Apple and peach fruit volatiles and the apple constituent butyl hexanoate attract female oriental fruit moth, Cydia molesta, in the laboratory

Volatiles emitted from immature and mature peach and apple fruits were all attractive to mated female oriental fruit moth, Cydia molesta (Busck), in a dual choice arena. Females did not discriminate between odours emitted by these two major host plants. The same natural blends were behaviourally ineffective for virgin females. A major component of apple fruit volatiles, butyl hexanoate, also attracted female C. molesta. Mated females were attracted to two medium dosages, while virgin females responded positively to the lowest of the five dosages tested. The time course of the captures of the moths shows a diurnal activity cycle known from the field. The possible implications of a semiochemical which attracts females are discussed in the context of previous findings that gravid females may immigrate from peaches into apple orchards particularly in the later phase of the season.     

Electrophysiological and behavioral response of the oriental fruit moth <Emphasis Type="Italic">Grapholita</Emphasis><Emphasis Type="Italic">molesta</Emphasis> (Busck, 1916) (Lepidoptera: Tortricidae) to the volatiles of apple fruits at different stages of development

The oriental fruit moth, Grapholita molesta, occurs in Southern Brazil throughout the year, and migrates from peach to apple orchards. Because moths rely on volatile organic compounds (VOCs) during the host-location process, variations in the emission of these compounds during fruit maturation can influence the time of infestation and preference of the moths for a particular genotype. The aim of this work was to identify VOCs emitted by the apples “Eva” and “Gala” at different stages of development and to determine the behavioral and electrophysiological responses of G. molesta to these compounds. For this purpose, VOCs from immature, maturing, and mature fruits of both cultivars were collected and analyzed by gas chromatography and gas chromatography-mass spectroscopy. The response of the antennae of virgin males and females and mated females to volatiles released by the three fruit stages was registered by gas chromatography coupled to an electroantennography. A dual-choice behavioral test for the different combinations of insect groups and fruit stage was also performed. Amongst the volatiles released by mature fruits, twelve compounds elicited a response. The antennae of the oriental fruit moth did respond to isoamyl hexanoate and α-farnesene emitted by “Eva” maturing fruits. In general, virgin females did not respond to volatiles in olfactometer bioassays and mated females were attracted to volatiles released by mature fruits. Our results show that the variation in the emission during the maturation of fruits can influence the orientation of G. molesta.     

Larval performance of the oriental fruit moth across fruits from primary and secondary hosts

A common characteristic of many invasive herbivorous insects is their ability to utilize a broad range of host plants. By using various hosts in phenological succession, multivoltine herbivores may increase the number of successful annual generations, at the same time as potentially increasing their overall fitness. To achieve such success, herbivores must be able to develop efficiently on the nutritional resources offered by their hosts. The oriental fruit moth Cydia (= Grapholita) molesta (Busck) (Lepidoptera: Tortricidae) is one of the most damaging invasive insect species. Peach (Prunus persica) is its primary host, whereas the pome fruits apple (Malus × domestica Borkh) and pear (Pyrus communis) are considered as secondary hosts. In many parts of its geographical range, including southern Europe, populations of the moth switch from peach to apple or pear orchards during the growing season. The present study tests whether this temporal switch is supported by the physiological capability of the larvae with respect to developing efficiently on fruits of these taxonomically‐related host plants. Larvae are reared on peach, apple or pear fruits; several life‐history traits are measured; and correlations between the traits are calculated. The results obtained show that larvae do not have the same physiological capability with respect to using apple or pear fruits as hosts compared with using peach fruit. Pear fruit in particular is a sub‐optimal diet. These findings suggest that, in the case of continuous geographical expansion, concomitantly with global warming, apple orchards might support oriental fruit moth populations better than pear orchards, and that the switch onto novel hosts might be accompanied by restricted population growth.     

