IOBC wprs Bulletin Vol 22(9), 1999
Sex pheromone of the Brazilian apple leafroller, Bonagota cranaodes (Lepidoptera: Tortricidae): effect of geometric isomers on male attraction to (E,Z)-3,5-dodecadienyl acetate
Miryan D. A. Coracini, Aurelia Reckziegel,1 Marie Bengtsson, Jan Löfqvist, Alvaro E. Eiras,2 Evaldo F. Vilela3 and Peter Witzgall
Department of Plant Protection Sciences, Swedish University of Agricultural Sciences, Alnarp, SwedenAbstract: The behavioural response of male Brazilian apple leafroller, Bonagota cranaodes (Meyrick), to the main sex pheromone compound (E,Z)-3,5-dodecadienyl acetate (E3,Z5-12Ac) and to female extracts was studied in a wind tunnel. A field trapping test showed that contamination of the main compound with the non-pheromonal isomers E,E; Z,E and Z,Z does not account for the discrepancy in male attraction to E3,Z5-12Ac and female extracts.
Key words: Bonagota cranaodes, Tortricidae, Lepidoptera, sex pheromone, (E,Z)-3,5-dodecadienyl acetate, geometric isomer, behavior, flight tunnel
Introduction
The Brazilian apple leafroller, Bonagota cranaodes, is a most important pest in apple orchards in Brazil and Uruguay. Populations increase between December and May, but B. cranaodes occurs throughout the year (Lorenzato 1984), necessitating multiple insecticide sprays. New methods to control this pest need to be developed since chemical control is costly and not efficient.
The main compound of the sex pheromone of B. cranaodes is (E,Z)-3,5-dodecadienyl acetate (E3,Z5-12Ac) (Unelius et al. 1996; Eiras et al. 1999), but traps baited with this compound are still not reliable enough for population monitoring. We have therefore investigated a possible antagonistic effect of the non-pheromonal isomers E,E-, Z,E-, and Z3,Z5-12Ac on male attraction to E3,Z5-12Ac. Male orientation to the main compound and female gland extracts was compared in a wind tunnel.
Material and methods
The field trials were carried out in an apple orchard in Videira (Brazil), January to February, 1999. Tetra traps (Arn et al. 1979) baited with E3, Z5-12Ac alone and binary blends with 5% and 20% of E,E-, Z,E-, and Z,3,Z5-12Ac, formulated on red rubber septa, were placed at eye level, along tree rows (N=10). Isomeric purity of the compounds was 98%.
Insects were reared on semiartificial diet. Extracts of sex pheromone glands were prepared during the scotophase. Fifty glands were extracted in 7 µl heptane at room temperature for 1 min.
Wind tunnel tests were done at a light intensity of 5 lux, 30 cm/s wind speed, and air temperatures ranging from 23 to 26°C. Males were flown towards live calling females, female extracts at release rates of 0.1, 1, 10, and 100 pg/min of the main compound E3,Z5-12Ac, and the main compound by itself at rates of 0.1, 1, and 10 pg/min. Quantified female extracts and synthetic compound were dispensed from the pheromone sprayer (El-Sayed et al., 1999). Calling females were placed individually inside small glass tubes stoppered by rigid gauze.
Batches of 15 males were transferred, 15 min before the tests, to glass tubes (2.5 x 15 cm) closed with gauze on both ends. Each test session comprised 3 batches of 15 males, and lasted 3 to 4 h, after onset of the scotophase. Males were released individually in the wind tunnel and the following behavioral responses were recorded: walking and wingfanning during activation phase in the release tube (AT); upwind flight (UW); touchdown at source (TD); walking and wingfanning at source (WW). Males were allowed 2 min to respond. Each treatment was tested once per day.
The numbers of males observed for each behavioral step in the wind tunnel, and the numbers of males caught in traps were transformed to log(x+1) and submitted to an analysis of variance, followed by a Tukey-test. Significance level was set at 0.05.
