IOBC wprs Bulletin Vol 22(9), 1999

Small Plot Mating Disruption Trials: Effect of Various Pheromone Doses Dispensed per Hectare on Male Prays oleae Trap Catches and Fruit Damage

Basilis E. Mazomenos, Dimitra Stefanou and Anastasia Pantazi-Mazomenou

Abstract: The effect of the pheromone concentration on mating disruption of the olive moth Prays oleae was studied in small olive groves. The major pheromone component (Z)-7-hexadecenal formulated in â-cyclodextrin was dispensed at the following doses per hectare; 5, 10, 20 and 40g/ha. Male inhibition and fruit damage were evaluated by recording the number of males caught in traps baited with 1 mg of pheromone and the number of fruits found to be infested. Results indicated that male inhibition and fruit damage depended on the amount of pheromone dispensed.

Key words: sex pheromone mating disruption, pheromone doses, Prays oleae, Lepidoptera Yponomeutidae

Introduction

The olive moth Prays oleae (Bern), is one of the most important insect pest of olives in the Mediterranean basin. The second generation females lay the eggs on the small fruits in June, and the emerging larvae bore within the olive fruit causing spectacular fruit drop in July and September.

Various methods are used for the suppression of the moth population. The larvae of the first generation are susceptible to standard strains of Bacillus thuriengiensis (var. kurstaki) (Yiambrias et al. 1986). The control measures for the second generation are insecticide treatments. The mating disruption technique evaluated during the last five years was effective in suppressing the moth population. The pheromone {(Z)-7-hexadecenal} (Campion et al. 1979), formulated in â-cyclodextrin and dispensed in olive groves at a rate of 40 to 50 g/ha, prior to the onset of the 2 nd generation inhibited male catches in pheromone traps. The fruit infestation remained below the economic threshold level (Mazomenos et al. 1999). The number of males caught in the pheromone traps in September (3 rd generation) was also low. This indicated that the pheromone concentration within the treated grove remained at relatively high levels resulting in a high proportion of trap catches inhibition.

The purpose of the work presented here is to evaluate the effect of various pheromone concentrations on male disorientation and fruit damage. The efficacy of the mating disruption was assessed by measuring male catches in the pheromone traps and fruit infestation levels in pheromone treated and control plots.

Material and methods

Experimental groves

Five small olive groves (one hectare each) were selected in the province of Attikis Greece. Each of the five groves consisted of 110 trees. The distance among the groves was more than 100 meters. The pheromone formulated in â-cyclodextrin was placed in plastic bags, in each tree three plastic bags were hung at head height on May 8. The bags were loaded with the appropriate amount of â-CD-pheromone complex so that to achieve total pheromone doses of 5, 10, 20, and 40 g/ha for each one of the four treated groves. The fifth grove was left untreated.

Assessment

The efficacy of the mating disruption was assessed by monitoring male catches in pheromone traps. Three Delta traps baited with plastic vials loaded with 1 mg of (Z)-7-14:Ald, were placed in each grove. Traps were serviced weekly and the number of males caught was recorded.

Fruit infestation

Ten trees were randomly chosen in each plot, twigs bearing olive fruits were collected, brought back to the laboratory and the level of infestation was assessed. A total of 500 fruits was collected from each grove.

Results

Trap catches

Male catches to the pheromone traps varied in each grove; in the grove treated with 5g/ha male catches were reduced. The total trap catches during 7 weeks after treatment were 91 males compared to 324 caught in the control grove. The dose of 10g/ha inhibited trap catches for 3 weeks, whilst the dose of 20 g/ha for 4 weeks. Although few males were caught in the pheromone traps, the proportion of male disorientation remained at high level 91.2 to 100 and 94.2 to 100% respectively. The number of males caught was progressively increased and most of them were caught during the last 3 weeks of the second generation flight. Male catches in the grove treated with 40g/ha was completely inhibited for the entire flight period. (Table 1).

Fruit infestation

The fruit infestation in the groves treated with pheromone was lower than the infestation found in control grove. Fruit infestation in the grove treated with 5 g/ha of pheromone was above the economic damage level. The fruit infestation in the groves treated with 10 and 20 g/ha was close to the economic acceptable levels and lower to the infestation occurred in the control grove and the grove treated with 5 g/ha. Fruit infestation in the grove treated with 40 g/ha was very low (Fig 1).

Table 1. Weekly pheromone trap catches and male disorientation in plots treated with 5,10,20 and 40 g of pheromone per hectare and untreated grove (Markopoulo, Attikis, Greece 1996).

Figure 1. Percentage of olive fruits infested with Prays oleae larvae in groves treated with different doses of pheromone and the control grove. A total of 500 fruits was examined per grove. Error bars indicate SD. Markopoulo Attikis 1998.

Discussion

The results obtained from these experiments indicated that successful mating disruption for P oleae depends on the concentration of the pheromone present in the atmosphere. In the olive grove where high concentration of pheromone was dispensed (40g/ha) mating disruption was successful. It seems that the level of pheromone concentration present in the atmosphere is maintained above the level required for male disorientation for long period. Similar concentration effects on male disorientation have been reported for other lepidopterous species (Flint et al. 1990; Suckling et al. 1996, Schmitz et al. 1977). Considering the total number of males caught and the time that trap catches began in the groves treated with 10 and 20 g/ha, the pheromone dose required for effective mating disruption may be lower than the dose of 40 to 50 g/ha currently used, in periods with low moth population densities.

References

Campion, D.C., McVmeich, L.O., Polyrakis, J., Michelakis, S. Stavrakis, G., Beevor, P., Hall, D.R., & Nesbitt, B.F. 1979: Laboratory and field studies of the female sex pheromone of the olive moth Prays oleae. Experientia 5: 1146-1147.

Flint, H.M., Yamamoto, A., Parks, N.J. & Nyomura, K. 1990: Aerial Concentration of Gossyplure, the sex pheromone of the Pink Bollworm (Lepidoptera:Gelechiidae), in Cotton Fields Treated with Long-Lasting Dispensers. Envir. Entomol. 19: 1845-1851.

Mazomenos, B.E., Ortiz, A., Mazomenos-Pantazi, A., Stefanou, D., Stavrakis, N., Karapati, C., & Fountoulakis, M. 1999: Mating disruption for the control of the olive moth Prays oleae (Bern) (Lep., Yponomeutidae) with the major sex pheromone component. J. Appl. Ent. 123.

Schmitz, V., Renou, R., Roehrich, R., Stockel, J., & Lechaprentier, P. 1977: Disruption Mechanisms of pheromone Communication in the European grape moth Lobesia botrana Den & Schiff. III. Sensory adaptation and habituation. J. Chem. Ecol. 23: 83-95.

Suckling, D.M., Karg, G. & Bradley 1996: Apple folliage enhances mating disruption of light-brown apple moth. J. Chem. Ecol. 22: 325-341.

Yiambrias, C., Broumas, T. Liaropoulos, C. & Anagnou, M. 1986: Lutte contre la teigne de l'olivier avec une preparation biologique. Annales l'Institut Phytopathologique Benaki 15: 1-10.

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