To what extent can the tiny parasitoid wasps,Eretmocerus mundus,fly upwind?

Body miniaturization in insects is predicted to result in decreased flight speed and therefore limited ability of these insects to fly upwind. Therefore, tiny insects are often regarded as relying on passive dispersal by winds. We tested this assumption in a wind tunnel by measuring the burst speed of Eretmocerus mundus (Mercet), a beneficial parasitoid wasp with body length <1 mm. Insects were filmed flying upwind towards a UV light source in a range of wind speed 0–0.5 m/s. The Insects flew towards the UV light in the absence and presence of wind but increased their flight speed in the presence of wind. They also changed flight direction to be directly upwind and maintained this body orientation even while drifted backwards relative to the ground by stronger winds. Field measurements showed that the average flight speed observed in the wind tunnel (0.3 m/s) is sufficient to allow flying between plants even when the wind speed above the vegetation was 3–5 folds higher. A simulation of the ability of the insects to control their flight trajectory towards a visual target (sticky traps) in winds show that the insects can manipulate their progress relative to the ground even when the wind speed exceeds their flight speed. The main factors determining the ability of the insects to reach the trap were trap diameter and the difference between insect flight speed and wind speed. The simulation also predicts the direction of arrival to the sticky target showing that many of the insects reach the target from the leeward side (i.e. by flight upwind). In light of these results, the notion that miniature insects passively disperse by winds is misleading because it disregards the ability of the insects to control their drift relative to the ground in winds that are faster than their flight speed.     

Electrical Stimulation of Coleopteran Muscle for Initiating Flight

Some researchers have long been interested in reconstructing natural insects into steerable robots or vehicles. However, until recently, these so-called cyborg insects, biobots, or living machines existed only in science fiction. Owing to recent advances in nano/micro manufacturing, data processing, and anatomical and physiological biology, we can now stimulate living insects to induce user-desired motor actions and behaviors. To improve the practicality and applicability of airborne cyborg insects, a reliable and controllable flight initiation protocol is required. This study demonstrates an electrical stimulation protocol that initiates flight in a beetle (Mecynorrhina torquata, Coleoptera). A reliable stimulation protocol was determined by analyzing a pair of dorsal longitudinal muscles (DLMs), flight muscles that oscillate the wings. DLM stimulation has achieved with a high success rate (> 90%), rapid response time (< 1.0 s), and small variation (< 0.33 s; indicating little habituation). Notably, the stimulation of DLMs caused no crucial damage to the free flight ability. In contrast, stimulation of optic lobes, which was earlier demonstrated as a successful flight initiation protocol, destabilized the beetle in flight. Thus, DLM stimulation is a promising secure protocol for inducing flight in cyborg insects or biobots.     

Distributed power and control actuation in the thoracic mechanics of a robotic insect

Recent advances in the understanding of biological flight have inspired roboticists to create flapping-wing vehicles on the scale of insects and small birds. While our understanding of the wing kinematics, flight musculature and neuromotor control systems of insects has expanded, in practice it has proven quite difficult to construct an at-scale mechanical device capable of similar flight performance. One of the key challenges is the development of an effective and efficient transmission mechanism to control wing motions. Here we present multiple insect-scale robotic thorax designs capable of producing asymmetric wing kinematics similar to those observed in nature and utilized by dipteran insects to maneuver. Inspired by the thoracic mechanics of dipteran insects, which entail a morphological separation of power and control muscles, these designs show that such distributed actuation can also modulate wing motion in a robotic design.     

The Effect of Rearing Temperature on Flight Initiation of Trichogramma sibericum Sorkina at Ambient Temperatures

Trichogramma sibericum Sorkina was reared in the laboratory at three temperatures: 16, 21, and 26°C. Individuals from each of these treatments were then tested for propensity to initiate flight at one of four ambient temperatures: 16, 19, 21, or 26°C. Both rearing and ambient temperatures had significant effects on flight initiation. Insects reared at 16°C had the highest mean proportion of flyers; insects reared at 26°C had the lowest. The proportion of insects initiating flight increased with increasing ambient temperature. Also, the interaction of these two temperature experiences was significant. Insects reared at 16°C were more likely to initiate flight at 16°C than insects reared at 21 or 26°C. These results indicate that performance (as assessed by flight initiation) at ambient temperature is dependent on the temperature previously experienced during rearing.     

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.     

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.     

