Environmental and physiological factors influencing phototactic flight of Bemisia tabaci

Abstract. Experiments were conducted in a glasshouse and in the laboratory to determine the environmental and physiological parameters that affect flight behaviour of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). The number of whiteflies taking off and exhibiting a positive response to sky light in the glasshouse was greatest from 08.30 to 10.00 hours. During peak flight activity less than 5% of the population engaged in phototactic orientation. Temperature was the best single predictor for the phototactic response, accounting for 75% of the variability in whitefly ascent. Sex ratios were determined for individuals remaining on poinsettia, Euphorbia pulcherrima (Willd.), and for individuals that exhibited phototactic orientation; both groups deviated from an expected 1:1 ratio. Males were more prevalent on the plants (1:0.76), whereas females were much more prevalent (1:3.02) among the whiteflies responding to sky light. A higher percentage of the females displaying a phototactic response contained eggs when compared to females remaining on poinsettia (87 v 65%). The two groups of females did not differ significantly in their weights, but males that remained on the plants were heavier than males that responded to sky light. Mark–recapture studies and experiments where phototactic individuals were removed from the population established that the response was short-lived. Whiteflies exhibiting a phototactic response in the glasshouse were more likely to exhibit long-duration, phototactic flights in a vertical flight chamber when compared to individuals that remained on poinsettia (80.7 ± 6.7 v 36.0 ± 5.8% phototactic response; 7.0 ±3.2 v 0.7±0.2min flights). There was also less deviation in flight across the horizontal plane among the individuals that exhibited a positive response to sky light in the glasshouse in comparison to individuals that remained on their host. However, initial rates of climb were not significantly different between the two groups of whiteflies.     

The effects of wild cruciferous host plants on morphology,reproductive performance and flight activity in the diamondback moth,Plutella xylostella (Lepidoptera: Yponomeutidae)

The wild crucifers,Rorippa indica andLepidium virginicum, are known to serve as host plants for the diamondback moth (DBM),Plutella xylostella, but they are less suitable than the preferred cultivated cruciferous plant, cabbage, in terms of adult body size and fecundity. The life history traits and flight activity of DBM adults grown on various host plants were investigated. The adults thus reared on each host plant were divided into three size groups (small, medium and large). In general, female adults grown on the wild crucifers were less fecund and lived longer than those reared on cabbage. Flight activity was higher in adults grown on wild crucifers than in those reared on cabbage. Male adults flew longer than females. Fecundity, longevity, flight activity and morphometrical characters of adults were positively correlated with pupal weight in individuals reared on the same host plant. A negative relationship was found between fecundity and flight activity in females of the same size group, but a positive one was observed in females reared on the same host plant.     

Tethered flight activity of Nephotettix virescens (Hemiptera: cicadellidae) in the Philippines

The flight potential of Nephotettix virescens (Distant), the most important vector of rice tungro virus disease, was assessed using tethered flight techniques. Most individuals tested were not willing to fly in response to stimulation, or flew for very short times. A small proportion of leafhoppers flew for long periods and one female flew for almost 7 h, indicating the potential for long distance dispersal of insects and inoculum. Few individuals flew before four days of age and thereafter flight profiles were similar for insects aged between four and 12 days. Mature females were more flight willing when kept as adults in mixed groups with males than when caged separately. There was no consistent effect on flight performance when insects were reared on rice varieties with different levels of leafhopper resistance. The flight activity of N. virescens was greater when leafhoppers were reared on mature, compared with young, rice plants. Leafhoppers reared through one generation on tungro-diseased rice plants were less willing to fly than individuals maintained on healthy plants of the same age and variety, whereas those tested after a 24-h access period to tungro-diseased plants were more flight-willing. The results are discussed in relation to the spread of tungro and to management interventions for the control of the disease.     

Longevity,flight ability and reproductive performance of the diamondback moth,Plutella xylostella (L.) (Lepidoptera: Yponomeutidae), related to adult body size

Plutella xylostella in the temperate zone shows a clear seasonal change in adult body size. In the laboratory, large and small moths were produced during immature stages at 15°C and 25°C, respectively. These moths were then used to evaluate longevity, age-specific flight ability, flight ability of mated and unmated females, and the influence of flight experience on the subsequent reproductive success. The large moths lived longer and displayed a greater flight ability over 3 weeks. Irrespective of body size, unmated females flew for a longer time than mated females, and flight experience affected their subsequent reproductive success. Females of both sizes mated and laid eggs soon after emergence, without any obvious pre-reproductive period. More flight experience did not delay oviposition, but did reduce egg production. It is likely that large moths with a longer adult life span and greater flight ability are better fitted for long-distance flight and more fecund than small ones. These experimental results may explain why long-distance migration ofP. xylostella is mostly seen during cool seasons, when relatively large moths with long forewing appear in the field.     

