Volatiles of Grape Inoculated with Microorganisms: Modulation of Grapevine Moth Oviposition and Field Attraction

VOCs from fungi-infected apples attract and increase the oviposition of yellow peach moth Conogethes punctiferalis

BACKGROUND

Plant volatile organic compounds (VOCs) modified by plant-associated microbes can attract or repel the oviposition of herbivores. Here, we explored the effects of three different fungi on apples' VOCs and the cascading impacts on the oviposition preference of yellow peach moth [YPM, Conogethes punctiferalis (Guenée)].

RESULTS

Among Penicillium crustosum-infected apples (PCA), Rhizopus oryzae-infected apples (ROA), Colletotrichum gloeosporioides-infected apples (CGA) and healthy apples (HA), mated YPM females preferred to oviposit eggs on ROA and CGA, and showed significant attractiveness to VOCs from PCA, ROA, and CGA under laboratory conditions. The VOCs analyses showed that there were significant differences between fungi-infected apples (ROA, CGA) and control treatments (mechanically damaged apples (MDA), HA) in terms of the relative contents of 13 VOCs. The relative contents of ethyl 2-methylbutyrate, ethyl caprylate, estragole, ethyl hexanoate in ROA and CGA were higher than those in MDA. The relative content of isopropyl 2-methylbutyrate in ROA was significantly higher than those in HA and CGA. The relative contents of 2-methylbutyl acetate, butyl 2-methylbutyrate, hexyl 2-methylbutyrate, amyl hexanoate, hexyl hexanoate, (E, E)-α-farnesene in ROA and CGA were lower than those in HA. The relative content of hexyl acetate in ROA and CGA was significantly higher than that in MDA, but lower than that in HA. Additionally, 10 fungi-induced VOCs were detected in ROA and/or CGA. When 20 VOCs from ROA and/or CGA were tested as individuals or mixed blends in Y-tube olfactometer assays, mated YPM females preferred amyl 2-methylbutyrate, isoamyl 2-methylbutyrate, isopropyl 2-methylbutyrate, hexyl propionate (common VOCs in ROA, CGA, and HA), and heptacosane (a fungi-induced VOC in ROA), but no significant preferences were observed between individual compounds and mixed blends, except for hexyl propionate.

CONCLUSION

Different fungi infection increased the relative contents of common VOCs from healthy and fungi-infected apples, which ultimately resulted in the significant attractiveness for the oviposition of mated YPM females. This study clarified why fungi-infected apples were more attractive to YPMs than healthy apples and screened out the crucial VOCs for YPM oviposition. © 2023 Society of Chemical Industry.

Biostimulant and Bioinsecticidal Effect of Coating Cotton Seeds with Endophytic Beauveria bassiana in Semi-Field Conditions

Increasing commercial demands from the textile and food industries are putting strong pressure on the cultivation of cotton and its derivatives to produce high yields. At the same time, cotton has high nutrient and irrigation requirements and is highly susceptible to insect pests. Coating cotton seeds with beneficial fungi could address these problems. The aim of this study was to investigate the growth of cotton using (A) conventional seeds and (B) seeds coated with the entomopathogenic fungus Beauveria bassiana (Hypocreales: Cordycipitaceae). The experiment was conducted in a greenhouse of the Department of Agriculture of the University of Ioannina, in a completely randomized design. The growth characteristics of cotton plants were recorded weekly while the fresh weight and dry matter of the leaves, shoots and roots of the developed cotton plants were calculated at the end of the experiment. Weekly determination of total chlorophyll content (TCHL) was used as an indicator of plant robustness during the 80-day experiment. Many cotton growth parameters of treated plants, like number of leaves, shoots and apical buds, plant height, stem diameter, fresh and dried biomass and TCHL, were significantly higher than those of the untreated ones. Apart from plant growth, naturally occurring by Aphis gossypii (Hemiptera: Aphididae) infestation which also monitored for six weeks. A significantly lower aphid population was recorded for inoculated plants after the fifth week compared to the control. The overall evaluation revealed that B. bassiana coating treatments appear to have a significant biostimulatory and bioinsecticidal effect. Our results could represent responsive applications to the demands of intensive cotton growing conditions.

