: Pymetrozine, a pyridine azomethine compound, represents a novel insecticide with a selective activity against homopteran insects. It acts in a unique way : aphids are not knocked down on contact but seem to die of starvation. This implies an e †ect of pymetrozine on feeding behaviour. The aim of the present work was to elucidate how and at which step pymetrozine interferes with the complex mechanisms underlying phloem feeding. The e †ect of pymetrozine, applied in various ways, on di †erent phases of stylet penetration and feeding activity of individual aphids was studied using the Electrical Penetration Graph technique (EPG). Initial choice experiments indicated that pymetrozine does not have a deterrent or antifeedant action. Topical application (150 ng pymetrozine mg~1 fresh weight) inhibited stylet insertion into the plant. When injected, less than 30 ng mg~1 was sufficient to produce the same e †ect. When pymetrozine was systemically applied via plant spraying or root uptake, aphids started feeding normally. After some time, however, they withdrew their stylets from the phloem and walked around with una †ected locomotion. At low doses aphids eventually recovered and resumed feeding. High doses, however, irreversibly disrupted feeding and prevented stylet reinsertion. Aphid motility was not a †ected up to an estimated haemolymph concentration of 1 mM pymetrozine. Aphids which eventually stopped feeding on pymetrozine-treated plants showed EPGs with distorted salivation/ingestion patterns. It is concluded that pymetrozine does not have a general toxic e †ect on aphids but selectively interferes with the nervous regulation of feeding behaviour which consequently results in death due to starvation after a few days.

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Summary. The production of volatile secondary plant substances during the evolution of terrestrial plants is reviewed in regard to the defensive systems of plants to microorganisms and herbivores. Plant volatiles can be produced by both anabolic and catabolic processes. Although attraction of pollinators is a well-studied phenomenon, functions of volatiles range from excretion of waste products to the production of compounds attracting natural enemies of herbivores. During the evolution of the angiosperms a diversity of volatiles were selected to defend generative parts against microorganisms. Many of these allomones were related to or even identical with sex pheromones of insects. As a result flowers of angiosperms became utilized as a mating site. Consequently insects visiting flowers became involved in pollination, facilitating the steps from anemophily to entomophily. The efficiency of entomophily was increased because of nutritional rewards.An evolutionary scenario for the impact of plant volatiles on insects is presented and the role of volatile allomones in the establishment of plant-insect relationships is emphasized by (1) their strong antimicrobial properties, (2) strategies to protect symbiotic microorganisms, (3) their function as repellents and deterrents, (4) the use of volatile allomones as kairomones. These facts speak for an adaptation of insects to plant physiology and a limited importance of phytophagous insects in selection pressure upon plants. Herbivorous insects have realized specific adaptations to be able to discriminate between complex odour blends, but the utilization of chemical groups among insect taxa is different.The main theories on plant chemical defence do not discuss the impact of volatiles on host plant selection and may be apt to revision when pheromones, allomones, kairomones and synomones are not taken into account.

Plant penetration by western flower thrips (Frankliniella occidentalis (Pergande)) was analysed with the electrical penetration graph technique (EPG, DC‐system). Thrips attached to a gold wire were included in an electrical circuit to record EPGs when penetrating the plant tissues with their stylets. Three basic EPG waveforms have been distinguished, correlated with stylet penetration into cells, salivation, and ingestion, respectively. The main difference with EPGs of Homoptera is the occurrence of continued separate penetrations that are not necessarily followed by ingestion. Insertion of the stylets causes strong voltage fluctuations in the EPG. We could confirm earlier evidence that penetration of cells and subsequent ingestion of (part of) the protoplast takes less than 20 seconds. Repeated short penetrations can be followed by a continuous feeding pattern during which the stylets are not withdrawn. The same sequence of waveforms is produced on other plant parts such as fruits or pollen grains. The specific waveforms are mainly caused by electromotive force (emf). The emf component was recorded with high resolution and the correlation of waveform details with activities of the cibarial muscle system is discussed.

Substances secreted by aphids into diets through a rubber‐wax membrane can be detected by their absorption of low wavelength ultraviolet light. Their detection can be simplified by presenting water as diet. Of the substances secreted into water by non‐crowded aphids within 24 h, ca 35–55% of the absorbance at 200 nm can be accounted for by reactions with protein reagents and/or electrophoresis. Macrosiphum euphorbiae secreted over 30 ng of salivary protein in bovine serum albumin equivalents per mg fresh body weight. SDS‐PAGE revealed that the proteins initially secreted had subunits mostly of > 100,000 Daltons. When dead or dying aphids were present on the membrane, however, e.g. due to crowding or prolonged confinement in the feeding chamber, additional subunits of < 30,000 Daltons also appeared in the water. When feeding continued for more than 24 h, proteins separable by electrophoresis began to disappear, possibly as a result of leakage of lyzing enzymes into the water from aphids that had died with their mouth parts still inserted through the membrane. The initial secretions possessed oxidase activity. Invertase was not detected but the secretion caused non‐enzymatic reduction of a copper reagent used for detection of reducing sugars. Marked contrasts were noted between the electrophoretic protein patterns of the saliva of different species of aphids. The saliva of Macrosiphum euphorbiae and Myzus persicae contained over twice as much catechol oxidase activity per unit of salivary protein as that of Nasonovia ribisnigri and Aphis fabae. The significance of these findings in relation to use of artificial diets for colony maintenance and feeding experiments and for studies of aphid‐plant interactions is discussed.