Pyriproxyfen effects on predators of Anopheles arabiensis larvae under semi-field setting: insights into ecosystem safety

• Pyriproxyfen exposure did not affect the survival of dragonfly, damselfly, or backswimmer nymphs. • Adult emergence was inhibited in damselflies but not in dragonflies. • Pyriproxyfen enhanced predation in dragonflies and backswimmers but not in damselflies. • Pyriproxyfen may complement existing mosquito control strategies, including biological control. Larviciding forms an integral part of larval source management, a supplementary intervention for malaria vector control. However, if chemical larvicides are not thoroughly evaluated, non-target organisms in aquatic habitats may be harmed. Among these are aquatic predators, which play an important role in regulating mosquito populations. This study evaluated the effects of pyriproxyfen, an insect growth regulator, on nymph survival, adult emergence, and predatory ability of field-collected dragonfly, damselfly, and backswimmer nymphs under semi-field settings. Nymphs were exposed to 300 ppb pyriproxyfen for 21 days to assess survival, while emergence inhibition in dragonflies and damselflies was measured at 50 and 300 ppb with daily mosquito‐larvae provisioning until emergence or death. Predation bioassays at 150 and 300 ppb across larval densities (3, 6, 9 larvae/200 mL) were conducted over 6-hour (every 40 min) and 9-day (daily) intervals, with larvae replenished after each count. The findings indicated that a 300 ppb did not compromise the survival of predator nymphs (p > 0.05). In addition, 50 ppb and 300 ppb significantly inhibited damselfly emergence (p < 0.05), without affecting dragonflies (p > 0.05). With exception of damselflies, pyriproxyfen enhanced the predatory abilities of backswimmers and dragonflies. These findings demonstrate that pyriproxyfen exhibits a species-specific safety profile rather than uniform safety across aquatic predators. While having a higher safety margin in aquatic ecosystems harboring dragonflies and backswimmers, the observed emergence inhibition in sensitive species such as damselflies underscores the need for cautious, context-dependent application. Based on these findings, autodissemination of pyriproxyfen could be effectively integrated with existing interventions, providing a dual impact on immature mosquitoes through both the direct effects of chemicals and the enhanced predatory activity.