Effect of fipronil on side-specific antennal tactile learning in the honeybee

In the honeybee, the conditioning of the proboscis extension response using tactile antennal stimulations is well suited for studying the side-specificity of learning including the possible bilateral transfer of memory traces in the brain, and the role of inhibitory networks. A tactile stimulus was presented to one antenna in association with a sucrose reward to the proboscis. The other antenna was either not stimulated (A+/0 training), stimulated with a non-reinforced tactile stimulus B (A+/B− training) or stimulated with B reinforced with sucrose to the proboscis (A+/B+ training). Memory tests performed 3 and 24 h after training showed in all situations that a tactile stimulus learnt on one side was only retrieved ipsilaterally, indicating no bilateral transfer of information. In all these groups, we investigated the effect of the phenylpyrazole insecticide fipronil by applying a sublethal dose (0.5 ng/bee) on the thorax 15 min before training. This treatment decreased acquisition success and the subsequent memory performances were lowered but the distribution of responses to the tactile stimuli between sides was not affected. These results underline the role of the inhibitory networks targeted by fipronil on tactile learning and memory processes.     

Central gustatory projections and side-specificity of operant antennal muscle conditioning in the honeybee

Gustatory stimuli to the antennae, especially sucrose, are important for bees and are employed in learning paradigms as unconditioned stimulus. The present study identified primary antennal gustatory projections in the bee brain and determined the impact of stimulation of the antennal tip on antennal muscle activity and its plasticity. Central projections of antennal taste hairs contained axons of two morphologies projecting into the dorsal lobe, which is also the antennal motor centre. Putative mechanosensory axons arborised in a dorso-lateral area. Putative gustatory axons projected to a ventro-medial area. Bees scan gustatory and mechanical stimuli with their antennae using variable strategies but sensory input to the motor system has not been investigated in detail. Mechanical, gustatory, and electrical stimulation of the ipsilateral antennal tip were found to evoke short-latency responses in an antennal muscle, the fast flagellum flexor. Contralateral gustatory stimulation induced smaller responses with longer latency. The activity of the fast flagellum flexor was conditioned operantly by pairing high muscle activity with ipsilateral antennal sucrose stimulation. A proboscis reward was unnecessary for learning. With contralateral antennal sucrose stimulation, conditioning was unsuccessful. Thus, muscle activity induced by gustatory stimulation was important for learning success and conditioning was side-specific.     

Behavioral and electrophysiological responses of the blowfly,Phormia regina meigen,to acids

Summary Flies of a standardized degree of thirst were tested for proboscis extension in response to mono- and dicarboxylic acids applied to the tarsi. Presence or lack of extension depended on pH for each acid, but acids of greater chain length were effective in preventing extension at higher pH values than those with shorter chain length (Fig. 1). Concentrated solutions of monocarboxylic acids at low pH values evoked a strange, delayed, hesitant form of proboscis extension which seemed to signify rejection rather than acceptance. It was not abolished by satiation with either water or sucrose (Fig. 2).Electrophysiological tests of tarsal hairs with NaCl and sucrose showed that the corresponding hairs of each type on opposite sides of the same individual leg had almost identical neural responses to a given stimulus (Table). This meant that hairs on one side of a leg could be used as controls for hairs on the other side.Comparisons were made of the neural responses to different pH values of each acid and of the responses to different acids at the same pH. For each acid, as the pH decreased the response increased both in number of neurons firing and in their firing frequency (Fig. 6). There were differences between the responses to different acids at the same pH correlated with the nature of the behavioral response at the pH value tested. In general, responses were greater to mono- than to dicarboxylic acids (Figs. 7–10).Lack of proboscis extension was correlated with the firing of a small spike of regular frequency, especially prominent in responses of D4 hairs, and with firing of the salt receptor. The strange, hesitant extension was correlated with the indiscriminate firing of a large number of neurons at irregular frequencies. It is concluded that flies have available information enabling them to distinguish acids from salts, sugars, and water. The basis for this distinction is at least in part anatomical. Flies also can distinguish between different specific acids at the same pH, depending on the molecular structure of the acids.This work was supported by National Science Foundation grant GB 1472 to Dr. V. G. Dethier and by a National Science Foundation Graduate Fellowship to the author.     

