The only insects known to live in the open ocean are oceanic sea skaters of the genus Halobates (Heteroptera: Gerridae). We have collected three species in the temperate and tropical western Pacific Ocean, and also tropical Indian Ocean and measured heat coma temperature (HCT) and super cooling point (SCP) in 503 specimens. The SCPs and HCT were widely ranged from -4°C to -21°C and 26°C to 41°C, respectively. Significant negative correlation between HCT and SCP was shown by Halobates sericeus Eschscholtz 1883 inhabiting temperate (30º-35ºN) and subtropical (20º-30ºN) Pacific Ocean, whereas no significant correlation was shown by Halobates germanus White, 1883 in and along Kurosiho current in the temperate Pacific Ocean. In the fix point of 5ºN, 140ºE in the tropical Pacific Ocean, Halobates micans Eschscholtz, 1822 is the dominant species and only females showed significant negative correlation between HCT and SCP. At the fixed point at 8ºS, 80ºE in the tropical Indian Ocean, H. micans is again the dominant species and showed no correlation between HCT and SCP and extremely high HCT with the average of 39°C. SCP can be an index of cold hardiness. Halobates sericeus distributes in wide latitude range from 0ºN to 40ºN in the Pacific Ocean probably using several currents and might have developed the cross tolerance of higher and lower temperature resistance with a common mechanism including for example “heat shock proteins” as a speculation.
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