Olfactory responses of Grapholita molesta to different developmental stages of immature fruit of peach,plum, and apple

The Oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), is known to shift its host use from stone fruits (the primary hosts) to pome fruits (secondary hosts) as the season progresses. Grapholita molesta recognizes potential hosts by semiochemicals from fruits, but few studies have addressed the olfactory responses of G. molesta to host fruits during the seasonal transition of the moth from stone to pome fruits. So, we investigated the olfactory responses of larvae and gravid females of G. molesta to different fruit stages (collected on May 31, June 11, and June 25) of immature peach, plum, and apple fruits, using both multiple and two choice tests. In the multiple choice tests, for fruits collected after June 11, larvae showed a significant preference for peach as their first choice, compared to plum or apple. The final choice rate (when larvae had stayed on the fruit for more than 1 h) of larvae was also highest for peach fruits collected on June 11 and June 25. In two choice tests (Y-tube test), the response rate and overall choice rate of larvae and mated ovipositing adult females were also highest on peaches collected on May 31 (larvae) and June 25 (adults), respectively. In conclusion, we found that both the adults and larvae of G. molesta were highly attracted to immature peach fruits in laboratory choice tests.     

High Genetic Diversity and Structured Populations of the Oriental Fruit Moth in Its Range of Origin

The oriental fruit moth Grapholita ( = Cydia) molesta is a key fruit pest globally. Despite its economic importance, little is known about its population genetics in its putative native range that includes China. We used five polymorphic microsatellite loci and two mitochondrial gene sequences to characterize the population genetic diversity and genetic structure of G. molesta from nine sublocations in three regions of a major fruit growing area of China. Larval samples were collected throughout the season from peach, and in late season, after host switch by the moth to pome fruit, also from apple and pear. We found high numbers of microsatellite alleles and mitochondrial DNA haplotypes in all regions, together with a high number of private alleles and of haplotypes at all sublocations, providing strong evidence that the sampled area belongs to the origin of this species. Samples collected from peach at all sublocations were geographically structured, and a significant albeit weak pattern of isolation-by-distance was found among populations, likely reflecting the low flight capacity of this moth. Interestingly, populations sampled from apple and pear in the late season showed a structure differing from that of populations sampled from peach throughout the season, indicating a selective host switch of a certain part of the population only. The recently detected various olfactory genotypes in G. molesta may underly this selective host switch. These genetic data yield, for the first time, an understanding of population dynamics of G. molesta in its native range, and of a selective host switch from peach to pome fruit, which may have a broad applicability to other global fruit production areas for designing suitable pest management strategies.     

Stimuli affecting selection of oviposition sites by female peach twig borer, Anarsia lineatella Zeller (Lepidoptera: Gelechiidae)

In laboratory and field experiments, stimuli were tested that might affect oviposition decisions by female peach twig borer moths, Anarsia lineatella Zeller (Lepidoptera: Gelechiidae). When given a choice between immature green peach fruits, green mature peach fruits and soft-ripe peach fruits, the latter received the fewest eggs. Fuzzy halves of peach fruits received ten times more eggs then shaved hairless halves. Volatiles from both almond and peach shoots induced more oviposition by females than by control stimuli. Similarly, volatiles from immature green peach fruits, mature green or mature hard-ripe peach fruits induced more oviposition than their respective control stimuli. In a choice experiment, volatiles from immature peach fruit stimulated three times more oviposition than those from soft-ripe peach fruit. Discrimination against mature soft-ripe peach fruits as potential oviposition sites may lie in the phenology of A. lineatella and host peach fruits. Larval development to the pupal stage takes 15–27 days. Therefore, any eggs laid on a ripe fruit 14 days before it falls from the tree will not likely develop into adult insects because developing larvae will only reach third or fourth instar before the fruit is decomposed, and only first and second instar larvae can overwinter.     

Mating disruption barriers in pome fruit for improved control of oriental fruit moth Grapholita molesta Busck (Lep., Tortricidae) in stone fruit under mating disruption

