A field test for host fruit odour discrimination and avoidance behaviour for Rhagoletis pomonella flies in the western United States

Prezygotic isolation due to habitat choice is important to many models of speciation-with-gene-flow. Habitat choice is usually thought to occur through positive preferences of organisms for particular environments. However, avoidance of non-natal environments may also play a role in choice and have repercussions for post-zygotic isolation that preference does not. The recent host shift of Rhagoletis pomonella (Diptera: Tephritidae) from downy hawthorn, Crataegus mollis, to introduced apple, Malus domestica, in the eastern United States is a model for speciation-with-gene-flow. However, the fly is also present in the western United States where it was likely introduced via infested apples ≤ 60 years ago. R. pomonella now attacks two additional hawthorns in the west, the native C. douglasii (black hawthorn) and the introduced C. monogyna (English ornamental hawthorn). Flight tunnel tests have shown that western apple-, C. douglasii- and C. monogyna-origin flies all positively orient to fruit volatile blends of their respective natal hosts in flight tunnel assays. Here, we show that these laboratory differences translate to nature through field-trapping studies of flies in the state of Washington. Moreover, western R. pomonella display both positive orientation to their respective natal fruit volatiles and avoidance behaviour (negative orientation) to non-natal volatiles. Our results are consistent with the existence of behaviourally differentiated host races of R. pomonella in the west. In addition, the rapid evolution of avoidance behaviour appears to be a general phenomenon for R. pomonella during host shifts, as the eastern apple and downy hawthorn host races also are antagonized by non-natal fruit volatiles.     

An Easy Method to Test Odour Recognition in Songbird Hatchlings

We describe an easy method to test odour detection and recognition in 1‐d‐old zebra finch hatchlings (Taeniopygia guttata). Day‐old chicks beg in a stereotypical posture, which can be induced by directing gentle puffs of air from a plastic wash bottle near the face. We used this method to experimentally test whether begging duration of chicks was indicative of nest odour recognition. We manipulated the olfactory environment of 12 nests throughout incubation and hatching with either an artificial odour (orange oil) or with a neutral control (tap water). We then presented these two stimulus odours to 25 day‐old chicks and measured the duration of the first begging bout exhibited for each odour. Zebra finches hatched in a nest environment enriched with orange oil scent begged significantly longer when exposed to orange oil odour, compared to control hatchlings. Our simple testing procedure can be used to efficiently quantify odour recognition and/or preference in altricial songbirds at a very early developmental stage.     

Odour boosts visual object approach in flies

Multisensory integration is synergistic—input from one sensory modality might modulate the behavioural response to another. Work in flies has shown that a small visual object presented in the periphery elicits innate aversive steering responses in flight, likely representing an approaching threat. Object aversion is switched to approach when paired with a plume of food odour. The ‘open-loop’ design of prior work facilitated the observation of changing valence. How does odour influence visual object responses when an animal has naturally active control over its visual experience? In this study, we use closed-loop feedback conditions, in which a fly''s steering effort is coupled to the angular velocity of the visual stimulus, to confirm that flies steer toward or ‘fixate’ a long vertical stripe on the visual midline. They tend either to steer away from or ‘antifixate’ a small object or to disengage active visual control, which manifests as uncontrolled object ‘spinning’ within this experimental paradigm. Adding a plume of apple cider vinegar decreases the probability of both antifixation and spinning, while increasing the probability of frontal fixation for objects of any size, including a normally typically aversive small object.     

Amino acid increases in fruit infested by fruit flies of the family Tephritidae

Solanum mauritianum Scop, (wild tobacco) fruit is the major host of the fruit fly Dacus cacuminatus (Hering), and is a major source of food for the brown pigeon Macropygia phasianella (Temminck) in eastern Queensland. Amino acid analyses were undertaken on fruit fly infested and uninfested S. mauritianum fruits. Infested fruits contained approximately twice the level of protein and essential amino acids compared to uninfested fruit. This increase is probably due to the plant adding additional amino acids to infested tissue and the accompanying growth of bacteria established in the fruit during oviposition. The infested fruit would provide a valuable source of protein during the pigeon breeding season.     

