Antennal responses of an oligolectic bee and its cleptoparasite to plant volatiles

Cleptoparasitic or cuckoo bees lay their eggs in nests of other bees, and the parasitic larvae feed the food that had been provided for the host larvae. Nothing is known about the specific signals used by the cuckoo bees for host nest finding, but previous studies have shown that olfactory cues originating from the host bee alone, or the host bee and the larval provision are essential. Here, I compared by using gas chromatography coupled to electroantennographic detection (GC-EAD) the antennal responses of the oligolectic oil-bee Macropis fulvipes and their cleptoparasite, Epeoloides coecutiens, to dynamic headspace scent samples of Lysimachia punctata, a pollen and oil host of Macropis. Both bee species respond to some scent compounds emitted by L. punctata, and two compounds, which were also found in scent samples collected from a Macropis nest entrance, elicited clear signals in the antennae of both species. These compounds may not only play a role for host plant detection by Macropis, but also for host nest detection by Epeoloides. I hypothesise that oligolectic bees and their cleptoparasites use the same compounds for host plant and host nest detection, respectively.Key words: Macropis fulvipes, Epeoloides coecutiens, Lysimachia punctata, oligolectic oil-bee, floral scent, dynamic headspace, GC-EAD, cuckoo bee, host nest findingBees are the most important animal pollinators worldwide, and guarantee sexual reproduction of many plant species.^1,2 This is especially true for female bees, which collect pollen and mostly nectar for their larvae and frequently visit flowers. For finding and detection of suitable flowers, bees are known to use, besides optical cues,^3,4 especially olfactory signals.^5–8 However, c. 20% of bees do not collect pollen for their larvae by their own, but enter nests of host bees and lay eggs into the broodcells.^1,9 The parasitic larvae subsequently feed the food that had been provided for the host larvae. These so called cuckoo or cleptoparasitic bees can be generalistic, indicating that they use species of several other bee groups as host, whereas others can be highly specialized, laying eggs in cells of only few host species.¹ Until now little is known about the cues used by the cuckoo bees for finding host nests. Nevertheless, Cane¹⁰ and Schindler¹¹ demonstrated that parasitic Nomada bees use primarily visual cues of the nest entrance holes for finding possible nests, and olfactory cues for detection of suitable host nests. The chemical cues used by the cleptoparasites originate from the host bee^10,11 and also pollen,¹⁰ the main larval provision. In most bee species, pollen is mixed together with nectar as larval provision, and both floral resources are known to emit volatiles.^12,13 It is unknown, whether cuckoo bees in search for host nests also use volatiles originating from nectar. While the odours of the host bee used as signal by the cleptoparasites, e.g., cuticiular hydrocarbons and glandular secretions, are often species-specific,¹⁴ the chemical cues from the larval provision may just indicate the presence of pollen in the nest without more specifity. As a consequence cuckoo bees could use species-specific host odours to detect nests of a suitable host, and odours released from the larval provision could indicate to them that broodcells are foraged. However, especially those cuckoo bees with oligolectic hosts foraging pollen only on few closely related plant species,¹ may also use the olfactory signals from host broodcell supplies as more specific cue for host nest detection. Thus the same signal from certain flowers may be used for different informations: for the host bee for host plant and for the cuckoo bee for host nest detection.In this concern I tested oligolectic Macropis (Melittidae, Melittinae) and its specific cuckoo bee, Epeoloides (Apidae, Apinae) by using gas chromatography coupled to electroantennographic detection (GC-EAD) on floral scent of Lysimachia (Myrsinaceae). Macropis is highly specialized on Lysimachia, because it is not only collecting pollen from plants of this genus, but also floral oil. Both floral products are the only provision for the larvae.^1,15 Recently, we have shown that the oil bee Macropis is strongly attracted to floral scent of its oil host Lysimachia though the compounds used for host plant finding are still unknown.⁷ Macropis is the only host of Epeoloides, and larvae of this cleptoparasite only feed on the Lysimachia pollen-oil mixture provided for the larvae of Macropis. Worldwide, there are only 2 species of this genus, one in North America and the other in Europe/Asia.^1,16,17 I hypothesized that both bee species respond to specific Lysimachia compounds, which may be used for host plant as well as host nest detection.The measurements with M. fulvipes (F.) and E. coecutiens (F.) antennae demonstrate that both bees, host as well as cuckoo bee, respond to some scent compounds emitted by inflorescences of Lysimachia punctata L. (Fig. 1), a plant being an important pollen and oil source for M. fulvipes. Macropis responded to much more Lysimachia compounds compared to the cuckoo bee, however, two compounds elicited clear signals in the antennae of both bee species: the benzenoid 1-hydroxy-1-phenyl-2-propanone, and the fatty acid derivative 2-tridecanone. Interestingly, both compounds are also emitted from the floral oil of this plant,⁷ and both compounds were also detected in scent samples collected by dynamic headspace in the entrance of a Macropis nest (Dötterl, unpublished data). Therefore, an Epeoloides female being in search for a host nest can detect volatiles emitted from the provision of the host bee at the entrance of a bee nest, and may use these specific compounds for detection of a Macropis nest provisioned with Lysimachia pollen and oil.Open in a separate windowFigure 1Coupled gas chromatographic and electroantennographic detection of a Lysimachia punctata headspace scent sample using antennae of a female oligolectic Macropis fulvipes and a female cleptoparasitic Epeoloides coecutiens bee. (1) 1-hydroxy-1-phenyl-2-propanone, (2) 2-tridecanone.Present results show that an oligolectic oil-bee as well as its cleptoparasite detects volatiles originating from the host plant of the pollen collecting bee, and that oligolectic bees as well as their cuckoo bees may use the same specific signals for host plant and host nest finding, respectively. Biotests are now needed to test this hypothesis.     

