Thermoregulatory abilities of Alaskan bees: effects of size, phylogeny and ecology

1. The thermoregulatory capabilities of 18 species of Alaskan bees spanning nearly two orders of magnitude of body mass were measured. Thoracic temperature, measured across the temperature range at which each species forages, was regressed against operative (environmental) temperature to determine bees' abilities to maintain relatively constant thoracic temperatures across a range of operative temperatures (thermoregulatory performance).
2. Previous studies on insect thermoregulation have compared thoracic temperature with ambient air temperature. Operative temperature, which integrates air temperature, solar radiation and effects of wind, was estimated by measuring the temperature of a fresh, dead bee in the field environment. It is suggested that this is a more accurate measure of the thermal environment experienced by the insect and also allows direct comparisons of insects under different microclimate conditions, such as in sun and shade.
3. Simple regression analysis of species and family means, and analysis of phylogenetically based independent contrasts showed thermoregulatory capability, ability to elevate thoracic temperature, and minimum thoracic temperature necessary for initiating flight all increased with body size.
4. Bumble-bees were better thermoregulators than solitary bees primarily as a consequence of their larger body size. However, their thermoregulatory abilities were slightly, but significantly, better than predicted from body size alone, suggesting an added role of pelage and/or physiology. Large solitary bees were better thermoregulators than small solitary bees apparently as a result of body-size differences, with small bees acting as thermal conformers.     

Evolution of Flight in Insects

Norberg, R. Å. (Department of Zoology, University of Gothenburg, Göteborg, Sweden.) Evolution of flight in insects. Zool. Scripta 1 (6): 247–250, 1972.–Two hypotheses on the origin of flight in insects are discussed. 1. Gliding hypothesis. If wings and flight originated in ca. 1 cm large, or larger, insects, a leaping type seems to be a more probable candidate than a non-leaping one, since the former type has, with certainty, a high frequency of voluntary air excursions, during which any extensions come into play. Furthermore, it may attain the equilibrium gliding speed by jumping, and need not, if arboreal, lose any height on a steep initial fall to gain speed. 2. Floating hypothesis. The hypothesis presented here is a modified version of that put forward by Wigglesworth in 1963. It is suggested that wings may have originated in very small insects as thin dorsolateral, fringed extensions (like the wings of the smallest flying insects) acting as viscous drag producers, enabling the insects to float in the air with a very slow sinking speed and to be dispersed passively over long distances by thermal convection currents. Mov-ability of the wings would have increased practicability on the ground, and selection pressure for this could have brought about preadaptation for active flapping flight. Monophyly versus convergence of insect wings of conventional type (aerofoil function) is discussed briefly.     

Structural-functional peculiarities of the wing apparatus of insects that do not have and do have the maneuvering flight

The work considers character of behavior in flight and discusses peculiarities of structural-functional organization of the wing apparatus of two representatives of insects—the migratory Asian locust Locusta migratoria (a low-maneuvering insect) and the dragonfly-darner Aeshna sp. (an insect able to perform complex maneuvers in air). The main principles underlying the insect wing apparatus activity are considered and the mechanisms allowing the dragonflies to perform complex maneuvers in the flight are analyzed in detail.     

Aerial distribution, flight behaviour and eggload: their inter-relationship during dispersal by the sweetpotato whitefly

1. The aerial distribution of Bemisia tabaci Gennadius (the sweetpotato whitefly) was studied during the early ascent phase of flight, to test the degree to which dispersal patterns reflect the flight behaviour of individuals.
2. Marked whiteflies were trapped at four heights between 0 and 7·2 m above fallow ground, and at six distances between 0 and 100 m from the insect source. Insects were trapped during a 2–3 h period after the initiation of flight activity during the summers of 1995 and 1996.
3. Analysis of trap catch data revealed a clear negative exponential relationship between height and aerial distribution, and a slightly weaker negative power relationship between distance and aerial distribution. Marked insects were caught in the uppermost traps adjacent to the source, indicating that a portion of the population had a strong capacity for ascent out of the flight boundary layer.
4. Eggload decreased with the height, but not the distance, at which whiteflies were trapped. Mean eggload close to the ground was significantly greater than that for those trapped at 4·8 and 7·2 m, supporting the hypothesis that there is a trade-off between flight and oogenesis in weak-flying insects.
5. Air temperatures during the trapping periods were positively correlated with the proportion of male and female B. tabaci caught in the highest traps, but not in the most distant traps.
6. The significance of these results for accurate prediction of whitefly dispersal is discussed, and the importance of individual's behaviour in determining dispersal patterns of small insects is emphasized.     

