Foraging behaviour of the whitefly parasitoidEncarsia formosa on tomato leaflets

IndividualEncarsia formosa parasitoids were observed continuously until the parasitoids flew away, either on clean tomato leaflets, on leaflets with honeydew, or on leaflets with unparasitized and parasitized whitefly larvae. Encounters with unparasitized and parasitized whitefly larvae, and contact with honeydew arrested the parasitoids on the leaflet. The walking speed increased linearly from 0.179 to 0.529 mm/s between 15 and 25–30°C. The walking activity showed another relationship with temperature: it was below 10% at 15 and 18°C, and increased to about 75% at 20, 25 and 30°C. It was not affected by host encounters or by 1 to 4 ovipositions. The total handling time of hosts was between 1.8–21.8% of the total time on the leaflet. Self-superparasitism was not observed. Conspecific-superparasitism did occur in 14% of the encounters with hosts containing a parasitoid egg, but was not observed anymore when the parasitoid egg had hatched. Experienced parasitoids superparasitized as often as naive females. The foraging behaviour ofE. formosa from landing on a leaf until departure has now been quantified and is discussed.     

Sugar transport in Coprinus cinereus

Two transport systems for glucose were detected: a high affinity system with a K_m of 27 μM, and a low affinity system with a K_m of 3.3 mM. The high affinity system transported glucose, 2-deoxy-d-glucose (K_m = 26 μM), 3-O-methylglucose (K_m = 19 μM), d-glucosamine (K_m = 652 μM), d-fructose (K_m = 2.3 mM) and l-sorbose (K_m = 2.2 mM). All sugars were accumulated against concentration gradients. The high affinity system was strongly or completely inhibited by N-ethylmaleimide, quercetin, 2,4-dinitrophenol and sodium azide. The system had a distinct pH optimum (7.4) and optimum temperature (45°C). The low affinity system transported glucose, 2-deoxy-d-glucose (K_m = 7.5 mM), and 3-O-methylglucose (K_m = 1.5 mM). Accumulation again occurred against a concentration gradient. The low affinity system was inhibited by N-ethylmaleimide, quercetin and 2,4-dinitrophenol, but not by sodium azide. The rate of uptake by the low affinity system was constant over a wide temperature range (30–50°C) and was not much affected by pH; but as the pH of the medium was altered from 4.5 to 8.9 a co-ordinated increase in affinity for 2-deoxy-d-glucose (from 52.1 mM to 0.3 mM) and decrease in maximum velocity (by a factor of five) occurred. Both uptake systems were present in sporelings germinated in media containing sodium acetate as sole carbon source. Only the low affinity system could initially be demonstrated in glucose-grown tissue, although the high affinity system was restored by starvation in glucose-free medium. The half-time for restoration of high affinity activity was 3.5 min and the process was unaffected by cycloheximide. Addition of glucose to an acetate-grown culture inactivated the high affinity system with a half-life of 5–7.5 s. Addition of cycloheximide to an acetate-grown culture caused decay of the high affinity system with a half-life of 80 min. Regulation is thus thought to depend on modulation of protein activity rather than synthesis, and the kinetics of glucose, 2-deoxy-d-glucose and 3-O-methylglucose uptake would be consistent with there being a single carrier showing negative co-operativity.     

Targeted transformation in Coprinus cinereus

Summary We examined the influence of DNA form and size on the arrangement and genomic location of transforming DNA sequences in the basidiomycete Coprinus cinereus. Protoplasts with either single or double mutations in the tryptophan synthetase (TRPI) gene were transformed with cloned copies of this gene which contained only a single DNA strand, contained a specific single nick within the C. cinereus sequences (4.8 kb), contained a specific double-strand break, or contained an additional 35 kb of flanking genomic sequences. Gene replacement events were recovered when each DNA type was used. However, none of these substrates offers a substantial improvement in transformation or targeting frequency when compared to supercoiled circular DNA, which has allowed recovery of both gene replacements as well as homologous insertions in 5 % of the transformants analyzed. The frequency of transformants carrying tandem insertions with multiple copies of the transforming DNA was reduced when single-stranded DNA was used, and increased when DNA containing double-strand breaks was used. These results have important implications for the efficient design of targeted transformation and co-transformation experiments.     