Olfactory cues explain differential attraction of the striped rice stem borer to different varieties of rice plant

In Iranian rice fields, different varieties of rice are cultivated which are differentially impacted by females of the rice stem borer, Chilo suppressalis. To elucidate the role odours may play in their host plant finding behaviour, female Ch. suppressalis were exposed to four varieties of rice plants and their volatiles in a four‐arm olfactometer. In whole plant tests, Ch. suppressalis were significantly attracted to the variety previously characterized as most susceptible, least attracted to one characterized as semisusceptible, and showed no attraction to those varieties characterized as semi‐ and highly resistant. Tests using headspace volatile extracts yielded similar results in the case of the most susceptible variety, but showed no attraction to the semisusceptible and highly resistant varieties, and low attraction to the semiresistant variety. Subsequent analysis of the volatile composition identified a panel of 27 components, some of which were either unique to, or abundantly present in, particular varieties, and may explain the observed variation in their attractiveness. Our findings show that rice plant volatiles can play a role in the host selection behaviour of this pest species, and we suggest compounds which may be important to this process and the future application of volatiles in rice pest management programs.     

Oviposition response of the moth Lobesia botrana to sensory cues from a host plant

The grapevine moth Lobesia botrana is a generalist insect herbivore and grapevine is one of its hosts. Previous studies have shown that insects use their olfactory abilities to locate hosts from a distance; whereas contact chemoreception mediates the stimulation of oviposition after landing. Little is known about the role of olfaction and its interactions with contact chemoreception and vision once the insect lands on the plant. Plant volatile compounds can be sensed by host-searching insects located some distance from the plant and insects sense both volatile and nonvolatile cues after landing on a plant. In the present study, we investigated the effects of these volatile and nonvolatile cues on the oviposition behavior of L. botrana. A behavioral bioassay with choice was developed in which insects were offered each sensory cue either alone or in combination with one or 2 other cues. Females were allowed to choose between a device with the stimulus and a blank device. Results were evaluated in terms of 2 parameters: quantity of eggs laid (egg counts) and preference for the stimulus (ODI: oviposition discrimination index). Our results suggest that olfaction significantly affects egg quantity and that there is significant synergism between olfaction and vision, in terms of their combined effect on egg quantity. In terms of preference (ODI), our results did not show a significant preference for any single cue; the highest ODI was measured for the full-cue stimulus (olfaction, vision, and contact). For ODI, a significant interaction was observed between olfaction and vision and a nearly significant interaction was observed between the olfactory and contact cues. The results are discussed in relation to the effects of plant sensory cues on the oviposition behavior of L. botrana.     

