Contrast sensitivity of insect motion detectors to natural images

How do animals regulate self-movement despite large variation in the luminance contrast of the environment? Insects are capable of regulating flight speed based on the velocity of image motion, but the mechanisms for this are unclear. The Hassenstein–Reichardt correlator model and elaborations can accurately predict responses of motion detecting neurons under many conditions but fail to explain the apparent lack of spatial pattern and contrast dependence observed in freely flying bees and flies. To investigate this apparent discrepancy, we recorded intracellularly from horizontal-sensitive (HS) motion detecting neurons in the hoverfly while displaying moving images of natural environments. Contrary to results obtained with grating patterns, we show these neurons encode the velocity of natural images largely independently of the particular image used despite a threefold range of contrast. This invariance in response to natural images is observed in both strongly and minimally motion-adapted neurons but is sensitive to artificial manipulations in contrast. Current models of these cells account for some, but not all, of the observed insensitivity to image contrast. We conclude that fly visual processing may be matched to commonalities between natural scenes, enabling accurate estimates of velocity largely independent of the particular scene

Local and landscape effects of field margins on aerially dispersing beneficial insects and spiders

Field margins were implemented in UK agri-environment schemes with the aim to increase farmland biodiversity. Recently aerially dispersing aphid enemies have been shown to provide the majority of aphid control in winter wheat fields but there is a lack of research conducted on the aerial predator guild. This thesis examines the effect field margins have on aphid predators at the single field scale, the landscape scale and, using results from a marking study, examines the direct use of a pollen and nectar rich field margin by Episyrphus balteatus. At the single field scale, field margins had a positive effect of the numbers of Cantharidae, Empididae, Linyphiidae and Tachyporus spp. in fields with sown margins compared to those without during wheat growth and total aphid predator numbers were significantly higher in fields with margin surrounds in early May but not later in the year. At the landscape scale, results from twelve winter wheat fields with varying densities of surrounding field margins showed predatory Tachyporus spp. to exhibit a positive correlation at scales above 500m radius and Cantharidae to exhibit a negative correlation at local scales. Implications for field margins exerting both positive and negative influences on the presence of aerially dispersing aphid predators in winter wheat fields are discussed. A marking study using rubidium chloride proved direct utilisation of a pollen and nectar rich field margin by the Syrphid Episyrphus balteatus, and the traps used in this study also highlighted the association in distributions between Empididae and cereal aphids. Overall it was concluded that the presence of field margins does have an effect on the spatial and temporal distributions of some aerially dispersing aphid predators, but the response of each predator group varies depending on numerous interlinking components of their life history and directions for future research are discussed

Hoverfly (Diptera: Syrphidae) diversity in Tapada da Ajuda, Lisbon - a preliminary study

Hoverflies are holometabolic insects, whose adults are pollinators feeding on nectar and pollen. Frequently, they are confused with wasps, bees and bumblebees. In the larval stage, some of them prey other insects, specially aphids (Hemiptera), and others are saprophagous. For this reason, they are important biological control agents. In this study, we carried out the prospection and specific identification of hoverflies in four habitats in Tapada da Ajuda (olive grove, a field of Apiaceae, herbaceous vegetation near Lagoa Branca and plum orchard), between March and May 2017. Hoverfly adults were mostly captured with an entomologic net, but also with jar and plastic bags. A preliminary evaluation on the importance of ecologic infrastructure fava bean inter-row in the plum orchard was also performed. For this purpose, we observed fava plants and plum trees, collecting eggs, larvae and pupae of hoverflies that we reared in the laboratory until the emergence of the adult of hoverfly or parasitoid. A total of 12 species were identified, being the most frequent and abundant Episyrphus balteatus and Sphaerophoria scripta. Species richness was higher in the Apiaceae field although this habitat was sampled only during the last fortnight of the study. In the hoverfly immature collected in the plum orchard we detected hymenopteran parasitoids belonging to Diplazontinae and Pteromalidaeinfo:eu-repo/semantics/publishedVersio

