Active and Passive Antennal Movements during Visually Guided Steering in Flying Drosophila

Insects use feedback from a variety of sensory modalities, including mechanoreceptors on their antennae, to stabilize the direction and speed of flight. Like all arthropod appendages, antennae not only supply sensory information but may also be actively positioned by control muscles. However, how flying insects move their antennae during active turns and how such movements might influence steering responses are currently unknown. Here we examined the antennal movements of flying Drosophila during visually induced turns in a tethered flight arena. In response to both rotational and translational patterns of visual motion, Drosophila actively moved their antennae in a direction opposite to that of the visual motion. We also observed two types of passive antennal movements: small tonic deflections of the antenna and rapid oscillations at wing beat frequency. These passive movements are likely the result of wing-induced airflow and increased in magnitude when the angular distance between the wing and the antenna decreased. In response to rotational visual motion, increases in passive antennal movements appear to trigger a reflex that reduces the stroke amplitude of the contralateral wing, thereby enhancing the visually induced turn. Although the active antennal movements significantly increased antennal oscillation by bringing the arista closer to the wings, it did not significantly affect the turning response in our head-fixed, tethered flies. These results are consistent with the hypothesis that flying Drosophila use mechanosensory feedback to detect changes in the wing induced airflow during visually induced turns and that this feedback plays a role in regulating the magnitude of steering responses

Antennal Mechanosensory Neurons Mediate Wing Motor Reflexes in Flying Drosophila

Although many behavioral studies have shown the importance of antennal mechanosensation in various aspects of insect flight control, the identities of the mechanosensory neurons responsible for these functions are still unknown. One candidate is the Johnston's organ (JO) neurons that are located in the second antennal segment and detect phasic and tonic rotations of the third antennal segment relative to the second segment. To investigate how different classes of JO neurons respond to different types of antennal movement during flight, we combined 2-photon calcium imaging with a machine vision system to simultaneously record JO neuron activity and the antennal movement from tethered flying fruit flies (Drosophila melanogaster). We found that most classes of JO neurons respond strongly to antennal oscillation at the wing beat frequency, but not to the tonic deflections of the antennae. To study how flies use input from the JO neurons during flight, we genetically ablated specific classes of JO neurons and examined their effect on the wing motion. Tethered flies flying in the dark require JO neurons to generate slow antiphasic oscillation of the left and right wing stroke amplitudes. However, JO neurons are not necessary for this antiphasic oscillation when visual feedback is available, indicating that there are multiple pathways for generating antiphasic movement of the wings. Collectively, our results are consistent with a model in which flying flies use JO neurons to detect increases in the wing-induced airflow and that JO neurons are involved in a response that decreases contralateral wing stoke amplitude

Octopamine Neurons Mediate Flight-Induced Modulation of Visual Processing in Drosophila

Background: Activity-dependent modulation of sensory systems has been documented in many organisms and is likely to be essential for appropriate processing of information during different behavioral states. However, the mechanisms underlying these phenomena remain poorly characterized. Results: We investigated the role of octopamine neurons in the flight-dependent modulation observed in visual interneurons in Drosophila. The vertical system (VS) cells exhibit a boost in their response to visual motion during flight compared to quiescence. Pharmacological application of octopamine evokes responses in quiescent flies that mimic those observed during flight, and octopamine cells that project to the optic lobes increase in activity during flight. Using genetic tools to manipulate the activity of octopamine neurons, we find that they are both necessary and sufficient for the flight-induced visual boost. Conclusions: This study provides the first evidence that endogenous release of octopamine is involved in state-dependent modulation of visual interneurons in flies

Non-equilibrium dynamics in an interacting nanoparticle system

Non-equilibrium dynamics in an interacting Fe-C nanoparticle sample, exhibiting a low temperature spin glass like phase, has been studied by low frequency ac-susceptibility and magnetic relaxation experiments. The non-equilibrium behavior shows characteristic spin glass features, but some qualitative differences exist. The nature of these differences is discussed.Comment: 7 pages, 11 figure

Spin Driven Jahn-Teller Distortion in a Pyrochlore system

The ground-state properties of the spin-1 antiferromagnetic Heisenberg model on the corner-sharing tetrahedra, pyrochlore lattice, is investigated. By breaking up each spin into a pair of 1/2-spins, the problem is reduced to the equivalent one of the spin-1/2 tetrahedral network in analogy with the valence bond solid state in one dimension. The twofold degeneracy of the spin-singlets of a tetrahedron is lifted by a Jahn-Teller mechanism, leading to a cubic to tetragonal structural transition. It is proposed that the present mechanism is responsible for the phase transition observed in the spin-1 spinel compounds ZnV$_2$O$_4$ and MgV$_2$O$_4$.Comment: 4 pages, 3 eps figures, REVTeX, to appear in Phys. Rev. Let

Species of Bursaphelenchus Fuchs, 1937 (Nematoda: Parasitaphelenchidae) and other nematode genera associated with insects from Pinus pinaster in Portugal

Insects associated with maritime pine, Pinus pinaster, in Portugal were collected and screened for the presence of Bursaphelenchus species. Nematodes were identified using Internal Transcribed Spacers-Restriction Fragment Length Polymorphism (ITS-RFLP) analysis of dauer juveniles and morphological identification of adults that developed from dauer juveniles on fungal cultures or on cultures in pine wood segments at 26 C. Several associations are described: Bursaphelenchus teratospicularis and Bursaphelenchus sexdentati are associated with Orthotomicus erosus; Bursaphelenchus tusciae, B. sexdentati and/or Bursaphelenchus pinophilus with Hylurgus ligniperda and Bursaphelenchus hellenicus with Tomicus piniperda, Ips sexdentatus and H. ligniperda. An unidentified Bursaphelenchus species is vectored by Hylobius sp. The previously reported association of Bursaphelenchus xylophilus with Monochamus galloprovincialis was confirmed. The association of Bursaphelenchus leoni with Pityogenes sp. is not definitively established and needs further studies for clarification. Other nematode genera besides Bursaphelenchus were found to be associated with the insects sampled, including two different species of Ektaphelenchus, Parasitorhabditis sp., Parasitaphelenchus sp., Contortylenchus sp. and other unidentified nematodes. The Ektaphelenchus species found in O. erosus is morphologically similar to B. teratospicularis found in the same insect; adults of both the species are found in cocoon-like structures under the elytra of the insects. Introduction Approximately one third of the nematodes belonging to the order Aphelenchida Siddiqi, 1980 are associated with insects (Poinar, 1983). These nematodes establish a variety of associations with the insects, which may be described as commensalism, e.g. phoresy (to the benefit of the nematode but not affecting the insect), mutualism (both the organisms benefit) or parasitism (nematodes benefit at the expense of the insect) (Giblin-Davis, 2004). Most Bursaphelenchus Fuchs, 1937 species are mycetophagous, feeding on fungi in the galleries of bark beetles and thu

Indication of intrinsic room-temperature ferromagnetism in Ti1-xCoxO2-d thin film: An x-ray magnetic circular dichroism study

Soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L2,3 edges of Co doped rutile TiO2 at room temperature have revealed clear multiplet features characteristic of ferromagnetic Co2+ ions coordinated by O2- ions, being in sharp contrast to the featureless XMCD spectrum of Co metal or metallic clusters. The absorption and XMCD spectra agree well with a full atomic-multiplet calculation for the Co2+ high-spin state in the D2h-symmetry crystal field at the Ti site in rutile TiO2. The results indicate that the ferromagnetism arises from the Co2+ ions substituting the Ti4+ ions.Comment: 11 pages including 3 figure