An overview of NMR-based metabolomics to identify secondary plant compounds involved in host plant resistance

Secondary metabolites provide a potential source for the generation of host plant resistance and development of biopesticides. This is especially important in view of the rapid and vast spread of agricultural and horticultural pests worldwide. Multiple pests control tactics in the framework of an integrated pest management (IPM) programme are necessary. One important strategy of IPM is the use of chemical host plant resistance. Up to now the study of chemical host plant resistance has, for technical reasons, been restricted to the identification of single compounds applying specific chemical analyses adapted to the compound in question. In biological processes however, usually more than one compound is involved. Metabolomics allows the simultaneous detection of a wide range of compounds, providing an immediate image of the metabolome of a plant. One of the most universally used metabolomic approaches comprises nuclear magnetic resonance spectroscopy (NMR). It has been NMR which has been applied as a proof of principle to show that metabolomics can constitute a major advancement in the study of host plant resistance. Here we give an overview on the application of NMR to identify candidate compounds for host plant resistance. We focus on host plant resistance to western flower thrips (Frankliniella occidentalis) which has been used as a model for different plant species.     

Discrepancy in laboratory and field attraction of apple fruit moth Argyresthia conjugella to host plant volatiles

Abstract.  Apple fruit moth Argyresthia conjugella is a specialist seed predator of rowan Sorbus aucuparia . Large-scale synchronous fluctuation of seed production in rowan (i.e. named masting) drives the apple fruit moth to seek alternative host plants such as apple, during years when rowan berries are not available for oviposition. The role of plant volatile compounds in the attraction of gravid apple fruit moth females is studied in a laboratory wind tunnel. Volatiles from rowan branches with green berries stimulate female moths to fly upwind and to land at the odour source. By contrast, females are not attracted to rowan branches without green berries, and they are not attracted to apple, demonstrating that the chemical stimulus from rowan berries is required for attraction. Attraction to synthetic compounds identified from rowan, anethole and 2-phenyl ethanol confirms the role of plant volatiles in host finding. These two compounds, however, show a discrepant behavioural effect in wind tunnel and field tests. Field traps baited with 2-phenyl ethanol capture female moths but anethole does not produce significant captures. Wind tunnel tests produce the opposite results: moths fly upwind towards the anethole lure, whereas 2-phenyl ethanol is not attractive at all. Wind tunnel attraction to 2-phenyl ethanol is achieved by adding odour from a rowan branch without berries, which is not attractive on its own. This finding demonstrates that interaction with the background odour contributes to the behavioural effect of plant volatile stimuli in the field.     

Plant volatiles mediate attraction to host and non-host plant in apple fruit moth, Argyresthia conjugella

Plant volatiles mediate host finding in insect herbivores and lead to host fidelity and habitat‐specific mating, generating premating reproductive isolation and facilitating sympatric divergence. The apple fruit moth, Argyresthia conjugella Zeller (Lepidoptera: Argyresthiidae), is a particularly suitable species to study the cues and behavioural mechanisms leading to colonization of a new host: it recurrently oviposits on the non‐host plant, apple Malus domestica Borkh. (Rosaceae), where the larvae cannot complete their development. The larval host of the apple fruit moth (Lepidoptera, Argyresthiidae), is rowan Sorbus aucuparia L. (Rosaceae). Fruit setting in rowan, however, fluctuates strongly over large areas in Scandinavia. Every 2–4 years, when too few rowanberries are available for egg laying in forests, apple fruit moth females oviposit instead on apple in nearby orchards, but not on other fruits, such as pear or plum. This poses the question of which cues mediate attraction to rowan and apple, and how apple fruit moth discriminates rowan from apple. Chemical analysis and antennal recordings showed that 11 out of 15 rowan volatiles eliciting an antennal response in A. conjugella females co‐occur in rowan and apple headspace, in a different proportion. In the field, A. conjugella was attracted to several of these plant volatiles, especially to 2‐phenyl ethanol, methyl salicylate, and decanal. Addition of anethole to 2‐phenyl ethanol had a strong synergistic effect, the 1 : 1 blend is a powerful attractant for A. conjugella males and females. These results confirm that volatiles common to both plants may account for a host switch in A. conjugella from rowan to apple. Some of the most attractive compounds, including 2‐phenyl ethanol, anethole, and decanal, which have been found in several apple cultivars, were not present in the headspace of the apple cultivar, Aroma, which is also susceptible to attack by A. conjugella. This supports the idea that the odour signal from apple is suboptimal for attraction of A. conjugella, but is nonetheless sufficient for attraction, during times when rowan is not available for egg laying.     

