Diel feeding periodicity of two predatory stoneflies (Plecoptera)

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Abstract
Diel periodicity in feeding activity has not yet been established as a general pattern for predatory stoneflies. This study demonstrates by gut content analysis and behavioural observation that two predatory stoneflies, Kogotus nonus (Needham and Claassen) and Kogotus modestus (Banks) (Plecoptera: Perlodidae), do exhibit diel periodicity, but are not exclusively nocturnal feeders. Furthermore, the particular pattern of periodic feeding appears to depend on the prey type, as chironomids were consumed from evening through to morning, while the mayfly, Baetis, was infrequently captured during the night. Manipulation of light regime in the field and in the laboratory showed that periodic feeding was not a direct response to light regime. The observed diel feeding pattern may be due to a response to temperature regime coupled with diel changes in prey behaviour.