Evidence for Batesian mimicry in a polymorphic hoverfly

Palatable Batesian mimics are avoided by predators because they resemble noxious or defended species. The striking resemblance of many hoverflies to noxious Hymenoptera is a “textbook” example of Batesian mimicry, but evidence that selection by predators has shaped the evolution of hoverfly patterns is weak. We looked for geographical and temporal trends in frequencies of morphs of the polymorphic hoverfly Volucella bombylans that would support the hypothesis that these morphs are Batesian mimics of different bumblebee species. The frequency of the black and yellow hoverfly morph was significantly positively related to the frequency of black and yellow bumblebees across 52 sites. Similarly, the frequency of the red-tailed hoverfly morph was positively related to the frequency of red-tailed bumblebees. However, the frequencies of hoverfly morphs were positively spatially autocorrelated, and after controlling for this, only one of the two common hoverfly morphs showed a significant positive relationship with its putative model. We conclude that the distribution of V. bombylans morphs probably reflects geographical variation in selection by predators resulting from differences in the frequencies of noxious bumblebee species

Teleosemantics and Productivity

There has been much discussion of so-called teleosemantic approaches to the naturalisation of content. Such discussion, though, has been largely confined to simple, innate mental states with contents such as There is a fly here. Even assuming we can solve the issues that crop up at this stage, an account of the content of human mental states will not get too far without an account of productivity: the ability to entertain indefinitely many thoughts. \ud The best-known teleosemantic theory, Millikan’s biosemantics, offers an account of productivity in thought. This paper raises a basic worry about this account: that the use of mapping functions in the theory is unacceptable from a naturalistic point of view

Evidence for Batesian mimicry in a polymorphic hoverfly

Palatable Batesian mimics are avoided by predators because they resemble noxious or defended species. The striking resemblance of many hoverflies to noxious Hymenoptera is a “textbook” example of Batesian mimicry, but evidence that selection by predators has shaped the evolution of hoverfly patterns is weak. We looked for geographical and temporal trends in frequencies of morphs of the polymorphic hoverfly Volucella bombylans that would support the hypothesis that these morphs are Batesian mimics of different bumblebee species. The frequency of the black and yellow hoverfly morph was significantly positively related to the frequency of black and yellow bumblebees across 52 sites. Similarly, the frequency of the red-tailed hoverfly morph was positively related to the frequency of red-tailed bumblebees. However, the frequencies of hoverfly morphs were positively spatially autocorrelated, and after controlling for this, only one of the two common hoverfly morphs showed a significant positive relationship with its putative model. We conclude that the distribution of V. bombylans morphs probably reflects geographical variation in selection by predators resulting from differences in the frequencies of noxious bumblebee species

Hoverflies in organic apple orchards in north-western Italy

A list is given of hoverflies collected by means of Malaise and white sticky traps in two organic apple orchards in north-western Italy. The total number of collected species was 17 and it was compared with literature, in order to discuss differences due to sampling methods. The predominant species collected were Sphaerophoria scripta (L.) (73% of the total sample) and Eupeodes corollae (F.) (14%). The trend of adult captures of this species is drawn and discussed. Data on wild plant species in the orchards are also given

Management and drivers of change of pollinating insects and pollination services. National Pollinator Strategy: for bees and other pollinators in England, Evidence statements and Summary of Evidence

These Evidence Statements provide up-to-date information on what is known (and not known) about the status, values, drivers of change, and responses to management of UK insect pollinators (as was September 2018). This document has been produced to inform the development of England pollinator policy, and provide insight into the evidence that underpins policy decision-making. This document sits alongside a more detailed Summary of Evidence (Annex I) document written by pollinator experts. For information on the development of the statements, and confidence ratings assigned to them, please see section ‘Generation of the statements’ below. Citations for these statements are contained in the Summary of Evidence document