AGGREGATION IN APHIS FABAE SCOP. I. AGGREGATION ON PLANTS

A study of free infestations of Aphis fabae Scop. on the leaves of its host plants, spindle and sugar beet, showed that the clustered distribution of the aphids within the boundaries of each leaf was not a matter of chance but involved active aggregation. Experiments in small leaf cages showed that aggregation could take place independently of any differences between portions of a leaf, being brought about by truly gregarious reactions between the aphids. Experiments in which walking aphids were made to encounter other live or dummy aphids fixed to leaves, showed that the gregarious reactions were of at least two kinds. The aphids both probed more often, and remained inserted for longer, near other aphids than apart from them.
It appears that the unequal distribution of aphids among the leaves of a plant is due primarily to intrinsic differences between leaves, but is aided by gregariousness, while the aggregations observed on leaves are due primarily to gregariousness, and only secondarily to differences between portions of a leaf. It is suggested that the primary function of gregariousness is to concentrate the aphids on to the best feeding sites, both among the parts of a plant, and among whole plants; that is, it acts as an aid in host selection, even with aphids which do not aggregate so compactly as A. fabae. The functions of compact aggregation and other specialized forms of gregarious behaviour remain to be discovered.     

Effect of spatial heterogeneity on the role of Coccinella septempunctata as an intra-guild predator of the aphid pathogen Pandora neoaphidis

The foraging behavior of starved and non-starved adult and larval Coccinella septempunctata on groups of plants in the presence of Pandora neoaphidis-infected Acyrthosiphon pisum, uninfected aphids or a mixture of these two prey types was compared. In general results of these studies confirmed the results of previous work comparing foraging behavior on a smaller spatial scale in Petri dishes. However, behaviors were modified in response to spatial complexity, prey quality, and the host plant. Starved C. septempunctata adults and larvae fed for longer and consumed more aphids than non-starved coccinellids. Both larvae and adults fed on infected aphids and in some cases entirely consumed them. This was thought to be due to the ease of capture of infected (dead) aphids and the feeding stimuli provided by the presence of the host plant and, where there was a choice of prey, uninfected aphids in the environment. Both larvae and adults spent the majority of the time foraging in the upper regions of plants and visited more plants when they were not starved or when they were in the presence of less suitable, infected aphid prey.     

Age and Sex-Based Differences in the Use of Prey Sensory Cues in Wolf Spiders (Araneae: Lycosidae)

Differences in foraging patterns mediated by sensory cues were examined between adult and juvenile male and female wolf spiders (Schizocosa rovneri; Lycosidae). Patch residence time for thirty-one spiders were tested among juveniles and adults in artificial foraging patches. Patches varied in sensory information provided by live prey (crickets) as follows: visual stimuli alone; vibratory stimuli alone; visual and vibratory stimuli together; and control (no stimuli). Spiders moved between patches for one hour, but could not feed. Adult Schizocosa rovneri use primarily visual information to determine patch residence time, but juveniles use vibratory cues as well. Significant age and sex-based differences in the use of sensory cues suggest that observed divergent foraging strategies are partly due to the use of different perceptual cues in prey detection.     

Oviposition avoidance of parasitized aphid colonies by the syrphid predator Episyrphus balteatus mediated by different cues

Oviposition decisions made by members of a guild of natural enemies can have evolved to avoid intraguild predation, potentially avoiding the disruption of the extraguild prey control. We have studied the oviposition preference of the aphidophagous predator Episyrphus balteatus De Geer (Diptera: Syrphidae) within colonies of Myzus persicae Sulzer (Hemiptera: Aphididae) in the presence of two developmental stages of the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae). Results from a greenhouse choice experiment showed that E. balteatus females lay significantly fewer eggs in colonies with mummified aphids than in unparasitized colonies. Colonies of parasitized, but not yet mummified did not contain significantly fewer eggs than colonies with unparasitized aphids. In three no-choice experiments, we assessed stimuli coming from aphid honeydew, from the aphids themselves and also from extracts of the aphid bodies, and all of these stimuli mediate the discrimination of mummified aphids from healthy aphids. To a lesser extent these stimuli also contribute to the discrimination against aphids that are parasitized but not yet mummified. These results suggest that the effects of these two species could be complementary for the control of M. persicae, since the species that acts as an intraguild predator, E. balteatus, avoids ovipositing on aphid colonies parasitized by the intraguild prey, A. colemani.     

Aggregation in the lime aphid (Eucallipterus tiliae L.)

