Impacts of a Sweet Orange Essential Oil–Based Biopesticide on Exorista larvarum, a Parasitoid Tachinid Fly With a Dual Role

Abstract

The use of biopesticides in agriculture has grown in recent years, but the effects on non-target species remain insufficiently understood. We assessed both the lethal (e.g., survival) and sublethal (e.g., fecundity and fertility) effects of Prev-Am Plus, a sweet orange essential oil-based biopesticide, on the parasitoid Exorista larvarum (L.) (Diptera: Tachinidae). This species was selected as a model non-target insect due to its dual role as a parasitoid of pest lepidopterans and as a pollinator. Fecundity was expressed as the number of eggs laid, whereas fertility was expressed as the proportion of eggs developing into puparia. The experimental techniques were adapted from internationally recognized protocols used for assessing pesticide toxicity on Apis mellifera L., a reference insect species in environmental risk assessment. Mated E. larvarum females were utilized in the experiments. Both acute contact (a) and oral (b) toxicity were tested by applying a single 1 μL drop of biopesticide solution onto the fly thorax (a) or offering 10 μL of biopesticide solution as food to flies (b). Different concentrations (0.25%, 0.5%, 5%, 10%, 20%) of the commercial product were tested. The results showed that both contact and oral exposure to Prev-Am Plus exhibited a dose–response relationship, with mortality increasing with concentration. In contact assays, the estimated LC₂₀ was 3.93%, while the LC₅₀ exceeded the highest tested concentration (20%). In oral assays, the proportion of females consuming the test solution decreased with increasing concentration. Among females that ingested more than 50% of the solution, mortality increased with concentration, with estimated LC₂₀ and LC₅₀ values of 2.5% and 10.8%, respectively. No effects on fecundity or fertility were detected following either exposure route.