Oriental fruit moth (OFM) Grapholita molesta Busck (Lep., Tortricidae) is a very important pest in commercial orchards in Victoria, Australia. Pheromone‐mediated mating disruption (MD) applied in stone fruit orchards successfully controlled OFM populations for many years, but damage to shoot tips and fruit at the edge of peach blocks located adjacent to pear blocks under insecticide treatments has become problematic. To improve protection of stone fruit against edge damage and outbreaks of OFM, all orchards were treated with sex pheromone dispensers for MD on an area‐wide basis. Area‐wide MD treatment, including all pome and stone fruit orchards in a discrete area, successfully controlled edge infestations of OFM, but was expensive. To reduce the cost of OFM control, sex pheromone dispensers for MD were applied as barrier treatments to 54–60 m of neighbouring pears adjacent to peaches under MD. Detailed monitoring of the OFM population, shoot tip and fruit damage assessments indicated that application of MD barriers on pears during two consecutive seasons provided sufficient control of OFM on peaches. This MD barrier treatment was able to reduce the number of OFM caught in all experimental peach blocks, with damage to shoot tips and fruit giving similar results to MD treatment of the whole neighbouring pear block. Extending the MD treatment area for 54–60 m into the neighbouring pear block significantly reduced the edge damage in MD‐treated peaches in the first season and almost eliminated OFM damage in the second season.     

果实种类及发育阶段对梨小食心虫幼虫钻蛀率和蛹重的影响

【目的】明确梨小食心虫Grapholitha molesta在寄主果实上的钻蛀率和蛹重与寄主种类和果实发育阶段的关系,为其田间预测预报和综合防控提供技术依据。【方法】在室内条件下测定了接卵后72 h梨小食心虫初孵幼虫在不同发育阶段的3个种共6个品种水果［苹果Malus pumila (嘎啦苹果), 桃Amygdalus persica (大久保毛桃、丰白毛桃和霞光油桃), 梨Pyrus bretschneideri (砀山酥梨和玉露香梨)］果实上的钻蛀率以及在不同果实状态的4个水果品种(大久保毛桃、丰白毛桃、砀山酥梨和玉露香梨)果实上72 h的钻蛀率;比较了接卵后24 h和72 h初孵幼虫在不同发育阶段的3个苹果品种(嘎啦苹果、富士苹果和金冠苹果)果实上的钻蛀率;并测定了不同发育阶段的金冠苹果、富士苹果、嘎啦苹果、砀山酥梨和丰白毛桃上的梨小食心虫蛹重。【结果】接卵后72 h梨小食心虫初孵幼虫在6个不同水果品种果实上的钻蛀率从高到低依次为：霞光油桃＞嘎啦苹果＞砀山酥梨＞玉露香梨＞大久保毛桃＞丰白毛桃;除霞光油桃外,其他5个水果品种果实的发育阶段显著影响初孵幼虫钻蛀率。对于嘎啦苹果,接卵后72 h初孵幼虫在其幼果上的钻蛀率最高(73.69%),在其着色期果实上钻蛀率最低(32.51%);在大久保毛桃、丰白毛桃、砀山酥梨和玉露香梨上,接卵后72 h初孵幼虫的钻蛀率均随果实生长发育而增加。初孵幼虫在3 个苹果品种着色期和成熟期果实上的钻蛀率随处理时间的增加而显著下降,而在其幼果上变化不显著。寄主种类及其发育阶段也显著影响梨小食心虫蛹重,成熟毛桃和梨饲养的雌、雄蛹重显著高于未成熟果实饲养的蛹重,着色期苹果不利于蛹重的增加。【结论】果实种类及发育阶段显著影响梨小食心虫初孵幼虫钻蛀率和蛹重,取食成熟期梨和桃的梨小食心虫初孵幼虫钻蛀率和蛹重显著高于取食未成熟果实的个体。     

Factors influencing adult male Grapholita molesta dispersal in commercial Malus and Prunus host crops

The oriental fruit moth (OFM), Grapholita molesta (Busck) (Lepidoptera: Tortricidae), has been an economic pest of apples (Malus spp.) and peaches (Prunus spp.; both Rosaceae) in the eastern USA since the 1930s. Successful management of G. molesta with insecticides requires careful timing of these products based on sex‐pheromone trap captures of male moths. In Pennsylvania, apple and peach orchards are often planted adjacently. Factors such as trap distance from release points, host crop, and wind were considered in relation to male moth movement within and between hosts. Our practical objective was to understand male G. molesta dispersal within and between these two hosts to achieve better management. Recapture of moths decreased over distance; the majority of moths were recaptured 50–100 m from the release point regardless of crop type. Male G. molesta released into commercial apple and peach orchards were most likely to remain in the crop of release and to not exhibit host shifts over the season, even after peach fruit were harvested. Our analyses of wind direction data with respect to recapture showed that the likelihood of recapture was similar regardless of the orientation of the traps relative to the mean wind direction at peak flight times. The apple and peach host crops appeared to affect male G. molesta dispersal to the extent that wind in orchards affects their perception of pheromone. Crop effects were most likely due to the traps closest to the release points being in the same crop as the release points.     

