Influence of pheromone concentration and ambient temperature on flight of the gypsy moth, Lymantria dispar (L), in a sustained-flight wind tunnel

Abstract. The effects of pheromone concentration and ambient temperature on male gypsy moth, Lymantria dispar (L.) (Lepidoptera), flight responses to pheromone were investigated in a wind tunnel. As the pheromone dose increased from 10 ng to 1000 ng, males flew at progressively slower airspeeds and ground speeds, and reduced their wingbeat frequencies. Furthermore, the moths steered significantly smaller course angles as the pheromone concentration increased, indicating that they were adopting a more upwind heading. The overall width of the flight tracks also decreased when males flew in more concentrated pheromone plumes. Estimation of plume dimensions using a male wing-fanning assay showed that as pheromone dosage increased, the resultant active spaces became wider, indicating that an inverse relationship existed between the dimensions of the time-averaged plume and the width of track reversals and that most turns were initiated within the plume. When males were flown at cool (20°C) and warm (26°C) ambient temperatures but to equivalent pheromone emission rates, they exhibited higher airspeeds and ground speeds at the higher temperature but steered larger course angles. Track widths, and length of track legs were, however, similar at the two temperatures. The mean turning frequency was nearly the same (c. 4 turns/s) across all the concentrations and temperatures tested even though the moths' thoracic temperature differed by 5°C when the ambient temperature was varied.     

Factors affecting the activity of alatae of the aphids Myzus persicae (Sulzer) and Brevicoryne brassicae (L.)

Apparatus was designed for testing the frequency of flights of aphids under different conditions of temperature, relative humidity, light and pressure. Young aphids (1–4 days after metamorphosis) flew more often and showed less individual variability than older ones; with all ages activity increased for the first few hours under experimental conditions. Starving increased activity for the first 1–2 hr. Aphids used in experiments on a second day flew less frequently than controls which had remained on the plant the first day. Alate B. brassicae were more active than M. persicae : both species showed alternating periods of activity and quiescence.
At light intensities between 100 and 1000 f.c. there was little difference in flight frequency, but below 100 f.c. activity declined rapidly and apparently ceased with darkness.
Changes in relative humidity temporarily affected flight frequency, a change to a higher humidity retarding, a change to a lower increasing it. After adjusting to the change aphids flew readily at all humidities tested between 50 and 100% with temperatures below 80° F. (26.7°C.). The combination of high humidity and high temperature (90°F. = 32·2°C.) sometimes inhibited flight.
Changes of pressure often increased activity temporarily and flight frequency was greater under fluctuating pressure than under constant pressure.
It is concluded that changes in microclimate in crops are adequate to influence frequency of flight of aphids and consequently the spread of virus diseases.     

The flight performance of tsetse flies.

The four species of tsetse used are shown to be aerodynamically rather similar. The wingbeat frequency, aerodynamic lift, flight duration, and number of wingbeats per flight are seen to undergo large increases during adult maturation. Tsetse can produce unusually large aerodynamic lifts, although the flight performance declines very quickly during individual flights. The large lifts appear to be associated with the high percentage of muscle in the fly, and the rapid decline with the inability of the fly to replenish rapidly its proline reserves. Wing mutilation has been shown to increase the wingbeat frequency. The potentiation of the flight performance during maturation appears to be causally linked to increases in the thoracic muscle, cuticle, and proline levels. The results presented here are at variance with those of an earlier study on the physics of flight in tsetse.     

Effects of flight behaviour on body temperature and kinematics during inter-male mate competition in the solitary desert bee Centris pallida

Abstract. Body temperatures and kinematics are measured for male Centris pallida bees engaged in a variety of flight behaviours (hovering, patrolling, pursuit) at a nest aggregation site in the Sonoran Desert. The aim of the study is to test for evidence of thermoregulatory variation in convective heat loss and metabolic heat production and to assess the mechanisms of acceleration and forward flight in field conditions. Patrolling males have slightly (1–3 °C) cooler body temperatures than hoverers, despite similar wingbeat frequencies and larger body masses, suggesting that convective heat loss is likely to be greater during patrolling flight than during hovering. Comparisons of thorax and head temperature as a function of air temperature (T_a) indicate that C. pallida males are thermoregulating the head by increasing heat transfer from the thorax to the head at cool T_a. During patrolling flight and hovering, wingbeat frequency significantly decreases as T_a increases, indicating that variation in metabolic heat production contributes to thermal stability during these behaviours, as has been previously demonstrated for this species during flight in a metabolic chamber. However, wingbeat frequency during brief (1–2 s) pursuits is significantly higher than during other flight behaviours and independent of T_a. Unlike most other hovering insects, C. pallida males hover with extremely inclined stroke plane angles and nearly horizontal body angles, suggesting that its ability to vary flight speed depends on changes in wingbeat frequency and other kinematic mechanisms that are not yet described.     