Oviposition in Yponomeuta cagnagellus: the importance of contact cues for host plant acceptance

Small ermine moths (Yponomeutidae: Lepidoptera) are specialist herbivores. Species within the genus Yponomeuta are each specialized on a limited number of plant species, mainly within genera belonging to the Celastraceae. European Yponomeuta species have developed new specialized host affiliations, mainly on rosaceous hosts. Since these host shifts are reputed to be of consequence for speciation, the role of the ovipositing female is of particular interest. Study of the pre-oviposition behaviour of gravid Y. cagnagellus (Hb.) moths on host (Euonymus europaeus), non-host (Crateagus monogyna) and artificial oviposition substrates, provided information on the nature of the cues used for host plant acceptance and the insect’s perception of these cues. Host selection by adult females occurs with contact chemoreceptors probably located on the antennae or tarsi. MeOH-soluble, non-volatile phytochemical compounds washed from the host plant’s surface and applied on an artificial twig are sufficient to stimulate a complete sequence of behavioural elements leading to oviposition. Volatiles do not have a large effect on the pre-oviposition behaviour.     

Mosquito-mediated attraction of female mosquitoes to a host

ABSTRACT. Female mosquitoes seeking blood respond primarily to kairomones emitted by potential hosts. We now confirm, in the laboratory, field evidence showing that the presence of other female mosquitoes at the host significantly enhances the host-seeking response. Olfactometry strongly suggests that a chemical of mosquito origin is responsible. The adaptive value of this behaviour is discussed.     

Genome scans reveal candidate regions involved in the adaptation to host plant in the pea aphid complex

A major goal in evolutionary biology is to uncover the genetic basis of adaptation. Divergent selection exerted on ecological traits may result in adaptive population differentiation and reproductive isolation and affect differentially the level of genetic divergence along the genome. Genome‐wide scan of large sets of individuals from multiple populations is a powerful approach to identify loci or genomic regions under ecologically divergent selection. Here, we focused on the pea aphid, a species complex of divergent host races, to explore the organization of the genomic divergence associated with host plant adaptation and ecological speciation. We analysed 390 microsatellite markers located at variable distances from predicted genes in replicate samples of sympatric populations of the pea aphid collected on alfalfa, red clover and pea, which correspond to three common host‐adapted races reported in this species complex. Using a method that accounts for the hierarchical structure of our data set, we found a set of 11 outlier loci that show higher genetic differentiation between host races than expected under the null hypothesis of neutral evolution. Two of the outliers are close to olfactory receptor genes and three other nearby genes encoding salivary proteins. The remaining outliers are located in regions with genes of unknown functions, or which functions are unlikely to be involved in interactions with the host plant. This study reveals genetic signatures of divergent selection across the genome and provides an inventory of candidate genes responsible for plant specialization in the pea aphid, thereby setting the stage for future functional studies.     

Orientation behavior of Propylaea japonica toward visual and olfactory cues from its prey–host plant combination

The lady beetle Propylaea japonica (Thunberg) (Coleoptera: Coccinellidae) is an important predator of aphids in agroecosystems. The inundative release of coccinellid beetles can be an effective biological control strategy. An understanding of how biological control agents perceive and use stimuli from host plants is the key to successfully implement commercially produced predators. Here, we studied the relative role of visual and volatile cues. Dual‐choice assays using foraging‐naïve and foraging‐experienced P. japonica adults were conducted using cotton plants [Gossypium hirsutum L. (Malvaceae)] with or without infestation by the cotton aphid, Aphis gossypii (Glover) (Hemiptera: Aphididae). Overall, experienced beetles were more attracted than naïve beetles toward cues associated with aphid‐infested plants. Experienced beetles were also more responsive to olfactory cues compared with naïve beetles. Both foraging‐naïve and ‐experienced lady beetles integrate olfactory and visual cues from plants infested with aphids, with an apparently greater reliance on olfactory cues. The results suggest that foraging experience may increase prey location in P. japonica.     

Partners-in-infection: host proteins involved in the transformation of plant cells by Agrobacterium

Genetic modification of plant cells by Agrobacterium is the only known natural example of DNA transport between kingdoms. While the bacterial factors involved in Agrobacterium infection have been relatively well characterized, studies of their host cellular partners are just beginning. Here, we describe the plant cell factors that might participate in Agrobacterium-mediated genetic transformation and discuss their possible roles in this process. Because Agrobacterium probably adapts existing cellular processes for its life cycle, identifying the host factors participating in Agrobacterium infection might contribute to a better understanding of such basic biological processes as cell communication, intracellular transport and DNA repair and recombination as well as help expand the host range of Agrobacterium as a genetic engineering tool.     

