Diving as an Anti-Predator Behavior in Mosquito Pupae

Diving is considered an anti-predator (escape) behavior in mosquito pupae. However, pupal diving has not yet been properly studied or characterized. Our videographic 2-dimensional observations in this study elucidate the pupal behavior of Culex pipiens quinquefasciatus in the presence and absence of the predatory fish Poecilia reticulata. Pupae exhibited significantly higher speeds and more-diverse escape responses in the presence of the fish compared to the control. These escape responses included shallow, medium, and deep diving, surface movements, floating up, and fish-following upward movement. The no-predator control showed merely shallow diving and surface movements. Pupae adjusted their self-righting behavior according to the fish-following speed and effectively shortened their self-righting time during a fast chase. Although diving pupae preferred smaller acute angles in the presence and absence of predators, the medium diving angles were significantly higher than the shallow diving angles in the presence of a predator. Pupae achieved complete escape success during diving down, but the escape success of a pupa depended on whether or not the predatory fish continued to pursue the pupa. Although 96% of pupae successfully escaped during the 1st fish attack, their ultimate escape success decreased when fish continued their pursuit. Pupae had more responses and significantly higher escape speeds in the presence of a predator than in the control. Mosquito pupae diving behaviors demonstrate their escape behavior during predator encounters. Diving tactics in Culex pupae that help them escape from aquatic predators lead to increased fitness.