Thoracic temperature,shivering, and flight in the monarch butterfly,Danaus plexippus (L.)

Summary Monarch butterflies, Danaus plexippus (L.), display a warm-up behavior characterized by wingstrokes of small amplitude. Thoracic temperature during this shivering and during fixed flight was measured by means of a smallbead thermistor inserted into the thorax. At ambient temperatures of 15–16°C, once shivering is initiated the thoracic temperature rises at a maximum rate of 1.3°C/min, and a thoracic temperature 4.0°C greater then ambient is produced (Table 1). Fixed flight at these low ambient temperatures results in a similar rate of increase in thoracic temperature, and a similar temperature excess is produced (Fig. 3). At ambient temperatures between 22 and 35°C the thoracic temperature of an animal starting to fly rises at a faster rate, 3.6°C/min, and reaches a greater excess, 7.9°C (Fig. 4). The wingbeat frequency of animals in fixed flight increases with increasing thoracic temperature (Fig. 2). In the absence of direct solar radiation, shivering typically occurs prior to flight at low ambient temperatures (13–17°C), and the resulting increase in thoracic temperature allows monarch butterflies to fly at these cool temperatures.I thank Miss Janice Ruppert and Mr. C. J. Doughty for their valuable technical assistance. The co-operation of the administrators of New Brighton Beach State Park in permitting me to collect in the park is appreciated. Financial support for this study was provided in part by a faculty research grant from the University of California.     

Effect of sex,age and morphological traits on tethered flight of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) at different temperatures

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a pest of fruit and vegetable production that has become established in 42 countries in Africa after its first detection in 2003 in Kenya. It is likely that this rapid expansion is partly due to the reported strong capacity for flight by the pest. This study investigated the tethered flight performance of B. dorsalis over a range of constant temperatures in relation to sex and age. Tethered flight of unmated B. dorsalis aged 3, 10 and 21 days was recorded for 1 h using a computerized flight mill at temperatures of 12, 16, 20, 24, 28, 32 and 36 °C. Variations in fly morphology were observed as they aged. Body mass and wing loading increased with age, whereas wing length and wing area reduced as flies aged. Females had slightly larger wings than males but were not significantly heavier. The longest total distance flown by B. dorsalis in 1 h was 1559.58 m. Frequent short, fast flights were recorded at 12 and 36 °C, but long-distance flight was optimal between 20 and 24 °C. Young flies tended to have shorter flight bouts than older flies, which was associated with them flying shorter distances. Heavier flies with greater wing loading flew further than lighter flies. Flight distances recorded on flight mills approximated those recorded in the field, and tethered flight patterns suggest a need to factor temperature into the interpretation of trap captures.     

Exposure to heat shock affects thermosensitivity of the locust flight system

The natural habitat of the migratory locust, Locusta migratoria, is likely to result in locusts being heat stressed during their normal adult life. It is known that locusts exhibit a heat-shock response: exposure to 45°C for 3 h induces thermotolerance and the expression of heat-shock proteins. We investigated the effects of exposure to heat-shock conditions on the thermosensitivity of flight rhythm generation in tethered, intact animals and in deafferented preparations. Heat shock had no effect on wingbeat frequency measured at the start of flight sequences, nor did it affect the postimaginal maturation of this parameter. During sustained flight, heat shock slowed the characteristic asymptotic reduction of wingbeat frequency. Wingbeat frequency of heat-shocked animals was less sensitive to temperature in the range 24° to 47°C than that of control animals, and the upper temperature limit, above which flight rhythms could not be produced, was 6° to 7°C higher in heat-shocked animals. These results were mirrored in the response of deafferented preparations, indicating that modifications in the properties of the flight neuromuscular system were involved in mediating the response of the intact animal. We propose that exposure to heat shock had the adaptive consequences of reducing thermosensitivity of the neural circuits in the flight system and allowing them to operate at higher temperatures. © 1996 John Wiley & Sons, Inc.     