Flight activity of adult stoneflies in relation to weather

Abstract. 1. Dispersal of adult aquatic insects between streams may have important consequences for local and regional population dynamics, but little is known about how dispersal is affected by weather conditions.
2. The influence of meteorological variables on flight activity of adult stoneflies (Plecoptera: Leuctridae, Nemouridae, and Chloroperlidae) was investigated using Malaise traps adjacent to three upland streams in the Plynlimon area of mid Wales, U.K.
3. Numbers of adult stoneflies captured weekly in the traps were related positively to air temperature and related negatively to wind speed. Meteorological conditions during daylight showed stronger relationships with flight activity than did conditions at night.
4. There was inter-site variation in the strength of weather effects on stonefly flight. Wind speed was significant at only one site, which had higher average wind speed than the other sites.
5. Annual variation in weather conditions during adult flight periods may result in varying extent of dispersal between sites, influencing community dynamics over a wide area.     

Do insect metabolic rates at rest and during flight scale with body mass?

Energetically costly behaviours, such as flight, push physiological systems to their limits requiring metabolic rates (MR) that are highly elevated above the resting MR (RMR). Both RMR and MR during exercise (e.g. flight or running) in birds and mammals scale allometrically, although there is little consensus about the underlying mechanisms or the scaling relationships themselves. Even less is known about the allometric scaling of RMR and MR during exercise in insects. We analysed data on the resting and flight MR (FMR) of over 50 insect species that fly to determine whether RMR and FMR scale allometrically. RMR scaled with body mass to the power of 0.66 (M0.66), whereas FMR scaled with M1.10. Further analysis suggested that FMR scaled with two separate relationships; insects weighing less than 10mg had fourfold lower FMR than predicted from the scaling of FMR in insects weighing more than 10mg, although both groups scaled with M0.86. The scaling exponents of RMR and FMR in insects were not significantly different from those of birds and mammals, suggesting that they might be determined by similar factors. We argue that low FMR in small insects suggests these insects may be making considerable energy savings during flight, which could be extremely important for the physiology and evolution of insect flight.     

Evolution of long-range myofibrillar crystallinity in insect flight muscle as examined by X-ray cryomicrodiffraction

Insect flight muscle is known for its crystal-quality regularity of contractile protein arrangement within a sarcomere. We have previously shown by X-ray microdiffraction that the crystal-quality regularity in bumble-bee flight muscle is not confined within a sarcomere, but extends over the entire length of a myofibril (>1000 sarcomeres connected in series). Because of this, the whole myofibril may be regarded as a millimetre-long, natural single protein crystal. Using bright X-ray beams from a synchrotron radiation source, we examined how this long-range crystallinity has evolved among winged insects. We analysed >4600 microdiffraction patterns of quick-frozen myofibrils from 50 insect species, covering all the major winged insect orders. The results show that the occurrence of such long-range crystallinity largely coincides with insect orders with asynchronous muscle operation. However, a few of the more skilled fliers among lower-order insects apparently have developed various degrees of structural regularity, suggesting that the demand for skillful flight has driven the lattice structure towards increased regularity.     

Optic flow-based collision-free strategies: From insects to robots

Flying insects are able to fly smartly in an unpredictable environment. It has been found that flying insects have smart neurons inside their tiny brains that are sensitive to visual motion also called optic flow. Consequently, flying insects rely mainly on visual motion during their flight maneuvers such as: takeoff or landing, terrain following, tunnel crossing, lateral and frontal obstacle avoidance, and adjusting flight speed in a cluttered environment. Optic flow can be defined as the vector field of the apparent motion of objects, surfaces, and edges in a visual scene generated by the relative motion between an observer (an eye or a camera) and the scene. Translational optic flow is particularly interesting for short-range navigation because it depends on the ratio between (i) the relative linear speed of the visual scene with respect to the observer and (ii) the distance of the observer from obstacles in the surrounding environment without any direct measurement of either speed or distance. In flying insects, roll stabilization reflex and yaw saccades attenuate any rotation at the eye level in roll and yaw respectively (i.e. to cancel any rotational optic flow) in order to ensure pure translational optic flow between two successive saccades. Our survey focuses on feedback-loops which use the translational optic flow that insects employ for collision-free navigation. Optic flow is likely, over the next decade to be one of the most important visual cues that can explain flying insects' behaviors for short-range navigation maneuvers in complex tunnels. Conversely, the biorobotic approach can therefore help to develop innovative flight control systems for flying robots with the aim of mimicking flying insects’ abilities and better understanding their flight.     