Octopamine mediates rapid stimulation of protein kinase A in the antennal lobe of honeybees

In the honeybee octopamine mediates mechanisms of arousal that interfere with the appetitive proboscis extension response to food-indicating chemosensory stimuli. This study demonstrates that injections of octopamine or cyclic adenosine monophosphate (cAMP) into the primary chemosensory neuropil of the honeybee, the antennal lobe, evokes a rapid and transient activation of cAMP-dependent protein kinase (PKA). Other monoamines detectable in the antennal lobe, dopamine and serotonin, do not affect the level of PKA activity. Stimulation of the bees' antenna with the appetitive stimulus water or sucrose solution in vivo also causes a short-term activation of PKA in the antennal lobe. The increased PKA activity can be detected immediately (0.5 s) after stimulation but reverts to the basal level within 3 s. This effect can be abolished by monoamine depletion with reserpine. Since octopamine is the only monoamine that stimulates PKA, it appears to mediate the PKA activation after sucrose stimulus and may contribute to the processing of this chemosensory input. © 1995 John Wiley & Sons, Inc.     

Directionality of antennal sweeps elicited by water jet stimulation of the tailfan in the crayfish Procambarus clarkii

Summary Directionality and intensity dependence of antennal sweeps elicited by water jet stimulation of the tailfan in tethered, reversibly blinded adult and juvenile crayfish (Procambarus clarkii) were analyzed.Resting crayfish keep their antennae at about 50° symmetrically to the longitudinal body axis (Figs. 2 bottom, and 3).In adults, tailfan stimulation elicits synchronous backward sweeps of both antennae, which increase for more caudal stimulus directions (Figs. 2–4 and 5A). Directions differing by 30°–60° are significantly distinguished (Fig. 4). The mean sweep of the ipsilateral antenna significantly overrides that of the contralateral antenna for rostrolateral stimulation at 40–200 mm/s stimulus velocity and lateral to caudolateral stimulation at 40 mm/s and thus lateralization of the stimulus is revealed (Figs. 2 top, 4 and 5A). Mean antennal sweeps at a given stimulus direction and distance increase with increasing stimulus velocity (40–250 mm/s, Fig. 5A).In juveniles, the directional dependence of antennal sweeps is reduced compared to that of adults, while a similar intensity dependence is found (Fig. 5B).The pronounced directionality of the antennal response in adult crayfish vanishes and response latencies increase after reversibly covering the tailfan with a small bag or the telson with waterproof paste (Figs. 6 and 7). Thus, tailfan and especially telson mechanoreceptors play an important role in the localization of water movements elicited by predators or prey behind the crayfish.     

An investigation of the role of dopamine in the antennal lobes of the honeybee,Apis mellifera

Summary The effects of dopamine applied to the antennal lobes of the honeybee are investigated using the proboscis conditioning paradigm (Kuwabara 1957). The percentage of bees responding to a conditioned olfactory stimulus after a single conditioning trial is reduced significantly by the application of dopamine (10^–6 M) to the antennal lobes of the bee brain. Reduction in response levels is significantly smaller in bees conditioned to the olfactory stimulus in multiple conditioning trials prior to treatment with dopamine. The effects of dopamine on the percentage of bees responding to a conditioned olfactory stimulus are blocked by the butyrophenone, haloperidol (10^–5 M). The possible role of dopaminergic interneurones in the antennal lobes of the bee brain is discussed.     

