Olfactory orientation responses of the eucalyptus woodborer, Phoracantha semipunctata, to host plant in a wind tunnel

The eucalyptus woodborer, Phoracantha semipunctata Fabricius (Coleoptera: Cerambycidae), attacks mainly species of Eucalyptus (Myrtaceae). This study investigated walking and flight behaviour of P. semipunctata males and females exposed to an odour plume originating from a log of E. globulus placed vertically in the upwind end of a wind tunnel. In control experiments, beetles were exposed to a PVC drainpipe in the same position as the log, providing a visual stimulus without host‐tree odour. No statistical differences were found between behavioural responses of either sex when exposed to the log or PVC pipe. No beetles landed on the PVC pipe, whereas 49% of the beetles exposed to host‐tree odour plume landed on the log. Beetles aged over 24 days after emergence from the host tree were more responsive than beetles aged 20–24 days, and accounted vor 86% of the beetles that landed on the log. While walking, host‐tree odour affected the behaviour of the beetles that landed on the log as follows: upwind movement and path linearity increased, whereas turning rate, stopping frequency, mean stopping time and time to take‐off flight decreased. During flight, host‐tree odour affected the behaviour of the beetles that landed on the log as follows: increased upwind flight, turning rate, flight time, flight distance, and decreased flight speed. For beetles that never lost contact with the odour plume, flight progressed upwind with narrow zigzags, and showed higher directedness upwind, path linearity, faster flight speed and lower turning rate than for beetles that lost contact with the odour plume. After loosing contact with the plume, beetles tended to decrease their upwind progression, exhibiting a sharp turn or quick counterturns followed by crosswind or downwind excursions. This led to regaining contact with the odour plume and resumed upwind progression at higher speed provided they flew within the boundaries of the plume. The results showed that host‐tree odour affects both walking and flight behaviour of P. semipunctata beetles, inducing a more directed upwind movement and landing on the visual stimulus of a tree trunk.     

The responses of the cabbage seed weevil (Ceutorhynchus assimilis) to the odour of oilseed rape (Brassica napus) and to some volatile isothiocyanates

The responses of the cabbage seed weevil,Ceutorhynchus assimilis Payk. (Coleoptera: Curculionidae) to volatiles from oilseed rape (Brassica napus L.) were tested using a linear track olfactometer. Weevils were attracted towards the odour of rape during a short period before diapause and for most of their postdiapause life. Odours from both the flowering and green parts of the plant were attractive, but the odour of a non-host plant (Bellis perennis L.) was not. An entrainment extract of flowering rape volatiles in pentane was attractive, but significantly less so than the odour of flowering rape itself. Attraction was found to 3-butenyl and 4-pentenyl isothiocyanate (NCS), but not to 2-phenylethyl isothiocyanate. A mixture of the three NCSs was more attractive than the individual NCSs. However, the concentration required to produce a response was still relatively high. Isothiocyanates, along with other volatiles from rape, probably play a role in host plant recognition by the seed weevil.     

Patch colonization by Trirhabda canadensis (Coleoptera: Chrysomelidae): effects of plant species composition and wind

Summary The goldenrod leaf beetle, Trirhabda canadensis, is known to respond to odors of host and non-host species in the laboratory. Here we report movements of T. canadensis in the field in response to volatile odors from monocultures and polycultures of host plants. Overall, beetles preferentially colonized plots with a higher density of host plants and lower diversity of allelochemicals, but under some wind conditions there were marked exceptions. At high windspeeds, they colonized whichever plot(s) was upwind. At low windspeeds, beetles colonized preferred plots even when they were not upwind. The data suggest that odor dispersion varies in a complex way with windspeed: at low windspeeds beetles received information from a wide are of vegetation and made choices while at high windspeeds information was available only from upwind plot(s).     