Insect diversity in Cape fynbos and neighbouring South African vegetation

Aim  It has often been suggested that South Africa's Cape fynbos shrublands, although extremely rich in plant species, are poor in insects, thus representing a notable exception from the broad plant–insect diversity relationship. The aims of this study were to compare the diversity patterns of plant-inhabiting insects in fynbos and the vegetation of three neighbouring biomes (grassland, subtropical thicket, and Nama-karoo), and to test for a general relationship between plant diversity and insect diversity across these biomes.
Location  South-western to south-eastern South Africa.
Methods  We conducted seasonal plant surveys and sweep insect sampling in 10 × 10 m plots in the Baviaanskloof Conservation Area (Eastern Cape), where all four biomes occur. We also conducted once-only collections in the core area of each biome.
Results  Fynbos plots had insect diversity values similar to those of grassland and subtropical thicket (a dense, evergreen and spinescent shrubland with a high abundance of succulents and climbers), and significantly higher than Nama-karoo (an open, semiarid shrubland). A remarkably strong positive relationship was found between plant and insect species richness.
Main conclusions  Previous generalizations were based on a few insect groups (e.g. butterflies, under-represented in fynbos), but ignored published results on other groups (e.g. galling insects, which are in fact over-represented in this vegetation). We show that, overall, insect diversity in fynbos is comparable to that of neighbouring biomes. Fynbos vegetation does not represent a significant exception from the broad positive relationship between plant diversity and insect diversity.     

Changing temperature regimes have advanced the phenology of Odonata in the Netherlands

Abstract.  1. Responses of biota to climate change have been well documented for a restricted number of taxa. This study examined shifts in phenology of 37 species of the aquatic insect order Odonata in the Netherlands over the last decade.
2. The present study shows that adults of the Dutch dragonflies and damselflies have advanced their flight dates over recent years due to complex effects of changing temperature regimes on the timing of adult flight dates.
3. Flight dates did not respond to changes in autumn/winter temperatures, advanced with increases in spring temperatures of the focal and previous year, and delayed with increases in summer temperatures of the previous year. Climate change consequently advanced the flight dates of the Odonata because only spring temperatures have increased during the study period.
4. The findings imply that climate change can evoke strong phenological responses in aquatic insects. Moreover, shifts in phenology due to climate change are likely to vary both spatially or temporally, depending on the exact nature of climate change.     

Costs of cannibalism in the presence of an iridovirus pathogen of Spodoptera frugiperda

Abstract.  1. The costs of cannibalism were examined in larvae of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in the presence of conspecifics infected by a lethal invertebrate iridescent virus (IIV). The hypothesis of a positive correlation between insect density and the likelihood of disease transmission by cannibalism was examined in laboratory microcosms and a field experiment.
2. Transmission was negligible following peroral infection of early instars with purified virus suspensions or following coprophagy of virus-contaminated faeces excreted by infected insects. In contrast, 92% of the insects that predated infected conspecifics acquired the infection and died prior to adult emergence in the laboratory. Diseased larvae were more likely to be victims of cannibalism than healthy larvae.
3. The prevalence of cannibalism was density dependent in laboratory microcosms with a low density (10 healthy insects + one infected insect) or high density (30 healthy insects + one infected insect) of insects, and field experiments performed on maize plants infested with one or four healthy insects + one infected insect.
4. Cannibalism in the presence of virus-infected conspecifics was highly costly to S. frugiperda ; in all cases, insect survival was reduced by between ≈ 50% (laboratory) and ≈ 30% (field) in the presence of the pathogen. Contrary to expectations, the prevalence of disease was not sensitive to density because cannibalism resulted in self-thinning. As infected individuals are consumed and disappear from the population, the prevalence of disease will be determined by the timescale over which transmission can be achieved, and the rate at which individuals that have acquired an infection become themselves infectious to conspecific predators.     