Flight activity ofProstephanus truncatus (Horn) (Coleoptera: Bostrichidae) in relation to population density,resource quality,age, and sex

Higher flight activity has been observed in aged, high-density cultures ofProstephanus truncatus (Horn) (Coleoptera: Bostrichidae), but adults in new, lowdensity culture jars showed less flight activity. In order to understand this change in behavior, the effects of population density, age, resource quality, and sex on the flight ofP. truncatus were studied in a wind tunnel. While an immediate density on the release platform had no significant effect on flight, beetles from high-density cultures were more inclined to fly than those from low-density cultures. Resource quality exerted a major influence on flight; insects in food suitable for boring and oviposition seldomly exhibited flight, however, when food was absent or of inferior quality for boring and oviposition, the dominant behavior was flight. Also, insects maintained for a week in food suitable for boring and oviposition were less ready to fly than those maintained in food unsuitable for boring and oviposition. The optimum age range for flight activity was before the peak of reproduction and insects rarely flew before 4 days or after 32 days of emergence. There were no significant differences between the flight activity of males and that of females. Based on these results, we conclude that age and resource quality are major influences on the flight activity ofP. truncatus and a hypothesis is proposed in which reproductively active male and female beetles disperse from habitats of low resource quality to those that support their reproductive behavior. The practical implications of these results and the possible role of the male-produced aggregation pheromone are discussed.     

昆虫飞行肌蛋白质

昆虫飞行肌的肌原纤维不仅含有粗肌丝、细肌丝、纤肌丝,还含有很多其它蛋白质参与肌原纤维的组装和调节,文章介绍了10余种蛋白质的结构、功能及其在肌原纤维中的位置和功能,对于了解昆虫飞行肌的发育和探索昆虫飞行能力差异的原因具有重要意义。     

Day-flying butterflies remain day-flying in a Polynesian, bat-free habitat.

To test the theory that insectivorous bats have selected for diurnality in earless butterflies I compared the nocturnal flight patterns of three species of nymphalid butterflies on the bat-free Pacific island of Moorea with those of three nymphalids in the bat-inhabited habitat of Queensland, Australia. Nocturnal flight, measured as the ratio of deep night (1 h following sunset to 1 h preceding sunrise) to twilight night (1 h before sunset to 30 min after sunrise) activity did not differ significantly between the two locations, nor did the percentage of individuals active and I conclude that living in a bat-released habitat has not produced nocturnal flight in these insects. This result is surprising considering the potential advantages of escaping diurnally active predators and suggests that physiological adaptations (e.g. thermoregulation and/or vision) currently constrain these insects to diurnal flight. Since taxonomic records suggest that gene flow does not exist with bat-exposed conspecifics, I suggest that insufficient time has elapsed since these species migrated to Moorea to have resulted in major phenotypic changes such as diel flight preferences.     

Flight metabolism in Panstrongylus megistus (Hemiptera: Reduviidae): the role of carbohydrates and lipids

The metabolism of lipids and carbohydrates related to flight activity in Panstrongylus megistus was investigated. Insects were subjected to different times of flight under laboratory conditions and changes in total lipids, lipophorin density and carbohydrates were followed in the hemolymph. Lipids and glycogen were also assayed in fat body and flight muscle. In resting insects, hemolymph lipids averaged 3.4 mg/ml and significantly increased after 45 min of flight (8.8 mg/ml, P < 0.001). High-density lipophorin was the sole lipoprotein observed in resting animals. A second fraction with lower density corresponding to low-density lipophorin appeared in insects subjected to flight. Particles from both fractions showed significant differences in diacylglycerol content and size. In resting insects, carbohydrate levels averaged 0.52 mg/ml. They sharply declined more than twofold after 15 min of flight, being undetectable in hemolymph of insects flown for 45 min. Lipid and glycogen from fat body and flight muscle decreased significantly after 45 min of flight. Taken together, the results indicate that P. megistus uses carbohydrates during the initiation of the flight after which, switching fuel for flight from carbohydrates to lipids.     

Nocturnal insects use optic flow for flight control

To avoid collisions when navigating through cluttered environments, flying insects must control their flight so that their sensory systems have time to detect obstacles and avoid them. To do this, day-active insects rely primarily on the pattern of apparent motion generated on the retina during flight (optic flow). However, many flying insects are active at night, when obtaining reliable visual information for flight control presents much more of a challenge. To assess whether nocturnal flying insects also rely on optic flow cues to control flight in dim light, we recorded flights of the nocturnal neotropical sweat bee, Megalopta genalis, flying along an experimental tunnel when: (i) the visual texture on each wall generated strong horizontal (front-to-back) optic flow cues, (ii) the texture on only one wall generated these cues, and (iii) horizontal optic flow cues were removed from both walls. We find that Megalopta increase their groundspeed when horizontal motion cues in the tunnel are reduced (conditions (ii) and (iii)). However, differences in the amount of horizontal optic flow on each wall of the tunnel (condition (ii)) do not affect the centred position of the bee within the flight tunnel. To better understand the behavioural response of Megalopta, we repeated the experiments on day-active bumble-bees (Bombus terrestris). Overall, our findings demonstrate that despite the limitations imposed by dim light, Megalopta-like their day-active relatives-rely heavily on vision to control flight, but that they use visual cues in a different manner from diurnal insects.     