Close encounters: contributions of carbon dioxide and human skin odour to finding and landing on a host in Aedes aegypti

In a wind‐tunnel study, the upwind flight and source location of female Aedes aegypti to plumes of carbon dioxide (CO₂) gas and odour from human feet is tested. Both odour sources are presented singly and in combination. Flight upwind along the plumes is evident for both CO₂ and odour from human feet when the odours are presented alone. Similarly, both odour sources are located by more than 70% of mosquitoes in less than 3 min. When both CO₂ and odour from human feet are presented simultaneously in two different choice tests (with plumes superimposed or with plumes separated), there is no evidence that females orientate along the plume of CO₂ and only a few mosquitoes locate its source. Rather, the foot odour plume is navigated and the source of foot odour is located by over 80% of female Ae. aegypti. When a female is presented a plume of CO₂ within a broad plume of human foot odour of relatively low concentration, the source of CO₂ is not located; instead, flight is upwind in the diffuse plume of foot odour. Although upwind flight by Ae. aegypti at long range is presumably induced by CO₂ and the threshold of response to skin odours is lowered, our findings suggest that, once females have arrived near a prospective human host, upwind orientation and landing are largely governed by the suite of human odours, whereas orientation is no longer influenced by CO₂.     

Incorporation of Novel <Emphasis Type="Italic">Ceutorhynchus obstrictus</Emphasis>-resistant Canola Genotypes Into Mixed Cropping Strategies: Evidence for Associational Resistance

Canola genotypes resistant to the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), have recently been developed through introgression of Sinapis alba L. to Brassica napus L. Several lines express antixenosis and antibiosis resistance and have been shown to be less attractive to weevils in visual and olfactory behavioral bioassays. This paper details a small-plot study that assessed the effects on distribution dynamics of weevil adults and larvae of interspersing susceptible among resistant genotypes relative to monocultures over two growing seasons. Results indicate that mixes reduced weevil numbers and oviposition in pods of susceptible genotypes. These results are consistent with associational resistance.     

Generalism Versus Specialism: Responses of Diadegma mollipla (Holmgren) and Diadegma semiclausum (Hellen), to the Host Shift of the Diamondback Moth (Plutella xylostella L.) to Peas

A population of the diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae) (DBM) was recently found to infest sugar snap- and snowpeas in the Rift Valley in Kenya, causing heavy damage. The influence of this host shift on host location preferences of two parasitoids was investigated: The indigenous Diadegma mollipla (Holmgren) regarded as a relative generalist, and Diadegma semiclausum(Hellen), regarded as highly specific to DBM. The attractiveness of different odour sources was compared for the two parasitoid species using a Y-tube olfactometer using naïve females. D. mollipla was not significantly attracted to any cabbage related odours but showed a significant preference for the DBM infested pea plant when tested against clean air. D. semiclausum was highly attracted to the undamaged cabbage plant and odours related to cabbage. On the other hand, peas infested with DBM, showed no attractiveness to this parasitoid. The results showed that specialisation of D. semiclausum is mediated by host plant signals, associated with crucifers, which are not encountered in DBM feeding on peas. For D. mollipla,although a frequent parasitoid on DBM in crucifers, volatiles emitted by these plants might not be used as primary cues for host location. This species may respond largely to chemicals yet unknown and associated with a variety of plant-herbivore interactions.     

Wind speed effects on odour source location by tsetse flies (Glossina)

Abstract. Tsetse flies (mainly Glossina pallidipes Aust.) were captured by various means at sources of artificial host odour in Zimbabwe and Kenya. Their rates of arrival and flight directions were compared with simultaneous data on the wind's speed and direction, on time-scales ranging from 1 s to 30 min. It was predicted that because increasing wind speed up to 1 m s^-1 straightens out the airflow (Brady et al. , 1989) it will straighten out odour plumes, make them easier to navigate, and should therefore increase the rate of arrival of flies at an odour source. In the event, the relationship proved to be more complex, with both positive and negative correlations of arrival rate on wind speed. It seems there is a bimodal relationship: odour source finding is positively related to increasing wind speed in weak winds up to ∼0.5 m s^-1 (presumably as the odour plume straightens out), but is negatively related to increasing wind speed in strong winds above ∼1.0 m s^-1 (presumably due to increasing turbulence breaking up the odour plume).     