Restriction enzyme-mediated DNA integration in Coprinus cinereus

Restriction enzyme-mediated DNA integration (REMI) has recently received attention as a new technique for the generation of mutants by transformation in fungi. Here we analyse this method in the basidiomycete Coprinus cinereus using the homologous pab1 gene as a selectable marker and the restriction enzymes BamHI, EcoRI and PstI. Addition of restriction enzymes to transformation mixtures results in an earlier appearance of transformants and influences transformation rates in an enzyme- and concentration-dependent manner. Low concentrations of restriction enzyme result in increased numbers of transformants compared to no addition of enzymes. Transformation rates decrease with higher enzyme concentrations. If protoplasts are made from cells stored in the cold, the transformation rates drop drastically even in the presence of low amounts of enzyme. In several transformants, plasmid integration directly correlated with the action of restriction enzyme at random chromosomal restriction sites. In some cases, restriction enzymes appear to reduce the number of integration events per transformant. Simultaneously, mutation rates can be enhanced due to the presence of restriction enzymes. Although restriction enzymes clearly promote plasmid integration into the host genome they also have cytotoxic and possibly mutagenic effects that result from processes other than plasmid integration. In consequence, for any given enzyme used in REMI mutagenesis, the enzyme concentration that gives the highest number of transformants must be defined experimentally. Such optimal transformation conditions should give the highest probability of obtaining mutations caused by a single restriction enzyme-mediated integration of the selection marker. Received: 2 September 1996 / Accepted: 7 April 1997     

Pathway analysis of radiation-sensitive meiotic mutants ofCoprinus cinereus

We have isolated 37 radiation-sensitive mutants of the basidiomyceteCoprinus cinereus. Each mutation is recessive, and the collection defines at least ten complementation groups for survival of gamma irradiation. Four complementation groups define the genesrad3, rad9, rad11 andrad12, which are required both for survival of gamma irradiation and for meiosis. Mutants in each of these four groups fail to complete meiosis and produce mushrooms with greatly reduced numbers of viable spores. Propidium iodide staining of meiotic nuclei showed a characteristic terminal appearance for each mutant: few cells of any of the meiotic mutants progress beyond prophase I, and both condensation and fragmentation or dispersal of meiotic chromatin are frequently observed. Scanning electron micrographs showed that the meiotic mutants make varying numbers (0–6) of basidiospore initials and that few of these initials develop into mature spores. When initials are present they are always symmetrically arrayed on the basidium, regardless of initial number. In quantitative measurements of gamma ray sensitivity, double mutants of every tested combination ofrad3, rad9, rad11 andrad12 consistently showed the same gamma ray sensitivity as the more sensitive single mutant parent of the cross. Therefore, these four genes are in the same pathway for the repair of gamma radiation damage, and this pathway also represents one or more functions essential for meiosis.     

A physical assay for meiotic recombination in Coprinus cinereus

We have used the polymerase chain reaction (PCR) method to monitor meiotic recombination in the basidiomycete Coprinus cinereus. We used DNA-mediated transformation to recover strains with modifications of the trp1 locus. The modifications were designed to introduce unique PCR priming sites separated by a homologous 2.4 kb region in which crossing over could occur. We showed that exchange occurred in this region at the frequency expected for a typical region of this genome (2.4 kb should correspond to a genetic length of 0.08 cM). We also detected products resulting from crossing over in DNAs extracted from cells in meiotic prophase. The assay should be useful for monitoring exchange in mutants that cannot complete meiosis. Received: 5 September 1996 / Accepted: 1 December 1996     

Foraging behaviour of planktivorous fish in artificial vegetation: the effects on swimming and feeding

