A STUDY OF OLFACTORY DISCRIMINATION IN THE RAT WITH THE AID OF A NEW ODOR DELIVERY TECHNIQUE

A technique for delivering odors at specific concentrationsand for precise periods into the nasal cavity of a freely movingrat is described. This is accomplished by linking the outletof an automatic micro-olfactometer to a cannula chronicallyimplanted into the nasal cavity of the rat. Details of the constructionand implantation of the cannula are given. Using this odor deliverytechnique rats were trained in a two-choice discrimination procedureto distinguish between the odors of benzaldehyde and benzonitrile(both are ‘almond like’), benzaldehyde and isobutylbutyrate(fruity), and benzonitrile-isobutylbutyrate. The rats foundthe olfactory properties of benzaldehyde and benzonitrile tobe similar, and each to be very different to the olfactory propertiesof isobutylbutyrate. It is proposed that the rat may use morethan a single olfactory property of each stimulus to discriminatebetween two odors. ^* This paper reports research undertaken at the School of BiologicalSciences, Macquarie University, and the CSIRO Division of FoodResearch.     

The impact of pests and diseases on the herbage yield of permanent grassland at eight sites in England and Wales

Plots at each of eight widespread permanent pasture sites below 300 m and representative of large areas of long established grassland in England and Wales, were treated with an insecticide plus molluscicide, a fungicide or nematicide treatment. Populations of various invertebrates and the occurrence of foliar fungal diseases were assessed. Leaf blotch (Drechslera) was the most common disease, but neither this nor other foliar fungal diseases were prevalent until late in the growing season. The fungicide treatment did not control diseases satisfactorily. The fungicide and nematicide treatment had little effect on total annual herbage yield. Leatherjackets, crambids, slugs and frit fly larvae were present, usually in low numbers, at most sites. The insecticide and molluscicide treatment increased yield by 11% on average across all sites and years. Losses caused by pests to UK grasslands were estimated to be over £500 million per year.     

Effect of chemical complexity of essential oils on feeding deterrence in larvae of the cabbage looper

The relationship between chemical composition and feeding deterrent activity of seven essential oils is explored, including those from Syzygium aromaticum (L.) Merr. & Perry (Myrtaceae), Cinnamomum zeylanicum Blume (Lauraceae), Lavendula latifolia (L.) Medicus, Lavendula angustifolia L., Mentha crispa L., Mentha arvensis L. and Mentha piperita L. (Lamiaceae) against an important agricultural pest, the cabbage looper (Trichoplusia ni Hübner, Noctuidae), using a leaf‐disc choice bioassay. Comparison of the deterrent activity of ‘full mixtures' with respective artificial blends missing individual constituents demonstrates that, for most oils, minor constituents in a mixture can be as important as major constituents with respect to the overall feeding deterrent effect. There is a lack of correlation between the feeding deterrent effect of an individual constituent of an essential oil and its contribution to the overall activity of the ‘full mixture’ in some cases. The effect of removing an individual constituent from the mixture of an essential oil depends on the unique properties of the mixture, which in turn may reflect the interaction of its constituents. Understanding the role and contribution of each constituent to the overall activity of the oil can facilitate the creation of artificial blends that optimize their efficacy against different pests.     

Social Insect Pheromones: Their Chemistry and Function

Exocrine secretions of social insects are often characterizedby extraordinarily complex mixtures of natural products. Thus,chemical communication in social insects must be interpretedin terms of signals generated by multicomponent systems, theindividual constituents of which can affect the informationalcontent of the message. Alarm pheromones have been identified chiefly in three subfamiliesof ants and their distribution appears to be chemosystematicallysignificant. Myrmicine genera emphasize 3-alkanones as alarmreleasers, whereas methyl ketones, primarily of terpenoidalorigin, are widely utilized as alarm pheromones in the subfamilyDolichoderinae. Formicine species may employ formic acidas analarm pheromone in addition to the compounds produced in themandibular and Dufour's glands. The mandibular gland pheromonesare chiefly acyclic monoterpene aldehydes (e.g., citronellal)which are relatively low boiling compounds. Higher boiling n-alkanesare produced in the Dufour's glands and may serve as more persistentreleasers of alarm behavior. Alarm pheromones as well as thecaste-specific pheromones of male bees and ants, probably alsoserve as defensive products. In many cases it is likely thatpheromones were originally utilized as defensive compounds andtheir communicative function is a secondary development.     

Effect of Support Material on the Development of Microbial Fixed Films Converting Acetic Acid to Methane*

A study of the development of methanogenic fixed films on pieces of polyvinyl chloride plastic, etched glass and baked clay showed that support material markedly affected the rate of attachment and growth of bacteria converting acetic acid to methane. Film development, as indicated by the rate of acetate conversion to methane and carbon dioxide, was threefold faster on fired clay than on either PVC plastic or etched glass. Scanning electron micrographs showed that the film of bacteria attached to clay was thick and uniform, while the film attached to PVC plastic was thin although still uniform. Attachment to etched glass was spotty. The characteristics of clay which made it a superior support appeared to be its rough, porous surface which offered attachment sites to the micro-organisms and the presence of minerals in the clay, particularly iron which is known to stimulate methanogenesis and growth.