Deciphering Plant-Insect-Microorganism Signals for Sustainable Crop Production

Agricultural crop productivity relies on the application of chemical pesticides to reduce pest and pathogen damage. However, chemical pesticides also pose a range of ecological, environmental and economic penalties. This includes the development of pesticide resistance by insect pests and pathogens, rendering pesticides less effective. Alternative sustainable crop protection tools should therefore be considered. Semiochemicals are signalling molecules produced by organisms, including plants, microbes, and animals, which cause behavioural or developmental changes in receiving organisms. Manipulating semiochemicals could provide a more sustainable approach to the management of insect pests and pathogens across crops. Here, we review the role of semiochemicals in the interaction between plants, insects and microbes, including examples of how they have been applied to agricultural systems. We highlight future research priorities to be considered for semiochemicals to be credible alternatives to the application of chemical pesticides.

The role of tetradecane in the identification of host plants by the mirid bugs Apolygus lucorum and Adelphocoris suturalis and potential application in pest management

The mirid bugs Apolygus lucorum and Adelphocoris suturalis are considered serious pests of many crops in China, the host plant recognition of these pests remains unclear. The current study investigated the vital odor cues of two mirid bugs and evaluated the role of olfactory recognition in host recognition. The GC-EAD response of mirid bugs to volatiles of their host plant Phaseolus vulgaris was tested. Tetradecane, 2-propyl-1-pentanol, and dodecanal elicited strong EAG responses by mirid bugs and were tested with field experiments. The results indicated tetradecane was significantly more attractive than other attractants, yielding 30.33 ± 2.19 mirid bugs trapped during 7 days. The selected response rates to tetradecane were above 60%, which was most attractive to female A. lucorum at 1.5 mg/ml. Among seven tetradecane derivatives, tetradecane and tetradecanoic acid were the most potent attractants to A. lucorum and A. suturalis. Tetradecane was present in the volatiles of 10 common hosts, and their difference in relative content was significant. The presence of tetradecane seemed relevant to the olfactory response intensity of two mirid bugs towards the different host plants. The artificial supplement of tetradecane increased the attractive effect of host plants. These results suggested that tetradecane plays a vital role in the olfactory selection by two mirid bugs, and it can be made into field baits as a novel ecological strategy to manage these pests with widely reported pesticide resistance. However, results suggested host recognition is not entirely dependent on odor cues. We demonstrated that A. suturalis and A. lucorum adults have similar olfactory recognition mechanisms to their hosts in long-distance host selection. While, the differences in host plant selection between the two pests should occur in close range due to differences in gustatory or tactile sensory organs of A. lucorum and A. suturalis.

Volatiles released by Beauveria bassiana induce oviposition behavior in the fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae)

Microbial volatile organic compounds may act as semiochemicals, inciting different behavioral responses in insects. Beauveria bassiana is an entomopathogenic fungus, and physiological and environmental factors are positively related to fungal virulence. In this study, we examined the volatile profiles produced by eight B. bassiana strains, isolated from soil plots and mycosed insect cadavers, with different speeds of kill and determined if these compounds induce oviposition behavior in Spodoptera frugiperda. Fungal volatilome analysis revealed differences between the isolates. Isolates from mycosed insects showed higher virulence, larger egg mass area and length, and a higher number of eggs by mass, than those obtained from soil. Furthermore, a dilution of the fungal odoriferous compounds increased the insect response, suggesting that S. frugiperda is highly susceptible to the fungal compound's fingerprint. Otherwise, the insect response to the natural blend of volatiles released by the fungus was different from that obtained with 3-methylbutanol, which was the most abundant compound in all isolates. The ability of an entomopathogen to produce volatiles that can induce olfactory stimulation of egg-laying behavior could represent an ecological adaptive advantage in which the entomopathogen stimulates the insect population growth.

