Influence des corpora cardiaca sur les possibilités de vol soutenu du criquet pélerin Schistocerca gregaria
Résumé
An attempt to determine the influence of the corpora cardiaca on sustained flight tendency shown by Schistocerca gregaria imagos reared in dense groups has been made, taking into consideration the presence or absence of corpora allata. Thus, nerves have been cut to isolate the corpora cardiaca from the brain (in the presence or absence of corpora allata) or from both brain and corpora allata. A brain isolated from the corpora cardiaca is often filled with neurosecretory tracts: these are found in the median ocellar nerve, corpora cardiaca nerves, and circum-oesophageal connectives among others. The effects of corpora cardiaca ablations with or without the corpora allata have been studied. These different interventions show that the glandular lobes do not seem to have any influence on sustained flight tendency, but after isolating the corpora cardiaca from the brain, or after cardiacectomy, the majority of locusts do not fly continuously any more. The neurohaemal part would therefore seem to be concerned. Some operated individuals are able to fly continuously for several hours; histologically these show corpora cardiaca regenerates (the neurohaemal part). Therefore cerebral neurosecretory material must be able to pass into the regenerated corpora cardiaca and probably be stocked there. This is necessary for flight but in itself not sufficient, as these conditions are fulfilled in intact individuals which do not fly. Insects without corpora allata express their flying tendency later. Possible reasons for the disappearance of sustained flight are discussed especially in connexion with energetic reserves and their possible utilization.