Summary Lime aphids feed on the contents of sieve tubes in the leaf veins. Aphids on the undersides of large leaves tend to select the smallest veins, while those on small leaves tend to select the larger veins. This tendency increases with the size of the aphid. Since only 4% of the total leaf area is covered by the larger veins, crowding is imposed on those aphids feeding from them. In spring, when the leaves are young and small, close spacing of the aphids results due to their tendency to select large veins. In summer, when the leaves are mature and large, wider spacing between aphids occurs due to their tendency to occupy more of the leaf surface.     

Adults with Dyslexia Demonstrate Large Effects of Crowding and Detrimental Effects of Distractors in a Visual Tilt Discrimination Task

Previous research has shown that adults with dyslexia (AwD) are disproportionately impacted by close spacing of stimuli and increased numbers of distractors in a visual search task compared to controls [1]. Using an orientation discrimination task, the present study extended these findings to show that even in conditions where target search was not required: (i) AwD had detrimental effects of both crowding and increased numbers of distractors; (ii) AwD had more pronounced difficulty with distractor exclusion in the left visual field and (iii) measures of crowding and distractor exclusion correlated significantly with literacy measures. Furthermore, such difficulties were not accounted for by the presence of covarying symptoms of ADHD in the participant groups. These findings provide further evidence to suggest that the ability to exclude distracting stimuli likely contributes to the reported visual attention difficulties in AwD and to the aetiology of literacy difficulties. The pattern of results is consistent with weaker and asymmetric attention in AwD.     

Visual and olfactory location of biotopes, prey patches, and individual prey by the ladybeetleChilocorus nigritus

Foraging behaviour of the predatorChilocorus nigritus (Fabricius) (Coleoptera: Coccinellidae) at the three spatial levels of biotope, prey patch and individual prey, was studied in the laboratory, and related to behaviour in the field. Vertically oriented parallel lines were more attractive than the same shapes in a horizontal position. A simulated horizon with a tree line was preferred to a simulated flat horizon. They were attracted to a tree image for the first 2 h of exposure, but were less attracted after longer exposure, possibly due to habituation. Leaf shape was recognised, and simple ovate leaves were preferred to compound bipinnate leaves and to squares. These responses were associated with biotope selection for feeding and aggregation at aestivation sites. The location of prey patches by adults involved prey odour but the location of such sites by larvae did not. Adults detected individual prey visually and olfactorily over short distances but physical contact with prey was required for detection by larvae. Location of individual prey and prey patches by adults and larvae was facilitated by alternation between intensive and extensive search. The differences in the ability of larvae and adults to locate prey, stem from the adults being the active locators of biotope and patch, whereas the comparatively immobile larvae depend on their parents’ ability for long-range location of prey. Two hypotheses concerning coccinellid foraging behaviour are proposed. Firstly, the duration of response to a visual cue is related to the distance over which such a cue may be perceived. It follows that habituation to closer range cues occurs more rapidly than to longer range cues. Secondly, visual cues used by adults at the different spatial levels of prey location, and the location of mates and aggregation sites, have the same or similar shape. These results also provide guidelines for orchard management to maximise the biocontrol value of this species.     

Effect of nymphal diet on adult predation behavior in Orius majusculus (Heteroptera: Anthocoridae)

The predatory bug Orius majusculus (Reuter) was reared on 2 different diets during the nymphal stages. The 1st group was exclusively offered eggs of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), a standard diet for O. majusculus production. The 2nd group was exclusively offered 4th instars of the pea aphid, Acyrtosiphon pisum (Harris). Subsequently, adult predatory behavior in experimental arenas containing A. pisium was recorded using 2 video cameras. One camera permitted observation of the predator's contact with the prey, where the 2nd camera viewed the arena from above to record the path taken by O. majusculus adults before and after contact with prey. When O. majusculus were reared on aphids, adult bugs successfully located and consumed 55% of experimental prey and continued prey search behavior after each aphid meal. O. majusculus adults that had no experience of aphid predation as nymphs, did not prey on aphids in the experimental arena. The mean walking speed of this group of predators increased from 5.9 +/- 1.2 mm/s to 9.8 +/- 0.7 mm/s after contact or detection of prey, indicating that predators rapidly moved away from unfamiliar prey. Moreover, for egg-reared O. majusculus, all contacts between aphid and predator were lateral, along the side of the prey and were effectively repelled by an aphid kicking response. In contrast, 83% of attacks by aphid-reared O. majusculus were directed at the head or posterior abdomen for which the prey could not defend themselves adequately. When egg-reared O. majusculus were exposed to novel aphid prey for 1-8 d, the frequency of aphid attack increased significantly. We conclude that the standard diet used for rearing O. majusculus may adversely affect the efficiency of this predator as an agent of biological control.     