Odour movement, wind direction, and the problem of host-finding by tsetse flies

ABSTRACT. Movement of host odour was modelled in natural tsetse habitats with smoke and ultra-light 7-cm-long wind vanes; the speed and direction of the air movements were analysed from video recordings thereof. Wind of <1 ms^-1 did not move in straight lines, since large packets of air (>10 m across) often changed direction together. The rate of this change of direction (meander) correlated negatively with windspeed. In open woodland with a shrubby understorey (in which windspeed was reduced by a factor of >5 from that above the canopy, to ax 0.3 m s^-1), this wind meander fell by 2d? s^-1 change of direction for each 0.1 m s^-1 increase in windspeed (r²=0.96). Over open ground without shrub cover, the meander fell by 0.5d? s^-1 per 0.1 m s^-1 increase in windspeed (r²=0.85). In both situations, such meandering virtually ceased in winds of > 1 m s^-1. In woodland, the relationship between the direction of air movement near the surface of bare earth (one potential tsetse landing site) and that c. 0.5 m above ground level (flight height) was often weak (r²=0.2-0.4), but this problem would be reduced if the fly averaged the ground-level wind for at least 30 s. Odour (smoke) travelling from a source 15 m ‘upwind’ over open ground arrived at a notional tsetse fly for 80% of the time from a direction within 10d? of the true source direction. In typical tsetse woodland, however, the ‘odour’ arrived from all directions (including >90d? away from the source), with only a 30% bias towards the true source direction (±10d?). Evidently, tsetse must navigate up odour plumes by means that get round these difficulties-simple, moth-type upwind anemotaxis alone seems unlikely to be adequate.     

Electronic traps for detection and population monitoring of adult fruit flies (Diptera: Tephritidae)

During the last decades, the economic importance of tephritid fruit flies (FF) has increased worldwide because of recurrent invasions and expansions into new areas, and reduced control capabilities of current control systems. Efficient monitoring systems, thus, are required to provide fast information to act promptly. With this aim in mind, we developed two electronic trap (e‐trap) versions for adult FF: one with specific volatiles for male and female adult Ceratitis capitata, and the second, based on the attraction of adult FF to yellow colour, targeting Dacus ciliatus, Rhagoletis cerasi and Bactrocera oleae. In the case of B. oleae, the female pheromone and ammonium bicarbonate were added as synergists. In the two versions, attracted FF were retained in the trap on glued surfaces. Real‐time images of the surfaces were automatically taken and transmitted to a server. We tested the two e‐trap versions in insect‐proof cages, where flies were released and recaptured, and in commercial orchards throughout the Mediterranean: C. capitata in peach orchards in Italy; R. cerasi in cherry orchards in Greece; B. oleae in olive orchards in Spain and in Greece; and D. ciliatus in melons in plastic tunnels in Israel. The e‐trap showed excellent abilities to transmit real‐time images of trapped FF and a high specificity for trapping different FF species. The ability of the entomologist to correctly classify FF from images in the office was >88%. In addition, average number of flies/trap in e‐trap grids did not differ from numbers reported on grids of conventional traps that were operating simultaneously. The e‐traps developed and tested in this study provide the basis for the real‐time monitoring of FF were no olfactory attractants are available, and for the surveillance of alien FF incursions where generic, but not specific, olfactory attractants exists.     

Declination affects geomagnetic field-modulated geotaxis in fruit flies

Decades of research have established that the Earth’s magnetic field (geomagnetic field, GMF) is broadly used as a sensory cue for magnetic orientation in various animal taxa, including insects. In contrast to the investigation of the total intensity or inclination of the GMF, the effect of declination on horizontal magnetic movement has been explored in a few species, including flies, cockroaches, and dogs. However, the potential role of declination in the vertical movement in magnetosensitive organisms is yet to be reported. In this study, we provide the first evidence that declination within a natural range of change can affect static geotaxis in fruit flies, as assessed using the tube-positioning assay. In open-field measurements conducted at 22 domestic and foreign locations, the variation in declination was notably dependent upon the specific location, regardless of altitude, with similar variation in total intensity. Flies subjected to a geographic range of declination under the same total intensity and inclination exhibited remarkably different geotactic positioning scores, irrespective of GMF polarity. Notably, we observed a significant negative correlation between the geotactic score and the absolute value of declination, indicating that declination can induce negative geotaxis effects in flies. These results reveal that flies have evolved to incorporate a declination compass into their multimodal sensorimotor system and suggest that declination may be complementary to gravity in terms of environmental factor-driven negative geotaxis in flies.     