Effects of pear fruit-derived volatiles and their concentrations on the responses of oriental fruit moths

Grapholita molesta (Busck) is an important pest of pear trees. Numerous esters accumulate consistently in mature pear fruits. However, little is known about the effects of single esters from pear fruits at different concentrations on the responses of male and female G. molesta. In this study, the responses of virgin males, virgin females, and gravid females to five esters (3-methylbutyl acetate, ethyl hexanoate, ethyl butanoate, butyl acetate, and hexyl acetate) of pear fruits at three dosage levels (1, 5 and 10 μg/μL) were investigated using electroantennography (EAG), wind tunnel experiments, and field tests. Our results showed that ethyl butanoate (5 μg/μL) elicited higher EAG responses in virgin females and males than a mixture of all five volatiles, and elicited an equal EAG response to that for the mixture in gravid females, with all responses to ethyl butanoate and the mixture being higher than the response to hexane alone. For upwind flight, ethyl butanoate (5 μg/μL) excited equal moth flight–location behavior in virgin and gravid females to that for the mixture, which were both higher than the response to hexane. For close flight, ethyl hexanoate (5 μg/μL) and 3-methylbutyl acetate (10 μg/μL) appeared to be the activating compounds, eliciting equal responses from virgin females to that of the mixture, and higher responses of gravid females to that of the mixture, both of which were higher than the responses to hexane. Upwind and close flight responses of virgin males were lower than those of virgin and gravid females. In field trials, we verified that traps baited with ethyl butanoate (5 μg/μL) captured more moths than the other esters. Therefore, from the esters and concentrations tested, we recommend ethyl butanoate (5 μg/μL) for potential use as an attractant for G. molesta in orchards.     

Response of female oriental fruit moth to volatiles from apple and peach trees at three phenological stages

The attractiveness of peach ( Prunus persica L. Batsch) and apple ( Malus domestica L. Borkh.) (both Rosaceae) tissue to gravid female oriental fruit moth, Grapholita (=  Cydia ) molesta (Busck) (Lepidoptera: Tortricidae), was assessed at three distinct stages throughout the growing season using a dual-choice bioassay. Plant material offered to the female moths consisted of a plant shoot in early spring, before fruit became available. Later, it consisted of a leaf-bearing twig and a fruit, either alone or in combination. The level of attraction of the female moths to the various plant tissues varied substantially over time and according to the plant species. Before fruit became available, female moths were significantly attracted to peach as well as to apple shoots. During the early fruit growth stage, moths were attracted to a leaf-bearing twig originating from a peach tree, but not to that from an apple tree. In peach, it was the vegetative tissue that accounted for the attraction, whereas in apple, it was the reproductive tissue (a developing fruit). During the late fruit growth stage, both peach fruit and apple fruit were highly attractive, whereas a twig with leaves from either an apple or a peach tree was neither attractive nor repellent to the female moths. This changing female olfactory response to volatiles emitted by vegetative tissue and fruits from the two host plant species with progressing season is discussed with respect to the biology and the dispersal of this moth species.     