In the littoral zones of lakes, aquatic macrophytes produce considerable structural variation that can provide protection to prey communities by hindering predator foraging activity. The swimming and feeding behaviour of a planktivore, Pseudorasbora parva(Cyprinidae) on its prey (Daphnia pulex) was studied in a series of laboratory experiments with varying densities (0, 350, 700, 1400, 2100 and 2800 stems m^–2) of simulated submerged vegetation. Prey availability was varied from 0.5, 1.0, 2.0, 5.0, 10.0 and 25.0 prey l^–1. As the stem density increased, the predator's swimming speed and the number of prey captured decreased relative to feeding in open water. A good relation existed between the number of successful prey captures and swimming speed with the average stem distance to fish body length ratio (D). An abrupt reduction in feeding and swimming was recorded when D was reduced to values less than one.     

Foraging behaviour and feeding habits in five species of Trinervitermes in West Africa

Foraging habits of five species of Trinervitermes occurring in W. Africa are described. The five species can be divided into two groups, comprising those which store grass fragments in the mounds and those which do not. Size distributions of stored grass fragments differ specifically. Experiments indicated that selective foraging of grass species may occur. Survival on various foods suggested adaptation to differing conditions in each species. The occurrence of all five species in one area seems to depend on a suitable mosaic of conditions.

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Resume Ce travail est l'un d'une série d'études comparatives de biologie et d'écologie de cinq espèces de Trinervitermes en Afrique Occidentale. On y décrit les habitudes d'approvisionnement et les différences spécifiques. Les cinq espèces forment deux groupes, contenant l'un, T. ebenerianus, T. carbonarius et T. suspensus, lesquels entassent dans leur nids des fragments d'herbe; l'autre, T. oeconomus et T. auriterrae, lesquels n'en entassent pas. Les fragments d'herbe entassés sont de taille différente selon les trois espèces. Les expériences sur les deux espèces T. ebenerianus et T. carbonarius suggèrent que des approvisionnements sélectionnés d'espèces d'herbe peuvent se produire quand c'est possible. L'adaptation aux différentes conditions pour chaque espèce est suggerée par la survie des ouvriers qui se nourrissent différemment. On pense que T. auriterrae se rapproche le plus d'un ancêtre qui ressemble à Nasutitermes. La coexistence des cinq espèces dans un même habitat étendu, paraîtrait dépendre de la présence d'une mosaïque de conditions approprées sur une plus petite échelle

     

Expression of A mating type genes of Coprinus cinereus in a heterologous basidiomycete host

The A mating factor of Coprinus cinereus determines compatibility in mating by regulating part of a developmental sequence that leads to dikaryon formation. The A genes that trigger development encode two different classes of homeodomain proteins, and for a successful mating, a protein of one class, HD 1, must interact with a protein of the other class, HD 2. In this report we show that C. cinereus A genes that encode HD 2 proteins, a2-1 and b2-1, can elicit A-regulated development in the heterologous host C. bilanatus. Transformation rates were very low, suggesting that the genes were poorly transcribed. The fact that the HD 2 genes are functionally expressed implies successful heteromultimeric association of putative DNA-binding proteins coded by the two Coprinus species. This interaction was sufficient to satisfy the need for different A factors in the formation of a fertile C. bilanatus dikaryon, but fertile dikaryons were more readily produced in matings with the a2-1 gene transformants. The C. cinereus A genes, b1-1 and d1-1, which encode HD1 proteins, were either not expressed or their proteins were non-functional in C. bilanatus. These experiments raise some interesting questions regarding HD1–HD2 protein interactions.     