实蝇肠杆菌科共生菌的研究进展

实蝇与体内微生物的共生关系是目前较受关注的研究课题。其中,肠杆菌科细菌是这些内共生微生物中的重要一类,广泛存在于实蝇肠道和生殖系统中。研究证明,共生肠杆菌科细菌在参与实蝇的碳氮循环、营养代谢、生殖免疫及生物防治等方面都发挥着极大的作用。近年来,人们利用分子生物学技术已鉴定出部分实蝇内共生肠杆菌科细菌的类群,发现许多优势的益生肠杆菌种和代谢产物,它们能增强实蝇的健康,提高昆虫不育技术的应用高效性。本文对实蝇共生肠杆菌科细菌的种类、分布和作用,以及它们在不育昆虫技术中的应用进展作一综述,这不仅有助于人们更深入地了解宿主与共生菌群落间的互作关系,而且对人类开发新型实蝇防治饵剂以及将此类共生益生菌应用于实蝇不育技术有重要意义。     

Laboratory evaluation of interspecific mating between Zeugodacus fruit flies and Bactrocera dorsalis

The increasing number of tephritid pest invasions worldwide highlights the importance of interspecific interactions among tephritid pests. The melon fly [Zeugodacus cucurbitae (Coquillett)], the pumpkin fruit fly [Zeugodacus tau (Walker)], and the oriental fruit fly [Bactrocera dorsalis (Hendel)] (all Diptera: Tephritidae) are neotropical fruit flies with overlapping distributions. Their interactions during mating hours have rarely been observed in nature due to their nocturnal behavior. Here, laboratory studies were conducted under no-choice and choice conditions to quantify interspecific mating. The interactions during mating hours resulted in interspecific mating, which reduced conspecific mating success and interrupted mating activity patterns. Successful interspecific mating pairs of Z. cucurbitae and Z. tau were recorded in no-choice and choice tests. Interspecific mating between male Z. cucurbitae and female Z. tau significantly reduced conspecific mating in Z. tau. Observations of the diel mating activity patterns showed that male Z. cucurbitae initiated calling behaviors earlier than Z. tau males, giving Z. cucurbitae more chances to court Z. tau. Though males of neither Zeugodacus species formed mating pairs with B. dorsalis, Zeugodacus males reduced conspecific mating in B. dorsalis in the choice trials. Thus, interspecific interactions among Z. cucurbitae, Z. tau, and B. dorsalis affected conspecific mating; interrupted conspecific mating activity patterns were recorded in all three species. This information could be used to improve management practices.     

A geomagnetic declination compass for horizontal orientation in fruit flies

The Earth's geomagnetic field (GMF) is known to act as a sensory cue for magnetoreceptive animals such as birds, sea turtles, and butterflies in long‐distance migration, as well as in flies, cockroaches, and cattle in short‐distance movement or body alignment. Despite a wealth of information, the way that GMF components are used and the functional modality of the magnetic sense are not clear. A GMF component, declination, has never been proven to be a sensory cue in a defined biological context. Here, we show that declination acts as a compass for horizontal food foraging in fruit flies. In an open‐field test, adopting the food conditioning paradigm, food‐trained flies significantly orientated toward the food direction under ambient GMF and under eastward‐turned magnetic field in the absence of other sensory cues. Moreover, a declination change within the natural range, by alteration only of either the east–west or north–south component of the GMF, produced significant orientation of the trained flies, indicating that they can detect and use the difference in these horizontal GMF components. This study proves that declination difference can be used for horizontal foraging, and suggests that flies have been evolutionarily adapted to incorporate a declination compass into their multi‐modal sensorimotor system.     