Information transmission in tarsal sugar receptors of the blowfly

Responses of the sugar receptors in the tarsal D hairs of theblowfly, Phormia regina, were examined electrophysiologically.The ability of these receptors to code information about sucroseconcentration was investigated using the concepts and methodsof information theory. The stimulus-response function was linearwith respect to the logarithm of sucrose concentration between0.01 and 1.0 M. When responses were pooled from several preparations,the amount of variability in response to each sucrose concentrationallowed only 3.8 discriminable levels of sucrose within thistwo log step range. However, when responses were obtained fromindividual receptors to repeated stimulations with a given sucroseconcentration, there was much less variability, allowing forgreater information transmission, providing for the discriminationof 5.3 levels of sugar between 0.1 M and 1.0 M. If a singleprothoracic leg was treated as a sensory channel, the combinedresponses of its D-hair sugar receptors provided for 4.0 discerniblelevels of sucrose within this range. Examination of the channelcapacities of these receptors for transmitting information aboutsucrose intensity suggested that the fly should be able to discriminatebetween 3.8 and 5.3 levels of sucrose intensity between 0.01M and 1.0 M, depending upon the patterns of neural convergencein the central nervous system. Examination of the stimulus-responsefunctions of these receptors over time demonstrated that informationtransmission increased markedly over the initial 500 ms of theneural response and tended to stabilize between 500 and 1000ms. Behaviorally, it has been shown that Phormia can discriminateabout four levels of sucrose within this two log step rangeof concentrations.     

The peripheral inhibition of the tarsal sugar receptor by sodium chloride in the proboscis extension response of the blowfly,Phormia regina M.

Summary The proboscis extension reponse of the blowfly during stimulation of the tarsal sugar receptors was inhibited by the presence of NaCl. Acceptance thresholds for sucrose in various concentrations of NaCl were measured. The median acceptance thresholds for sucrose in mixtures of 0.01, 0.25, 0.5 and 1.0 M NaCl were 1.8 × 10^–3, 6.0 × 10^–3, 1.2 × 10^–2, and 2.0 × 10^–2 M, respectively. Concentration-response curves for sucrose in the tarsal D-type sugar receptor shifted to the right under the existence of high concentration of NaCl. Number of impulses per D-type sugar receptor at the median acceptance thresholds described above were 7.5, 8.4, 6.8 and 10.4 for the first 0.1 s of stimulation, respectively. The average number was 8.2 impulses per 0.1 s. Comparisons were made between the behavioral acceptance thresholds (1) on one leg exposed to sucrose mixed with 0.01 M NaCl and (2) on two contralateral legs, one of which was exposed to sucrose in 0.01 M NaCl and the other to 0.5 M NaCl alone. The acceptance thresholds from two experiments agreed with each other. The median threshold value was 1.7 × 10^–2 M sucrose. Behavioral inhibition by NaCl in mixtures with sucrose can be explained by its peripheral inhibition of sugar receptors.This research was supported in part by ITO foundation and Scientific Research Fund from the Ministry of Education of Japan.     

Variation of acceptance thresholds in the blowfly by increasing sugar concentrations in the food

Summary Aduld blowflies,Phormia regina M., were raised on different concentrations of sucrose. The thresholds of the behavioral responses to tarsal stimulation were elevated in blowflies raised on high concentrations of sucrose. The relationship between the median acceptance thresholds and the raising concentration of sucrose was logarithmically linear. Two groups of experimental flies were prepared: (1) coated flies, in which only D-type chemosensory hairs could respond physiologically, and (2) treated flies, in which all chemosensory hairs except D-type hairs functioned physiologically. Proboscis extension responses were ascertained in both groups. Median acceptance thresholds for the coated and treated flies, respectively, were presumed to be logarithmically linear in relation to the raising concentration of sucrose. It was supposed that D-type sugar receptor impulses initiate mainly the proboscis extension responses under the 0.01 M sucrose threshold and that B-type sugar receptor impulses initiate the responses above the 0.01 M sucrose threshold. Median acceptance thresholds for whole labellar stimulation were elevated to 0.026 M sucrose in blowflies raised on 1.0 M sucrose. Median acceptance thresholds were again lowered in blowflies raised on sucrose of more than 1.0 M.This research was supported in part by ITO foundation and Scientific Research Fund from the Ministry of Education of Japan.     