Flight behaviour of tsetse flies in host odour plumes: the initial response to leaving or entering odour

ABSTRACT. Free-flying, wild male and female Glossina pallidipes Aust. and G. m. morsitans Westw. were video-recorded in the field in Zimbabwe as they entered or left the side of a host-odour plume in cross-wind flight, or as they overshot a source of host odour in upwind flight (camera 2.5 m up looking down at a 3 times 2.5 m field of view at ground level). 80% of cross-wind odour leavers turned sharply ( turns 95^o), but without regard to wind direction (overshooters behaved essentially the same except that nearly 100% turned). Many fewer flies entering a plume cross wind turned ( c . 60%), and when they did they made much smaller turns ( 58^o); these turns were, however, significantly biassed upwind ( c . 70%). All three classes of fly had similar groundspeeds ( 5.5–6.5 m s^_1) and angular velocities ( 350–400^o s^-1). Clear evidence was obtained of in-flight sensitivity to wind direction: significantly more flies entering odour turned upwind than downwind, and odour losers turning upwind made significantly larger turns than average. The main basis for the different sizes of turn was the different durations of the turning flight, rather than changes in angular velocity or speed. No evidence was found of flies landing after losing contact with odour.     

The olfactory response of cabbage root fly Delia radicum to the host plant volatile allylisothiocyanate

The responses of gravid female cabbage root flies, Delia radicum (L.), to brassica odour and allylisothiocyanate (ANCS) presented in either a discrete plume or uniformly dispersed in air passing through a wind tunnel were investigated. Relatively fast, straight flights occurred in diffuse odour conditions, while in discrete plumes flights were slower with more frequent changes of direction.Flies maintained a constant ground speed and track angle over the straight legs of their flight tracks in two different wind speeds by changing air speed and course. As flies approached an odour source in a discrete plume ground speed was progressively decreased and frequency of turning increased but track angles remained constant. This was achieved by reducing air speed and course angle.Flies released at increasing distances from an odour source moved upwind towards it in a series of short flights, the number relating to distance.The results are discussed in the light of current theories of anemotactic odour source locations and a sequence of orientated behaviour for host plant finding is proposed.

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Les réactions olfactives de Delia radicum à l'allylisothiocyanate volatil émis par les plantes-hôtes

Résumé L'étude a porté sur les réactions de femelles fécondées de Delia radicum L. à l'odour de chou et à l'allylisothiocyanate (ANCS) offerts, soit sous forme d'un fin panache, soit uniformément répartis dans l'air traversant un tunnel à vent.Avec une odeur diffuse les vols étaient relativement rapides et rectilignes, tandis qu'avec un fin panache les vols étaient plus lents avec des changements de direction plus fréquents.En présence de deux vitesses du courant d'air les mouches ont maintenu leur vitesse au sol et leur angle de vol par rapport à la direction du déplacement constants en modifiant leur vitesse de vol et leur direction.Quand les mouches approchaient de la source odorante dans un fin panache, la vitesse au sol diminuait progressivement et la fréquence des virages augmentait, les angles de vol restant constant. Ceci était obtenu en réduisant de la vitesse de l'air et l'angle du déplacement.Les mouches paraissent utiliser une anémotaxie optomotrice et mécanique pendant la localisation de l'hôte. Les résultats sont discutés à la lumière des théories classiques sur la localisation anémotactique des sources odorantes.

     

Avoiding conflicts between insect and weed biological control: selection of non-target species to assess host specificity of cabbage seedpod weevil parasitoids

Abstract:  Classical biological control of insect pests and weeds may lead to potential conflicts, where insect pests are closely related to weed biological control agents. Such a conflict may occur in the classical biological control of the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) in North America, which belongs to the same subfamily, Ceutorhynchinae, as a number of agents introduced or proposed for introduction against non-indigenous invasive weed species. We propose a step-by-step procedure to select non-target species and thereby to develop a non-target species test list for screening candidate entomophagous biological control agents of a herbivore pest insect in a way that would simultaneously evaluate non-target potential on weed biological control agents and other non-target species. Using these recommendations, we developed a non-target test list for host specificity evaluations in the area of origin (Europe) and the area of introduction (North America) for cabbage seedpod weevil parasitoids. Scientifically based predictions on expected host–parasitoid interactions and ecological information about the ecological host range in the area of origin can help avoid conflicts, while still allowing the introduction of safe and effective agents against both insect pests and weeds.     