Learning affects mate choice in female fruit flies

Learning in the context of mate choice can influence sexualselection and speciation. Relatively little work, however, hasbeen conducted on the role of learning in the context of matechoice, and this topic has been mostly ignored in insects eventhough insects have served as a prime model system in researchon sexual selection and incipient speciation. Extending recentwork indicating apparently adaptive learning in the contextof sexual behavior by male fruit flies (Drosophila melanogaster),I tested for the effect of learning on mate choice by femalefruit flies. Compared to young virgin females that experiencedcourtship by large males, young virgin females that experiencedcourtship by small males were more likely to mate with smalland large males in a test conducted a day after the experiencephase. These results, which are the first clear empirical demonstrationof learning in the context of mate choice by female insects,lay the foundation for research on the role of learning in insectsexual selection and speciation.     

Odour learning and decision-making during food collection in the leaf-cutting antAcromyrmex lundi

Summary Recruited workers of the leaf-cutting antAcromyrmex lundi learn the odour of the food fragment initially carried by a successful scout, and use this cue as a decision criterion during food collection. Citral, a natural deterrent odour, can also be associated as a food signal, showing how powerful olfactory learning is in this species. The role of both food-odour learning and a previously reported leaf-marking pheromone during diet selection by leaf-cutting ants is discussed.     

An effective trapping method for field studies of opiine braconid parasitoids of tephritid fruit flies

A simple but effective trap for conducting field studies with opiine braconid parasitoids of fruit fly larvae was designed from yellow plastic balls containing an internal odor source and coated on the exterior with Tanglefoot. Tests of the trap in large field cages showed that it was simpler to use, less expensive, and more effective than previously reported designs.      

Male fruit flies learn to avoid interspecific courtship

Experimental data suggest, and theoretical models typicallyassume, that males of many fruit flies (Drosophila spp) areat least partially indiscriminate while searching for mates,and that it is mostly the females who exert selective mate choice,which can lead to incipient speciation. Evidence on learningby male D. melanogaster in the context of courtship, however,raises the possibility that the initially indiscriminate malesbecome more selective with experience. I tested this possibilityby comparing the courtship behavior of male D. melanogasterexperienced at courting females of the closely related species,D. simulans, and inexperienced males. I found that comparedwith the inexperienced males, the males experienced with courtingD. simulans females showed significantly lower courtship towardfemale D. simulans. Both male treatments, however, showed virtuallyidentical courtship durations with female D. melanogaster. Theseresults indicate that male fruit flies adaptively refine theircourtship behavior with experience and suggest that the malescontribute more to assortative mating and incipient speciationthan is commonly assumed.     

Conditioning odor-shock associations in the black blowfly,Phormia regina

Discriminative classical conditioning of an olfactory avoidance response was demonstrated in the blowfly, Phormia regina.Learning indices were calculated as the fraction of flies avoiding the CS+ (conditioned stimulus paired with electric shock reinforcement) minus the fraction of flies avoiding the CS-(conditioned stimulus not paired with electric shock), averaged over two different groups of flies, in which reciprocal odors were used as the CS+. Avoidance responses to both odors presented simultaneously at a T-maze choice point yielded mean learning indices of zero for naive flies or pseudoconditioned (shock alone) or sensitized (odors alone) controls. In contrast, pairing an odor with electric shock produced a mean learning index significantly greater than zero. These results are similar to those reported for Drosophila melanogaster.Blow flies, however, showed much lower levels of associative learning than fruit flies.     