Proboscis extension in the blowfly: directional responses to stimulation of identified chemosensitive hairs

Summary We studied the direction of proboscis extension elicited by stimulating each of an identified array of gustatory sensilla, the largest hairs, on the labellum of the flyPhormia regina. Individual hairs, or pairs of hairs, were stimulated with sucrose or water and the angle of the ensuing extension of the proboscis was recorded. The direction of the response was graded and depended on the identities of the hairs stimulated. Hairs situated on the anterior region of the labellum elicited anterior extensions, mid-level hairs elicited lateral extensions and posterior hairs resulted in posterior extensions. Previous studies of the labellar hairs have been concerned with their encoding of the chemical nature of the stimulus. Our findings show that each hair also relays information about the location of the stimulus. The positional information provided by these sensilla may help the fly to orient itself with respect to a food source.Abbreviation CES central excitatory state     

Sugar cell responses to lactose and sucrose in labellar and tarsal taste hairs of Musca domestica

Receptor cell responses in the largest labellar (LL) and tarsal (D) taste hairs of the housefly Musca domestica were investigated electrophysiologically using the tip-recording technique. In LL hairs, test series with lactose in concentrations of 12.5–400 mmol · l⁻¹ yielded a threshold concentration around 12 mmol · l⁻¹ and a calculated concentration eliciting half-maximal response of around 40 mmol · l⁻¹, the maximal response varying between 18 and 30 impulses/300 ms. D hairs are more sensitive towards lactose, indicated by a slightly lower threshold and a by 60% higher response to 400 mmol · l⁻¹ lactose. The high variation in the relative stimulating effectiveness of lactose and sucrose and experiments with sugar mixtures imply that these sugars bind to different receptor sites without noticeable cross affinity. A comparison of the concentration response characteristics for sucrose and lactose in LL and D hairs suggests that sucrose can combine with more than one site type, expressed in different proportions in both hair types. Results obtained with p-nitrophenyl-β-galactoside as stimulus indicate that a β-galactoside link is not sufficient for a substance to interact specifically with the lactose binding site. The exceptional lactose sensitivity of the sugar cell in M. domestica is discussed in the context of food acquirement and digestion. Accepted: 14 November 1997     

Behavioural evidence for detection of the repellent polygodial by aphid antennal tip sensilla

Abstract. Close-up video was used to record responses of the aphid Myzus persicae (Sulzer) (Homoptera: Aphididae) to the plant-derived repellent polygodial. When 0.1% (±)-polygodial was painted onto one half of a Chinese cabbage leaf disc, and the other half treated with the ethanol solvent, apterous adult aphids avoided walking onto the polygodial-treated area during 15 min access periods. Similarly, when the rim of a small plastic Petri dish was treated with polygodial, aphids took significantly longer to walk off the base of the dish and onto the rim, compared with insects in solvent-treated control dishes. Analysis of video-recordings indicated that aphids were repelled following contact of antennal tips with the polygodial-treated areas of leaf or plastic. In contrast, aphids with both antennal tips surgically removed showed no apparent response to polygodial treatment of leaf or plastic surfaces. Aphids were placed between polygodial- and solvent-treated angled glass cover slips to enable unilateral presentation of polygodial on either the left or right side of the insects. Most aphids with antennae intact moved away from the polygodial-treated side, but removal of both antennal tips again negated the response. When the tip was removed from only one antenna, and the other remained intact, unilateral presentation caused a repellent response only if polygodial occurred on the same side as the intact antenna. Presentation of polygodial on both sides of aphids (bilaterally) caused no response if both antennal tips were intact or removed, but aphids with only one antennal tip removed were repelled from the side where the antenna remained intact. The results indicate that aphids detect polygodial upon contact with sensilla located on the antennal tips, and that the repellent response occurs as a negative chemotropotaxis following unilateral stimulation of these sensilla. Contact between the antennal tips and glass substrates was demonstrated using a fluorescent pigment.     

