Effect of light intensity and nutritional value of food resources on flight response of adult parasitoid, Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae)

Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) is the major larval parasitoid of Plutella xylostella (L) (Lepidoptera: Plutellidae), which is a serious pest of cruciferous plants throughout the world. We evaluated the influence of light intensities and feeding conditions on the vertical angle of flight in freshly emerged wasps in a cylinder having diameter 15cm and height 30cm. Light intensity was found to directly affects the flight activity. Increase in light intensity causes increase in vertical flight of the female wasps. However, Increase in light intensity did not influence the inclination of vertical flight in males. Feeding condition was also found to affect the vertical flight of the wasps. Honey odour, from below the flight chamber, arrested the flight of unfed or sucrose fed wasps. However, flight of honey fed wasps was not affected by honey odour. Male flight response was also influenced by feeding condition and light intensity but the response was not as higher as shown by females. The present study is useful for selecting suitable food prior to inundative release of parasitoid in the field at suitable time period of the day.

Hawkmoth flight in the unsteady wakes of flowers

Flying animals maneuver and hover through environments where wind gusts and flower wakes produce unsteady flow. Although both flight maneuvers and aerodynamic mechanisms have been studied independently, little is known about how these interact in an environment where flow is already unsteady. Moths forage from flowers by hovering in the flower’s wake. We investigate hawkmoths tracking a 3D-printed robotic flower in a wind tunnel. We visualize the flow in the wake and around the wings and compare tracking performance to previous experiments in a still air flight chamber. Like in still air, moths flying in the flower wake exhibit near perfect tracking at low frequencies where natural flowers move. However, tracking in the flower wake results in a larger overshoot between 2-5 Hz. System identification of flower tracking reveals that moths also display reduced-order dynamics in wind, compared to still air. Smoke visualization of the flower wake shows that the dominant vortex shedding corresponds to the same frequency band as the increased overshoot. Despite these large effects on tracking dynamics in wind, the leading edge vortex (LEV) remains bound to the wing throughout the wingstroke and does not burst. The LEV also maintains the same qualitative structure seen in steady air. Persistence of a stable LEV during decreased flower tracking demonstrates the interplay between hovering and maneuvering.Summary statementWe examined how moths maneuver in the wake of flowers and discover that flower tracking dynamics are simplified compared to still air, while the leading edge vortex does not burst and extends continuously across the wings and thorax.

Time-restricted foraging under natural light/dark condition shifts the molecular clock in the honey bee, Apis mellifera

Honey bees have a remarkable sense of time and individual honey bee foragers are capable to adjust their foraging activity with respect to the time of food availability. Although, there is plenty of experimental evidence that foraging behavior is guided by the circadian clock, nothing is known about the underlying cellular and molecular mechanisms. Here we present a first study exploring whether the time-restricted foraging under natural light-dark condition affects the molecular clock in honey bees. In an enclosed flight chamber (12m × 4m × 4m), food was presented either for 2 hours in the morning or 2 hours in the afternoon for several consecutive days and daily cycling of the two major clock genes, cryptochrome2 (cry2) and period (per), were analyzed in three different tissues involved in feeding-related behaviors: brain, antennae and subesophageal ganglion (SEG). We found that morning and afternoon trained foragers showed significant phase-differences in the cycling of both clock genes in all three tissues. Furthermore, the phase-differences were more pronounced when the feeder was scented with the general plant odor linalool. Our results clearly demonstrate that foraging time functions as a strong circadian Zeitgeber in honey bees. More surprisingly our results suggest that foraging time might have the potential to override the entrainment effect of the light-dark cycle.

Unsteady Vortex Interactions for Performance Enhancement of a Free Flying Dragonfly

Bioinspired designs offer a viable solution to the design challenges of micro air vehicles (MAVs) desired to operate in the same size region under similar conditions as flying vertebrates and insects. Inspired by our previous studies of tethered live dragonflies, here, a quantitative characterization of the unsteady aerodynamic features of a live, freely flying dragonfly under well-established level flight condition will be presented. In particular with regard of the span-wise features of vortex interactions between the fore- and hind-pairs of wings, that highly contributes to the flight agility and efficiency of dragonflies. Flow fields of free flying dragonflies in still air have been measured by time-resolved stereo particle image velocimetry (TRS_PIV). A specifically designed dark flight chamber has been built, where hand hold dragonflies (Pantala flavescens) were released and made to fly nearly parallel to the measurement plane toward a guiding light. Realistic kinematics of the dragonfly wings in free flight were measured by filming with 2 synchronized high-speed video cameras. Using the recorded images, several dozens of landmarks on the fore- and hind-wing surfaces and several landmarks on the body were traced with high precision and the three-dimensional coordinates were then reconstructed with a direct linear transformation (DLT) method. Using the reconstructed wing-body model, Navier-Stokes-based computational fluid dynamics (CFD) analyses, with wing shapes prescribed based on the experimental measurement, dynamically moving multi blocked, and an overset-grid system were conducted. The numerical results are in overall agreement with the PIV data, and the combined numerical and experimental approach offers valuable insight into aerodynamic analyses. The results show that the interaction with the forewing leading edge vortex (LEV) strongly influences the flow structures around the inner spanwise region of the hindwing, while aerodynamic enhancement via vortex capture in the outer span is observed. The interaction depends not solely on wing phasing, geometrical arrangement, but also the flight mission.

