IOBC wprs Bulletin Vol 22(9), 1999

Pheromone analogues with ether structure: a preliminary report

Lidia Pop, Heinrich Arn1, Ioan Oprean, Stefan Rauscher1,Viorica Chis, Alexandru Szabo2

Abstract: Two ether structure pheromone analogues corresponding to the sex pheromone of Mamestra brassicae and Lobesia botrana were tested. The field and laboratory preliminary tests have demonstrate that they are not attractive for the insects. At higher doses, the mating of the preexposed males was suppressed by 60-80%.

Key words: sex pheromone analogues, Mamestra brassicae., Lobesia botrana

Introduction

Sex pheromone analogues are considered the structural analogues compounds which mimic their biological activity. In the pheromone analogues with ether structure we try to keep the important sites for the biological activity of the pheromone molecules. The changes were done at the double bound structure, one of the sp2 hybridised carbon was replaced with an oxygen. By replacing the p electrons from the double bond with the p electrons from oxygen an electronic similitude of the two molecules can be assumed.

tested on Mamestra brassicae insects

tested on Lobesia botrana insects

Material and methods

Two biological properties of pheromone analogues were tested: the attractivity and the ability to suppress mating. Tests with Lobesia botrana males were carried out in the wind tunnel in Wädenswil at 20°C and 30 lux (Witzgall and Arn 1990) and the behaviour of the insects recorded.

In Mamestra brassicae the attractivity to males was measured in the olfactometer and in the field, for Lobesia botrana males in the wind tunnel. Mating suppression for Mamestra brassicae were done in the olfactometer and the field, for Lobesia botrana in the wind tunnel.

Olfactometric tests. We used an olfactometer consisting of two glass cylinders of 30 cm. dia. and 50 cm long, connected with a glass tube of 2 cm dia. and 20 cm long, with access at the upwind and downwind ends (Tomescu et al. 1980). One cylinder contained the insects to be tested and the other the attraction source. Testing time was 10 minutes. The positive answer, R, was considered for males moving towards the source ( female, pheromone or analogue) across the connection tube, showing their ability to sense, to lock on and touch down on the source by a complete mating sequence behaviour.

Pre-exposure: Mamestra brasicae males were preexposed to the analogue for 8 hours before the experiment and left to fly towards calling females in the olfactometer. Each experiment was performed with 50 insects in 4-5 replicates. Unexposed males from the same generation were used as control.

Mating tests were run as follows: Mamestra brassicae males, preexposed to the ether analogue for 8-10 hours, were placed with females in Berzelius glasses, one pair per glass. After 48 hours the spermatophores from the female abdomens were counted under the microscope.

Field tests. For Mamestra brassicae, the attractivity of the ether analogue was tested in a cabbage culture and in the forest. Lures baited with 1 up to 10 mg did not attract any Mamestra species. In a mixture with 11Z-HDA the attraction was not diminished (Pop et al.1998).

The ability of two pheromone analogues to suppress the insects mating was tested in a cabbage culture. The dispensers baited with 200µl of analogue were placed at 20m intervals (36 dispensers/ha or 7.2 g/ha). An untreated field was used as control. Pheromone traps were used to check insect flight in the treated and untreated fields. The number of egg masses was recorded.

Results

No attractivity of the ether analogue of the sex pheromone of Mamestra brassicae insects could be observed in field or olfactometric test. Various mixtures of Z11-16Ac and analogue were also tested. A mixture of Z11-16Ac and analogue, in the ratio 19:1, at a dose of 4 mg has an increased attractivity, in the olfactometric test, Table 1. This result suggest that the analogue is not an antagonist.

In a wind tunnel the attractancy of the ether sex pheromone analogue was tested on Lobesia botrana males (Fig 1). As a reference, calling females were used. The high activation and take-off demonstrate that an interaction between the insects antenna and released analogue exist,. However, no orientation of the insects towards the source could be observed.

In the mating suppression experiments on Mamestra brassicae it is important to notice the correlation between the laboratory (Fig. 2 and Fig. 3) and field tests (Fig. 4 and Fig. 5). A 60-70% suppression of mating was recorded in each case.

Table 1. Response of Mamestra brassicae males on Z11-16Ac and its ether analogue in the olfactometer.

Attractant source	amount	R %
virgin females	4 females	65
11Z-16Ac	3µg	76.2
analogue	3 µg	0
analogue	10 µg	0
11Z-16Ac + analogue (19 : 1)	3 µg	97.2
11Z-16Ac + analogue (9 : 1)	3 µg	67.4
11Z-16Ac + analogue (8 : 2)	3 µg	63.2

Figure 1. Attractancy of ether analogue of Z9-12Ac at different dose on Lobesia botrana males in the wind tunnel.

Figure 2. Response of Mamestra brassicae males to calling females in the olfactometer after pre-exposure to ether sex pheromone analogue.

Figure 3. Mating suppression of Mamestra brassicae pairs exposed to analog in Berzelius glasses.

Figure 4. Mating suppression of analog on Mamestra brassicae in the field, determined by counting the number of eggs.

Figure 5. Mating suppression experiment on Mamestra brassicae insects, determined by counting the medium number of the egg plaques. Field tests.

Conclusion

The preliminary biological tests performed with the pheromone analogues with ether structure encourage us to continue our work. The possibility of using a non attractive compound to suppress mating could have a practical advantage, besides of the advantage of the low price of the ether analogues. Further experiments are requested to answer many unclear scientific aspects.

References

Tomescu, N., Stan, G., Chis, V., Jeleriu, S., & Pãstinaru, C. 1980: Laboratory bioassay of the sex pheromone of Mamestra brassicae L. (Lepidoptera : Noctuidae). Studia Univ. Babes-Bolyai Biologia 25: 50.

Witzgall, P. & Arn, H. 1990: Direct measurement of the flight behavior of male moths to calling females and synthetic sex pheromones. Z. Naturforsch. 45c: 341.

Pop, L.M., Chis, V., Stan, G., Subchev, M. 1998: Pheromone analogues with ether structure of Z(11)-hexadecenyl acetate. Entomologica Romanica 2: 95.

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