚁肠道共生体的纤维素代谢体系

白蚁是大陆生态系统中木质纤维素降解的生力军,其肠道共生系统纤维素酶对纤维素的消化起到了关键的作用.本文概述了白蚁自身及其肠道共生微生物的纤维素水解系统的特点、相互关系以及相互作用的研究进展.     

The ommatidium of the termite mastotermes darwiniensis

An electron microscope study of the compound eye of the termite Mastotermes darwiniensis shows that the ommatidia have both primitive and specialized features. The ommatidia are of the apposition type with eight similar retinular cells, a fused rhabdom, irregularly orientated rhabdomere tubules and no tracheae. The retinula cells contain lipid. The cone cells have unusual processes, which thicken towards the basement membrane and contain rough endoplasmic reticulum, granules and dense bodies. These processes may act as a primitive transport system for nutrients.     

The cellulolytic system of the termite gut

The demand for the usage of natural renewable polymeric material is increasing in order to satisfy the future needs for energy and chemical precursors. Important steps in the hydrolysis of polymeric material and bioconversion can be performed by microorganisms. Over about 150 million years, termites have optimized their intestinal polysaccharide-degrading symbiosis. In the ecosystem of the “termite gut,” polysaccharides are degraded from lignocellulose, such as cellulose and hemicelluloses, in 1 day, while lignin is only weakly attacked. The understanding of the principles of cellulose degradation in this natural polymer-degrading ecosystem could be helpful for the improvement of the biotechnological hydrolysis and conversion of cellulose, e.g., in the case of biogas production from natural renewable plant material in biogas plants. This review focuses on the present knowledge of the cellulose degradation in the termite gut.     

The chemistry of a termite fungus comb

Summary The chemical and spectroscopic data presented herein show that about 50% of the weight of the termite fungus comb consists of carbohydrates (⊂40%) and proteinaceous materials (⊂10%). Of the remaining material about 30% appears to be aliphatic in nature (long-chain and branched alkanoic acids) and 20% aromatic and phenolic. The data on monosaccharide composition indicate that the fungus comb material, rich in glucose, arabinose and xylose, is predominantly of plant origin.     

Local interleukin 2 therapy is most effective against cancer when injected intratumourally

Local interleukin 2 (IL-2) therapy is more effective against systemic tumours than systemic IL-2 therapy, but it remains unclear whether IL-2 should be injected intratumourally or peritumourally. To investigate this question, we treated DBA/2 mice bearing a large subcutaneous syngeneic SL2 lymphoma with either intra or peritumoural IL-2 therapy. Both applications enhanced survival, but intratumourally injected IL-2 was more effective than peritumourally injected IL-2. Tumours started to regress 4 days after IL-2 injection. Tumour cells died at the IL-2 injection site, although IL-2 is not directly cytotoxic for SL2 cells in vitro. Tumour cell death correlated well with oedema and extravascular erythrocytes, but less with leukocyte infiltrates. In mice bearing two s.c. tumours, intratumoural application therapy of IL-2 in one tumour caused decrease in size of both tumours in 4–9 days after therapy. However, the IL-2 treated tumours regressed more strongly than the untreated tumours. We conclude that vascular leakage and/or tissue destruction inside the tumour may contribute to the enhanced effect of intratumoural IL-2 therapy compared to peritumoural IL-2 therapy. Hence, we recommend applying of intratumoural rather than peritumoural IL-2 therapy.     

Mosquito repellents in frog skin

The search for novel insect repellents has been driven by health concerns over established synthetic compounds such as diethyl-m-toluamide (DEET). Given the diversity of compounds known from frog skin and records of mosquito bite and ectoparasite infestation, the presence of mosquito repellents in frogs seemed plausible. We investigated frog skin secretions to confirm the existence of mosquito repellent properties. Litoria caerulea secretions were assessed for mosquito repellency by topical application on mice. The secretions provided protection against host-seeking Culex annulirostris mosquitoes. Olfactometer tests using aqueous washes of skin secretions from L. caerulea and four other frog species were conducted to determine whether volatile components were responsible for repellency. Volatiles from Litoria rubella and Uperoleia mjobergi secretions were repellent to C. annulirostris, albeit not as repellent as a DEET control. The demonstration of endogenous insect repellents in amphibians is novel, and demonstrates that many aspects of frog chemical ecology remain unexplored.     

The relative efficacy of repellents against mosquito vectors of disease

Laboratory tests of insect repellents by various different methods showed that An.stephensi Liston was consistently more susceptible than An.gambiae Giles, An.albimanus Wiedemann or An.pulcherrimus Theobald. The six repellents tested were di-ethyl toluamide (deet), di-methyl phthalate (DMP), ethyl-hexanediol, permethrin, citronella and cedarwood oil. Testing systems in which the mosquitoes were presented with a choice gave consistently lower ED50 values than when there was no choice, i.e. the standards of tolerance are not absolute but depend on the options available. In field tests in an experimental hut a curtain with a high dose of di-ethyl toluamide (deet) reduced biting in the hut but had to be re-impregnated frequently. Deet-impregnated anklets gave about 84% protection against Culex quinquefasciatus Say for 80 days after one impregnation, in a trial in which the anklets were brought out of sealed storage and tested for 2 h nightly. Similar protection was found against An.funestus Giles but the protection against An.gambiae s.l., An. coustani Laveran and Mansonia spp. was not as good. There were highly significant differences between the four collectors' mosquito attractiveness but this varied highly significantly between the mosquito species.     

IncP plasmids are most effective in mediating conjugation between Escherichia coli and streptomycetes

Mobilizable shuttle plasmids containing the origin of transfer (oriT) region of plasmid F (IncFI), ColIb-P9 (IncI1), and RP4/RP1 (IncPα) were constructed to test the ability of the cognate conjugation system to mediate gene transfer from Escherichia coli to Streptomyces. The conjugative system of the IncPα plasmids was shown to be most effective in conjugative transfer, giving peak values of (2.7 ± 0.2) × 10⁻² S. lividans TK24 exconjugants per recipient cell. To assess whether the mating-pair formation system or the DNA-processing apparatus of the IncPα plasmids is crucial in conjugative transfer, an assay with an IncQ-based mobilizable plasmid (RSF1010) specifying its own DNA-processing system was developed. Only the IncPα plasmid mobilized the construct to S. lividans indicating that the mating-pair formation system is primarly responsible for the promiscuous transfer of the plasmids between E. coli and Streptomyces. Dynamic of conjugative transfer from E. coli to S. lividans was investigated and exconjugants starting from the first hour of mating were obtained. The text was submitted by the authors in English.