Influence of ambient and thoracic temperatures upon sexual behaviour of the gypsy moth, Lymantria dispar

ABSTRACT. In an ambient temperature ( T _a) range of 18–28°C, thoracic temperatures ( T _th) of individual male Lymantria dispar (L.), caught at flight in the field, ranged from 21 to 36.5°C, with a correlation coefficient of 0.63 between T _th and ambient temperature ( T _a). Ambient temperature (and insolation) altered the insect's body temperature and the probabilities, latencies, and durations of preflight responses to pheromone. In a wind tunnel at 16 and 20°C, quiescent males exposed to pheromone raised their T _th by sustained wing fanning from 17 and 21°C, respectively, to c. 24°C before takeoff. At 24 and 28°C ambient, T _th rose by takeoff to 28 and 31°C, respectively. The latencies of male wing fanning in response to pheromone decreased from 1.44 min at 16°C ambient, to 0.58 min at 20°C, to 0.26 min at 24°C, and to 0.16min at 28°C. The components of behaviour (antennal twitch, body jerk, step and wing tremor) that occurred between quiescence and wing fanning were more frequent at ambients of 16 and 20°C than at 24 and 28°C.     

Flight initiation in the egg parasitoid Trichogramma minutum: Effects of ambient temperature, mates, food, and host eggs

Emergence, preening, and flight initiation were studied in laboratory-reared Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae). Male parasitoids emerged first and flew before females. When both sexes were present in flight cylinders, female parasitoids flew before males. Flight propensity in males was negatively related to the number of emerging females, while flight propensity in females was independent of the number of males present. Ambient temperature significantly affected the propensity and timing of flight; between 70–80% of the parasitoids flew at 25 and 30 °C while less than 4%, mostly males, flew at 20 °C. No flights were observed at 15 °C. The presence of fresh host eggs caused a reduction in the proportion of female parasitoids that flew and a delay in the time to flight for the females that did fly. The presence of food increased the flight propensity of female parasitoids, but did not affect the timing of flight. The relationship between flight behaviour and the efficiency of mass-reared Trichogramma is discussed in terms of its importance for inundative release programmes.     

Temperature influences walking speed and walking activity of Trichogramma brassicae (Hym., Trichogrammatidae)

Walking speeds and walking activities (walking time divided by total time) of Trichogramma brassicae were determined at 12, 16, 20 and 25°C. Walking speed was measured during a 5-min period, and walking activity over a 4-day period. Both walking speed and walking activity were strongly influenced by temperature. Walking speed increased linearly with the temperature and was twice as high at 20 as at 12°C. At 25°C, walking activity was high during the whole day, at 20 and 16°C it decreased during the afternoon, whereas at 12°C the wasps became most active only at noon or later. At low temperatures, there was a strong individual variation in walking activity. At 25°C, T. brassicae was active most of the time, so the area searched per time unit can only increase at temperatures above 25°C if walking speed increases. At temperatures below 20°C, searching was more restricted by low walking activity than by low walking speed. Even disregarding other effects of temperature, the reduction in walking speed and walking activity at suboptimal temperatures means that T. brassicae can only search half of the area at 20°C, and only one-seventh at 15°C that it can search at 25°C.     

The effect of temperature on the ability of Tilapia mossambica Peters to enter deep water

The ability of adult Tilapia mossambica Peters to enter deep water was determined at 15, 22 and 30°C. At 30°C adults compensate to about 20m depth but at 15°C to only 7 m. Compensation is more rapid at high than at low temperatures. T. mossambica haemoglobin has a marked Root effect which is the same at 22 and 30°C. The oxygen affinity of the haemoglobin is higher at 15°C than at 30°C. There was no measurable difference in the rate of passive oxygen diffusion across the swimbladder wall in the temperature range 15–30°C. It is concluded that the ability to enter deeper water at higher temperatures is related to decreased oxygen affinity of the haemoglobin and higher rates of oxygen secretion and blood circulation.     

The effect of temperature and ageing on root apical meristems during seedling growth of Triticum aestivum L.: a specific effect on nucleoli

Abstract. Growth and cytology of root apical meristems of Chinese Spring wheat were studied in relation to temperature. The maximum rate of growth increased with temperature, a marked rise occurring between 10°C and 12°C. At all temperatures studied nucleolar volume increased to a maximum and then declined. The maximum nucleolar size achieved showed particular temperature sensitivity, higher volumes being attained at lower temperatures. The peak at 5°C was 70% higher than at 20°C. However, in comparison, cell and nuclear volumes were only 38% and 47% larger, respectively. Ultrastructural analysis of the nucleoli revealed a temperature-dependent relationship between the proportion of granular component and dense fibrillar component. The results are discussed in relation to the regulation of ribosome synthesis and function during growth and development at different temperatures.     