Results and discussion
The field attraction of the Brazilian apple leafroller, B. cranaodes, to blends of E3,Z5-12Ac and its geometric isomers is shown in Table 1. Gradual isomerization of initially pure dienic compounds in the rubber septa used as dispensers has been shown to enhance or reduce male attraction in other tortricids (Davis et al. 1984; Witzgall et al. 1996). However, addition of nonpheromonal isomers had no significant effect in the trap catch of B. cranaodes, suggesting that isomeric impurities or isomerization of the main compound on rubber septa do not affect trap catch of B. cranaodes in the field. Poor attractivity of E3,Z5-12Ac in the field is accordingly rather due to missing pheromone synergists.
The number of males completing successive behavioural steps in response to calling females, female gland extracts containing known amounts of E3,Z5-12Ac, and synthetic E3,Z5-12Ac is shown in Figure. The male response to calling females was superior to the response to E3,Z5-12Ac at three release rates. In contrast to synthetic E3,Z5-12Ac, the male response to female extracts increased with higer release rates. When gland extracts were released at 100 pg E3,Z5-12Ac/min, male upwind attraction and landing at the source equalled calling females. This shows that the sex pheromone of B. cranaodes contains further compounds. Identification of these compounds is required for the development of a reliable monitoring lure and control by mating disruption.
Figure. Percentage of B. cranaodes males (N = 60) responding to calling females, synthetic E3,Z5-12Ac, and female extract at different release rates of E3,Z5-12Ac (0.1, 1, 10, and 100 pg/min). (AT) walking during activation phase in the release tube; (UW) upwind flight; (TD) touchdown at source; (WW) walking and wingfanning at source.
Table 1. Field attraction of Bonagota cranaodes males to geometric isomers of 3,5-12Ac.
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* Means are not significantly different at P = 0.05 (Tukey´s multiple-range test; N=10)
Acknowledgements
We tank Dr. Eduardo R. Hickel and Empresa de Pesquisa Agropecuária e Extensão Rural de Santa Catarina (EPAGRI), Videira, SC, Brazil, for assistance during the field bioassays. This study was supported by the International Foundation for Science (IFS).
References
Arn, H., Rauscher, S. & Schmid, A. 1979: Sex attractant formulations and traps for the grape moth Eupoecilia ambiguellla HB. Mitt. Schweiz. Entomol. Ges. 52: 49-55.
Davis, H.G., McDonough, L.M., Burditt, Jr A.K. & Bierl-Leonhardt B.A. 1984: Filbertworm sex pheromone. Identification and field tests of (E,E)- and (E,Z)-8,10-dodecadien-1-ol acetates. J. chem. Ecol. 10: 53-61.
Eiras, A.E., Kovaleski, A., Vilela, E.F., Chambon, J-P., Unelius, C.R., Borg-Karlson, A-K., Liblikas, I., Mozuraitis, R., Bengtsson, M. & Witzgall, P. 1999: Sex pheromone of the Brazilian apple leafroller, Bonagota cranaodes Meyrick (Lepidoptera: Tortricidae). Z. f. Naturf. (in press)
El-Sayed, A., Gödde, J. Witzgall, P. & Arn, H. 1999. Characterization of the pheromone blend for the grapevine moth, Lobesia botrana (Lepidoptera: Tortricidae) by using flight track analysis. J. Chem. Ecol. 25: 389-400.
Lorenzato, D. 1984: Ensaio laboratorial de controle da "traça da maçã" Phtheocroa cranaodes Meyrick, 1937 com Bacillus thuringiensis Berliner e inseticidas químicos. Agronomia Sulriograndense 20: 153-163.
Unelius, C.R., Eiras, A.E., Witzgall, P., Bengtsson, M., Kovaleski, A., Vilela, E.F. & Borg-Karlson, A-K. 1996: Identification and synthesis of the sex pheromone of Phtheocroa cranaodes (Lepidoptera: Tortricidae). Tetrahedron Letters 37: 1505-1508.
Witzgall, P., Bengtsson, M., Unelius, C.R., Löfqvist, J. 1993: Attraction of pea moth Cydia nigricana F. (Lepidoptera:Tortricida) to female sex pheromone (E,E)-8,10-dodecadien-1-yl acetate, is inhibited by geometric isomers E,Z, Z,E and Z,Z. J. chem. Ecol. 19: 1917-1928.