棉田十一星瓢虫种群动态及空间分布

通过田间系统调查,对棉田十一星瓢虫CoccinellaundecimpanctataL.种群动态及空间分布方面进行研究,探明捕食性天敌十一星瓢虫各虫态在南疆棉区的种群消长趋势,分析表明该虫4种虫态在棉田中均为聚集分布,成虫、幼虫和蛹的聚集原因主要是由棉蚜密度等引起,而其卵的聚集主要是由于其习性及环境因素引起。     

How aphids find their host plants,and how they don't

There is a considerable interest in trying to understand how aphids find their host plants because they are a major cause of economic losses in agricultural and horticultural production systems. Indeed, the specific behavioural sequences during host finding by aphids are one of the main reasons for their prominent role as vectors of plant pathogenic viruses. This paper reviews the visual and olfactory stimuli involved in host‐finding behaviour of aphids, both basic and applied aspects are covered. Although controlling aphids by manipulation of visual and olfactory stimuli involved in host finding and host selection can be highly successful, as shown by research, most of these measures can still be further optimised and adoption in practice is currently limited. Research therefore needs to address some critical open questions, including (a) the effects of visual contrasts on aphid behaviour; (b) the specific responses of aphids to ultraviolet (UV) light during different stages in host finding; (c) the quantification of behavioural sequences in the field and (d) the response of aphid behaviour to plant diversity at varying spatial scales; further, (e) a much more comprehensive coverage of aphid taxa and aphid ecological groups is needed in host‐finding related research to uncover ecological principles underlying this critical behaviour.     

Subitization and attentional engagement by transient stimuli

A series of experiments investigated the visual selection of moving and static items during enumeration. Small numbers of visual targets can be enumerated with little increase in reaction time and error with set size, a process referred to as 'subitization'. The number of items that can be subitized' is typically between one and four and known as the subitization range. This study looked for evidence of subitizing of subsets of items presented on a computer display. Fast and accurate enumeration was found for random configurations of moving targets even when presented among static distracters. This was not the case for static targets presented among moving or transient distracters. RTs to these targets were longer and showed a steady increase in RT with target number, even in the subitization range. However, when static targets and moving distracters were presented foveally, fast enumeration/subitization of the static targets was again possible. This was not due to reduced inter-item spacing, since linear effects of the number of targets still emerged when stimuli were presented peripherally but the size-spacing ratio was matched to the foveal presentations. There was indication that instead performance reflected perceived differences in movement speed for stimuli presented in parafoveal and more peripheral retinal regions. In support of this, subitization of static items improved as the movement speed of the distracters increased. The data suggest that the processes supporting subitization are highly sensitive to dynamic stimuli and depend on the ease of segmentation between static and moving arrays.     

Human blood platelets, PMN leukocytes and their interactions in vitro. Responses to selective and non-selective stimuli.

Using simultaneous recording of aggregation and chemiluminescence, responses of human polymorphonuclear leukocytes, blood platelets and their mixture were investigated after stimulation by specific as well as non-specific stimuli for each cell. In our experimental settings, aggregation of platelets and PMN leukocytes was increased in the following order of stimuli: PMA相似文献   

Evidence for male- and juvenile-specific contact pheromones of the common bed bug Cimex lectularius

Males and females of the common bed bug, Cimex lectularius L. (Heteroptera: Cimicidae), have been shown to produce and respond to an aggregation pheromone. We tested whether juvenile C. lectularius also produce and respond to aggregation pheromone, and whether the pheromone is perceived by contact chemoreception. In dual‐choice laboratory experiments, juveniles, but not males or females, preferred juvenile‐exposed paper discs to control discs. Unlike juveniles, males and females preferred male‐exposed paper discs to control discs. Neither juveniles, males, nor females preferred female‐exposed discs to control discs. When test stimuli were inaccessible, C. lectularius failed to show any preference. Male‐ and juvenile‐specific contact pheromones may have contrasting functions of marking shelters as safe refugia for development and growth (juveniles) or mate encounter (adults), but result in the same phenomenon, the aggregation of conspecifics.     