Convergent patterns of long-distance nocturnal migration in noctuid moths and passerine birds

Vast numbers of insects and passerines achieve long-distance migrations between summer and winter locations by undertaking high-altitude nocturnal flights. Insects such as noctuid moths fly relatively slowly in relation to the surrounding air, with airspeeds approximately one-third of that of passerines. Thus, it has been widely assumed that windborne insect migrants will have comparatively little control over their migration speed and direction compared with migrant birds. We used radar to carry out the first comparative analyses of the flight behaviour and migratory strategies of insects and birds under nearly equivalent natural conditions. Contrary to expectations, noctuid moths attained almost identical ground speeds and travel directions compared with passerines, despite their very different flight powers and sensory capacities. Moths achieved fast travel speeds in seasonally appropriate migration directions by exploiting favourably directed winds and selecting flight altitudes that coincided with the fastest air streams. By contrast, passerines were less selective of wind conditions, relying on self-powered flight in their seasonally preferred direction, often with little or no tailwind assistance. Our results demonstrate that noctuid moths and passerines show contrasting risk-prone and risk-averse migratory strategies in relation to wind. Comparative studies of the flight behaviours of distantly related taxa are critically important for understanding the evolution of animal migration strategies.     

Optic flow cues guide flight in birds

Although considerable effort has been devoted to investigating how birds migrate over large distances, surprisingly little is known about how they tackle so successfully the moment-to-moment challenges of rapid flight through cluttered environments [1]. It has been suggested that birds detect and avoid obstacles [2] and control landing maneuvers [3-5] by using cues derived from the image motion that is generated in the eyes during flight. Here we investigate the ability of budgerigars to fly through narrow passages in a collision-free manner, by filming their trajectories during flight in a corridor where the walls are decorated with various visual patterns. The results demonstrate, unequivocally and for the first time, that birds negotiate narrow gaps safely by balancing the speeds of image motion that are experienced by the two eyes and that the speed of flight is regulated by monitoring the speed of image motion that is experienced by the two eyes. These findings have close parallels with those previously reported for flying insects [6-13], suggesting that some principles of visual guidance may be shared by all diurnal, flying animals.     

Quantifying interspecific variation in dispersal ability of noctuid moths using an advanced tethered flight technique

Dispersal plays a crucial role in many aspects of species' life histories, yet is often difficult to measure directly. This is particularly true for many insects, especially nocturnal species (e.g. moths) that cannot be easily observed under natural field conditions. Consequently, over the past five decades, laboratory tethered flight techniques have been developed as a means of measuring insect flight duration and speed. However, these previous designs have tended to focus on single species (typically migrant pests), and here we describe an improved apparatus that allows the study of flight ability in a wide range of insect body sizes and types. Obtaining dispersal information from a range of species is crucial for understanding insect population dynamics and range shifts. Our new laboratory tethered flight apparatus automatically records flight duration, speed, and distance of individual insects. The rotational tethered flight mill has very low friction and the arm to which flying insects are attached is extremely lightweight while remaining rigid and strong, permitting both small and large insects to be studied. The apparatus is compact and thus allows many individuals to be studied simultaneously under controlled laboratory conditions. We demonstrate the performance of the apparatus by using the mills to assess the flight capability of 24 species of British noctuid moths, ranging in size from 12–27 mm forewing length (~40–660 mg body mass). We validate the new technique by comparing our tethered flight data with existing information on dispersal ability of noctuids from the published literature and expert opinion. Values for tethered flight variables were in agreement with existing knowledge of dispersal ability in these species, supporting the use of this method to quantify dispersal in insects. Importantly, this new technology opens up the potential to investigate genetic and environmental factors affecting insect dispersal among a wide range of species.     