Chemical attraction of Dermacentor variabilis ticks parasitic to Peromyscus leucopus based on host body mass and sex

Macroparasites are commonly aggregated on a small subset of a host population. Previous explanations for this aggregation relate to differences in immunocompetence or the degree to which hosts encounter parasites. We propose active tick host choice through chemical attraction as a potential mechanism leading to aggregated tick burdens. We test this hypothesis using a Y-maze olfactometer, comparing chemical attraction responses of larval and nymphal Dermacentor variabilis ticks parasitic to the white-footed mouse, Peromyscus leucopus, as a function of host sex and host body mass. We hypothesized that larger hosts and male hosts would be most attractive to searching ticks, as these hosts commonly have higher tick burdens in the field. Chemical attraction trials were run in the presence and absence of a known tick attractant, host-produced carbon dioxide (CO₂). Male hosts and larger hosts were preferred by nymphal D. variabilis in the presence and absence of CO₂, whereas larvae had no detectable host preference. The current study suggests that host-produced chemical cues may promote aggregated tick burdens among hosts of a single species based on host body mass and sex.     

Importance of plant physical cues in host acceptance for oviposition by Busseola fusca

Plant and surrogate stems exhibiting specific combinations of physical cues were used to determine which plant‐related stimuli influence the oviposition of Busseola fusca (Fuller) (Lepidoptera: Noctuidae). The number of eggs and egg batches laid per female increased with an increase in diameter of both natural and artificial stems. Direct observations of the oviposition behaviour (walking, antennating, and sweeping with the ovipositor) indicated that the female moths preferred oviposition supports with a large diameter and non‐pubescent or smooth surfaces over pubescent or rough ones. Pubescence and rough surfaces significantly affected the behavioural steps leading to oviposition by interfering with the ovipositor sweep process necessary to find a suitable oviposition site. Furthermore, more eggs and egg batches were laid on soft than rigid supports. The rigidity of the support affected the proper insertion of the ovipositor for egg deposition. Our results underline the importance of physical stimuli in B. fusca's choice of an oviposition site, which may facilitate the identification of potential host plants or preferred oviposition sites on a plant for this species.     

Detection of a plant virus in cryosections of its host plant

The technique of cryo-ultramicrotomy was used for the detection of a plant reovirus in the tissue of its host plant. The observations made on cryosections, compared to those made on conventional sections, show that virus and related structures are well preserved, and that this technique can be usefully employed in plant virology.     

Concurrent modulation of neuronal and behavioural olfactory responses to sex and host plant cues in a male moth

Mating has profound effects on animal physiology and behaviour, not only in females but also in males, which we show here for olfactory responses. In cotton leafworm moths, Spodoptera littoralis, odour-mediated attraction to sex pheromone and plant volatiles are modulated after mating, producing a behavioural response that matches the physiological condition of the male insect. Unmated males are attracted by upwind flight to sex pheromone released by calling females, as well as to volatiles of lilac flowers and green leaves of the host plant cotton, signalling adult food and mating sites, respectively. Mating temporarily abolishes male attraction to females and host plant odour, but does not diminish attraction to flowers. This behavioural modulation is correlated with a response modulation in the olfactory system, as shown by electro-physiological recordings from antennae and by functional imaging of the antennal lobe, using natural odours and synthetic compounds. An effect of mating on the olfactory responses to pheromone and cotton plant volatiles but not to lilac flowers indicates the presence of functionally independent neural circuits within the olfactory system. Our results indicate that these circuits interconnect and weigh perception of social and habitat odour signals to generate appropriate behavioural responses according to mating state.     

A new oligolectic bee species of the genus Rhophitulus Ducke (Hymenoptera,Andrenidae) from South Brazil

The genus Rhophitulus Ducke, 1907 is a large and complex group of bees of the tribe Protandrenini comprising small, slender, mostly black ground-nesting species that are restricted to South America. We describe a new species of Rhophitulus from Parque Nacional São Joaquim, Urubici, state of Santa Catarina, Brazil. Rophitulus ater sp. nov. is distinctive and easily distinguished from other species of the genus by a unique combination of morphological characters in both sexes, but especially by the following: dull black body, coarsely and densely punctate integument, basal area of metapostnotum depressed and areolate rugose, posterior margin of hind tibia and pygidial fimbria of female with blackish pilosity, and characters of the male genitalia with hidden sterna. The new species is closely associated with Blumenbachia catharinensis (Loasaceae), which is restricted to cloud forest of the southeastern rim of Serra Geral. Flowers of B. catharinensis are pollen and nectar resources and mating sites for the new species.     

