Mating disruption field trials to control the olive moth, Prays oleae  Bern: a four-year study

• Introduction
• Materials and methods
• Results and discussion
  • Trap catch
  • Fruit infestation
• Conclusion
• References

Key words - sex pheromone, mating disruption, (Z)-7-tetradecenal, olive moth, Prays oleae, Yponomeutidae, Lepidoptera

Introduction
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The olive moth Prays oleae  is one of the most serious pests of olives in the Mediterranean basin. This moth has three generations per year. The first generation appears in April and the females lay their eggs on the blossoms, the hatching larvae live and feed within the blossom and on the flower at the later stage of their development. The second generation emerging early June is the most economic damaging. The females lay the eggs on the small fruits close to the stem, that holds the fruit, the larvae bores within the stone of the olive fruit and when they complete their development in September, coming out from the fruits are causing spectacular fruit drop with major crop losses. The third generation attacks the leaves the emerging larvae mine the olive leaves in autumn hibernate as larvae and complete their development early next spring. Two to three sprays by chemical pesticides are required annually to prevent premature olive fruit drop.

The major sex pheromone (Z)-7-tetradecenal (Z7-14Ald) produced by the female olive moth was identified by Campion et al. (1979). Pheromone traps have been used to monitor the moth population and have been found to be very effective in trapping males (Ramos et al. 1988). An integrated pest management system that uses pheromone baited traps to monitor the olive moth population and to time the application of control measures has been reported (Ramos et al. 1989).

Pheromones are used in mating disruption trials to control several lepidopterous species (Carde & Minks 1995). Here we present the results obtained when the mating disruption method was evaluated, for four consecutive years. The effectiveness of the mating disruption was assessed by male captures in pheromone traps and measuring fruit infestation levels in mating disruption plots compared with those treated with B. thurigiensis, or left untreated.

Materials and methods
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Plot selection and description. The area where the method was evaluated is located in the province of Attikis. The grove approx. 8 ha, is the main grove in this region surrounded by vineyards, pistatio and pasture fields. The grove was divided into 2 plots, a third olive field approx. 2 ha and 300 m apart was used as control this field was left untreated during this study.

Pheromone formulations. The major sex pheromone component Z7-14Ald was formulated in ß-cyclodextrin (ß-CD) (Mazomenos & Moustakali-Mavridis 1993), or black polyvinyl chloride (PVC) strings (AgriSence BCS Ltd., Pontypridd, UK).

Mating disruption. The pheromone dispensers were applied prior to the emergence of the moths that give rise to the second generation. The pheromone formulated in (ß-CD) was dispensed from plastic bags. The release rate of the pheromone was measured by capillary GC and was ranged from 43.2 mg/h/ha initially to 12.5 mg/h/ha, 15 weeks later. The pheromone release rate was not measured for (PVC)-Z7-14Ald formulation, according to the producer's this formulation release sufficient amounts of pheromone for mating disruption for 45-50 days. Three bags or (PVC) strings were hanged at head height outside the canopy of each tree the pheromone concentration per hectare was 40 g.

Results and discussion
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Trap catch

The total number of males captured in pheromone traps for each generation every year in pheromone treated, or untreated plots are presented in Table. During the first year of the experiment in 1992 the grove was treated with B. thurigiensis, when 10% of the flowers were open. In order to suppress the larvae population of the flower generation and minimise the potential failure of the mating disruption treatment.

The number of males caught in pheromone baited traps in the plot 2 that received only a B. thurigiensis treatment was slightly reduced compared to the males caught in the untreated plot.The ß-CD pheromone dispensers installed in plot 1, prior to the emergence of the second generation inhibited male captures in the pheromone traps by 99.2%. The number of males caught in the pheromone traps during the third generation September and October was also low. This indicated that the pheromone concentration within the treated plot remain at relatively high levels resulting in a high proportion of male disorientation. In 1993 the moth population was low in the pheromone treated plot during the first generation. All the plots were left untreated in this generation. At the second generation where plot 1 and 2 were treated with ß-CD and PVC dispensers respectively, 98% reductions in trap catches were achieved. Reduction in trap catches was also observed during the third generation. In 1994 and 1995 the moth population in plots 1 and 2 was low in the first generation. The ß-CD pheromone dispensers applied prior to the second generation completely inhibited pheromone traps catches. The level of male disorientation to pheromone traps was also high for the third generation and reached 99.4%.