Sex,life history and morphology drive individual variation in flight performance of an insect parasitoid

1. The movement of organisms can be driven by multiple factors and has implications for fitness and the spatial distribution of populations. Insects spend a large proportion of their adult lives foraging by flying for resources; however, their capability and motivation to move can vary across individuals. 2. The aims of this study were to examine interindividual and sex differences in flight performance and flight characteristics, using a flight mill bioassay, in Megarhyssa nortoni (Hymenoptera; Ichneumonidae), a parasitoid of the invasive woodwasp Sirex noctilio (Hymenoptera: Siricidae), one of the most important pests of pine afforestation worldwide. We also assessed the influence of morphological traits in combination with sex on flight and explored the cost of flight on longevity and mass loss. 3. The results show a difference between sexes in flight characteristics and performance. Females show greater total distance flown than males, and have a better capacity to undergo sustained flight. Sexual size dimorphism was also found and it was noted that size positively affects distances travelled. Females have a longer life span than males, yet no differences were noted in longevity within sex between individuals that did not fly and those that flew. Age did not influence flight performance of females or impacted on post‐flight longevity. Females lost less body mass than males even after flying longer distances. 4. These results suggest that sex‐specific behaviours probably govern flight abilities together with (and not only because of) morphological traits. The paper discusses sex‐specific life‐history strategies in parasitoids and their implications for biocontrol programmes.     

Changes in amino acids in Cucumis melo in relation to life-history traits and flight propensity of Bemisia tabaci

Phloem amino acids in Cucumis melo L. were measured to determine whether changes in nitrogen availability might affect life-history traits and flight activity of Bemisia tabaci Gennadius (Homoptera: Aleyrodidae). During plant development, nineteen of the twenty common amino acids, plus hydroxyproline, citrulline, ornithine and -aminobutyric acid (GABA) were identified. For most essential amino acids, there were two peaks observed: an initial large peak associated with young plants, and a later small peak associated with senescing plants. For histidine, ornithine and citrulline, medium to large peaks in relative abundance were observed in mature plants. Arginine peaked during the first few weeks of development and was no longer detectable after wk 7. Serine and glutamine/glutamic acid were the only amino acids that peaked during plant senescence. Factor analysis was used to create a reduced number of orthogonal factors, which corresponded well with the trends that were observed for the various groups of amino acids. No single or combination of factors explained a significant amount of the variability in oviposition. For both males and females, factor 1 (predominantly essential amino acids) was the single most important predictor of adult weight. As the relative concentrations of essential amino acids decreased, whitefly weights decreased. Factors 1 and 3 (predominantly histidine and ornithine) were the most important predictors of developmental time. As these amino acids decreased in relative concentration, developmental time increased. Percent emergence was positively associated with factor 1 and negatively associated with factor 6 (predominantly aspartic acid). The distributions of flight duration for whiteflies emerging from young, mature and senescing melon plants were compared and they were always skewed towards short flights; however, the frequency of long-duration flights increased when melon plants began to senesce. Whiteflies from all plant-age categories were capable of flying for more than 2 h with fully developed eggs, but the presence of more than four mature eggs was associated with flights of reduced duration.     

Flight behaviour of the bird cherry aphid, Rhopalosiphum padi

Abstract Seasonal winged forms of the bird cherry aphid, Rhopalosiphum padi L., were flown in an automated flight chamber. During their maiden flights, autumn migrants (gynoparae) had a greater initial rate of climb than summer (exules) and spring migrants (emigrants). Autumn migrants, presented with a laterally-positioned green-illuminated target for 2.5 s during each minute of flight, flew for a longer period before responding to the target (110 min) than summer migrants (36 min), while spring migrants responded after an intermediate time (72 min). This period is equivalent to the migratory phase of flight. The summer migrants were maximally responsive to targets illuminated by green monochromatic light (X, 555 nm). Targets illuminated with ultraviolet (γλ 360 nm) were attractive during the migratory and green-responsive phases of flight, but infrared (γλ700 nm) wavelengths were not attractive. The results are discussed with respect to aphid behaviour in the field.     

