Antonio De Cristofaro

ANTENNAL AND BEHAVIORAL RESPONSES OF GRAPEVINE MOTH Lobesia botrana FEMALES TO VOLATILES FROM GRAPEVINE

Grapevine moth Lobesia botrana is the economically most important insect of grapevine Vitis vinifera in Europe. Flower buds, flowers, and green berries of Chardonnay grapevine are known to attract L. botrana for oviposition. The volatile compounds collected from these phenological stages were studied by gas chromatography—mass spectrometry, and the antennal response of L. botrana females to these headspace collections was recorded by gas chromatography—electroantennography. The compounds found in all phenological stages, which consistently elicited a strong antennal response, were pentadecane, nonanal, and α -farnesene. In a wind tunnel, gravid L. botrana females flew upwind to green grapes, as well as to headspace collections from these berries released by a piezoelectric sprayer release device. However, no females landed at the source of headspace volatiles, possibly due to inappropriate concentrations or biased ratios of compounds in the headspace extracts.

Synthetic Grape Volatiles Attract Mated Lobesia botrana Females in Laboratory and Field Bioassays

In laboratory experiments, we identified and quantified volatiles emitted by inflorescences and berries of two grape varieties (Trebbiano and Sangiovese) and examined the effects of the volatiles on oviposition by the grapevine moth Lobesia botrana. Compared to Trebbiano, Sangiovese is relatively more susceptible to L. botrana infestations under natural conditions. Chemical and electrophysiological analysis indicated only quantitative differences between the volatiles released by the two varieties. In a dual-choice oviposition bioassay based only on volatile cues, females did not show any preference between the two varieties. The six major components of the odor profiles that were GC-EAD-active to female antennae included: limonene, 4,8-dimethyl-1,(E)-3,7-nonatriene, (±)-linalool, (E)-caryophyllene, (E,E)-α-farnesene, and methyl salicylate. At the beginning of the berry touch phenological stage, their proportions were about 10:0.6:0.4:0.5:0.9:0.6 in Trebbiano and 10:1:0.4:1.5:0.4:0.3 in Sangiovese. A six-component synthetic lure (with the proportion 10:1:1:1:1:1, which approximated the ratio of components released by both varieties) was used in further laboratory oviposition bioassays. Depending on its dosage, the synthetic lure either attracted or repelled oviposition. L. botrana females laid significantly more eggs in the presence of either the grape bunches or the synthetic lure at the attractive dosage. In a release-capture experiment conducted in a field cage that covered two grapevine rows, the synthetic lure was more attractive than a grape cluster or a blank control, and it stimulated oviposition on the vegetation near the lure. The results indicate that L. botrana uses olfactory cues to select oviposition sites and that an artificial lure, containing the major volatiles released by two grape varieties, may be useful in monitoring female activity in the field.

Oviposition response of the moth Lobesia botrana to sensory cues from a host plant

The grapevine moth Lobesia botrana is a generalist insect herbivore and grapevine is one of its hosts. Previous studies have shown that insects use their olfactory abilities to locate hosts from a distance; whereas contact chemoreception mediates the stimulation of oviposition after landing. Little is known about the role of olfaction and its interactions with contact chemoreception and vision once the insect lands on the plant. Plant volatile compounds can be sensed by host-searching insects located some distance from the plant and insects sense both volatile and nonvolatile cues after landing on a plant. In the present study, we investigated the effects of these volatile and nonvolatile cues on the oviposition behavior of L. botrana. A behavioral bioassay with choice was developed in which insects were offered each sensory cue either alone or in combination with one or 2 other cues. Females were allowed to choose between a device with the stimulus and a blank device. Results were evaluated in terms of 2 parameters: quantity of eggs laid (egg counts) and preference for the stimulus (ODI: oviposition discrimination index). Our results suggest that olfaction significantly affects egg quantity and that there is significant synergism between olfaction and vision, in terms of their combined effect on egg quantity. In terms of preference (ODI), our results did not show a significant preference for any single cue; the highest ODI was measured for the full-cue stimulus (olfaction, vision, and contact). For ODI, a significant interaction was observed between olfaction and vision and a nearly significant interaction was observed between the olfactory and contact cues. The results are discussed in relation to the effects of plant sensory cues on the oviposition behavior of L. botrana.