Synergism between aromatic compounds and green leaf volatiles derived from the host plant underlies female attraction in the oriental fruit moth

Blends of volatile compounds emitted by host plants are known to mediate the attraction of gravid female herbivores to oviposition sites, but the role of individual odor components is still little understood. We characterized the olfactory response of mated female Cydia (Grapholita) molesta (Busck) (Lepidoptera: Tortricidae) to synthetic mixtures of compounds emitted by peach shoot, a key host plant of this herbivore, and investigated the role of important constituents of bioactive mixtures in moth attraction. Relative ratios of constituents of the mixtures corresponded to the natural ratio of volatile compounds collected in the plant's headspace. A significant attractant effect was found for a comparatively complex 10‐compound mixture that included four green leaf volatiles [(Z)‐3‐hexen‐1‐ol, 1‐hexanol, (E)‐2‐hexenal, and (Z)‐3‐hexen‐1‐yl acetate], five aromatics (benzaldehyde, methyl salicylate, methyl benzoate, benzonitrile, and phenylacetonitrile), and a carboxylic acid (valeric acid). Using a subtraction approach, the number of compounds was progressively decreased, resulting in a bioactive 5‐compound mixture composed of two constituents, green leaf volatiles and aromatic compounds. Further evaluations revealed that benzaldehyde and benzonitrile must be present in association with three distinct green leaf volatiles to produce an attractant effect on the female moths. This 5‐compound mixture was as attractive as natural peach shoot volatiles, which are known to comprise over 20 compounds. Results are discussed in light of the documented synergistic effect between the three general green leaf volatiles and the two specific aromatic compounds.     

Spatio‐temporal distribution of Ceratitis capitata population in a heterogeneous landscape in Central Italy

The spatio‐temporal dynamics of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), was investigated to evaluate the effect of the landscape elements and host plants on pest distribution, in an agricultural landscape of 500 ha located in Central Italy. Two farms (farm 1 and farm 2) are located in the experimental area, composing mixed fruit orchards and surrounded by hedgerows, small woodlots, private gardens and cereal fields. Ceratitis capitata population fluctuation was monitored, from 2006 to 2008, using traps baited with trimedlure. Geostatistical methods such as Inverse distance squared weighted were used to obtain distributional maps of adults, mainly males. Results showed that the adult Mediterranean fruit flies were primarily distributed inside farm 1, with the maximum density found in the months of September and October. Away from the principal host plants, particularly in cereal fields, the number of trapped individuals was always low or zero. In both farms, flies were caught sequentially in traps located on host plants (i.e. peach, apple, pear, oriental persimmon and prickly pear) at varying times of maturation, especially when fruits remained on the trees. Distributional maps provided evidence that allowed to identify habitats in which the fly developed early in the season (mixed peach orchards) and afterwards during the periodic flights.     

Preference and performance of Diachasmimorpha kraussii (Fullaway) (Hymenoptera: Braconidae) on five commercial fruit species

Diachasmimorpha kraussii is a polyphagous endoparasitoid of dacine fruit flies. The fruit fly hosts of D. krausii, in turn, attack a wide range of fruits and vegetables. The role that fruits play in host selection behaviour of D. kraussii has not been previously investigated. This study examines fruit preference of D. kraussii through a laboratory choice‐test trial and field fruit sampling. In the laboratory trial, oviposition preference and offspring performance measures (sex ratio, developmental time, body length, hind tibial length) of D. kraussii were investigated with respect to five fruit species [Psidium guajava L. (guava), Prunis persica L. (peach), Malus domestica Borkh. (apple), Pyrus communis L. (pear) and Citrus sinensis L. (orange)], and two fruit fly species (Bactrocera jarvisi and B. tryoni). Diachasmimorpha kraussii responded to infested fruit of all fruit types in both choice and no‐choice tests, but showed stronger preference for guava and peach in the choice tests irrespective of the species of fly larvae within the fruit. The wasp did not respond to uninfested fruit. The offspring performance measures differed in a non‐consistent fashion between the fruit types, but generally wasp offspring performed better in guava, peach and orange. The offspring sex ratio, except for one fruit/fly combination (B. jarvisi in apple), was always female biased. The combined results suggest that of the five fruits tested, guava and peach are the best fruit substrates for D. krausii. Field sampling indicated a non‐random use of available, fruit fly infested fruit by D. kraussii. Fruit fly maggots within two fruit species, Plachonia careya and Terminalia cattappa, had disproportionately higher levels of D. krausii parasitism than would be expected based on the proportion of different infested fruit species sampled, or levels of fruit fly infestation within those fruit.     