Flight movement of Scapanes australis australis (Boisduval) (Coleoptera: Scarabaeidae: Dynastinae) in Papua New Guinea: a radiotelemetry study

Abstract We used radiotelemetry and/or chemical light-tags to track the flight of 15 individuals of Scapanes australis in Madang Province, Papua New Guinea. This species causes severe economic impacts on coconut palms in young plantations. Flights to feeding, mating, resting, and possibly oviposition sites covered distances of 52 to 835 m in males, and from 245 m to>1000 m in females. Upon release, females flew in a tight upward spiral above canopy level (>20 m), then usually flew along a single bearing out of radio reception within 1 min of initiating flight. Dispersing females probably follow scent trails to pheromone-releasing males that occupy feeding galleries excavated most frequently in coconut palms, or search for oviposition sites. Most tagged females were not found again, because they dispersed beyond the tracking capabilities of our radio-receivers, but one female was followed for 245 m to a feeding gallery excavated by an adult male. Males typically flew within 5 m of the ground, took erratic flight paths with numerous turns, and frequently circled coconuts and other host plants. We followed males from the release point until they ceased flight for a night. Males passed daylight hours either in a feeding gallery within a host plant or under soil litter.     

Comparative flight performance of the seasonal morphs of the cabbage whitefly, Aleyrodes brassicae (Wlk.), in the laboratory

Abstract. 1. The flight capacity of the summer (non-diapausing) and the winter (diapausing) females of A.brassicae was assessed in terms of the climbing flight directed phototactically toward an overhead source of light in a laboratory flight chamber.
2. The summer morph took off only when prodded and its flight bouts were much briefer than those of the winter morph.
3. Immediately on take-off, the summer morph sank in flight and was negatively phototactic in the horizontal plane whereas the winter morph climbed on take-off, being positively phototactic both vertically and horizontally.
4. Three phases of behaviour during flight were observed in the winter morph: a short period of widely fluctuating rate of climb, a long 'cruising' phase of steady climbing, and a final erratic phase when the rate of climb had fallen to and below zero.
5. In general, the mean rate of climb was significantly higher on re-take-off after a landing than immediately before the landing.     

Interrelation of mating,flight, and fecundity in navel orangeworm females

The navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae, Phycitini), is an economically important pest of nut crops in California, USA. Improved management will require better understanding of insect dispersal, particularly relative to when mating occurs. A previous study demonstrated a more robust laboratory flight capacity compared to other orchard moth pests, but it was unclear how mating affects dispersal, and how dispersal affects fecundity. In this study, 1‐ and 2‐day‐old females were allowed to fly overnight on a flight mill either before or after mating, respectively, and were then allowed to oviposit. Data on fecundity were compared between treatments to minimally handled or tethered‐only control females. Females that mated before flight flew longer and covered a greater distance than those flying prior to mating. However, timing of flight relative to mating did not affect fecundity, nor did any measure of flight performance. There was no effect on fecundity when females were forced to fly for designated durations from 3 min to 2 h. Together, our data revealed no obvious trade‐off between flight activity and reproductive output. Distances measured on the flight mills (mean ca. 15 km for mated females) may overestimate net displacement in the field where flight tracks are often meandering. The results suggest that most females mate and oviposit in or near their natal habitat, but that some may disperse potentially long distances to oviposit elsewhere.     

Probing and feeding characteristics of the greenhouse whitefly in association with host-plant acceptance and whitefly strains

Host-plant and whitefly strain effects and their interactions on the probing and sap feeding of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), have been investigated in this study using the DC-EPG (Electrical Penetration Graph) technique. Whiteflies generally displayed fewer but longer probes on highly acceptable cucumber than on less acceptable tomato. Both whitefly strains, the T(omato)-strain and the C(ucumber)-strain, showed a significantly lower number of phloem phases on cucumber than on tomato. However, the duration of total phloem phases achieved by either of the whitefly strains on these two host plants was not significantly different. These data indicate that a more continuous phloem feeding has occurred on cucumber plants. Indeed, the percentage of phloem feeding time after the first sustained phloem phase (longer than 15 min) was higher on cucumber for the C-strain whiteflies. When comparing these two whitefly strains, the T-strain whiteflies probed less frequently but longer than the C-strain whiteflies did on both host plants. Also, the T-strain whiteflies displayed a longer duration of total phloem phases on tomato. An interaction between the whitefly strain and plant effects was detected on a parameter, which showed that whiteflies probed significantly longer before reaching the first phloem phase on the host plants that had been previously experienced. In conclusion, both plant species and whitefly strains affect whitefly's probing and feeding behaviour, though plant effects are much stronger.     