Constant amplitude of postsynaptic responses for single presynaptic action potentials but not bursting input during growth of an identified neuromuscular junction in the lobster, Homarus americanus

As lobsters grow from early juveniles to adults their body size increases more than 20-fold, raising the question of how function is maintained during these ongoing changes in size. To address this question we studied the pyloric 1 (p1) muscle of the stomach of the lobster, Homarus americanus. The p1 muscle receives multiterminal innervation from one motor neuron, the lateral pyloric neuron of the stomatogastric ganglion. Staining with antibodies raised against synaptotagmin showed that as the muscle fibers increased in length, the spacing between the terminal innervation increased proportionally, so the number of synaptic contact regions/muscle fiber did not change. Muscle fibers were electrically coupled in both juveniles and adults. The amplitude of single intracellularly recorded excitatory junctional potentials evoked by motor nerve stimulation was the same in both juveniles and adults. Nonetheless, the peak depolarizations reached in response to ongoing pyloric rhythm activity or in response to high-frequency trains of stimuli similar to those produced during the pyloric rhythm were approximately twofold larger in juveniles than in adults. This suggests that homeostatic regulation of synaptic connections may operate at the level of the amplitude of the single synaptic potential rather than on the summed depolarization evoked during strong rhythmic activity.     

Effect of mulching with cereal straw and row spacing on spread of bean yellow mosaic potyvirus into narrow-leafed lupins (Lupinus angustifolius)

Two field experiments examined the effect of straw spread on the soil surface on the incidence of bean yellow mosaic potyvirus (BYMV) in plots of narrow-leafed lupin (Lupinus angustifolius) sown at narrow (17.5 cm) vs wide (35 cm) row spacing and low (25–30 kg/ha) vs medium (50–60 kg/ha) seeding rates. Virus ingress was by vector aphids flying from adjacent pastures dominated by subterranean clover. In Expt 1, in which BYMV infection was extensive, straw greatly decreased the rate and amount of virus spread regardless of row spacing or plant density, decreasing infection more than 70% by the final assessment date. This effect of straw was attributed to decreased landing rates of incoming vector alates. In the plots without added straw, narrow row spacing decreased BYMV % infection by 38% by the last assessment date. Sowing at the medium seeding rate also decreased infection. The effect of wide row spacing seemed due to delayed canopy closure between rows which is likely to have increased the landing of aphids while the effect of medium seeding rate was attributed partly to the dilution effect of greater plant numbers and partly to the effects of partial canopy development in decreasing landing rates. In Expt 2, in which the incidence of BYMV infection was low, added straw again decreased BYMV spread, but by only 25–27% at final assessment; there were no effects of row spacing or seeding rate. In both experiments, an additional “reference” treatment was included which had a high (90–100 kg/ha) seeding rate, narrow rows and no straw. The dense canopy it developed also decreased BYMV incidence but less than in the plots with added straw in Expt 1. In Expt 1, adding straw and the resulting decrease in plants killed by BYMV, were associated with an overall increase in lupin grain yield of 20%. The greater plant densities resulting from the medium seeding rate also increased grain yield but row spacing did not affect it significantly. These results indicate that retaining stubble on the soil surface at seeding will assist in management of BYMV infection in lupin crops but that wide row spacing in the absence of retained stubble is undesirable.     

Factors affecting aphid infestation of chrysanthemums

Large differences exist between chrysanthemum cultivars in their susceptibility to attack by Myzus persicae (Sulz.). This is due to a repellent factor which increases in the leaves as they age, but which varies from one cultivar to another. Aphid population growth is retarded, or even prevented, on resistant cultivars. If susceptible and resistant plants are in contact, the rate of population increase will be the same on both, but numbers will remain proportionately lower on the resistant cultivars. For instance, aphid numbers are normally forty times as high on B.G.A. Tuneful as on Portrait. Aphids appear to select the cultivar or region of plant most suitable for reproduction (usually apical and basal leaves) but, as the plants and population grow, the aphids continually redistribute themselves. Within the limits of normal growing practice, cultural and environmental conditions have little effect on the aphids. Brachycaudus helichrysi (Kaltenbach) and Aphis fabae Scop, have similar varietal preferences but, unlike Myzus persicae, they avoid senescent leaves and only colonize the apex.     