Plant volatiles mediate attraction to host and non-host plant in apple fruit moth, Argyresthia conjugella

Plant volatiles mediate host finding in insect herbivores and lead to host fidelity and habitat‐specific mating, generating premating reproductive isolation and facilitating sympatric divergence. The apple fruit moth, Argyresthia conjugella Zeller (Lepidoptera: Argyresthiidae), is a particularly suitable species to study the cues and behavioural mechanisms leading to colonization of a new host: it recurrently oviposits on the non‐host plant, apple Malus domestica Borkh. (Rosaceae), where the larvae cannot complete their development. The larval host of the apple fruit moth (Lepidoptera, Argyresthiidae), is rowan Sorbus aucuparia L. (Rosaceae). Fruit setting in rowan, however, fluctuates strongly over large areas in Scandinavia. Every 2–4 years, when too few rowanberries are available for egg laying in forests, apple fruit moth females oviposit instead on apple in nearby orchards, but not on other fruits, such as pear or plum. This poses the question of which cues mediate attraction to rowan and apple, and how apple fruit moth discriminates rowan from apple. Chemical analysis and antennal recordings showed that 11 out of 15 rowan volatiles eliciting an antennal response in A. conjugella females co‐occur in rowan and apple headspace, in a different proportion. In the field, A. conjugella was attracted to several of these plant volatiles, especially to 2‐phenyl ethanol, methyl salicylate, and decanal. Addition of anethole to 2‐phenyl ethanol had a strong synergistic effect, the 1 : 1 blend is a powerful attractant for A. conjugella males and females. These results confirm that volatiles common to both plants may account for a host switch in A. conjugella from rowan to apple. Some of the most attractive compounds, including 2‐phenyl ethanol, anethole, and decanal, which have been found in several apple cultivars, were not present in the headspace of the apple cultivar, Aroma, which is also susceptible to attack by A. conjugella. This supports the idea that the odour signal from apple is suboptimal for attraction of A. conjugella, but is nonetheless sufficient for attraction, during times when rowan is not available for egg laying.     

Response of female Cydia molesta (Lepidoptera: Tortricidae) to plant derived volatiles

Peach shoot volatiles were attractive to mated female oriental fruit moth, Cydia molesta (Busck), in a dual choice arena. No preference was observed between leaf odours from the principle host plant, peach, and the secondary host plant, apple. Twenty-two compounds were identified in headspace volatiles of peach shoots using gas chromatography-mass spectrometry. Green leaf volatiles accounted for more than 50% of the total emitted volatiles. A bioassay-assisted fractionation using different sorbent polymers indicated an attractant effect of compounds with a chain length of 6-8 carbon atoms. The major compounds of this fraction were tested either singly or in combinations for behavioural response of females. Significant bioactivity was found for a three-component mixture of (Z)-3-hexen-1-yl acetate, (Z)-3-hexen-1-ol and benzaldehyde in a 4:1:1 ratio. This synthetic mixture elicited a similar attractant effect as the full natural blend from peach shoots as well as the bioactive fraction.     

Attraction of the West Indian fruit fly to mango fruit volatiles

In this study, we investigated the attraction of West Indian fruit fly, Anastrepha obliqua (Macquart) (Diptera: Tephritidae), to volatiles of three mango [Mangifera indica L. (Anacardiaceae)] cultivars in field cage tests. The number of flies captured with Multilure traps baited with Amate mature green mangoes was significantly higher than that captured in traps baited with Coche and Ataulfo fruits. There was no significant difference between the number of flies captured in traps baited with Coche or Ataulfo mangoes. Gas chromatography‐mass spectrometry analysis of mango fruit volatiles identified 24, 22, and 19 compounds for Amate, Ataulfo, and Coche mango cultivars, respectively. A principal component analysis of the volatiles revealed that the Amate mango was more distant from the Ataulfo mango, and the latter cultivar was closer to the Coche mango. The compounds myrcene, α‐pinene, β‐selinene, and trans‐β‐ocimene were the most abundant in Amate mangoes, whereas 3‐carene, β‐selinene, terpinolene, and α‐pinene were the predominant compounds of Ataulfo cultivars. In the Coche mango, the predominant compounds were 3‐carene, β‐selinene, terpinolene, and limonene. Traps baited with a blend of myrcene, α‐pinene, and trans‐β‐ocimene captured more A. obliqua females and males than control traps. Flies were more attracted to the Super Q volatile extracts of Amate mango than to the three‐component blend formulated in a ratio of 1:1:1. However, there was no significant difference between the number of flies caught by traps baited with Amate mango extracts and that caught by traps baited with the three‐blend component when this was formulated according to the relative proportions in the mango extracts. Traps baited with myrcene, the major component, caught fewer flies than traps baited with Amate mango extracts.     