Foraging behaviour and diet of the Alpine ChoughPyrrhocorax graculus in the Italian Alps in summer

Summary The foraging behaviour of the Alpine Chough was studied around Cervinia (Aosta, Italy) in June and July 1989 and 1990. The birds foraging in loose flocks (of mean size 32.4) which flew to new foraging patches at very frequent intervals (median stay time 74.5 s in 1989 and 75.0 s in 1990). The Choughs' peck rates declined significantly through the summer, from around 17 items per min in mid-June to around 9 per min in late July. Examination of faeces and regurgitated pellets showed that the most common food items were Orthoptera (grasshoppers) which occurred in 83 % of samples, Coleoptera Curculionidae (55 %) and Elateridae (27 %), invertebrate eggs (26 %), Lepidopteran larvae (24 %), Hymenoptera Formicidae (18 %) and vegetable matter (18 %). Grasshoppers remained very small until mid-July and varied greatly in size and density between different parts of the study area. The Choughs' very short stay time in any one patch of meadow is consistent with their high intake rates and apparently low costs of movement between feeding sites, but they may also be sampling in a highly variable environment.

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Zusammenfassung Die Nahrungssuche von AlpendohlenPyrrhocorax graculus wurde im Juni und Juli 1989 und 1990 in der Umgebung von Cervinia (Aosta, Italien) untersucht. Die Vögel bewegten sich in losen Gruppen (mittlere Gruppengröße 32,3) und wechselten in regelmäßigen Intervallen zu neuen Futterplätzen (Median der Aufenthaltsdauer 74,5 s 1989 und 75,0 s 1990). Die Pickraten der Alpendohlen nahmen im Lauf des Sommers signifikant von ca. 17 Objekten (Mitte Juni) auf 9 pro min (Ende Juli) ab. Untersuchungen von Kot, Gewöllen und einem Magen erbrachten als häufigste Nahrungsbestandteile Geradflügler (wahrscheinlich Heuschrecken) in 83 % der Proben, Käfer Curculionidae (55 %) und Elateridae (27 %), Eier von Wirbellosen (26 %), Schmetterlingslarven (24 %), Ameisen (18 %) und pflanzliches Material (18 %). Heuschrecken blieben bis Mitte Juli sehr klein und unterschieden sich in verschiedenen Teilen des Untersuchungsgebietes beträchtlich in Größe und Dichte. Die sehr kurze Aufenthaltsdauer der Alpendohlen an allen Futterplätzen stimmt mit ihren hohen Nahrungsaufnahmeraten und den offensichtlich niedrigen Kosten für Ortsveränderungen zwischen den Plätzen überein; es ist aber ebensogut möglich, daß die Beutedichte in den genutzten Gebieten sehr variabel ist.

     

The feeding behaviour of the rice leaf folder, Cnaphalocrocis medinalis

During feeding, the larva sits longitudinally on the leaf, bends the head sideways, and scrapes out the soft tissue between bundles longitudinally up and down, leaving only the bundle unit + bundle sheath, sclerenchyma, and the abaxial epidermis + cuticle between the bundles intact, when feeding on the upper side. Feeding on the underside also includes most of the bulliform cells, sparing again the bundle unit plus the remaining adaxial epidermis cells + cuticle between the bundles. Feeding is essentially restricted to green mesophyll tissue and may occur practically over the whole leaf surface. Of the eaten portion of a leaf, about two-thirds is consumed (by dry weight). Regular longitudinal feeding was observed in many other species of Gramineae, and in several Cyperaceae. In a few cases of thick or tough leaves feeding ocurred also in irregular non-linear fashion. Extensive irregular feeding was also observed in one specimen of a soy plant. Young larvae up to the early second instar are gregarious, but subsequently become solitary, with only one larva per leaf roll.

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Zusammenfassung Während die Raupen fressen, sitzen sie in Längsrichtung auf dem Blatt, neigen den Kopf seitlich und scharren das weiche Gewebe zwischen den Leitbündeln aus. Unberührt bleibt beim Fressen von der Oberseite her nur das Leitbündel mit der Bündelscheide, das Sklerenchym, die abaxiale Epidermis mit der Kutikula. Beim Fressen auf den Unterseite wird auch der grösste Teil der Bulliformzellen erfasst. Dabei wird das Gefässbündel mit der nun adaxialen Epidermiszellen und der Kutikula zwischen den Bündeln ausgeschlossen. Das Fressen ist hauptsächlich auf das grüne Mesophyllgewebe beschränkt und kann praktisch über die ganze Blattoberfläche stattfinden. Ungefähr zwei Drittel des Trockengewichtes eines befressenen Blattabschnittes wird verzehrt. Regelmässiges Fressen in Längsrichtung wurde auch an vielen andern Gramineen- und Cyperaceenarten beobachtet. An einigen dicken und harten Blättern, z.B. Bambus, wurde manchmal in einer ganz unregelmässigen Weise gefressen. Solch unregelmässiges Fressen wurde auch einmal auf einer Soyapflanze beobachtet. Junge Raupen, sind bis zum frühen zweiten Stadium gregär, werden aber später solitär mit einer einzigen Raupe in einer Blattrolle.