Table Pheromone trap catches of Prays oleae  males in plots treated with pheromone dispensers (mating disruption), Bacillus thurigiensis , and untreated.

^a Plots 1, 2 were treated with B. thurigiensis  during the 1st generation, plot 1 was treated with ß-CD-Z7-14Ald dispensers during the 2nd generation;
^b plot 1 was treated with ß-CD Z7-14Ald dispensers, plot 2 with PVC-Z7-14Ald dispensers during the 2nd generation;
^c plots 1, 2 were treated with ß-CD-Z7-14Ald dispensers during the second generation.

Fruit infestation
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In 1992 the level of fruit infestation in plot 1, remained low 3.4% of the olives were infested while in B. thurigiensis  and the untreated plots 33% and 26% of the fruit were infested. In 1993 although the male catches to the pheromone traps were reduced by 98%, the fruit infestation was 32% and 30% for plots 1 and 2 respectively compared to 38% found in the untreated plot. The high level of fruit infestation during this year is the result of limited oviposition substrate available to the females because of the year's very low olive fruits production. 1994 was a year of high fruit production and the level of fruit infestation remained below the 2% in the treated plot compared with the 28% observed in the untreated plot. In 1995 the fruit infestation in mating disruption plots remained at low level, only 3.7% of the fruits were infested compared to 27% found in the untreated plot, despite the fact that 1995 was a low fruiting year.

Conclusion
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The results presented here suggest that the mating disruption can be used successfully to control the olive moth. Both pheromone formulations used, proved to be very effective controlled release devices for the pheromone in the field and both provide adequate protection of the aldehyde molecule from rapid degradation. The pheromone release rate seems to be higher in the (PVC) dispensers and they need to be replaced at least once to provide satisfactory male disorientation for the three adult flight periods. The (ß-CD)-pheromone complex maintained high pheromone release rate for longer period. It was also observed that the effectiveness of the mating disruption depends on the availability of ovipositional sites. In a low fruiting year, fruit damage is higher compared to that of a high fruiting year. Continuous application of these methods in the same olive groves progressively reduced pest population from one year to the next.

Acknowledgements

We thank Mr. D. Papadopoulos for allowing us to use his olive grove and for his assistance during the field trials. The contribution of pheromone dispensers by AgriSence-BCS Ltd. is appreciated. This study was partially supported by the EU programmes VALUE Cont. No CTT-472 and ECLAIR Cont No AGRE-0013C.

References
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Campion DC. McVeigh LO, Polyrakis J, Michelakis S, Stavrakis G, Beevor PS, Hall DR, Nesbitt BF (1979) Laboratory and field studies of the female sex pheromone of the olive moth Prays oleae . Experientia 35, 1146-1147

Cardé RT, Minks AK (1995) Control of moth pests by mating disruption: successes and constrains. Annu Rev Entomol 40, 559-585

Mazomenos BE, Moustakali-Mavridis I (1993) New inclusion complexes of cyclodextrin, process for their preparation and their use in slow release formulation for attracting insects. International Patent, Appl Nr PCT/EP93/01536, Publ Nr WO 93/25076, 23/12/93

Pelekasis CE (1962) A contribution to the study of nomenclature, taxonomy, biology and natural parasitization of the olive kernel borer Prays oleae  (Bern). Annales de l'Institute Phytopathologique. Benaki 4, 180-308

Ramos P, Ramos JM, Jones OT (1988) An integrated pest management strategy for the olive moth Prays oleae based on the relationship between the catches of adults in pheromone traps and subsequent infestation of olive fruit, pp. 121-122 in H. Arn, R. Bues (eds.) Use of pheromones and other semiochemicals in integrated control. IOBC wprs Bulletin 12(2)

Ramos P, Campos M,. Ramos JM, Jones OT (1989) Nine years of studies on the relationship between captures of male olive moth Prays oleae Bern (Lepidoptera:Yponomeutidae) in sex pheromone baited traps and fruit infestation by subsequent larval generations (1979-1987). Tropical Pest Management 35, 201-204
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