Survey of parasitoids associated with the San Jose scale in Uruguay: selection and optimization of the rearing of a promising parasitoid for biological control

The San Jose scale, Comstockaspis perniciosa (Comstock, 1881) (Hemiptera: Diaspididae), is a pest of deciduous fruit trees. In Uruguay, it is controlled through winter treatments with mineral oils and pyriproxyfen, the latter being the only insecticide recommended outside the winter season, thereby increasing the risk of resistance development. Therefore, alternative control strategies that promote agroecosystem sustainability are needed. In Diaspididae, inundative releases of parasitoids constitute an effective control option. Since the parasitoids associated with this pest in southern Uruguay were surveyed more than three decades ago in a single orchard, crop, and season, an updated survey is necessary. The objectives of this study were to characterize the parasitoid community associated with the San Jose scale in deciduous fruit orchards of southern Uruguay, to select a species with potential for use in biological control, and to evaluate biological aspects of this species in order to optimize its production and use in inundative releases. Six orchards with different crops and management systems were sampled over a two-year period. The developmental stage and parasitism status of the scales were recorded, and the emerged parasitoids were identified using morphological and molecular approaches. Their relative abundance and frequency were estimated according to sampling date, season, crop, and year. Fifteen parasitoids taxa were identified, among which Aphytis sp. nov. stood out because it was present in both years and in all crops, and was frequently the most abundant. Based on these results and previous literature, it was selected as a promising candidate for the biological control of the San Jose scale. Under laboratory conditions, its rearing was initiated on an alternative host, and the most productive host stage, longevity, and daily parasitism were evaluated. The highest production was obtained by parasitizing adult scales. The parasitoids lived for 10 ± 1 days (mean ± SE), with the highest oviposition on the first day and the highest adult emergence from day 7 onward. An optimal parasitoid–host exposure period of 10 days is proposed, allowing a sevenfold increase in production in each parasitism event and supporting the feasibility of its use in inundative releases as an alternative to insecticides.