Pesticide use can impact not only cultivated land, but also protected ecosystems that receive pesticide inputs due to aquatic connectivity or atmospheric transport from agricultural regions. In Costa Rica's Caribbean lowlands, pesticides applied to banana and pineapple plantations are a potential source of pollution to ecological reserves. Macroinvertebrates and fish are both potentially useful bioindicators of agrochemical pollution in aquatic systems, and our goal was to determine whether three common stream consumer species (one fish and two aquatic insect species) could serve as bioindicators for the organophosphate pesticide ethoprophos. We identified thresholds at which ethoprophos impacts the survival (LC₅₀) and observed behavior (LOEC – lowest observed effect concentration) for each species. The LC₅₀ of the guppy Priapichthys annectens was 1530 µg/L, with observable behavioral changes occurring at 1000 µg/L. Insects were more sensitive: the mayfly Traverella holzenthali had an LC₅₀ of 15 µg/L and an LOEC of 2.5 µg/L, and the caddisfly Leptonema sp. had an LC₅₀ of approximately 30 µg/L and an LOEC of 5 µg/L. The LC₅₀ values are notably higher than ambient concentrations recorded from polluted Costa Rican streams and suggest that these taxa are not ideal indicator species. However, the lower LOEC values (in the same order of magnitude as ambient concentrations) highlight the potential ecological importance of behavioral modification due to pesticides. Quantifying the thresholds at which common pesticides impact ecosystems is a key step in identifying bioindicator species and protecting tropical biodiversity.