Dynamics of Microbial Communities across the Life Stages of Nilaparvata lugens (Stål)

Understanding the composition of microorganismal communities hosted by insect pests is an important prerequisite for revealing their functions and developing new pest control strategies. Although studies of the structure of the microbiome of Nilaparvata lugens have been published, little is known about the dynamic changes in this microbiome across different developmental stages, and an understanding of the core microbiota is still lacking. In this study, we investigated the dynamic changes in bacteria and fungi in different developmental stages of N. lugens using high-throughput sequencing technology. We observed that the microbial diversity in eggs and mated adults was higher than that in nymphs and unmated adults. We also observed a notable strong correlation between fungal and bacterial α-diversity, which suggests that fungi and bacteria are closely linked and may perform functions collaboratively during the whole developmental period. Arsenophonus and Hirsutella were the predominant bacterial and fungal taxa, respectively. Bacteria were more conserved than fungi during the transmission of the microbiota between developmental stages. Compared with that in the nymph and unmated adult stages of N. lugens, the correlation between bacterial and fungal communities in the mated adult and egg stages was stronger. Moreover, the core microbiota across all developmental stages in N. lugens was identified, and there were more bacterial genera than fungal genera; notably, the core microbiota of eggs, nymphs, and mated and unmated adults showed distinctive functional enrichment. These findings highlight the potential value of further exploring microbial functions during different developmental stages and developing new pest management strategies.

Mutualism between Gut-Borne Yeasts and Their Host, Thaumatotibia leucotreta, and Potential Usefulness in Pest Management

Thaumatotibia leucotreta is endemic to southern Africa and is highly significant for various fruit industries, including the South African citrus industry, due to its classification as a phytosanitary pest. Mutualistic associations between C. pomonella, closely related to T. leucotreta, and yeasts have previously been described and reported to reduce larval mortality and enhance larval development. Here, we determined which yeast species occur naturally in the gut of T. leucotreta larvae and investigated whether any of the isolated yeast species affect their behaviour and development. Navel oranges infested with T. leucotreta larvae were collected from geographically distinct provinces in South Africa, and the larvae were processed for analysis of naturally occurring associated yeasts. Six yeast species were isolated and identified from the guts of these T. leucotreta larvae via PCR amplification and sequencing of the ITS region of rDNA and D1/D2 domain of large ribosomal subunit. Larval development and attraction assays were conducted, and T. leucotreta larvae that fed on Navel oranges inoculated with yeast had accelerated developmental periods and reduced mortality rates. Neonate T. leucotreta were also attracted to YPD broth cultures inoculated with yeast for feeding. Oviposition preference assays were conducted with adult T. leucotreta females. Navel oranges inoculated with yeast were shown to influence the oviposition preference of adult females. Yeasts harbour the potential for use in biocontrol, especially when combined with other well-established control methods. This study provides a platform for future research into incorporating yeast with current biological control agents as a novel option for controlling T. leucotreta in the field.

Biogenic volatile organic compounds in the grapevine response to pathogens, beneficial microorganisms, resistance inducers, and abiotic factors

The synthesis of volatile organic compounds (VOCs) in plants is triggered in response to external stimuli, and these compounds can migrate to distal tissues and neighbouring receivers. Although grapevine VOCs responsible for wine aroma and plant-insect communications are well characterized, functional properties of VOCs produced in response to phytopathogens, beneficial microorganisms, resistance inducers, and abiotic factors have been less studied. In this review, we focused on the emission patterns and potential biological functions of VOCs produced by grapevines in response to stimuli. Specific grapevine VOCs are emitted in response to the exogenous stimulus, suggesting their precise involvement in plant defence response. VOCs with inhibitory activities against pathogens and responsible for plant resistance induction are reported, and some of them can also be used as biomarkers of grapevine resistance. Likewise, VOCs produced in response to beneficial microorganisms and environmental factors are possible mediators of grapevine-microbe communications and abiotic stress tolerance. Although further functional studies may improve our knowledge, the existing literature suggests that VOCs have an underestimated potential application as pathogen inhibitors, resistance inducers against biotic or abiotic stresses, signalling molecules, membrane stabilizers, and modulators of reactive oxygen species. VOC patterns could also be used to screen for resistant traits or to monitor the plant physiological status.