Frequency tuning and response latencies at three levels in the brainstem of the echolocating bat,Eptesicus fuscus

To determine the level at which certain response characteristics originate, we compared monaural auditory responses of neurons in ventral cochlear nucleus, nuclei of lateral lemniscus and inferior colliculus. Characteristics examined were sharpness of frequency tuning, latency variability for individual neurons and range of latencies across neurons.Exceptionally broad tuning curves were found in the nuclei of the lateral lemniscus, while exceptionally narrow tuning curves were found in the inferior colliculus. Neither specialized tuning characteristic was found in the ventral cochlear nuclei.All neurons in the columnar division of the ventral nucleus of the lateral lemniscus maintained low variability of latency over a broad range of stimulus conditions. Some neurons in the cochlear nucleus (12%) and some in the inferior colliculus (15%) had low variability in latency but only at best frequency.Range of latencies across neurons was small in the ventral cochlear nucleus (1.3–5.7 ms), intermediate in the nuclei of the lateral lemniscus (1.7–19.8 ms) and greatest in the inferior colliculus (2.9–42.0 ms).We conclude that, in the nuclei of the lateral lemniscus and in the inferior colliculus, unique tuning and timing properties are built up from ascending inputs.Abbreviations AVCN anteroventral cochlear nucleus - BF best frequency - CV coefficient of variation - DCN dorsal cochlear nucleus - FM frequency modulation - IC inferior colliculus - NLL nuclei of lateral lemniscus - PSTH post stimulus time histogram - PVCN posteroventral cochlear nucleus - SD standard deviation - SPL sound pressure level - VCN ventral cochlear nuclei - VNLLc ventral nucleus of the lateral lemniscus, columnar division     

The functions of antennal mechanoreceptors and antennal joints in tactile discrimination of the honeybee (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.)

Honeybees learn and discriminate excellently between different surface structures and different forms of objects, which they scan with their antennae. The sensory plate on the antennal tip plays a key role in the perception of mechanosensory and gustatory information. It is densely covered with small tactile hairs and carries a few large taste hairs. Both types of sensilla contain a mechanoreceptor, which is involved in the antennal scanning of an object. Our experiments test the roles of the mechanoreceptors on the antennal tip in tactile antennal learning and discrimination. Joints between head capsule and scapus and between scapus and pedicellus enable the bee to perform three-dimensional movements when they scan an object. The role of these joints in tactile antennal learning and discrimination is studied in separate experiments. The mechanoreceptors on the antennal tip were decisive for surface discrimination, but not for tactile acquisition or discrimination of shapes. When the scapus–pedicellus joint or the headcapsule–scapus joint was fixed on both antennae, tactile learning was still apparent but surface discrimination was abolished. Fixing both scapi to the head capsule reduced tactile acquisition.     

Properties of olfactory conditioning in the housefly, Musca domestica

The housefly, Musca domestica, was conditioned to odours using the proboscis extension response to labellar stimulation with sucrose solution as an unconditioned response and the properties of conditioning were investigated. Among trials including forward pairing of the conditioned stimulus (CS) with the unconditioned stimulus (US), backward pairing and isolated presentations of CS and US, only forward pairing is effective on the acquisition of conditioning. Backward pairing combined with forward pairing does not influence the effectiveness of the forward pairing. CS given overlapping with a US presentation permits only weak conditioning. The acquisition of conditioning decreases with increase of the CS-US interval. In the differential conditioning situation to two odours, discriminative responses are observed. In the flies conditioned with one antenna, the conditioned response is elicited not only by stimulation of the antenna used for conditioning but also by stimulation of the antenna not used for conditioning, although the response using the former is higher than with the latter. The ability to be conditioned is reduced immediately after fastening on a clay bed and increases with time. Ability can also be improved by transection of the ventral nerve cord.     

Bumblebees require visual pollen stimuli to initiate and multimodal stimuli to complete a full behavioral sequence in close‐range flower orientation

