Solitary and Gregarious Parasitoid Strategies in Dipteran Host–Resource Systems in Brazil: Reproductive Amplification, Realized Parasitism, and Biological-Control Implications

Abstract

Solitary and gregarious parasitoids can produce markedly different relationships between host mortality and adult parasitoid abundance, making reproductive strategy essential for interpreting biological-control potential. This study quantitatively reanalyzed eight experimental articles on hymenopteran parasitoids associated with Diptera in Brazil, using the host pupa as the principal biological unit. Realized parasitism was calculated from parasitized host pupae, whereas emerged adults were treated separately as parasitoid production. Reproductive amplification was expressed as emerged parasitoid adults per parasitized host pupa. In a discrete gregarious dataset, 24 parasitized pupae produced 499 adults, an overall amplification of 20.79 adults per attacked pupa. In the multisubstrate Peckia chrysostoma system, 1.819 host pupae included 377 parasitized pupae that produced 1.742 parasitoid adults. Solitary parasitoids accounted for 83.6% of parasitized pupae but only 18.1% of emerged adults, whereas gregarious parasitoids accounted for 16.4% of parasitized pupae and 81.9% of adult output; aggregate amplification was 1.00 and 23.02 adults per parasitized pupa, respectively. Aphaereta sp. and Nasonia vitripennis showed especially strong reproductive amplification. A strategy-by-substrate comparison based exclusively on parasitized host pupae was significant (χ² = 75.32; df = 4; p < 0.0001), demonstrating that reproductive strategy and resource context jointly structured host exploitation. These findings show that parasitoid abundance does not equal host suppression. Biological-control interpretation should therefore distinguish realized host parasitism, adult parasitoid production, reproductive amplification, and the ecological context in which each strategy is expressed.