实蝇共生菌研究进展

实蝇类昆虫(双翅目Diptera:实蝇科Tephritidae)是重要的农业害虫,为害农作物茎秆和水果,严重影响农业生产和果蔬贸易,被许多国家列为重要的检疫性有害生物。实蝇共生菌对宿主实蝇的取食、生殖、发育及环境适应能力具有重要作用。目前,已有21个属的共生细菌(Enterobacter、Klebsiella、Citrobacter、Pseudomonas、Providencia、Erwinia、Acetobacter、Serratia、Proteus、Hafnia、Cedecea、Arthrobacter、Lactobacillus、Micrococcus、Streptococcus、Staphylococcus、Vibrio、Hafnia、Deinococcacea、Bacillus、Wolba-chia)以及1个属的共生真菌(Candida)被鉴定。其中,肺炎杆菌Klebsiella pneumoniae、产酸克雷伯氏菌Klebsiella oxytoca、成团泛菌Pantoea agglomerans、费氏柠檬酸杆菌Citrobter freundii、阴沟肠杆菌Enterobacter cloaca...     

雌性根田鼠断奶后对亲本尿气味的记忆

为研究亲子分开后雌性根田鼠对亲本气味的记忆持续时间,分别在未分开(20日龄)、分开10d(30日龄)、20d(40日龄)、30d(50日龄)、40d(60日龄)时,以新鲜尿作气味源,在行为观察箱中记录雌性根田鼠对不同气味源的行为响应模式,结果表明(1)未分开时,雌鼠遭遇父本气味时自我修饰的频次极显著高于陌生雄鼠气味,在分开10d时,雌鼠接近父本气味的频次显著多于接近陌生雄鼠气味的频次,其对前者反标记显著少于后者;(2)分开20d后,雌鼠对父本和陌生雄鼠气味的行为响应无明显差异;(3)未分窝时,雌性根田鼠幼仔对母本和陌生雌鼠气味的行为响应无差异;(4)分开10—40d时,雌性根田鼠对母本和陌生雌鼠气味表现出不同的行为响应模式。以上结果表明,在亲子分开10d时,雌鼠仍能识别父本和陌生雄鼠的气味;分开20d后,雌鼠不再能够识别父本和陌生雄鼠的气味;在亲子分开40d时,雌鼠仍能识别母本和陌生雌鼠的气味。因此,雌鼠对父本气味的嗅觉记忆时间可以持续到亲子分开10—20d之间;而对母本气味的嗅觉记忆时间则可以持续到亲子分开40d以上。     

Geographic variation in fruit volatiles emitted by the hawthorn Crataegus mollis and its consequences for host race formation in the apple maggot fly,Rhagoletis pomonella

The shift of the apple (AP) maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), from its ancestral host downy hawthorn, Crataegus mollis (DH) (Torr. & A. Gray) Scheele, to introduced domesticated AP, Malus domestica Borkh. (both Rosaceae), is a model for ecological divergence and incipient sympatric speciation with gene flow. However, a portion of the variation contributing to the sympatric host shift from DH to AP appears to have a different biogeographic history, pre‐dating the shift. One potential source of standing variation may trace to a number of different native hawthorn species infested by R. pomonella in the southern USA, where the AP‐attacking race is absent. Herein, we investigate this possibility for the southern red hawthorn (SR) endemic to Texas, Crataegus mollis var. texana (Buckl.), which has been described as a member of the Molles series that includes the more northern distributed DH. We report results from chemical analyses of host fruit volatiles, fly behavioural responses to synthetic fruit blends, and microsatellite surveys of fly populations, implying that R. pomonella infesting SR may behaviourally and genetically represent a native host race differing from the DH‐infesting fly. No fly reared from SR responded to AP fruit volatiles in flight tunnel assays. However, coupled gas chromatographic‐electroantennographic detection (GC‐EAD) profiles for SR fruit contain all five of the component esters that comprise the standard AP volatile blend inducing behavioural orientation for AP‐infesting flies, compounds that appear to be largely missing from volatile profiles for DH fruit. Thus, SR‐infesting flies do not represent a source for a preassembled AP‐accepting phenotype. However, they may help explain why the ancestral DH race that shifted to AP in the northeastern USA had the ability to recognize AP fruit esters, potentially enabling the shift to AP. Our results highlight how categorizing speciation into different geographic modes may not adequately describe the evolutionary origins of important genetic variation fuelling adaptive radiation and the genesis of new biodiversity.