Influences of wild crucifers on life history traits and flight ability of the diamondback moth,Plutella xylostella (Lepidoptera: Yponomeutidae)

The larvae ofPlutella xylostella were fed on five wild crucifers,Capsella bursa-pastoris, Lepidium virginicum, Cardamine flexuosa, Rorippa indica, R. islandica and a crop, cabbage. The developmental period of the immature stages, adult longevity, preoviposition period, fecundity and morphometrical characters of the adults were measured. The flight activity of the adults was also measured by the tethered flight method. All the wild plants except forR. islandica were less suitable host plants than cabbage, and larvae which were fed on these less suitable plants emerged as smaller adults with shorter wings. The smaller female adults had lower fecundity but a higher flight activity. Smaller adults measured in terms of their pupal weight among individuals fed on the same host plant had longer wings. These smaller adults with longer wing flew more actively.     

METHOPRENE INFLUENCES REPRODUCTION AND FLIGHT CAPACITY IN ADULTS OF THE RICE LEAF ROLLER,Cnaphalocrocis Medinalis (GUENỂE) (LEPIDOPTERA: PYRALIDAE)

Juvenile hormone (JH) influences many aspects of insect biology, including oogenesis‐flight syndrome tradeoffs between migration and reproduction. Drawing on studies of many migratory insects, we posed the hypothesis that JH influences migratory capacity and oogenesis in the rice leaf roller, Cnaphalocrocis medinalis. We treated adults moths (days 1, 2 and 3 postemergence) with the JH analog (JHA), methoprene, and then recorded the influences of JHA treatments on reproduction. JHA treatment on day 1 postemergence, but not on the other days, shortened the preoviposition period, although JHA did not influence total fecundity, oviposition period, or longevity. We infer day 1 postemergence is the JH‐sensitive stage to influence reproduction. Therefore, we treated moths on day 1 postemergence with JHA and recorded flight capacity, flight muscle mass, and triacylglycerol (TAG) accumulation. JHA treatments did not influence flight speed, but led to reductions in flight durations and flight distances. At day 3 posttreatment (PT), JHA‐treated females flew shorter times and less distance than the controls; JHA‐treated males, however, only flew shorter times than the controls. JHA treatments led to reductions in flight muscle mass in females at days 2–3 PT and reductions in TAG content in females at day 3 PT, but, these parameters were not influenced by JHA in males. These findings strongly support our hypothesis, from which we infer that JH is a major driver in C. medinalis oogenesis‐flight syndrome tradeoffs. Our data also reveal a JH‐sensitive stage in adulthood during which JH influences the oocyte‐flight syndrome in C. medinalis.     

Effects of gender and mating status on self-directed dispersal by the whitefly parasitoid Eretmocerus eremicus

1. The impacts of gender and mating on short‐range (< 10 km) dispersal by the whitefly parasitoid Eretmocerus eremicus Rose and Zolnerowich (Hymenoptera: Aphelinidae) were examined. A fluorescent dust‐marking technique was also tested. 2. In a vertical flight chamber, female flight duration was significantly longer than that of males, and unmated parasitoids flew for longer than mated parasitoids. The mean flight durations were: unmated females 34 min, mated females 10 min, unmated males 7 min, mated males < 1 min. 3. The dispersal behaviour of E. eremicus was investigated in the field using fluorescent dust. Before doing so, it was determined in the laboratory that this dust did not affect flight behaviour, was retained over the length of the experiments, and allowed large samples to be processed quickly and inexpensively. 4. In the field, traps were placed along annuli at 3, 5, 7, and 10 m from release points. Eighty‐seven per cent of the 4153 parasitoids captured were males. Sex ratios were near parity on release. 5. The difference in dispersal characteristics between males and females may be resource based, suggesting that certain requirements were met within the field plots for males that were not met for females. 6. Locally, males dispersed in a manner consistent with a simple diffusion model while females engaged in wind‐directed flight soon after leaving release sites. The fact that the genders exhibited dissimilar dispersal characteristics, supports the claim that insect flight, even by small species, can be self‐directed.     

