Friedrich Louis, Karl-Josef Schirra1 and Michael Feldhege2
Fachbereich Phytomedizin, Staatliche Lehr- und Forschungsanstalt für Landwirtschaft, Weinbau und Gartenbau, 67435 Neustadt/Weinstrafle, Germany
Abstract - Population densities, migration and long-term effects of mating disruption of Lobesia botrana were investigated in German vineyards during several years. Furthermore, the effect of beneficial organisms on pest control was studied.
Key words - sex pheromone, mating disruption, viticulture, population density, Lobesia botrana, Eupoecilia ambiguella, Sparganothis pilleriana, Tortricidae, Lepidoptera
Introduction
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In German wine-growing areas, the grape moth Lobesia botrana Schiff. and the grape berry moth Eupoecilia ambiguella Hbn. are the most widespread pests. During the last ten years there has been a distinct shift in the abundance of these two species: the population density of L. botrana has increased considerably in many regions, while the density of E. ambiguella has decreased concurrently.
In 1986, the pheromone dispenser RAK 1 Plus, containing (Z)-9-dodecen-1-yl acetate as active ingredient, was officially registered for mating disruption of E. ambiguella in Germany. In 1994, the RAK 1+2 dispenser, with (E,Z)-7,9-dodecadien-1-yl acetate and (Z)-9-dodecen-1-yl acetate) as active ingredients, was registered for mating disruption of both species. In 1996, 17% of all German vineyards were treated with pheromone for control of E. ambiguella and L. botrana by mating disruption. During several years, various aspects of L. botrana population dynamics and the effect of beneficial organisms on control by mating disruption have been investigated.
Population densities of L. botrana
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By conventional trapping methods, for example pheromone traps, it is impossible to determine absolute moth densities. A sampling system based on a non-luring principle was developed which enabled us to determine the real density of male and female moths. For this purpose, a 2 x 5 m gauze tent was used, which was easily set up anywhere within a vineyard. After the moths had been disturbed by shaking the foliage within the tent, they gathered mostly at the tent-roof from were they could be sampled by a vacuum cleaner (Feldhege et al. 1994). Based on measurements on 10 m2, we estimated the number of moths/ha. In addition to the described sampling method, we also used a suction-trap, light traps and liquid bait traps for specific investigations.
The tent-system proved to be very suitable for recording the number of moths during the second generation. At the onset of the flight period of the second generation, the number of males was superior to the number of females (1:0.36), whereas at the end of the flight period females dominated (1:3.84). In total, the sex ratio was roughly balanced.
During the second generation, the densities of moths in the border zones of the vineyard differed widely compared to those found in the centre of the same vineyard. For example in 1994, the estimated density of L. botrana in the border zone was 210 000 moths/ha; compared to 98 000 moths/ha in the centre. In 1995, sampling with a suction-trap revealed a density of about 260 000 moths/ha in the border zone and only 10 000 moths/ha in the centre. In general, the moth density correlated significantly to the density of eggs and larvae counted in the respective vineyard zones. Therefore, monitoring of oviposition and first appearance of larvae in border zones of vineyards should have first priority.
During the first generation, the density of moths in vineyards which were not treated with pheromones, was rather low with a maximum of 3 500 moths/ha. It seems that the low density of moths during the first generation in the vines was due to the sparse vine foliage at this early stage - high numbers of female L. botrana moths were detected within greencover plants on the vineyard ground and in the adjoining hedges. This may also explain increased L. botrana -attacks in border zones of vineyards adjacent to gardens.
In 1993, migration of L. botrana was investigated in a 50-ha vineyard. The vines had been removed during winter and along with them all L. botrana pupae. Using bait traps and pheromone traps, it was shown that mainly male moths flew up to 450 m into the centre of this area, during the first year of recultivation. Already in the second year, the density of female moths in the center of the recultivated vineyard was the same as in the surrounding vineyards. A surprising result was obtained from release-recapture experiments. Two female moths covered a distance of about 2 600 m within one day.
With modified light traps we investigated the migration of L. botrana moths between pheromone-treated and untreated areas. The light traps were equipped with four funnels pointing in four different directions. The trapping results showed that a significant number of male moths was attracted to the pheromone atmosphere, whereas no significant migration of female moths was detected. Higher densities of male L. botrana moths in the border zones and consequently higher rates of mating could explain the increased infestation levels observed in the border zone of pheromone-treated vineyards. Under German cultivation conditions, it seems to be absolutely necessary to apply pheromone dispensers to a border zone of 30 metres within adjacent, untreated vineyards in order to avoid higher infestation rates.
Critical population density
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The tent system was also used to obtain an estimation of the "critical density of moths" in pheromone-treated vineyards, above which mating disruption is no longer effective. In 1994, nearly no matings or oviposition occured at densities of up to 4 000 males/ha and 4 000 females/ha in the experimental area. When the number of moths exceeded the critical threshold of 8 000 moths/ha, nearly all female moths were mated and there was also a significant increase in the number of eggs on the grapes (Feldhege et al. 1995).