Responses of <Emphasis Type="Italic">Ceutorhynchus obstrictus</Emphasis> (Marsham) (Coleoptera: Curculionidae) to olfactory cues associated with novel genotypes developed by <Emphasis Type="Italic">Sinapis alba</Emphasis> L. × <Emphasis Type="Italic">Brassica napus</Emphasis> L.

Many herbivorous insects use olfactory cues for host location. Extracts from Brassica napus L. have been shown to elicit electrophysiological and behavioural responses in the cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (syn. C. assimilis (Paykull)) (Coleoptera: Curculionidae). These include volatile products of the hydrolysis of glucosinolates. Here we present results of a laboratory olfactometer study examining the attractiveness of odours from flowering racemes and foliage of Sinapis alba L. (an inappropriate host for larval development), B. napus (an excellent host for larval development) and lines derived from S. alba × B. napus selected from colonization studies to demonstrate resistance or susceptibility. Results of this study indicate differential attraction of C. obstrictus to the odours of resistant and susceptible lines and suggest the role of hydrolysis products of glucosinolates, particularly the attractive effects of 2-phenylethyl isothiocyanate.     

Habitats as Complex Odour Environments: How Does Plant Diversity Affect Herbivore and Parasitoid Orientation?

Plant diversity is known to affect success of host location by pest insects, but its effect on olfactory orientation of non-pest insect species has hardly been addressed. First, we tested in laboratory experiments the hypothesis that non-host plants, which increase odour complexity in habitats, affect the host location ability of herbivores and parasitoids. Furthermore, we recorded field data of plant diversity in addition to herbivore and parasitoid abundance at 77 grassland sites in three different regions in Germany in order to elucidate whether our laboratory results reflect the field situation. As a model system we used the herb Plantago lanceolata, the herbivorous weevil Mecinus pascuorum, and its larval parasitoid Mesopolobus incultus. The laboratory bioassays revealed that both the herbivorous weevil and its larval parasitoid can locate their host plant and host via olfactory cues even in the presence of non-host odour. In a newly established two-circle olfactometer, the weeviĺs capability to detect host plant odour was not affected by odours from non-host plants. However, addition of non-host plant odours to host plant odour enhanced the weeviĺs foraging activity. The parasitoid was attracted by a combination of host plant and host volatiles in both the absence and presence of non-host plant volatiles in a Y-tube olfactometer. In dual choice tests the parasitoid preferred the blend of host plant and host volatiles over its combination with non-host plant volatiles. In the field, no indication was found that high plant diversity disturbs host (plant) location by the weevil and its parasitoid. In contrast, plant diversity was positively correlated with weevil abundance, whereas parasitoid abundance was independent of plant diversity. Therefore, we conclude that weevils and parasitoids showed the sensory capacity to successfully cope with complex vegetation odours when searching for hosts.     

Nutritional Effects on the Appearance of Canola and its Attractiveness to the Cabbage Seedpod Weevil

To investigate visual cues as a mechanism to explain phytophagous insect intraspecific host selection and to explain the effects of plant nutrition on visual cues associated with host selection we assessed the response of the cabbage seedpod weevil, Ceutorhynchus obstrictus, to plants of canola (oilseed rape), Brassica napus supplied with varied nitrogen (N) rates and sulfur to nitrogen (S:N) ratios. We assessed the effects of these treatments on B. napus appearance using photography and spectrophotometry. Plant nutrition had a significant effect on C. obstrictus; host plant attractiveness declined with increasing S:N ratios. We found strong evidence that attractiveness of host plants to C. obstrictus was mediated by several components of B. napus appearance supporting the role of visual cues in intraspecific host selection.     