Activity of the forewing stretch receptor in immature and mature adult locusts

Maturation of the flight system of Locusta migratoria occurs during the first two weeks following imaginal ecdysis. One aspect of maturation is an increase in the wingbeat frequency from about 13 Hz to about 23 Hz. We investigated physiological and anatomical mechanisms that may contribute to this process. The difference between the frequencies of the central flight rhythms of immature and mature deafferented preparations was not as great as that between the wingbeat frequencies of immature and mature intact animals. Results from static and dynamic wing elevation showed that the intensity of the forewing stretch receptor response to a given stimulus increased during maturation. The diameter of the main stretch receptor axon was larger and the conduction velocity of signals conveyed along the forewing stretch receptor and the dorsal longitudinal motoneuron was faster in mature than in immature animals. We conclude that during maturation of the flight system the forewing stretch receptor responds to wing elevation with a higher frequency signal that reaches the central circuitry faster. These findings are discussed in the context of a model that describes the influence of stretch receptor input on wingbeat frequency along with other potential mechanisms involved in flight maturation.Abbreviations fDLMn forewing dorsal longitudinal motoneuron - fSR forewing stretch receptor - SR stretch receptor     

The effect of temperature on the size and population density of dinoflagellates in larvae of the reef coral Porites astreoides

Abstract. Pre-settlement events play an important role in determining larval success in marine invertebrates with bentho-pelagic life histories, yet the consequences of these events typically are not well understood. The purpose of this study was to examine the pre-settlement impacts of different seawater temperatures on the size and population density of dinoflagellate symbionts in brooded larvae of the Caribbean coral Porites astreoides. Larvae were collected from P. astreoides at 14–20 m depth on Conch Reef (Florida) in June 2002, and incubated for 24 h at 15 temperatures spanning the range 25.1°–30.0°C in mean increments of 0.4±0.1°C (±SD). The most striking feature of the larval responses was the magnitude of change in both parameters across this 5°C temperature range within 24 h. In general, larvae were largest and had the highest population densities of Symbiodinium sp. between 26.4°–27.7°C, and were smallest and had the lowest population densities at 25.8°C and 28.8°C. Larval size and symbiont population density were elevated slightly (relative to the minimal values) at the temperature extremes of 25.1°C and 30°C. These data demonstrate that coral larvae are highly sensitive to seawater temperature during their pelagic phase, and respond through changes in size and the population densities of Symbiodinium sp. to ecologically relevant temperature signals within 24 h. The extent to which these changes are biologically meaningful will depend on the duration and frequency of exposure of coral larvae to spatio-temporal variability in seawater temperature, and whether the responses have cascading effects on larval success and their entry to the post-settlement and recruitment phase.     

Development of mitochondrial and contractile components of the flight muscle in adult tsetse flies, Glossina morsitans

Estimates have been made of the phospholipid, the water, and the cytochrome-c content of the dorsal longitudinal flight muscles of the tsetse fly, and of the total non-fatty dry weight of the thorax, at different stages of adult development. The results have served as a basis for the partitioning of the dry weight of flight muscle into its three main components—contractile protein, mitochondrial protein, and phospholipid. Development is shown to involve a twofold increase in the amount of contractile protein, and a threefold increase in the amount of mitochondrial protein. These changes are discussed in relation to associated changes in wingbeat frequency.     

Upper thermal limits for feeding and growth of 0+ Arctic charr

When Arctic charr Salvelinus alpinus from two diVerent stocks were fed live Neomysis integer , the upper thermal limits for feeding and growth were established in the range 21·5–21·8° C. These critical temperatures might have been underestimates, because fish tend to show increased sensitivity to handling at high experimental temperatures. In the second experiment, the proportion of feeding undisturbed charr from four stocks decreased initially as temperature was raised in steps from 18 to 22° C. At the lower temperatures, 18 and 20) C, almost all fish resumed feeding, but the recovery time was longer and more fish ceased to feed at 20) C than at 18° C. When the temperature was increased to 21° C, 50% of the fish ceased feeding permanently, and all fish ceased feeding within 2 days at 22° C. It is concluded that 0+ charr cease to feed and grow at c .21·5) C and that the critical temperatures for feeding and growth coincide.     

Temperature-induced changes in the locomotor capacity of juveniles of Marenzelleria viridis (Polychaeta, Spionidae)

Abstract. Populations of Marenzelleria viridis in the Chester River (Kent County, Maryland) experience temperatures ranging from over 30°C in summer to near freezing in winter. Interestingly, M. viridis swims actively in winter. This observation led us to examine the relationship between locomotor capacity and temperature in individuals of M. viridis . Juvenile specimens were collected in February ("cold animals") and June ("warm animals"). Video analysis revealed that swimming is achieved by flexing the body in cyclic, helical waves. Wave frequencies were measured as an index of locomotor capacity at 5°C, 15°C, and 25°C. The mean wave frequencies of cold animals were 5.4 Hz at 5°C and 7.1 Hz at 15°C (Q₁₀= 1.3); the mean wave frequencies of warm animals were 6.1 Hz at 15°C and 7.8 Hz at 25°C (Q₁₀= 1.3). The effects of changes in water viscosity on wave frequency between 5–25°C were not significant. These results demonstrate that the temperature sensitivity of locomotor capacity in juvenile M. viridis is quite low. We conclude that low temperature sensitivity enables M. viridis to be active throughout the year.     