Biological Activity of Ethyl (E, Z)-2,4-Decadienoate on Different Tortricid Species: Electrophysiological Responses and Field Tests

Abstract Ethyl (E,Z)-2,4-decadienoate (pear ester) is known to be a kairomonal attractant for both male and female codling moths, Cydia pomonella (L.) (Lepidoptera: Tortricidae). Electroantennographic (EAG) studies were conducted to investigate the sensitivities of codling moth, the chestnut torticid species Cydia fagiglandana (Zeller), Cydia splendana (Hübner), and Pammene fasciana L., and the green budmoth Hedya nubiferana Haworth to pear ester. The attractiveness of this compound to the different species was tested in several field-trapping experiments conducted in Italy. The EAG responses of the different tortricids species were dose-dependent. The field-trapping experiments confirmed the attractiveness of the compound to codling moth; similar activity was also shown on the chestnut tortricids in their respective host plant environment.

Bisorbicillinoids produced by the fungus Trichoderma citrinoviride affect feeding preference of the aphid Schizaphis graminum.

We report the effects of some bisorbicillinoids isolated from biomass of the fungus Trichoderma citrinoviride on settling and feeding preference of the aphid Schizaphis graminum. Purification of the fungal metabolites was carried out by a combination of column chromatography and thin-layer chromatography using direct and reverse phases. Chemical identification was performed by spectroscopic methods including nuclear magnetic resonance and mass spectrometry. The identified bisorbicillinoids appeared to be bislongiquinolide, its 16,17-dihydro derivative, trichodimerol, and dihydrotrichodimerol. A feeding preference test with alate morphs of S. graminum was used to identify the active fractions. Among the four bisorbicillinoids, dihydrotrichodimerol and bislongiquinolide influenced aphid feeding preference, restraining specimens from settling on leaves treated with metabolites. Taste neurons sensitive to these compounds, particularly to bislongiquinolide, were located on tarsi of the S. graminum alate morphs.

Disruption of Phthorimaea operculella (Lepidoptera: Gelechiidae) oviposition by the application of host plant volatiles

BACKGROUND Phthorimaea operculella is a key pest of potato. The authors characterised the P. operculella olfactory system, selected the most bioactive host plant volatiles and evaluated their potential application in pest management. The electrophysiological responses of olfactory receptor neurons (ORNs) housed in long sensilla trichodea of P. operculella to plant volatiles and the two main sex pheromone components were evaluated by the single-cell recording (SCR) technique. The four most SCR-active volatiles were tested in a laboratory oviposition bioassay and under storage warehouse conditions. RESULTS The sensitivity of sensilla trichodea to short-chained aldehydes and alcohols and the existence of ORNs tuned to pheromones in females were characterised. Male recordings revealed at least two types of ORN, each of which typically responded to one of the two pheromone components. Hexanal, octanal, nonanal and 1-octen-3-ol significantly disrupted the egg-laying behaviour in a dose-dependent manner. Octanal reduced the P. operculella infestation rate when used under storage conditions. CONCLUSIONS This work provides new information on the perception of plant volatiles and sex pheromones by P. operculella. Laboratory and warehouse experiments show that the use of hexanal, octanal, nonanal and 1-octen-3-ol as host recognition disruptants and/or oviposition deterrents for P. operculella control appears to be a promising strategy.

Bioactivity of short-chain aliphatic ketones against adults of the granary weevil, Sitophilus granarius (L.)

