The present study was conducted to evaluate annual changes in the abundance of the parasitoids Opiinae and in their percentage of parasitism in Anastrepha larvae under influence of the climatic factors and the availability of host fruits in Seropedica, RJ, Brazil. The Opiinae Doryctobracon areolatus (Szépligeti), Utetes (Bracanastrepha) anastrephae (Viereck) and Opius bellus Gahan were collected in association with five species of Anastrepha: A. fraterculus (Wied.), A. leptozona Hendel, A. obliqua (Macquart), A. serpentina (Wied.) and A. sororcula Zucchi. During both years of sampling (1998 and 1999), D. areolatus was the most abundant species and was present in all monthly collections. U. anastrephae and O. bellus were not present in the fruit samples collected during winter (June to August). These Opiinae responded similarly to seasonal changes in climatic conditions and number of emerged flies. Although the percentages of parasitism of Anastrepha by the three species of Opiinae were not correlated with the climatic factors studied, there was a tendency of the parasitoids to parasitize more actively in the warmer and wetter months of the year (summer). In these months, the highest availability of native fruit hosts was also observed. The correlations between monthly number of adults of each parasitoid species and the average monthly rainfall and mean temperature were significant and positives. There was no correlation with the average monthly relative humidity. The three species of parasitoids were more abundant during the warmer and wetter period of the year (summer, December to February, and autumn, March to May). Decreasing of temperature and rainfall recorded from May determined a reduction in the number of parasitoid and flies emerged during winter. The fluctuations in number of Opiinae between seasons were significantly correlated with the changes in numbers of Anastrepha populations, indicating a direct density-dependent relationship. The Opiinae become more effective at high host densities, indicating that they exhibit a low host-searching capacity.
Insecta; fruit flies; tritrophic relationship; population dynamics