Some factors affecting flight in field populations of the Australian plague locust, Chortoicetes terminifera (walker), in New South Wales

An attempt was made to determine some of the factors regulating flight activity in the Australian plague locust, Chortoicetes terminifera (Walk.) by comparing the physiological characteristics of flying and non-flying locusts at different times of the day. Flight during the day did not appear to involve extensive displacements of the insects and was dependent largely on the, environmental conditions. The physiological state and age did not seem important and the milling flight of swarms involved insects of all ages and states of sexual maturity and the insects were commonly fully fed. There was probably at this time a continual interchange of insects between the air and the ground provided wind speeds are not too high and the air temperature was not below 19°C. Night flight, however, was observed only in locusts after the teneral period, when cuticle deposition was nearing completion around 10 days after the imaginal ecdysis and, in the case of the females, the oocytes were relatively undeveloped. Night flight was also associated with a failure to feed prior to sunset; only those with empty foreguts being stimulated to fly with the drop in light intensity, when the temperature was not too low and certainly not below 17·5°C. It is probably the older insects which take-off in these circumstances for by the time of sunset 30 to 40 per cent of the older, ones apparently fail to feed on any one evening and empty locusts tend to be more active than fully fed ones. The females appeared to show a flight periodicity related to the oviposition cycle, which under suitable conditions, leads to the displacement of about one-third of the population which is sexually immature or which has already recently oviposited. The flight activity of females is probably greater than that of the males for the sexes were in equal ratio in insects caught in flight while males exceeded females in ground populations. At sunset, fewer females than males still had full foreguts and were perhaps more likely to take-off while a higher proportion of younger females than males may soon re-alight if their physiological state is unfavourable for prolonged flight at night.     

If a bird flies in the forest,does an insect hear it?

Birds are major predators of many eared insects including moths, butterflies, crickets and cicadas. We provide evidence supporting the hypothesis that insect ears can function as ‘bird detectors’. First, we show that birds produce flight sounds while foraging. Eastern phoebes (Sayornis phoebe) and chickadees (Poecile atricapillus) generate broadband sounds composed of distinct repetitive elements (approx. 18 and 20 Hz, respectively) that correspond to cyclic wing beating. We estimate that insects can detect an approaching bird from distances of at least 2.5 m, based on insect hearing thresholds and sound level measurements of bird flight. Second, we show that insects with both high and low frequency hearing can hear bird flight sounds. Auditory nerve cells of noctuid moths (Trichoplusia ni) and nymphalid butterflies (Morpho peleides) responded in a bursting pattern to playbacks of an attacking bird. This is the first study to demonstrate that foraging birds generate flight sound cues that are detectable by eared insects. Whether insects exploit these sound cues, and alternatively, if birds have evolved sound-reducing foraging tactics to render them acoustically ‘cryptic’ to their prey, are tantalizing questions worthy of further investigation.     

GENETIC CORRELATIONS AMONG TRAITS DETERMINING MIGRATORY TENDENCY IN THE SAND CRICKET,GRYLLUS FIRMUS

Migration by flight is an important component of the life cycles of most insects. The probability that a given insect will migrate by flight is influenced by many factors, most notably the presence or absence of fully-developed wings and functional flight musculature. Considerable variation has also been reported in the flight propensity of fully-winged individuals with functional flight musculature. We test the hypothesis that these components of migratory tendency are genetically correlated in a wing-dimorhic cricket, Gryllus firmus. Flight propensity and condition of the dorsal longitudinal flight muscles (DLM) are examined in fully-winged (LW) crickets from lines selected for increasing and for decreasing %LW, as well as from unselected control lines. Increased %LW is found to be associated with increased flight propensity among individuals with intact DLM, and with retention of functional DLM. The opposite is true for lines selected for decreased %LW. These results indicate both phenotypic and genetic correlations among behavioral, physiological, and morphological traits determining migratory tendency. We propose that these correlations may result from the multifunctional role of juvenile hormone, which has been reported to influence wing development, flight muscle development and degeneration, and flight propensity. Finally, we discuss the potential influence of genetic correlations for migratory traits on the evolution and maintenance of migratory polymorphisms in insects.     

