The superimposition of heat-induced chiasma frequency changes in Locusta migratoria

Inbred laboratory stocks of the locust Locusta migratoria were used in two different types of experiment involving the superimposition of heat-induced changes in chiasma frequency. The first involved the administration of two heat-treatments at 40 degrees C alternating with a return to 30 degrees C. This was designed to superimpose two small changes, which have been called Effect 1 (increase) and Effect 2 (decrease) upon a single larger Effect 4 (increase). Unlike the response previously reported in a similar experiment carried out with Schistocerca gregaria, an intermediate response was found here in Locusta, with recognisable Effects 1 and 2 components being superimposed upon a reduced Effect 4 increase. The aim of the second experiment was to determine the effects of chiasma frequency of an alternating programme of one day at 40 degrees C, followed by a return to 30 degrees C, maintained for a period of several weeks. This would continually superimpose small effects of all types upon one another. It was found that, rather than falling, as might have been expected, chiasma frequencies rose substantially after the first five days and remained well above control levels for the remainder of the experiment. This readily induced increase in recombination frequencies could be of practical application to those breeders interested in the production of new varieties by conventional selection.