Role of visual and olfactory cues from agricultural hedgerows in the orientation behavior of multicolored Asian lady beetle (Coleoptera: Coccinellidae)

Harmonia axyridis Pallas is an introduced lady beetle common in eastern North American agroecosystems. Two-choice behavioral bioassays were performed to determine whether visual and olfactory stimuli from prey and host habitats could elicit taxis in wild-collected H. axyridis adults and whether beetles exhibit a preference among stimuli. Soybean aphid (Aphis glycines Matsumura) spends much of the year in agricultural hedgerows residing on buckthorn (Rhamnus cathartica L), and H. axyridis is frequently observed feeding on aphids in this habitat. Olfactory bioassays were performed in a Y-tube olfactometer and tested the response of beetles to the odor of buckthorn leaves, apple leaves (Malus domestica Borkh.), and buckthorn leaves both naturally and artificially infested with A. glycines. No differences were observed between the numbers of beetles moving toward the odor of buckthorn artificially infested with A. glycines and uninfested buckthorn, but more beetles preferred naturally infested buckthorn over uninfested buckthorn. Visual bioassays were performed in an acrylic tube arena,and tested beetle response to silhouettes and to apple and buckhorn leaves. Beetles were significantly more likely to choose silhouettes over blank space in visual trials. Significantly more beetles moved toward buckthorn leaves than blank space, but beetles did not discern between apple and buckthorn until olfactory cues were also included. This study lays the foundation for future work examining the response of H. axyridis to visual and olfactory cues in Ontario agroecosystems, which could help enhance effectiveness of H. axyridis as a biological control and mitigate its impacts as a pest species.     

温室瓜蚜种群动态的研究

瓜蚜AphisgossypiiGlover在温室黄瓜上的空间格局为聚集分布,分布的基本成分为个体群,聚集强度随密度的上升而下降;瓜蚜主要分布于中部和下部叶片。瓜蚜在温室黄瓜上呈指数增长,模型为Nt=0.1745e0.7414t(r=0.9676)。应用最优分割法将瓜蚜种群动态划分为3个阶段:初建期、发展期和高峰期。在种群初建期,有翅蚜开始迁入,数量较低,以扩散为主,分布不均匀,聚集强度较高;在发展期,瓜蚜种群不断繁殖扩散,分布日趋均匀,聚集强度逐渐下降;在高峰期,瓜蚜种群数量急剧增长到最高峰,分布至所有植株,聚集强度继续下降,此阶段后由于黄瓜植株受害枯萎,瓜蚜缺少食物而数量急剧下降。     

A Receptor-Based Explanation for Tsetse Fly Catch Distribution between Coloured Cloth Panels and Flanking Nets

Tsetse flies transmit trypanosomes that cause nagana in cattle, and sleeping sickness in humans. Therefore, optimising visual baits to control tsetse is an important priority. Tsetse are intercepted at visual baits due to their initial attraction to the bait, and their subsequent contact with it due to landing or accidental collision. Attraction is proposed to be driven in part by a chromatic mechanism to which a UV-blue photoreceptor contributes positively, and a UV and a green photoreceptor contribute negatively. Landing responses are elicited by stimuli with low luminance, but many studies also find apparently strong landing responses when stimuli have high UV reflectivity, which would imply that UV wavelengths contribute negatively to attraction at a distance, but positively to landing responses at close range. The strength of landing responses is often judged using the number of tsetse sampled at a cloth panel expressed as a proportion of the combined catch of the cloth panel and a flanking net that samples circling flies. I modelled these data from two previously published field studies, using calculated fly photoreceptor excitations as predictors. I found that the proportion of tsetse caught on the cloth panel increased with an index representing the chromatic mechanism driving attraction, as would be expected if the same mechanism underlay both long- and close-range attraction. However, the proportion of tsetse caught on the cloth panel also increased with excitation of the UV-sensitive R7p photoreceptor, in an apparently separate but interacting behavioural mechanism. This R7p-driven effect resembles the fly open-space response which is believed to underlie their dispersal towards areas of open sky. As such, the proportion of tsetse that contact a cloth panel likely reflects a combination of deliberate landings by potentially host-seeking tsetse, and accidental collisions by those seeking to disperse, with a separate visual mechanism underlying each behaviour.     

Locomotory behavior of flightless Harmonia axyridis Pallas (Col., Coccinellidae)

To improve the efficiency of the ladybeetle Harmonia axyridis as a biological control agent against aphids, a flightless population was produced by feeding adults with a mutagen and selecting their progeny for non-flying but otherwise morphologically normal individuals. The inability to fly could result from a change in their flying behavior compared with control adults. Flight duration was very much shorter, wing beat frequency and more particularly the amplitude of the wing beats were clearly lower. More time was spent on the other components of flight behavior such as wing rotation, wing immobility and wing folding. The sequence of these patterns differed slightly mainly due to changes in their frequency. The locomotory behavior was not modified by the mutation, which only affected the wing muscles. The searching behavior of mutant adults differed from that of control adults only in that they took longer to encounter and ingest aphids. As this difference is not important, it should be possible to use this flightless population in biological control programs.