Changes ih nuclear phenotypes following cold shock in Panstrongylus megistus (Burmeister)

The nuclear phenotypes of Malpighian tubule epithelial cells of 5th instar male nymphs of the blood-slicking insect Panstrongylus megistus were studie d immediately, after a short (1 h) cold shock at 0 degreesC, and 10 and 30 days later. The objective was to compare the responses to a cold shock with those known to occur after hyperthermia in order to provide insight into t he cellular effect of cold in this species. Nuclei which usually exhibited a conspicuous Y chromosome chromocenter were the mst frequent phenotype in control and treated specimens. Phenotypes in which the heterochromatin was unravelled, or in which there was nuclear fusion or cell death were more ab undant in the shocked specimens. Most of the changes detected have also bee n found in heat-shocked nymphs, except for nuclear fusion which generates g iant nuclei and which appeared to be less effective or necessary than that elicited after heat shock Since other studies showed that a short cold shoc k does not affect the survival of more than 14% of 5th instar nymphs of P. megistus with domestic habit and can induce tolerance to a prolonged cold s hock, heat shock proteins proteins are probably the best candidates for eff ective protection of the cells and the insects from drastic damage caused b y low temperature shocks.