Feeding Volatiles of Larval Sparganothis pilleriana (Lepidoptera: Tortricidae) Attract Heterospecific Adults of the European Grapevine Moth

Plants release volatiles in response to caterpillar feeding. These herbivore-induced plant volatiles (HIPVs) attract natural enemies of the herbivores and repel or attract conspecific adult herbivores in a tri-trophic interaction which has been considered to be an indirect plant defense against herbivores. Recently, we demonstrated the attraction of male and female European grapevine moth, Lobesia botrana (Denis & Schiffermüller) (Lepidoptera: Tortricidae) to a blend of phenylacetonitrile and acetic acid, two compounds identified as HIPVs in heterospecific apple-leafroller interactions. The ecological basis of our findings is not clearly understood. Thus, this work was undertaken to investigate HIPVs in the grapevine-leafroller interaction and study the response of heterospecific adults L. botrana, to these volatiles. We collected headspace volatiles emitted from uninfested grapevines and grapevines infested with larvae of a generalist herbivore, the grapevine leafroller moth, Sparganothis pilleriana (Denis & Schiffermüller), and analyzed them using gas chromatography/mass spectrometry. Infested grape leaves released three compounds (phenylacetonitrile, indole, and 2-phenylethanol) not found from uninfested leaves. Nine different blends, comprising a full factorial set of the three compounds with each blend containing acetic acid, were tested in a field-cage trial. Only lures containing phenylacetonitrile caused a significant increase in trap catches compared to the other lures and blank traps. Electroantennographic tests show that L. botrana can detect the compounds. The results confirm our hypothesis that phenylacetonitrile is released during grapevines infestation with herbivores, and attracts adult L. botrana.

Texture features explain the susceptibility of grapevine cultivars to Drosophila suzukii (Diptera: Drosophilidae) infestation in ripening and drying grapes

Grapevine is a well-known host plant of the invasive pest Drosophila suzukii, but its susceptibility to pest oviposition and development greatly depends on the cultivar. To address environmental sustainability during viticultural zoning planning, new vineyard plantation and Integrated Pest Management programmes, it is essential to take pest pressure and cultivar susceptibility into account. To determine the different grapevine cultivars susceptibility to D. suzukii, we tested twelve widely spread cultivars during the ripening period. We also tested three cultivars during the drying period for raisin wine production. The infestation and emergence rates were consequently related to chemical and texture features of the berries to explain the role of skin and pulp characteristics in determining the nature of the susceptibility. Our results showed that susceptibility to D. suzukii infestation varies across cultivars. On ripening grapes, infestation is primarily influenced by skin and pulp firmness, elasticity and consistency. Suitability for egg development resulted mainly related to skin and pulp deformation. In a drying loft, infestation may also occur in relation to skin and pulp consistency. Lastly, we discuss the practical implication of the underestimated role of berry texture in D. suzukii oviposition and emergence success, in both ripening and drying grapes.

Designing a species-selective lure based on microbial volatiles to target Lobesia botrana

Sustainable, low impact control methods, including mating disruption and microbial insecticides against L. botrana have been available for decades. Yet, successful implementation has been restricted to only a few grapevine districts in the world. A limiting factor is the lack of a female attractant to either monitor or control the damaging sex. Volatile attractants for both female and male insects can be used to assess when L. botrana populations exceed economic thresholds, and to decrease the use of synthetic pesticides within both conventional and pheromone programs. Rather than using host-plant volatiles, which are readily masked by background volatiles released by the main crop, we tested the attractiveness of volatiles that signify microbial breakdown and more likely stand out against the background odour. A two-component blend of 2-phenylethanol (2-PET) and acetic acid (AA) caught significant numbers of both sexes. Catches increased with AA and, to a minimal extent, 2-PET loads. However, a higher load of 2-PET also increased bycatches, especially of Lepidoptera and Neuroptera. Major (ethanol, ethyl acetate, 3-methyl-1-butanol) or minor (esters, aldehydes, alcohols and a ketone) fermentation volatiles, did surprisingly not improve the attraction of L. botrana compared to the binary blend of 2-PET and AA alone, but strongly increased bycatches. The most attractive lure may thus not be the best choice in terms of specificity. We suggest that future research papers always disclose all bycatches to permit evaluation of lures in terms of sustainability.

Is the existence of a mutualistic relationship between Lobesia botrana and Botrytis cinerea well-founded?

