Anna-Carin Bäckman

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.

Behavioral observations of codling moth, Cydia pomonella, in orchards permeated with synthetic pheromone

Mating disruption of codling moth, Cydia pomonella, was studied in apple orchards treated with the main pheromone compound codlemone, (E,E)-8,10-dodecadienol, and a blend of codlemone and codlemone acetate, (E,E)-8,10-dodecadienyl acetate, a strong pheromone antagonist. Codlemone alone and the pheromone/antagonist-blend had a similar effect on the behavior of males emerging into air-permeated orchards. Male flights within tree canopy and upwind orientation along tree rows were strongly enhanced by both formulations, compared to untreated plots. However, the codlemone/codlemone acetate-blend increased the rate of cross-wind and downwind flights within the orchard, compared to codlemone alone. The major difference between these two formulations was that males from nearby, untreated orchards were attracted towards orchards treated with codlemone, but not towards treatments with codlemone/codlemone acetate. Additional tests were done with an equilibrium blend of codlemone and its geometric isomers. Aerial pheromone concentrations in the orchards were recorded by the field electroantennogram technique. Decreasing pheromone concentrations towards the upper part of the tree canopy, together with the stimulation of male flight activity by synthetic pheromone explains failures to control codling moth at high population densities with current dispenser formulations.

Identification of further sex pheromone synergists in the codling moth, Cydia pomonella

Pheromone gland extracts of codling moth females were examined by gas chromatography coupled with mass spectrometry and electroantennography. Nine compounds elicited antennal activity: the main pheromone compound codlemone (E,E)‐8,10‐dodecadienol, the E,Z and Z,E isomers of codlemone, codlemone acetate (E,E)‐8,10‐dodecadienyl acetate, codlemone aldehyde (E,E)‐8,10‐dodecadienal, the monounsaturated alcohols (E)‐8‐dodecenol and (E)‐9‐dodecenol, and dodecanol. In wind tunnel experiments, addition of dodecanol, the E,Z isomer of codlemone and codlemone acetate augmented male attraction to codlemone at the proportions found in female glands. Larger amounts of the E,Z isomer of codlemone and codlemone acetate had a strong antagonistic effect on male attraction. The identification of pheromone synergists in codling moth is of importance for the development of pheromone‐ based control methods.

Attraction of Female Grapevine Moth to Common and Specific Olfactory Cues from 2 Host Plants

In herbivorous insects with more than 1 host plant, attraction to host odor could conceptually be mediated by common compounds, by specific compounds released by each plant or by combinations of common and specific compounds. We have compared the attraction of female grapevine moth, Lobesia botrana, with specific and common (shared) odors from 2 different plants: a wild host (Daphne gnidium) and a recently colonized host (Vitis vinifera). Odor blends eliciting female attraction to V. vinifera have previously been identified. In this study, olfactory cues from D. gnidium were identified by electroantennographic detection and chemical analysis. The attraction of mated females to synthetic odor blends was then tested in a wind tunnel bioassay. Female attraction was elicited by a blend of compounds released by both from D. gnidium and V. vinifera and by 2 blends with the compounds released specifically from each host. However, more complete odor blends of the 2 plants elicited stronger attraction. The common compounds in combination with the specific compounds of D. gnidium were the most attractive blend. This blend was tested with the common compounds presented both in the ratio emitted by D. gnidium and by V. vinifera, but there was no difference in female attraction. Our findings suggest that specific as well as common plant odor cues play a role in L. botrana host recognition and that there is plasticity in attraction to partial blends. The results are discussed in relation to mechanisms behind host odor recognition and the evolution of insect-plant associations.

PHEROMONE RELEASE BY INDIVIDUAL FEMALES OF CODLING MOTH, Cydia pomonella

The gland titer and release of sex pheromone was studied in individual Cydia pomonella females. An increase of the main compound (E,E)-8,10-dodecadien-1-ol (codlemone) from 5.5 to 9 ng/gland, during the first 2 hr of calling, matched an increase in the release rate from 5 to 7 ng/hr/female. The average proportion of the minor compounds dodecan-1-ol, (E)-9-dodecen-1-ol, and tetradecan-1-ol in the effluvium decreased within 2 hr from 59% to 33%. Their proportion in the gland peaked 1 hr before the onset of the scotophase at 78% and decreased to 16% at 2 hr after onset of calling. Addition of these minor components to codlemone did not increase male attraction to field traps.