Effects of flooding on avian top-predators and their invertebrate prey in a monsoonal Taiwan stream

1. The effects of flooding on top predators are poorly understood globally, but particularly in monsoonal streams. We therefore attempted to assess how inter-annual and intra-annual variations in flood magnitude affected an obligate riverine predator, the brown dipper ( Cinclus pallasii ), and its invertebrate prey, in the mountain Tachia River, Taiwan. Major flooding in one of the study years (2005) allowed an insight into the effects of abnormally large flows.
2. The abundance and biomass of insects, and the abundance of dippers, decreased steadily from 2003 to 2005 as flood magnitude grew, but then increased in 2006 when more typical discharge returned. Dipper abundance, insect abundance and insect biomass were all strongly positively inter-related, but negatively related to discharge. Insect biomass, rather than abundance, was more useful in predicting brown dipper abundance.
3. Aquatic insect composition fluctuated among sampling years, revealed by non-metric multidimensional scaling, and these fluctuations were also related to discharge. In turn, dipper abundance and the mean body size of aquatic insects declined with the shift in insect composition as flow increased.
4. These data illustrate how discharge fluctuations can have pronounced effects on top predators in streams, mediated in this case by fluctuating prey abundance. While contributions from bird movement, breeding performance and mortality were not clearly differentiated, our data reveal how dippers have strategies to accommodate varying discharge in river systems. We suggest that the effects of floods on dippers should be taken into account when using this group as indicators of river quality.     

Flight behaviour of vegetable pests and their natural enemies under different ultraviolet‐blocking enclosures

Ultraviolet (UV) radiation, particularly in the UV‐A + B range (280–400 nm) is a fraction of the solar spectrum that regulates almost every aspect of insect behaviour, including orientation towards hosts, alighting, arrestment and feeding behaviour. To study the role of UV radiation on the flight activity of five insect species of agricultural importance (pests Myzus persicae, Bemisia tabaci and Tuta absoluta, and natural enemies Aphidius colemani and Sphaerophoria rueppellii), one‐chamber tunnels were covered with six cladding materials with different light transmittance properties ranging from 2% to 83% UV and 54% to 85% photosynthetically active radiation (PAR). Inside each tunnel, insects were released from tubes placed in a platform suspended from the ceiling. Specific targets varying with insect species were placed at different distances from the platform. Evaluation parameters were designed for each insect and tested separately. The ability of insects to leave the platform was assessed, as well as the number of captures, eggs or mummies in each target, either sticky traps or plants. Our results suggest differences in flight activity among insect species and UV‐blocking nets. The UV‐opaque film drastically prevented aphids, and whiteflies from flying outside the tubes whereas T. absoluta, syrphids and parasitoids were not affected. Aphid flight behaviour was affected by the UV‐opaque film compared to the other nets, especially in the furthest target of the tunnel. Fewer aphids reached distant traps under UV‐absorbing nets, and significantly more aphids could fly to the end of tunnels covered with non‐UV‐blocking materials. Orientation of B. tabaci and T. absoluta was also negatively affected by the UV‐opaque film although in a different trend. Unlike aphids, differences in B. tabaci captures were mainly found in the closest targets. UV transmittance did not have any effects on parasitoids, and S. rueppellii, implying cues other than visual for these insects under our experimental conditions. Further effects of photoselective enclosures on greenhouse pests and their natural enemies are discussed.     

Visuomotor Response to Object Expansion in Free-Flying Bumble Bees

The flight control systems of flying insects enable many kinds of sophisticated maneuvers, including avoidance of midair collisions. Visuomotor response to an approaching object, received as image expansion on insects’ retina, is a complex event in a dynamic environment where both animals and objects are moving. There are intensive free flight studies on the landing response in which insects receive image expansion by their own movement. However, few studies have been conducted regarding how freely flying insects respond to approaching objects. Here, using common laboratory insects for behavioral research, the bumblebee Bombus ignitus, we examined their visual response to an approaching object in the free-flying condition. While the insect was slowly flying in a free-flight arena, an expanding stripe was projected laterally from one side of the arena with a high-speed digital mirror device projector. Rather than turning away reported before, the bumble bees performed complex flight maneuvers. We synchronized flight trajectories, orientations and wing stroke frequencies with projection parameters of temporal resolution in 0.5 ms, and analyzed the instantaneous relationship between visual input and behavioral output. In their complex behavioral responses, we identified the following two visuomotor behaviors: increasing stroke frequency when the bumble bees confront the stripe expansion, and turning towards (not away) the stripe expansion when it is located laterally to the bee. Our results suggested that the response to object expansion is not a simple and reflexive escape but includes object fixation, presumably for subsequent behavioral choice.     