Response of Eretmocerus eremicus to skylight and plant cues in a vertical flight chamber

In the southwestern United States, Eretmocerus eremicus (Hymenoptera: Aphelinidae) is a native parasitoid of the Bemisia complex (Homoptera: Aleyrodidae). However, little information currently exists on its potential as a biological control agent of whiteflies or on the factors that influence its tendencies to disperse. In this study, we examined the flight behavior of male and female E. eremicus in response to skylight (here simulated by a mercury-vapor lamp) and plant cues (a 550-nm filtered light) in a vertical flight chamber. Approximately 90% of the parasitoids took off in response to the skylight cue. Both sexes were capable of sustained flights in excess of 60 min; however, males had higher rates of climb than females (3.31±0.17 and 2.63±0.19 cm s^–1, respectively). When a plant cue was presented during the parasitoid's phototactic flight, four relatively distinct responses were observed. Fifty-one percent of the individuals responded to the plant cue throughout their flight by flying toward or by landing on the cue. The majority of these parasitoids were females. Approximately 12% of the wasps exhibited an intermittent, positive response to the plant cue. Twenty percent exhibited a `migratory' response. These parasitoids, which were predominantly males, failed to respond to the plant cue until they had flown for a considerable period. Finally, 17% failed to respond to the target during their flight. Approximately 37% of the individuals that showed a positive response to the plant cue actually landed on it and the majority of these were female. The differential response to the plant cue by male and female parasitoids could be, in part, because females are driven to locate hosts in which to oviposit, and males are driven to find mates.     

Relative flight responses of Rhagoletis indifferens as influenced by crowding, sex, and resources

Although flight is believed to be the primary mechanism for dispersal in the Western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), an orchard pest of both sweet (Prunus avium L.) and sour (Prunus cerasus L.) (Rosaceae) cherry crops, the movement of these flies between host patches is difficult to quantify in the field. A tethered flight mill system was used in the laboratory to examine the flight behaviour of sexually mature flies exposed to different levels of conspecific contact and resource availability. A complete 2 × 2 × 3 factorial design compared the relative influence of the factors ‘context’ (crowded, isolated), ‘sex’ (female, male), and ‘resources’ (low = food only; medium = food + leaf; high = food + leaf + cherries) on flight performance measures including distance flown, net trial time, and stopping patterns. Rather than using a minimum time or distance to determine trial length, flight observations were continued for each fly until a behavioural protocol based on stopping time was met. In this protocol each successful trial was composed of three consecutive flight intervals and included a minimum of three stops lasting a combined total of 5 min. Of the 160 flies tested, 86.9% flew <500 m on the flight mill. Individuals from both sexes were capable of maximum flights in the same order of magnitude, ca. 3 km on the flight mill. Distance flown was significantly influenced by ‘context’ such that crowded individuals flew >1.5-fold farther than isolated individuals. Sex influenced the frequency and duration of stops made, with females stopping more often and longer than males. Although females and males in high resource treatments had the shortest net trial times, the factor ‘resources’ did not produce any highly significant main effects, but did generate significant interaction terms with the factors ‘context’ and ‘sex’, suggesting that past experience with ‘resources’ modifies individual flight behaviour. We have shown for the first time using a tethered flight mill system that R. indifferens flight behaviour is context dependent and sensitive to adult crowding. The implications of this study for improved field experiments on dispersal are discussed.     

Tethered flight of the potato moth, Phthorimaea operculella

ABSTRACT. The effects of sex, age and mated state on average flight speed, duration and distance were determined for potato moths, Phthorimaea operculella (Zeller) (Lepidoptera, Gelechiidae), tethered to flight mills. Moths were classified as non-fliers (NFs), good-fliers (GFs) and remaining-fliers (RFs) on the basis of their performance over the first two flights. Some moths flew for over 5 h non-stop, while others tethered overnight flew between 20 and 30 km. Speed, duration and distance flown were greater during the first flight. First flight duration and distance flown by females decreased with age, whereas no trend was evident for males. Mated males and females flew slower first flights with increasing age, whereas virgin moths showed no marked trend. The analysis of fliers and NFs revealed that GFs were heavier than both RFs and NFs, GFs were faster than RFs, the percentage of NFs increased with age especially for mated females, and the percentage of GFs decreased with age. Age and mated state are important factors influencing flight performance especially for female moths. The relevance of these results to the field situation and the possible application of tethered flight to tests of potato moth quality are discussed.     