Long-term effects of pheromone application
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The results obtained between 1992 and 1996 on an area covering 60 ha revealed very clearly long-term effects of the mating disruption treatment. RAK 1+2, for mating disruption of L. botrana and E. ambiguella, was applied at 500 dispensers/ha. Further vineyard plots which were not sprayed with insecticides were set in distances of 150 m up to 500 m to the pheromone-treated area. In some years the density of larvae grew considerably in these control plots. In the second generation of 1994, for instance, there was an average of 6.7 larvae per cluster of grapes (Figure). In the pheromone-treated area only L. botrana appeared. However, in the pheromone treated area the density of moths decreased significantly and we gained stable degrees of effectiveness up to 98.7%. This leads to the conclusion that pheromone treatment applied over many years obviously reduces the population density of L. botrana .
Figure Control of the grape moth L. botrana by mating disruption with pheromone in Neustadt/W.-Haardt. Infestation rates during the second generation in pheromone-treated and control plots
Another long-term project focussed on mating disruption and its side effects on beneficial organisms in viticulture. In a three-year-study it was proven that, in pheromone-treated plots, the European red spider mite, Panonychus ulmi Koch, did not occur anymore due to high densities of the predator Typhlodromus pyri Scheuten. Plots which were treated with the insecticide Deltamethrin showed high densities of P. ulmi, but only low numbers of T. pyri. Nowadays, treatments with acaricides is the exception in Germany, due to the long-term use of pheromones or due to the application of pesticides without negative side-effects on beneficials as T. pyri.
From 1987 to 1990, further experiments focussed on arthropodes in insecticide- and pheromone-treated plots. In total, more than 34 000 individuals were recorded and investigated. Representative for all other studies one result will be presented here.
The experiments were conducted in four replicates. Compared to the insecticide treated plots, the pheromone-treated sites showed more than twice the number of individuals at the vine trunks. Most of the species belonged to the order Araneida. In addition to a larger number of individuals, the diversity of species was much higher in the pheromone-treated plots (Schirra et al. 1991).
From 1991 to 1994, another project was carried out to study the effects of beneficial organisms in pheromone-treated areas on the pest populations. It was not definitely proven that predators have a regulating influence on pests because the density of E. ambiguella and L. botrana was too low due to the high efficiency of the pheromone treatment. At the vine trunks, the araneid species Salticus scenicus and Marpissa muscosa were predominant. A regulation of the immigration of larvae of pests in the vine-trunk section by predators seems conceivable.
In contrast to the predators, there was a significant effect of parasitoids on grape moths. Up to 43% of the overwintering grape moth pupae were infested with parasitoids. The ichneumonid species Itoplectis alternans was predominant among the parasitoids attacking the grape moths; Braconidae and Calcidoidae were found to a lesser extent.
Remarkable densities of another grape moth, Sparganothis pilleriana Schiff. were recorded in the investigated areas. However, the density of S. pilleriana in vineyards treated with pheromone against L. botrana and E. ambiguella was not significantly higher than in insecticide-treated plots. The rate of pupae of S. pilleriana infested by parasitoids was 28% (1 917 pupae examined) in the pheromone-treated sites. In addition, up to 25% of S. pilleriana pupae had been prey of predators. In laboratory assays it was established that Forficula auricularia, a most important predator, was responsible for the specific damage of the S. pilleriana pupae (Schirra & Louis 1995).
Acknowledgements
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The investigations were made possible by financial support from the German Ministry of Science and Technology (BMFT) and BASF, Germany.
References
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Feldhege M, Louis F, Schmutterer H (1994) Eine neue Methode zur Bestimmung von Traubenwickler-Falterdichten im Weinbau (New method for determination of densities of grape moths in viticulture). Anz Schädlingskde Pflanzenschutz Umweltschutz 67, 137-142
Feldhege M, Louis F, Schmutterer H (1995) Untersuchungen über Falterabundanzen des Bekreuzten Traubenwicklers Lobesia botrana Schiff. im Weinbau (Investigations on abundances of the grape moth Lobesia botrana Schiff. in viticulture). Anz Schädlingskde Pflanzenschutz Umweltschutz 68, 85-91
Schirra KJ, Eichhorn KW, Tretzel E, Louis F (1991) Integrierter Pflanzenschutz im Weinbau, Einfluß einer insektizidfreien Spritzfolge im Weinbau auf die Populationsentwicklung von Nützlingen und Gelegenheitsschädlingen in Schriftenreihe des Bundesministers für Ernährung, Landwirtschaft und Forsten, Reihe A, Angewandte Wissenschaft, Heft 396. Landwirtschaftsverlag GmbH, Münster-Hiltrup
Schirra KJ, Louis F (1995) Auftreten von natürlichen Antagonisten des Springwurmwicklers Sparganothis pilleriana in der Pfalz. Deutsches Weinbau-Jahrbuch 46, 129-140