Rates of progress up odour plumes by tsetse flies: a mark-release video study of the timing of odour source location by Glossina pallidipes

Abstract. The arrival of individually marked Glossina pallidipes Austen at a host odour source after their video-timed release from 30–75 m downwind was measured in the field in Zimbabwe. In the absence of odour, the proportion recaptured was <2% (= - random expectation); when synthetic ox odour was released, the probability of recapture at the source increased with proximity of release, from 6% at 75 m to 21% at 30 m (about twice this number arrived within ∼2 m of the source). There were two distinct distributions of recaptures: a 'fast' cohort which found the source within 40 s, and a 'slow' cohort which took from one to >20 min, with ∼50% of the flies in each cohort. The fastest flies probably reached the source in a single, mainly straight flight from take-off, at an overall average (straight line) displacement speed of 2.8-4.5 ms^-1 (i.e. close to the preferred flight speed of ∼5 m s^-1). The flies apparently maintained their ground speed largely independent of the wind speed they headed into. The 'slow' cohort had a constant probability of arrival at the source, presumably after losing and re-contacting the plume, and after having stopped at least once on the way. There were no marked correlations with wind parameters, although the probability of recapture increased slightly with the directness of the wind from the source, and the probability of 'slow' flight increased slightly with wind speed. It is inferred that a repeated sequence of anemotactic 'aim-then-shoot' orientation at take-off plus optomotor-steered in-flight correction of direction is used as a form of biassed random walk to bring the flies close to the odour source, rather than the use of moth-type anemotactic zigzagging.     

Flower and fruit volatiles assist host‐plant location in the Tomato fruit fly Neoceratitis cyanescens

Mature females of the tomato fruit fly Neoceratitis cyanescens can detect host fruit at a short distance using only visual stimuli, but little is known about the role of airborne volatile cues in the host searching strategy. A series of experiments is conducted in a laboratory wind tunnel, in which the behavioural responses of individual flies to volatiles from Solanaceae host plants (including tomato Lycopersicum esculentum Mill., bug weed Solanum mauritianum Scop. and Turkey berry Solanum torvum Sw.) are observed, according to some environmental (air speed) and physiological (age and mating status of females, time of day) factors. Mature females respond primarily to specific olfactory cues from blends of flowers or host fruit, preferentially unripe fruit for bug weed, as opposed to ripe fruit for Turkey berry or tomato. Males are also highly attracted by the odour of unripe fruit of bug weed. Wind plays a key role, as shown by the proportion of flies that reach the upwind section of the tunnel in the presence of both fruit odour and air flow (66.7%) and in the absence of either fruit odour (13.3%) or wind (36.7%). In response to fruit volatiles carried by wind, flies embark in a ‘plume tracking’ or ‘aim and shoot' flight, consistent with odour‐conditioned anemotaxis. Females respond to host fruit odour regardless of their age, egg load or mating status, and also more consistently in the afternoon, which is their preferential time of day for egg‐laying. Searching behaviour and response to host volatiles in N. cyanescens are discussed in the light of host‐finding and an adaptive strategy.     

Oriented responses of the triatomine bugs Rhodnius prolixus and Triatoma infestans to vertebrate odours on a servosphere

Oriented responses of both R. prolixus and T. infestans adults were recorded on a servosphere to mouse-odour, one of its components (CO₂), and to rabbit urine-odour. The volatiles were delivered in an air-stream under controlled conditions which excluded other sensory modalities. In stimulus-free air the triatomines walked preferentially downwind in straight bouts interrupted by stops or periods at relatively low speeds, all of variable duration. In odour-laden air, bugs maintained their typical walking habit but switched from negative to positive anemotaxis. The characteristic response to odour onset was to stop, sample the air with the antennae, turn upwind in situ, and then walk off in the direction of the source for at least a few seconds, i.e., odour mediated anemotaxis. Mouse-odour caused T. infestans to increase its speed to 5.3 cms^-1. Both species continued with the upwind response for some time after odour delivery ceased, but the crosswind component of the tracks was more prominent during this period — an effort, we presume, by the bugs to re-contact an odour plume. This investigation provides unequivocal evidence for host finding in triatomines by olfactory cues alone.     