Aphid orientation and performance in glasshouses under different UV‐A/UV‐B radiation regimes

Visual cues leading to host selection and landing are of major importance for aphids and evidence suggests that flight activity is very dependent on ultraviolet (UV)‐A radiation in the environment. At the same time research on insect plant hosts suggest that the UV‐B component can deter some pests via changes in secondary metabolite chemistry. Here, we examine the potential of UV (UV‐A/UV‐B) radiation to control insect pests in the glasshouse environment. We first examined artificial exposure to UV‐B and the potential to trigger morphological and biochemical modifications in pepper (Capsicum annuum L., Solanaceae) with implications for the fitness of green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae). UV‐B caused accumulation of leaf secondary metabolites and soluble carbohydrates, and stimulated photosynthetic pigments. However, UV‐B did not impact on foliar protein content and aphid performance was unaffected. Next, we studied how altering the UV‐A/UV‐B ratio environment affected aphid orientation and spatial distribution over time, either directly or by exposing plants to supplemental UV before insect introduction. Aphids directly settled and dispersed on their host pepper plants more readily in the presence of supplemental UV‐A and UV‐B. In the control treatment with ambient glasshouse UV‐A and UV‐B, insects remained more aggregated. Furthermore, insects were less attracted to peppers pre‐exposed to supplemental UV‐A and UV‐B radiation. Our results suggest that suppression of UV‐A and UV‐B inside the protected environment reduces aphid colonization and dispersal. Furthermore, application of moderate exposure of young pepper plants to supplemental UV‐B radiation could aid in protection from the colonization by phytophagous insects.     

Evolution of Hypervariable Regions, V4 and V7, of Insect 18S rRNA and Their Phylogenetic Implications

We compared primary and secondary structures of V4 (helices E23-2 to E23-5) and V7 (helix 43) regions of 18S rRNAs in insects and the other three major arthropod groups (crustaceans, myriapods, and chelicerates) known so far. We found that the lengths of primary sequences and the shapes of secondary structures of these two hypervariable regions of insect 18S rRNA even at infraclass levels are phylogenetically informative and reflect major steps in insect evolution. The long sequence insertion and bifurcated shape of helices E23-2 to E23-5 in the V4 region are unique synapomorphic characters for winged insects (Pterygota). The long sequence insertion and expanded stem length of helix 43 in the V7 region are synapomorphic characters for holometabolous insects which conduct complete metamorphosis. The strongly conserved secondary structures suggest the possibility that these hypervariable regions may be related with certain important cellular functions unknown thus far. The comparison with insect fossil records revealed that the pterygote synapomorphy (V4) and the holometabolous synapomorphy (V7) were established prior to the acquisition of insect wings (flight system) and prior to the development of complete metamorphosis, respectively. These synapomorphies have been also relatively stable over at least 300 Myr and 280 Myr, respectively as well. It implies that the expansion events of the V4 and V7 regions have not occurred simultaneously but independently at different periods during the insect evolution. Then this suggests that V4 and V7 regions are not functionally correlated as recently suggested by Crease and Coulbourn.     

Coordination and Integration of Metabolism in Insect Flight*

Insect flight is the most energy-demanding activity of animals. It requires the coordination and cooperation of many tissues, with the nervous system and neurohormones controlling the performance and energy metabolism of muscles, and of the fat body, ensuring that the muscles and nerves are supplied with essential fuels throughout flight. Muscle metabolism can be based on several different fuels, the proportions of which vary according to the insect species and the stage in flight activity. Octopamine, which acts as neurotransmitter, neuromodulator or neurohormone in insects, has a central role in flight. It is present in brain, ventral ganglia and nerves, supplying peripheral tissues such as the flight muscles, and its concentration in hemolymph increases during flight. Octopamine has multiple effects during flight in coordinating and stimulating muscle contraction and also energy metabolism partly by activating phosphofructokinase via the glycolytic activator, fructose 2,6-bisphosphate. One important muscle fuel is trehalose, synthesized by the fat body from a variety of precursors, a process that is regulated by neuropeptide hormones. Other fuels for flight include proline, glycerol and ketone bodies. The roles of these and possible regulation in some insect species are discussed.