Flower visits are complex encounters, in which animals are attracted by floral signals, guided toward the site of the first physical contact with a flower, land, and finally take up floral rewards. At close range, signals of stamens and pollen play an important role to facilitate flower handling in bees, yet the pollen stimuli eliciting behavioral responses are poorly known. In this study, we test the response of flower‐naive bumblebees (Bombus terrestris) toward single and multimodal pollen stimuli as compared to natural dandelion pollen. As artificial pollen stimuli, we used the yellow flavonoid pigment quercetin, the scent compound eugenol, the amino acid proline, the monosaccharide glucose, and the texture of pollen‐grain‐sized glass pellets as a tactile stimulus. Three test stimuli, dandelion pollen, one out of various uni‐ and multimodal stimulus combinations, and a solvent control were presented simultaneously to individual bumblebees, whose response was recorded. The results indicate that bumblebees respond in an irreversible sequence of behavioral reactions. Bumblebees approached the visual stimulus quercetin as often as natural dandelion pollen. An additional olfactory stimulus resulted in slightly more frequent landings. The multimodal stimulus combinations including visual, olfactory, gustatory, and tactile stimuli elicited approaches, antennal contacts, and landings as often as natural pollen. Subsequent reactions like proboscis extension, mandible biting, and buzzing were more often but not regularly observed at dandelion pollen. Our study shows that visual signals of pollen are sufficient to trigger initial responses of bumblebees, whereas multimodal pollen stimuli elicit full behavioral response as compared to natural pollen. Our results suggest a major role of pollen cues for the attraction of bees toward flowers and also explain, why many floral guides mimic the visual signals of pollen and anthers, that is, the yellow and UV‐absorbing color, to direct bumblebees toward the site where they access the floral rewards.     

Morphological synergism in root hair length,density, initiation and geometry for phosphorus acquisition in Arabidopsis thaliana: A modeling approach

Low phosphorus availability regulates root hair growth in Arabidopsis by (1) increasing root hair length, (2) increasing root hair density, (3) decreasing the distance between the root tip and the point at which root hairs begin to emerge, and (4) increasing the number of epidermal cell files that bear hairs (trichoblasts). The coordinated regulation of these traits by phosphorus availability prompted us to speculate that they are synergistic, that is, that they have greater adaptive value in combination than they do in isolation. In this study, we explored this concept using a geometric model to evaluate the effect of varying root hair length (short, medium, and long), density (0, 24, 48, 72, 96, and 120 root hairs per mm of root length), tip to first root hair distance (0.5, 1, 2, and 4 mm), and number of trichoblast files (8 vs. 12) on phosphorus acquisition efficiency (PAE) in Arabidopsis. SimRoot, a dynamic three-dimensional geometric model of root growth and architecture, was used to simulate the growth of Arabidopsis roots with contrasting root hair parameters at three values of phosphorus diffusion coefficient (D _e=1×10^–7, 1×10^–8, and 1×10^–9 cm² s^–1) over time (20, 40, and 60 h). Depzone, a program that dynamically models nutrient diffusion to roots, was employed to estimate PAE and competition among root hairs. As D _e decreased from 1×10^–7 to 1×10^–9 cm² s^–1, roots with longer root hairs and higher root hair densities had greater PAE than those with shorter and less dense root hairs. At D _e=1×10^–9 cm² s^–1, the PAE of root hairs at any given density was in the order of long hairs > medium length hairs > short hairs, and the maximum PAE occurred at density = 96 hairs mm^–1 for both long and medium length hairs. This was due to greater competition among root hairs when they were short and dense. Competition over time decreased differences in PAE due to density, but the effect of length was maintained, as there was less competition among long hairs than short hairs. At high D _e(1×10^–7 cm² s^–1), competition among root hairs was greatest among long hairs and lowest among short hairs, and competition increased with increasing root hair densities. This led to a decrease in PAE as root hair length and density increased. PAE was also affected by the tip to first root hair distance. At low D _e values, decreasing tip to first root hair distance increased PAE of long hairs more than that of short hairs, whereas at high D _e values, decreasing tip to first root hair distance increased PAE of root hairs at low density but decreased PAE of long hairs at very high density. Our models confirmed the benefits of increasing root hair density by increasing the number of trichoblast files rather than decreasing the trichoblast length. The combined effects of all four root hair traits on phosphorus acquisition was 371% greater than their additive effects, demonstrating substantial morphological synergy. In conclusion, our data support the hypothesis that the responses of root hairs to low phosphorus availability are synergistic, which may account for their coordinated regulation.     