Cold tolerance in tomato. I. Seed germination and early seedling growth of Lycopersicon esculentum

Tomato seed germination times were evaluated foi three "cold germinating" Lycopersicon esculentum Mill, accessions, PI 120256, PI 174263 and PI 341988 and a control breeding line, T3, at temperatures of 6 to 20°C. Accelerated failure analysis indicated that although PI 120256, 174263 and 341988 germinated more rapidly than T3 from 20 to 9°C, the minimum temperatures for germination were similar, and germination times of PI 120256 and 341988 were relatively more inhibited by progressively lower temperatures than was T3. Rapid germination of these three Pls at 10°C may not be due to cold tolerance, but to seed characteristics that promote rapid germination. Hypocotyl and root elongation over time were described by a three-parameter logistic equation; the growth rate parameter for hypocotyl elongation of all four genotypes was greatly inhibited from 20 to 15 and 10°C. Multivariate and univariate analyses of hypocotyl growth parameters indicated significant differences among accessions, but no significant genotype by temperature interaction. Rapid emergence reported for these Pis at 10°C is attributable to early germination, rather than rapid hypocotyl growth.     

Behavioural thermoregulation by subyearling fall (autumn) Chinook salmon Oncorhynchus tshawytscha in a reservoir

This study investigated behavioural thermoregulation by subyearling fall (autumn) Chinook salmon Oncorhynchus tshawytscha in a reservoir on the Snake River, Washington, U.S.A. During the summer, temperatures in the reservoir varied from 23° C on the surface to 11° C at 14 m depth. Subyearlings implanted with temperature-sensing radio transmitters were released at the surface at temperatures >20° C during three blocks of time in summer 2004. Vertical profiles were taken to measure temperature and depth use as the fish moved downstream over an average of 5·6–7·2 h and 6·0–13·8 km. The majority of the subyearlings maintained average body temperatures that differed from average vertical profile temperatures during most of the time they were tracked. The mean proportion of the time subyearlings tracked within the 16–20° C temperature range was larger than the proportion of time this range was available, which confirmed temperature selection opposed to random use. The subyearlings selected a depth and temperature combination that allowed them to increase their exposure to temperatures of 16–20° C when temperatures <16 and >20° C were available at lower and higher positions in the water column. A portion of the subyearlings that selected a temperature c. 17·0° C during the day, moved into warmer water at night coincident with an increase in downstream movement rate. Though subyearlings used temperatures outside of the 16–20° C range part of the time, behavioural thermoregulation probably reduced the effects of intermittent exposure to suboptimal temperatures. By doing so, it might enhance growth opportunity and life-history diversity in the population of subyearlings studied.     

A model for blood meal digestion and fat metabolism in male tsetse flies (Glossinidae)

Abstract. Fat and haematin levels of mature male Glossina morsitans morsitans Westwood were estimated at different times after feeding at temperatures between 15 and 30°C. Flies were kept (largely inactive) in 7.5 × 2.5 cm tubes, or in actograph cages, where flight activity increased with time after feeding. Haematin excretion was modelled as a series of three first order reactions, all with the same rate parameter. The model accounted for > 98% of the variance in mean haematin in each of seven experiments; the rate parameter increased linearly with temperature and activity level. A similar approach was adopted for modelling fat metabolism. The rate coefficients of lipogenesis increased with temperature, and that for lipolysis with temperature, activity level and their interaction. All experiments were analysed simultaneously to provide equations predicting haematin or fat levels for all times, for active or inactive flies, and for temperatures between 15 and 30°C. Haematin exhibited large variations between individuals, but for active flies the expected haematin content at a given time varied little between flies kept at 25 and at 30°C. In inactive flies kept at 25°C, lipogenesis peaked at ≈ 24 h and lipolysis at ≈ 48 h. For active flies the times were 12 and 24 h, respectively; both rates were about twice as high as in inactive flies. Active flies produced (up to 1 mg) more fat out of a given size of blood meal than inactive flies. Curves of fat content against logarithm of haematin content differed little with temperature, and can therefore be useful for comparative studies of field populations of tsetse.