Delayed metamorphosis and diapause in the sugar cane borerDiatraea saccharalis

Summary The problem of arrested or delayed development was examined in the sugar cane borer,Diatraea saccharalis. It was found that the insect can either enter diapause or exhibit a period of delayed metamorphosis according to the photoperiod conditions prevailing. We have observed the development characteristics ofD. saccharalis and conclude that a distinction should be made between a delayed metamorphosis phase and a diapause stage.This work was supported by a grant from NSERC.     

Cell-to-cell communication in the heart: structure-function correlations

The communicating cell junctions that ensure the electrical and diffusional continuity of the intracellular space in the heart fibres can be switched from their normal conducting, or opened state, to an exceptional non-conducting, or closed state. This electrical uncoupling is observed after cell injury in the presence of Ca2+ ions in the extracellular fluid, after metabolic inhibition and in the presence of aliphatic alcohols (C6 to C9). The correlations between electrical uncoupling and gap junction morphology in the heart are briefly reviewed. A decrease of the distance between P-face particles and between the E-face pits has been found in all investigations, but the functional significance of this observation is not understood at present. A quantitatively very similar decrease of the average particle diameter (about -0.7 nm) has been measured in glutaraldehyde-fixed sheep Purkinje fibres and in unfixed, quickly frozen rat auricles that had been electrically uncoupled by three different procedures. About half of this decrease was reversible on short-term electrical recoupling (within 20 min). It is concluded that a measurable decrease of the connexon diameter correlates with electrical uncoupling.