Olfactory response of three parasitoid species (Hymenoptera: Braconidae) to volatiles of guavas infested or not with fruit fly larvae (Diptera: Tephritidae)

The olfactory responses of the native parasitoids Doryctobracon areolatus (Szépligeti) and Asobara anastrephae (Muesebeck) and of the exotic parasitoid Diachasmimorpha longicaudata (Ashmead) to guava (Psidium guajava L.) infested or not with fruit fly larvae were evaluated. D. areolatus and D. longicaudata females responded to the odors of uninfested rotting guavas, although D. areolatus was also attracted to fruits at the initial maturation (turning) stage. The females of these species recognized the volatiles of guavas containing Ceratitis capitata (Wied.) larvae. However, in bioassays involving fruits with larvae of different instars, D. longicaudata females were not able to separate between fruits containing C. capitata larvae at the initial instars and larvae at the third instar. In the evaluations of volatiles released by guavas containing C. capitata and Anastrepha fraterculus (Wied.) larvae, the D. longicaudata females were oriented toward the volatiles of fruits containing both host species, but differed significantly from volatiles of guavas containing C. capitata larvae. The D. areolatus females also showed responses to both species, although with a preference for volatiles of fruits containing A. fraterculus larvae. The A. anastrephae females were oriented toward the odors of fruits infested with both fruit fly species. In the shade house, D. longicaudata females were oriented to volatiles of rotting fruits containing larvae or not, but could not significantly differentiate between hosts. D. areolatus females were not attracted toward fruits on the ground in the shade house, regardless of host, suggesting that this parasitoid does not forage on fallen fruits.     

Visualization of fruit scent using photoluminescence

Photoluminescence with visible emission spectrum was observed and visualized at the surface of certain fruits. This photoluminescence is associated with vapors of natural organic volatiles (odorants) emitted from the fruit surface. The photoluminescence spectra of various fruits (apple, pear, kiwi, and strawberry) were measured in vivo using a number of fluorimetric methods. Fruit aging was found to be accompanied by modification of the photoluminescence spectrum shape and a noticeable increase in the photoluminescence intensity. Laser photoluminescence microscopy in vapors of fruit extracts and artificial compounds was used to assess the contribution of various substances to natural odor emission of fruits. The results of the study show that fluorimetry of odors is a promising method for studying fruits and other objects.     

Oviposition preferences in Grapholita molesta: the relative importance of visual and olfactory cues

The oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), is a major pest of fruit trees worldwide. Females oviposit on the young leaves of peach [Prunus persica (L.) Batsch (Rosaceae)] shoots at twilight, when light intensity changes markedly. Previous researches have shown that the oviposition response of this moth is guided particularly by visual and olfactory cues from host plants. However, the relative importance of visual and olfactory cues in their oviposition preference is largely unknown. As a crepuscular moth, how do choices change as light intensity drops rapidly from day to night? In the present study, through two‐choice behavioural experiments, the oviposition responses of G. molesta to visual and olfactory cues (alone or in combination) from peach shoots were tested at four light intensities ranging from daylight to starlight. Grapholita molesta showed similar oviposition responses to plant cues under 1 000, 100, 1 and 0.01 mW m^?2 illumination. Olfactory cues from peach shoots attracted significantly more oviposition than the negative control, whereas visual cues alone did not. Furthermore, olfactory cues were more attractive than visual cues, and no significant interaction was observed between the responses to the two cues. Our findings indicate that G. molesta females mainly rely on olfactory cues to recognize oviposition sites, regardless of differences in light intensity. These results do not provide evidence for attraction to visual cues, but the possibility that the brightness of leaves might be used to guide oviposition is discussed.