Behavior of Carpophilus hemipterus in a vertical flight chamber: transition from phototactic to vegetative orientation

The freeflight behavior of Carpophilus hemipterus (L.) (Coleoptera: Nitidulidae) was investigated in a vertical flight chamber to measure takeoff propensity relative to beetle age and to determine the effect of food odors on phototactic orientation. A high-pressure sodium lamp presented from above induced a phototactic flight response, especially in beetles 3–7 days old. The majority of phototactic flights lasted less than 15 min for both males (73%) and females (85%), but ranged up to 100 min. A bimodal periodicity in flight propensity was recorded during the photophase with a small peak in activity occurring 14–10 h prior to scotophase and a large 4 h peak occurring from 3 h prior to scotophase to 1 h after when the onset of scotophase would normally have occurred. Beetles maintained with water as adults usually displayed higher levels of flight activity than did beetles maintained with artificial diet.After a period of vertical flight, photokinetic and phototactic response declined, and flight instability increased, as indicated by an overall decrease in the mean rate of climb, accompanied by an increase in the variability of this measure and an increase in horizontal displacement.When food odor (apple cider vinegar) was introduced the rate of climb dropped rapidly and beetles usually landed regardless of how long they had been in flight. When the food odor was removed, takeoff occurred and the beetle returned to its previous rate of climb. When food odor was repeatedly introduced during the same flight, there was no apparent cumulative effect, and each time it was removed, the beetle re-initiated phototactic flight. Unlike true migratory flight in which response to vegetative cues is temporarily inhibited until the insect has engaged in a period of phototactic flight, C. hemipterus flight could be better characterized as extended foraging in which phototactic flight is readily interrupted by encounters with food odor.

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Résumé Le comportement de vol libre de C. hemipterus L. a été examiné dans une chambre à vent verticale pour déterminer la tendance au vol après l'émergence et observer l'influence de l'odeur d'aliments sur le vol phototactique. Une lampe à haute pression de sodium induit une réponse de col phototactique, qui débute le 3^e jour et reste puissante jusqu'au 8^e jour. La majorité des vols phototactiques duraient moins de 15 pour les mâles (73%) et les femelles (85%), mais pouvait se prolonger jusqu'à 100. Les femelles nourries sur régime artificiel présentaient la plus forte proportion de vol dépassant 35. Cependant, les adultes maintenus exclusivement en présence d'eau ont présenté un niveau d'activité de vol encore supérieur. Une tendance au vol à périodicité quotidienne bimodale a été notée avec un petit pic d'activité à 14–10 heures avant la scotophase et un grand pic durant 4 heures, de 3 heures avant la scotophase à une heure après le début de la scotophase.Après une période de vols verticaux, les réactions photocinétiques et phototactiques ont diminué, et l'instabilité des vols augmenté comme en a témoigné la diminution du taux total d'ascensions et l'accroissement de la variabilité de ce paramètre et des déplacements horizontaux. L'introduction d'odeurs d'aliments pendant le vol phototactique provoque une diminution immédiate du taux d'ascension et conduit généralement à un atterrissage indépendamment du temps antérieur de vol. Quand l'odeur était supprimée le décollage avait lieu et l'insecte retrouvait sont taux antérieur d'ascension. Quand la même odeur d'aliment a été réintroduite à répétition pendant le même vol, il n'y a pas eu d'effets cumulatifs apparents. Par opposition avec d'autres insectes présentant un véritable comportement migrateur pour lesquels la désinhibition des réactions végétatives ne se produit qu'après une longue période de locomotion continue, le vol de C. hemipterus est mieux caractérisé comme un comportement de prospection pour lequel les aliments inhibent immédiatement la dispersion.

     

Light versus pheromone-bearing wind in the control of flight direction by bark beetles, Scolytus multistriatus

ABSTRACT. A wind tunnel lit from above was used to measure the relative effectiveness of light as opposed to pheromone-bearing wind in directing the flight of male S.multistriatus. Upward flight in the tunnel was overridingly phototactic not geotactic, while horizontally upwind flight toward the pheromone source was anemotactic not chemotactic, since the pheromone concentration was uniform in the tunnel. The flight tracks of newly-emerged unfed and previously unflown beetles were preponderantly upwards and downwind; the longer the beetles had spent in flight activity beforehand, the more of them flew upwind.     

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.