Cold hardiness and overwintering survival of the cabbage seedpod weevil,Ceutorhynchus obstrictus

The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), is a serious pest of brassicaceous crops in temperate regions and a chronic member of the pest complex that attacks canola in Canada. We conducted several laboratory and field experiments to quantify winter survival and its role in the population dynamics of this insect. We estimated the supercooling point of the weevil at ?7 °C and its survival over 8 weeks decreased significantly at ?5 °C relative to 5 °C, but extending the overwintering period at 5 °C to 18.5 weeks had no effect on mortality. Cumulative sub‐freezing degrees estimated from air temperature, and especially from soil temperature, were highly correlated with weevil survival. Our linear regression model predicted poor survival of the weevils in typical winters in northern Alberta. Our results indicate that if milder winters prevail, as predicted by global warming, there is potential for the weevils to establish and become a serious pest in northern canola‐growing regions of Canada.     

Upwind flight of tsetse (Glossina spp.) in response to natural and synthetic host odour in the field

Abstract. In Zimbabwe, studies were made of the flight responses of tsetse ( Glossina spp.) to synthetic and natural ox odour using arrangements of electric nets.Tsetse flying away from a target showed a significant upwind bias when a blend of carbon dioxide (2/1 min), acetone (500 mg/h), octenol (0.4 mg/h), 4-methylphenol (0.8 mg/h) and 3-n-propylphenol (0.1 ma) was dispensed 15 m upwind, with c. 35% flying upwind.Without carbon dioxide this percentage was significantly reduced to 15% which was not significantly different from that with no odour (8%).This pattern was not altered by reducing the doses of acetone, octenol and phenols by 10–100 times, to levels comparable to those produced by an ox.With natural ox odour or a synthetic equivalent of ox odour dispensed from a ventilated pit 8 m upwind of the target, c. 28% flew upwind.This was reduced significantly to 15% if carbon dioxide was removed.In studies using a 17 m line of nets arranged orthogonally across the prevailing wind line, c. 50% of the catch was caught on the downwind side in the absence of odour.This increased significantly to c.60% when acetone, octenol and phenols were dispensed 15 m upwind, with or without carbon dioxide.With a shorter line (9 m) or an incomplete one (16.5 m long with 5 times 1.5 m wide gaps along its length) there was no change in the proportion caught downwind.For all three lines, dispensing odour upwind increased the catch 2–5 times on both the up-and downwind sides of the nets.It is concluded that a stronger upwind response to host odour is elicited when carbon dioxide is present.It is suggested that in nature upwind flight is very imprecisely orientated, with tsetse making flights up and down an odour plume 'searching' for a host.     

Flight activity and dispersal of the cabbage seedpod weevil (Coleoptera: Curculionidae) are related to atmospheric conditions

The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), is an invasive pest of canola (Brassica napus L. and Brassica rapa L.) in western Canada. Under current climatic conditions, C. obstrictus is spreading from established populations in southwestern Alberta at ≈ 55 km/yr. We studied the influence of climatic conditions on C. obstrictus flight behavior in 2007 and 2008 and eastward dispersal from the western border of Saskatchewan from 2002 to 2007. Positive linear relationships between increases in mean temperature and flight height and between greater mean maximum temperature and expanded dispersal distances were significant. Increases in relative humidity were associated with reduced flight heights and dispersal distances. We developed models that predict the relationships of temperature and relative humidity with flight height and with dispersal distance. We also discuss implications for C. obstrictus dispersal under current climatic conditions and in the context of predicted climate change.     

Influence of host log age and refuge from natural enemies on colonization and survival of Phoracantha semipunctata

The pine cone weevil, Pissodes validirostris Gyll. (Coleoptera: Curculionidae), attacks seed cones of most Eurasian pine species, except these of Swiss stone pine (Pinus cembra L.). Behavioural responses of adult weevils to cone volatile emissions of Swiss stone pine and to those of a common host, mountain pine (Pinus uncinata Ram.), were compared in an olfactometer. Weevils were significantly attracted by the volatile blend emitted by mountain pine, but Swiss stone pine volatiles elicited an inverse response, with most weevils moving in the opposite direction to the odour source. However, the majority of second instar weevil larvae that were extracted from mountain pine cones and transferred into Swiss stone pine cones were capable of developing to the adult stage. This suggests that Swiss stone pine cones do not contain strong feeding deterrents that could prevent larval development. The possible factors involved in the absence of colonization of Swiss stone pine cones by cone weevils are discussed.