Some studies have highlighted benefits for Lobesia botrana by adding Botrytis cinerea mycelium to an artificial larval diet and have suggested a mutualistic relationship between the two organisms on grapevine, hypothesizing that fungal sterols were the nutritional factor involved. Because the nutritional quality of an artificial diet should be similar to grapes to allow extrapolation of the results to the field conditions, in the current study L. botrana larval performance was compared when larvae were fed on grapes (berries) or two artificial diets either with or without enrichment with B. cinerea. Based on sterol analysis, the two artificial diets had high cholesterol content, but relative to berries showed comparable and low phytosterol contents, respectively (high- and low-phytosterol, HPh, and LPh). While larval fitness on the HPh diet was similar to berries, the LPh diet led to higher mortality and worse larval performance. The addition of the fungus compensated for the shortage in the LPh diet but did not improve the HPh diet. Supplementing the LPh diet with linoleic acid, which is supplied also from B. cinerea, partially improved larval performance. In a field experiment, females did not show any egg-laying preferences towards naturally botrytized bunches. The positive effect of B. cinerea on the moth's next generation that is reported in the literature could be a consequence of fungus developed inside berry tunnels bored by larvae. Therefore, based on our data and previous reports the existence of a mutualistic relationship between L. botrana and B. cinerea is not well-founded.

Hippophae rhamnoides berry related Pichia kudriavzevii yeast volatiles modify behaviour of Rhagoletis batava flies

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Pichia kudriavzevii yeasts were isolated from ripe Hippophae rhamnoides berries.

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Thirty-five yeast volatiles were identified from the headspace of P. kudriavzevii.

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Esters and alcohols contributed by 32% and 66% to the total blend amount.

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Ten of those volatiles elicited antenna responses of Rhagoletis batava flies.

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Mixture of synthetic olfactory active compounds attracted R. batava males and females.

Olfactory cues have a large impact on insect behaviour and fitness consequently showing potential in pest management. Yeast released volatiles are used by insects as olfactory cues for finding feeding and oviposition sites. The yeast strain SB-16-15 was isolated from spontaneous fermentation of Hippophae rhamnoides berries and identified as Pichia kudriavzevii. Thirty-nine volatiles were sampled from the headspace of P. kudriavzevii yeasts by solid phase micro extraction and identified by gas chromatography and mass spectrometry techniques. Ten of those volatiles elicited antennal responses of Rhagoletis batava flies, one of the most serious pest of H. rhamnoides berries. In the two-choice experiments, R. batava flies preferred the mixture composed of nine synthetic compounds analogous to electroanntenographic active volatiles released by the yeasts compare to the solvent control. Female flies were significantly attracted to the mixture at the concentration 0.1 µL mL⁻¹ and showed no preference to the mixture at the concentration 1 µL mL⁻¹ versus control while males reacted positively to the synthetic blend at the concentration 1 µL mL⁻¹. Herein, for the first time, behaviour modifying effect of H. rhamnoides berry related yeast volatiles was shown suggesting these semiochemicals have potential in use for monitoring R. batava flies.

Comparative genomics of Paraburkholderia kururiensis and its potential in bioremediation, biofertilization, and biocontrol of plant pathogens

Burkholderia harbors versatile Gram-negative species and is β-Proteobacteria. Recently, it was proposed to split the genus in two main branches: one of animal and plant pathogens and another, Paraburkholderia, harboring environmental and plant-beneficial species. Currently, Paraburkholderia comprises more than 70 species with ability to occupy very diverse environmental niches. Herein, we sequenced and analyzed the genome of Paraburkholderia kururiensis type strain KP23T , and compared to P. kururiensis M130, isolated in Brazil, and P. kururiensis susbp. thiooxydans, from Korea. This study focused on the gene content of the three genomes with special emphasis on their potential of plant-association, biocontrol, and bioremediation. The comparative analyses revealed several genes related to plant benefits, including biosynthesis of IAA, ACC deaminase, multiple efflux pumps, dioxygenases, and degradation of aromatic compounds. Importantly, a range of genes for protein secretion systems (type III, IV, V, and VI) were characterized, potentially involved in P. kururiensis well documented ability to establish endophytic association with plants. These findings shed light onto bacteria-plant interaction mechanisms at molecular level, adding novel information that supports their potential application in bioremediation, biofertilization, and biocontrol of plant pathogens. P. kururiensis emerges as a promising model to investigate adaptation mechanisms in different ecological niches.