Accumulation and turnover of 2-tridecanone in Tetranychus urticae and its consequences for resistance of wild and cultivated tomatoes

In this study we assessed the dynamic changes of 2-tridecanone in a herbivorous mite (Tetranychus urticae) on tomato (Lycopersicon esculentum, cv. Moneymaker), a plant with methyl ketones in the tetracellular tips of the glandular trichomes (Type VI). We showed that spider mites accumulate 2-tridecanone when foraging on cultivated tomato. Thus, the rate of mite–trichome contact multiplied by the amount of toxin per trichome tip exceeded the relative rate of toxin turnover multiplied by the amount of toxin per mite. The relative rate of toxin turnover was estimated to be 1.1 per day on cucumber, a plant without this toxin. The amount per trichome tip varied from 0.33 ng for middle-leaf trichomes to 1.26 ng for main-stem trichomes. Hence, to achieve a static level of 2-tridecanone equal to 8–17 ng per mite – representing the level we found in mites on middle leaves – the rate of mite–trichome contact should be 26–57 per day. Because methyl ketone apparently accumulates in the spider mites on tomato, the rate of mite–trichome contact is probably higher than that. We expect the accumulation of ketones to occur especially on the stems of cultivated tomato, since this is the area most densely occupied with glandular hairs and because here the hairs have higher levels of the methyl ketones.Using dose–response relationships assessed earlier (Chatzivasileiadis and Sabelis, 1997, 1998), we estimated that the number of mite–trichome contacts causing 50% mortality per day is equal to 88 on a tomato stem, whereas it equals 70 for another strain of spider mites collected from cucumber. On wild tomato, L. hirsutum f. glabratum (PI 134417), just one to two contacts would suffice to cause 50% mortality per day. We suggest that methyl ketones from glandular hairs on tomato are an important mortality factor for spider mites on wild tomato and probably also on cultivated tomato.     

Hydrodynamic orientation of crayfish (Procambarus clarkii) to swimming fish prey

Reversibly blindfolded crayfish (Procambarus clarkii) react to small swimming fish (Astyanax fasciatus mexicanus) approaching or passing nearby with antennal and cheliped movements and body turns (Fig. 3). We studied the accuracy and dynamics of crayfish orientation responses to the previously analyzed hydrodynamic disturbances caused by the fish, mostly produced by tail flicks.Antennal and cheliped movements started slightly before the onset of turning responses (Fig. 4). Antennal sweeps were performed most rapidly. 50% of the appendage sweeps resulted in contacts with the fish (Fig. 5).Most turns were directed toward the stimulus (Fig. 6). Response amplitudes increased with increasing stimulus angle. Turns were accurate for small stimulus angles, but smaller than expected for larger ones. Sweeps of ipsilateral antennae and chelipeds were generally directed backwards, while those of contralateral appendages were smaller and directed forwards. The amplitudes of appendage sweeps first increased with increasing stimulus angle and then decreased again for more caudal stimulus directions. Lateral stimuli (60°–120°) from opposite sides were usually significantly distinguished. The amplitudes of the different elements of orientation behaviour were highly correlated with each other, indicating that they were directed by the same sensory input.     

Different ratios of sucrose/raffinose-induced membrane depolarizations in the mesophyll of species with symplasmic (Catharanthus roseus, Ocimum basilicum) or apoplasmic (Impatiens walleriana, Vicia faba) minor-vein configurations

In mesophyll cells of species with a symplasmic (Ocimum basilicum, Catharanthus roseus, Magnolia denudata) or an apoplasmic (Vicia faba, Impatiens walleriana, Bellis perennis) minor-vein configuration, membrane depolarizations in response to 20 or 200 mol·m^–3 raffinose and sucrose were measured. Ageing period and resting potential marginally affected the degree of depolarization. The symplasmic species showed similar depolarization responses to 20 and 200 mol·m^–3 sucrose or raffinose. In the apoplasmic species, depolarization increased statistically significantly from 20 to 200 mol·m^–3 sucrose, whereas the depolarization response to raffinose was equal at both concentrations. In the apoplasmic species, moreover, the depolarization response to raffinose was significantly weaker than to sucrose at all concentrations. A major difference between symplasmic and apoplasmic species seems to lie in the scantiness of raffinose carriers in the mesophyll plasma membrane of species with the apoplasmic mode of phloem loading.Abbreviations 20R(200R) 20(200) mol·m^–3 raffinose - 20S(200S) 20(200) mol·m^–3 sucrose