BACKGROUND The granary weevil, Sitophilus granarius (L.), is one of the most damaging pests of stored grains, causing severe quantitative and qualitative losses. Sustainable control means, alternative to the commonly used fumigants and broad-spectrum contact insecticides, are urgently needed owing to legislative limits, the development of resistant insect strains and increasing consumer demand for safe food. Short-chain aliphatic ketones, known to be emitted by cereal grains and previously identified as repellents to adult granary weevils, were evaluated for their ability to disrupt insect orientation towards wheat grains and as possible natural fumigants. RESULTS In behavioural bioassays, 2-pentanone, 2-hexanone, 2-heptanone and 2,3-butanedione significantly reduced insect orientation towards odours of wheat grains, with 2-hexanone and 2-heptanone being the most active. In fumigation tests, all compounds were effective in killing weevil adults, but they performed differently according to chemical structure, speed of action and presence of wheat grains. In the presence of grains, the highest fumigant toxicity was shown by 2-pentanone (LC(50) = 8.4 ± 1.0 mg L(-1)) after 24 h exposure, and by 2-pentanone (LC(50) = 4.5 ± 0.3 mg L(-1)), 2-heptanone (LC(50) = 7.1 ± 0.3 mg L(-1) ) and 2-hexanone (LC(50) = 8.1 ± 0.6 mg L(-1)) 1 week after the treatment end. CONCLUSION Short-chain aliphatic ketones have potential for applications in IPM programmes for the granary weevil because of their behaviour-altering activity and fumigant toxicity.

Chemical cues for host location by the chestnut gall wasp, Dryocosmus kuriphilus.

Dryocosmus kuriphilus is one of the most damaging pests of Castanea spp. Behavioral, chemical, and electrophysiological investigations were employed to examine the role of plant volatiles for host location by this thelytokuos cynipid. Y-tube olfactometer bioassays showed that adult wasps are significantly attracted by C. sativa twigs with at least 1-hr-old mechanical damage. Odors of undamaged host seedlings, intact twigs, and twigs with a fresh mechanical damage were not attractive. Wasps were repelled by plant materials of the non-host Prunus laurocerasus. Fourteen compounds, mainly general green leaf volatiles, were identified in the head-space of attractive host plant twigs by gas chromatography coupled to mass spectrometry. All compounds elicited dose-dependent antennal responses in adult wasps. A synthetic blend comprising all identified compounds in the same ratio as in the attractive host source induced significant positive responses in Y-tube olfactometer bioassays. The study gives a basis for future identification of host plant attractants that could contribute to semiochemical-based monitoring and management practices of this pest.

Detection of fungal metabolites of various Trichoderma species by the aphid Schizaphis graminum

The feeding preferences of alate and apterous morphs of the aphid Schizaphis graminum (Rondani) (Homoptera: Aphididae) were evaluated using leaves treated with powdered rice cultures of four fungal isolates belonging to different species of the genus Trichoderma (Deuteromycotina: Hyphomycetes). All of the fungal isolates restrained alate morphs of S. graminum from visiting treated leaves, but only Trichoderma citrinoviride Bisset also influenced the preference of apterous morphs. Trials carried out with supernatants obtained by centrifuging aqueous suspensions of the fungal cultures showed that the feeding preference of aphids was maintained in the absence of fungal spores and mycelia, supporting the hypothesis that at least part of the fungal metabolites responsible for this effect were water‐soluble compounds. Electrophysiological studies showed that the structures involved in the perception of the fungal metabolites are located on the aphid tarsomeres.

Attractiveness of year-old polyethylene Isonet sex pheromone dispensers for Lobesia botrana

In this study, we have compared the release of sex pheromone from mating disruption dispensers exposed in the field for 12 months and from calling females. The main pheromone component of the grapevine moth, Lobesia botrana (D. and S.) (Lepidoptera: Tortricidae), is (E)‐7,(Z)‐9‐dodecadienyl acetate, and a minor component is (Z)‐9‐dodecenyl acetate. Aged dispensers from two different years emitted a much higher amount of both pheromone components than calling females. However, the summer temperature during field exposure influenced the release from mating disruption dispensers the following year. In the wind tunnel, male L. botrana were equally attracted to 12‐month, field‐exposed dispensers, a standard monitoring pheromone lure, and to synthetic (E)‐7,(Z)‐9‐dodecadienyl acetate sprayed at the rate of 0.6–60 ng h−1. Field trapping tests confirmed that aged dispensers from both years were at least as attractive to L. botrana males as a standard monitoring pheromone lure. The possible contribution of previously applied dispensers to the mating disruption efficacy during following applications is discussed.