16S rRNA gene profiling of bacterial communities mediating production of tsetse attractive phenols in mammalian urine

Several types of odours are involved in the location of host animals by tsetse (Diptera: Glossinidae), a vector of animal African trypanosomiasis. Host animals' ageing urine has been shown to be the source of a phenolic blend attractive to the tsetse. Nevertheless, limited research has been performed on the microbial communities' role in the production of phenols. This study aimed at profiling bacterial communities mediating the production of tsetse attractive phenols in mammalian urine. Urine samples were collected from African buffalo (Syncerus caffer), cattle (Bos taurus) and eland (Taurotragus oryx) at Kongoni Game Valley Ranch and Kenyatta University in Kenya. Urine samples, of each animal species, were pooled and left open to age in ambient conditions. Bacteriological and phenols analyses were then carried out, at 4 days ageing intervals, for 24 days. Phenols analysis revealed nine volatile phenols: 4-cresol, ortho-cresol, 3-cresol, phenol, 3-ethylphenol, 3-propylphenol, 2-methyloxyphenol, 4-ethylphenol and 4-propylphenol. Eight out of 19 bacterial isolates from the ageing urine revealed the potential to mediate production of phenols. 16S rRNA gene characterisation of the isolates closely resembled Enterococcus faecalis KUB3006, Psychrobacter alimentarius PAMC 27887, Streptococcus agalactiae 2603V, Morganella morganii sub.sp. morganii KT, Micrococcus luteus NCTC2665, Planococcus massiliensis strain ES2, Ochrobactrum pituitosum AA2 and Enterococcus faecalis OGIRF. This study established that some of the phenols emitted from mammalian urine, which influence the tsetse's host-seeking behaviour, are well characterised by certain bacteria. These results may allow the development of biotechnological models in vector control that combines the use of these bacteria in the controlled release of semiochemicals.

Effects of Endophytic Entomopathogenic Ascomycetes on the Life-History Traits of Aphis gossypii Glover and Its Interactions with Melon Plants

Entomopathogenic fungi are sprayed commercially for aphid control in greenhouses. Recently, their ability to grow endophytically within plants was discovered, offering the opportunity for systemic biological control. Endophytic colonization of host plants could also influence life-table parameters and behavior of herbivores. We investigated lethal and pre-mortality effects of Beauveria bassiana and Metarhizium brunneum on Aphis gossypii; aphids either received inoculum while feeding on recently sprayed leaves (surface inoculum and endophytically-colonized) or while feeding on unsprayed but endophytically-colonized leaves. We used choice assays to identify any preferences for endophytically-colonized or control plants. Volatile emissions from endophytically-colonized plants and control plants were also compared. Aphid mortality rates ranged between 48.2 and 56.9% on sprayed leaves, and between 37.7 and 50.0 on endophytically-colonized leaves. There was a significant effect of endophytic colonization on the rate of nymph production, but this did not result in an overall increase in the aphid population. Endophytic colonization did not influence host-plant selection even though there were qualitative and quantitative differences in the blend of volatiles released by endophytically-colonized and control plants. Although endophytic colonization did not change herbivore behavior, plants still benefit via indirect defense, resistance to plant pathogens or abiotic stress tolerance.

Leafroller-induced phenylacetonitrile and acetic acid attract adult Lobesia botrana in European vineyards

We recently identified unique caterpillar-induced plant volatile compounds emitted from apple leaves infested with the larvae of various leafroller species. In subsequent field tests, binary blends of phenylacetonitrile+acetic acid and 2-phenylethanol+acetic acid were found to be attractive to a range of tortricid leafroller species (Tortricidae: Tortricinae) in both the Southern and Northern Hemispheres. In this work, the caterpillar-induced plant volatiles from the apple-leafroller system were tested in two vineyards in Spain and Hungary for their attractiveness to the grape frugivore Lobesia botrana (Tortricidae: Olethreutinae). As seen for Tortricinae species, a binary blend of phenylacetonitrile+acetic acid attracted significantly more male and female L. botrana to traps than acetic acid or blank lures. Traps baited with other caterpillar-induced plant volatile compounds (benzyl alcohol, 2-phenylethanol, indole, and (E)-nerolidol, each as a binary blend with acetic acid) did not catch significantly more moths than traps containing acetic acid alone. The catches of male and female moths support an optimistic future for new products in female tortricid surveillance and control that are based on combinations of kairomone compounds released from larval-damaged foliage.