The role of plant chemical cues in determining host preference in the generalist aphid parasitoid Aphidius colemani

The host preference behaviour of the generalist aphid parasitoid Aphidius colemaniwas investigated using a Y-tube olfactometer. Female A. colemanishowed a preference for the host-plant complex on which they had been reared, even though the same aphid host was involved, demonstrating a host plant preference. This preference was not evident when the parasitoids were dissected from their mummies prior to adult emergence. Host plant preference exhibited during host selection appeared to be induced by chemical cues encountered on the mummy case at the time of emergence, but preferences could be changed by subsequent foraging experiences. It is concluded that plant chemical cues play a major role in determining initial preferences through a process of emergence conditioning but that learning processes, involving cues encountered during oviposition in or contact with the host, can modify these initial preferences.     

Differential expression of proteins in response to the interaction between the pathogen Fusarium graminearum and its host, Hordeum vulgare

Using proteomic techniques, a study aimed at isolating and identifying proteins associated with resistance to fusarium head blight (FHB) was conducted on six barley genotypes of varying resistance. At anthesis, barley spikelets were point inoculated with Fusarium graminearum macroconidial suspensions or mock inoculum. In total, 43 acidic protein spots out of 600 were detected 3 days postinoculation to be differentially expressed due to FHB and were identified. Identification of proteins responsive to FHB included those associated with oxidative burst and oxidative stress response, such as malate dehydrogenase and peroxidases, and pathogenesis-related (PR). An increase in abundance of PR-3 or PR-5 could be associated with the resistant genotypes CI4196, Svansota, and Harbin, as well as the intermediate resistant genotype CDC Bold. On the contrary, the susceptible genotype Stander showed a decrease in abundance of these acidic PR-proteins. In the susceptible and intermediate resistant genotypes Stander and CDC Bold, as well as CI4196, the increased abundance of proteins associated with an oxidative response might have prepared the terrain for saprophytic fungal invasion. On the contrary, in the resistant sources Harbin and Svansota we did not observed change in abundance of these proteins. Not a single significant change in acidic protein abundance could be detected in Chevron. Three distinct response patterns are reported from these six barley genotypes.     

Chemical basis of host selection and plant resistance in oligophagous insects

Recent investigations of the Colorado potato beetle and the alfalfa weevil reveal many similarities in their modes of host selection. Many plant chemicals influence their behavioral responses and physiological processes. Chemical stimuli influencing host finding and acceptance or rejection of plants include attractants, repellents, sign stimulants, feeding stimulants and deterrents. Both species are highly sensitive to deterrent chemicals present in many plants. Feeding stimulants are indispensible for these insects and are supplied by both primary nutrients (i.e. sugars, amino acids, phospholipids and potassium salts) and secondary plant substances. The important role played by different plant chemicals in host selection and plant resistance is discussed.

---

Zusammenfassung Neuere Untersuchungen am Kartoffelkäfer und am Luzerneblattnager förderten viele Übereinstimmungen in der Art ihrer Wirtswahl zu Tage. Viele Pflanzenstoffe beeinflussen ihre Verhaltensweisen und physiologische Prozesse. Chemische Reize, welche die Auffindung des Wirtes, Annahme oder Ablehnung der Pflanzen beeinflussen, umfassen Attractants, Repellents, Signalstoffe, Fraß-Stimulatoren und Abschreckstoffe. Beide Arten sind hochempfindlich gegenüber abschreckenden Verbindungen in vielen Pflanzen. Fraß-Stimulatoren sind für beide Insekten unabdingbar notwendig und werden sowohl von primären Nährstoffen (wie Zucker, Aminosäuren, Phospholipiden und Natriumsalzen) wie von sekundären Pflanzenstoffen gestellt. Die bedeutsame Rolle, welche Pflanzenstoffe bei der Wirtswahl und der Resistenz der Pflanzen spielen, wird diskutiert.

---

---

Journal paper No. ...., Utah Agricultural Experiment Station, Logan, Utah.