Flight fuels in the brown planthopper Nilaparvata lugens

The flight fuels of Nilaparvata are a combination of carbohydrate and lipid. In insects of constant age, lipid deposits are proportional to body weight, as is the rate of utilisation of lipid in flight. Reserves of glycogen are more variable and show no correlation with body weight. They are also always extremely low, approximately 0.2% of the live weight, in flight-willing insects. During flight there is evidence that, unlike other migrant insects, carbohydrate metabolism may continue for some hours and some lipid utilisation may begin almost immediately flight is initiated.     

Flight duration and flight muscle ultrastructure of unfed hawk moths

Flight muscle breakdown has been reported for many orders of insects, but the basis of this breakdown in insects with lifelong dependence on flight is less clear. Lepidopterans show such muscle changes across their lifespans, yet how this change affects the ability of these insects to complete their life cycles is not well documented. We investigated the changes in muscle function and ultrastructure of unfed aging adult hawk moths (Manduca sexta). Flight duration was examined in young, middle-aged, and advanced-aged unfed moths. After measurement of flight duration, the main flight muscle (dorsolongitudinal muscle) was collected and histologically prepared for transmission electron microscopy to compare several measurements of muscle ultrastructure among moths of different ages. Muscle function assays revealed significant positive correlations between muscle ultrastructure and flight distance that were greatest in middle-aged moths and least in young moths. In addition, changes in flight muscle ultrastructure were detected across treatment groups. The number of mitochondria in muscle cells peaked in middle-aged moths. Many wild M. sexta do not feed as adults; thus, understanding the changes in flight capacity and muscle ultrastructure in unfed moths provides a more complete understanding of the ecophysiology and resource allocation strategies of this species.     

Animal locomotion: a new spin on bat flight

Biologists and engineers have long struggled to understand the hovering flight of insects, birds, and bats. The enormous diversity of these groups would suggest they fly using a variety of mechanisms, but a new study shows that hovering bats use the same aerodynamic mechanisms as do moths and other insects.     

Visual flight control in naturalistic and artificial environments

Although the visual flight control strategies of flying insects have evolved to cope with the complexity of the natural world, studies investigating this behaviour have typically been performed indoors using simplified two-dimensional artificial visual stimuli. How well do the results from these studies reflect the natural behaviour of flying insects considering the radical differences in contrast, spatial composition, colour and dimensionality between these visual environments? Here, we aim to answer this question by investigating the effect of three- and two-dimensional naturalistic and artificial scenes on bumblebee flight control in an outdoor setting and compare the results with those of similar experiments performed in an indoor setting. In particular, we focus on investigating the effect of axial (front-to-back) visual motion cues on ground speed and centring behaviour. Our results suggest that, in general, ground speed control and centring behaviour in bumblebees is not affected by whether the visual scene is two- or three dimensional, naturalistic or artificial, or whether the experiment is conducted indoors or outdoors. The only effect that we observe between naturalistic and artificial scenes on flight control is that when the visual scene is three-dimensional and the visual information on the floor is minimised, bumblebees fly further from the midline of the tunnel. The findings presented here have implications not only for understanding the mechanisms of visual flight control in bumblebees, but also for the results of past and future investigations into visually guided flight control in other insects.     

A Simple Flight Mill for the Study of Tethered Flight in Insects

Flight in insects can be long-range migratory flights, intermediate-range dispersal flights, or short-range host-seeking flights. Previous studies have shown that flight mills are valuable tools for the experimental study of insect flight behavior, allowing researchers to examine how factors such as age, host plants, or population source can influence an insects'' propensity to disperse. Flight mills allow researchers to measure components of flight such as speed and distance flown. Lack of detailed information about how to build such a device can make their construction appear to be prohibitively complex. We present a simple and relatively inexpensive flight mill for the study of tethered flight in insects. Experimental insects can be tethered with non-toxic adhesives and revolve around an axis by means of a very low friction magnetic bearing. The mill is designed for the study of flight in controlled conditions as it can be used inside an incubator or environmental chamber. The strongest points are the very simple electronic circuitry, the design that allows sixteen insects to fly simultaneously allowing the collection and analysis of a large number of samples in a short time and the potential to use the device in a very limited workspace. This design is extremely flexible, and we have adjusted the mill to accommodate different species of insects of various sizes.