     

The effect of ozone fumigation and different Brassica rapa lines on the feeding behaviour of Pieris brassicae larvae

Elevated levels of tropospheric ozone and their effects on plants have been studied for a great number of years. Ozone is a gaseous pollutant and acts as a phytotoxin. Even though ozone is known to change the physiology of plants, little attention has been given to the indirect effects of ozone on plant-insect interactions. This paper addresses this question by investigating the interactive effects of ozone and plant genotype on insects. Lines of rapid-cycling Brassica rapa (L.) selected for their contrasting sensitivity to ozone and Pieris brassicae (L.) (Lepidoptera: Pieridae) were used as a model system. The effect of differences in ozone sensitivity and ozone fumigation on the plant's carbon and nitrogen pools, the feeding preference, and behaviour of P. brassicae larvae were investigated. The results show that the plant's susceptibility to ozone interacts in a complex way with ozone induced alterations in the suitability of the plant for the insect. Only the larval performance on the sensitive line was affected by ozone exposure. Biochemical changes in the resistant B. rapa line made the plant a better food source for the insects, since the digestibility of this plant was significantly higher than that of the sensitive line, and the larvae pupated more quickly and were heavier.     

Isolation and characterization of recessive sporeless mutants in the basidiomycete Coprinus cinereus

Summary Twenty-four sporeless mutants were isolated from an Amut Bmut strain (mutant in the incompatibility factors) of the basidiomycete Coprinus cinereus. All the sporeless mutations were recessive to the wild type. These mutants and a previously isolated recessive sporeless strain, N2-7 (Kanda and Ishikawa 1986) were crossed with a wildtype strain. An F1 random spore analysis indicated that sporulation deficiencies in these mutants were caused by single nuclear gene mutations. These mutations were all complementary to each other, thus twenty-five sporulation genes were identified. Five of them were linked to the A incompatibility factor. Cytological observations classified these mutants into the following four types according to the stage of the blockage: (1) meiosis stopped at meta-anaphase I; (2) meiosis was completed, but further basidial development did not occur; (3) basidial development stopped at the sterigma stage; (4) basidial development stopped at the prespore stage.     

Inhibition of copepod feeding by exudates and transparent exopolymer particles (TEP) derived from a Phaeocystis globosa dominated phytoplankton community

We investigated if (1) dissolved compounds excreted by Phaeocystis globosa and (2) transparent exopolymer particles (TEP) formed from carbohydrates excreted into the water affect the feeding of nauplii and females of the calanoid copepod Temora longicornis during a P. globosa bloom. Copepod grazing on the diatom Thalassiosira weissflogii in the presence of these possible grazing deterrents was measured during three successive weeks of a mesocosm study, simulating the development of a P. globosa bloom. Our results demonstrate no indication for the presence of feeding deterrents in the dissolved phase, but a strong inhibitory effect of transparent exopolymer particles (TEP) on the consumption of algae by both nauplii and adult copepods. The inhibitory effect of TEP was connected to the accumulation of DOM during the progress of the bloom. We suggest that a reduction in the grazing pressure of zooplankton may increase the survival of the liberated single cells during disruption of colonies and allow seeding populations to persist. Furthermore, P. globosa reduces the trophic efficiency of the food web not only by withdrawal of its colonies from grazing but also by a relaxation of the grazing pressure on co-occurring phytoplankton and by alteration of the food web structure via TEP production.