Seasonal dynamics of larvae and adults of two Enochrus (Coleoptera: Hydrophilidae) species in urban temporary and permanent water bodies in Buenos Aires

The dynamics of Enochrus variegatus (Steinheil) and Enochrus vulgaris (Steinheil) in temporary pools and permanent ponds were studied in an urban park of Buenos Aires, Argentina. Samples were collected from both type of habitats weekly throughout one year, and water surface area was recorded each time. In permanent ponds, adults of both species were found throughout the study period, while in temporary pools their presence depended on the availability of water. Differences in their reproductive seasons and breeding sites were observed. E. vulgaris was characterized by an opportunistic strategy, and its larvae were detected in both types of habitats, associated mainly with spring and summer seasons. Conversely, E. variegatus larvae were recorded almost exclusively in temporary pools, during the winter and spring seasons. First instar larvae showed the highest abundance and were captured more frequently, in consecutive weeks and simultaneously with third instar larvae, suggesting that the two populations studied are not synchronized in oviposition time or development of immature stages. In several occasions, second instar larvae of both species were captured in a pool that had been dry during the previous sampling date, suggesting that they had not hatched from fresh laid eggs. Our findings suggest that adults of these species are capable of dispersal to and from temporary pools to avoid drought. In addition, their larval stages may also be able to resist drought in the pools by burrowing into the substrate.