Volatiles from apple (Malus domestica) eliciting antennal responses in female codling moth Cydia pomonella (L.) (Lepidoptera : Tortricidae): Effect of plant injury and sampling technique

Abstract The antennal responses of codling moth females, Cydia pomonella, to volatiles from apple branches with green fruits were recorded by electroantennography coupled to gas chroma tography. The antennae strongly responded to 4,8-dimethyl-1,3(E),7-nonatriene, linalool, β-caryophyllene, (E)-β-farnesene, germacrene D, (Z,E)-α-farnesene, (E,E)-α -farnesene and methyl salicylate. These compounds were all present in volatile collections on Porapak Q from both living and cut branches. Analysis by the solid phase microextraction technique (SPME) showed that the emission of some electrophysiologically active compounds increased after branches had been cut, especially 4,8-dim ethyl-1,3(E),7-nonatriene, linalool and (E,E)-α-farnesene. The identification of apple volatiles eliciting antennal responses is the first step towards the identification of compounds mediating host-finding and oviposition in codling moth females.

Antennal response of codling moth males, Cydia pomonella L. (Lepidoptera: Tortricidae), to the geometric isomers of codlemone and codlemone acetate.

Abstract Single sensillum recordings from Cydia pomonella male antennae showed three different types of receptor neurons. The most abundant type was most sensitive to the main pheromone compound (E,E)-8,10-dodecadienol, while its response to the geometric isomers E,Z, Z,E and Z,Z was comparable to a tenfold lower dose of (E,E)-8,10-dodecadienol. This neuron type also responded to the four behaviorally antagonistic isomers of (Δ,Δ)-8,10-dodecadienyl acetate, among which it was most sensitive to the E,E isomer. Cross-adaptation studies showed that these compounds were all detected by the same receptor neuron type. Receptor neurons specifically tuned to (E,Z) or (Z,Z)-8,10-dodecadienol were not found, although these two compounds are behaviorally active. A second type of receptor neuron responded to all isomers of (Δ,Δ)-8,10-dodecadienyl acetate and was most sensitive to the E,E isomer. This neuron type did not respond to any of the isomers of (Δ,Δ)-8,10-dodecadienol. A third receptor neuron type was highly sensitive to the plant compound α-farnesene. The finding that the receptor neuron type tuned to the main pheromone compound responded even to strong behavioral antagonists aids the interpretation of ongoing behavioral studies for the development of the mating disruption technique in codling moth.

New Pheromone Components of the Grapevine Moth Lobesia botrana

Analysis of extracts of sex pheromone glands of grapevine moth females Lobesia botrana showed three previously unidentified compounds, (E)-7-dodecenyl acetate and the (E,E)- and (Z,E)-isomers of 7,9,11-dodecatrienyl acetate. This is the first account of a triply unsaturated pheromone component in a tortricid moth. The monoenic acetate (E)-7-dodecenyl acetate and the trienic acetate (7Z,9E,11)-dodecatrienyl acetate significantly enhanced responses of males to the main pheromone compound, (7E,9Z)-7,9-dodecadienyl acetate, in the wind tunnel. The identification of sex pheromone synergists in L. botrana may be of practical importance for the development of integrated pest management systems.

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.

Potential of a blend of E8,E10-120H and E8,E10-12Ac for mating disruption of codling moth, Cydia pomonella L. (Lep., Tortricidae)

Abstract: Dispensers of E8,E10‐12OH (codlemone), E8,E10‐12Ac (codlemone acetate), or both dispenser types were placed on the corners of 100 m2 and 300 m2 plots within apple orchards. Communication disruption of male codling moths, Cydia pomonella, was monitored with pheromone traps in the centres of these plots. In the 300 m2 plots, trap catch was reduced only by codlemone. In the 100 m2 plots, trap catch was reduced in all three treatments, fewest males were caught in plots treated with both codlemone and codlemone acetate. Males were attracted to codlemone dispensers, they were also flying actively around the tree crowns, well above the dispensers. This behaviour was not observed in treatments with codlemone acetate, where male orientation flights were directed only towards the trap in the plot centre. The antagonistic effect of each of the four geometric isomers of codlemone acetate was shown by another trap test. Addition of 20% E,E‐; E,Z‐; Z,E‐ or Z8,Z10‐12Ac decreased male attraction to traps baited with E8, E10‐12OH.