Wing wear, but not asymmetry in wear, affects load-lifting capability in bumble bees Bombus impatiens

Wing wear is widespread in flying insects, but its effects on flight are controversial. In this research, we examine the separate and combined effects of wing area and wing area asymmetry on maximum load-lifting capability in bumble bees Bombus impatiens Cresson, 1863. Individual bees with experimentally induced forewing wear (0%–24% forewing area loss, 0%–38% forewing area asymmetry) were harnessed with a string to which small bead groups were attached and tested in a flight chamber to measure the maximum weight that they could lift incrementally. Wing wear significantly decreased load-lifting ability: the higher the mean wing area loss, the less mass a bee could lift (2.66 mg load reduction per 1% forewing area loss, which represents ∼1.6% of mean body mass or ∼5.2% of expected mean nectar load). However, wing area asymmetry, both alone and in combination with area loss, had no detectable effect on maximum lift. The clear cost of wing wear for bumble bees is a linear reduction in weight-lifting capability through loss of wing area. This relatively strong diminution of load lifting by wing wear, observed over the range of wing area losses naturally accrued by wild bees, provides a potential mechanism for declining foraging ability and survivorship of worker bees with wing wear. What remains to be explained is the utter insensitivity of maximum load lifted to forewing asymmetry.

Role of vision throughout the flight initiation sequence of the Colorado potato beetle

The role of vision in the flight initiation sequence of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), was assessed by comparing the behavioral sequences and frequencies of takeoffs of untethered and tethered beetles with and without vision. Results showed that vision plays a critical role in the successful completion of the launch and the maintenance of lift for the adult Colorado potato beetle. The sequence was interrupted immediately before or during the lifting of the mesothoracic legs or before the launch for most blind beetles. Liftoffs of untethered beetles over a 1-h period in a flight chamber were reduced significantly, by 77%, in blind beetles compared with normal beetles. In addition, the preponderance of upward (dispersal) flights following successful liftoffs of normal beetles was replaced by a preponderance of downward (short) flights for blind beetles. Blind beetles that did not have to launch themselves because they were tethered initiated flight as frequently as tethered normal Colorado potato beetles. The duration and repeatability of flights initiated by tethered blind Colorado potato beetles were also similar to those of flights initiated by tethered normal Colorado potato beetles in a stationary environment. Together, the results of the tests with untethered and tethered beetles indicate that vision is a key factor during flight launching and for flight continuation.

Use of Bee-Borne Attractants for Pollination of Nonrewarding Flowers: Model System of Male-Sterile Tomato Flowers

The use of bee natural product for enhancing pollination is especially valuable in problematic crops that are generally avoided by bees. In the present research we attempted to enhance bee visitation to Male Sterile (M-S) tomato flowers generally used in the production of hybrid seeds. These flowers that lack both pollen and nectar are unattractive to bees that learn rapidly to avoid them. The specific objects were to elucidate the chemical composition of the exocrine products of two bumble bee species the North American Bombus impatiens and the Israeli B. terrestris. Of these, to isolate and identify a bee attractant which when sprayed on M-S tomato flowers will enhance bee visitation, and to provide a procedure of the pheromone application regime. During the research we realized that our knowledge of B. impatiens is too little and we narrowed the objective to learning the basic social behavior of the bees and the pattern of foraging in a flight chamber and how it is affected by biogenic amines. Colonies of B. impatiens are characterized by a high number of workers and a relatively small number of queens. Size differences between queens and workers are pronounced and the queen seems to have full control over egg laying. Only about 9% of the workers in mature colonies had mature oocytes, and there were no signs of a "competition phase" as we know in B. terrestris. Queens and workers differ in their exocrine bouquet. Queen's Dufour's gland possesses a series of linear, saturated and unsaturated hydrocarbons whereas that of workers contains in addition a series of wax-type esters. Bees were trained to either visit or avoid artificially scented electronic flowers in a flight chamber. Since bee also learned to avoid scented non-rewarding flowers we attempted to interfere with this learning. We tested the effect of octopamine, a biogenic amine affecting bee behavior, on the choice behavior of free-flying bumblebees. Our results show that octopamine had no significant effect on the bees' equilibrium choice or on the overall rate of the behavioral change in response to the change in reward. Rather, octopamine significantly affected the time interval between the change in reward status and the initiation of behavioral change in the bee. In B. terrestris we studied the foraging pattern of the bees on tomato flowers in a semi commercial greenhouse in Yad Mordechai. Bee learned very quickly to avoid the non- rewarding M-S flowers, irrespective of their arrangement in the plot, i.e., their mixing with normal, pollen bearing flowers. However, bees seem to "forget" this information during the night since the foraging pattern repeats itself the next morning. Several exocrine products were tested as visitation enhancers. Among these, tarsal gland extracts are the most attractive. The compounds identified in the tarsal gland extract are mostly linear saturated hydrocarbons with small amounts of unsaturated ones. Application was performed every second day on leaves in selected inflorescences. Bee visitation increased significantly in the treated inflorescences as compared to the control, solvent treated. Treatment of the anthers cone was more effective than on the flower petals or the surrounding leaves. Methanol proved to be a non-flower-destructive solvent. We have shown that bumble bees (B. terrestris) can be manipulated by bee-borne attractants to visit non-rewarding flowers. We have further demonstrated that the bees learning ability can be manipulated by applying exogenously octopamine. Both methods can be additively applied in enhancing pollination of desired crops. Such manipulation will be especially useful in tomato cultivation for hybrid seed production.