Environmental stress in the pasture scarab Serichesthis nigrolineata Boisd. I. Mortality in larvae caused by high temperature.
In tests in Australia, first and second-instar larvae of Sericesthis nigrolineata (Boisd.) were exposed for short periods to temperatures between 30 and 45 deg C, to define empirically the effects of duration, number of exposures and recovery periods on mortality. The data were needed to collate field microclimate measurements to predict larval survival in the field. At moderate soil moistures, the longest exposure to 30 deg C (192 h) was harmless and the shortest exposure to 40 deg C (45 min) was lethal. Above 30 deg C, the effect of temperature for any one duration of exposure was exponential. At any one temperature, the relation between duration of exposure and mortality appeared to be linear, but the gradients between the 2.5 deg C temperature intervals were too steep to be clearly defined. Repeated exposures to sublethal temperatures caused a slightly lower percentage mortality than at the previous exposure to the same temperature. When the interval between repeated exposures was extended from 1 day to 2 or 4 days, the mortality was slightly less than that after the same number of exposures on consecutive days, but the difference was not statistically significant over all temperatures. All these exposures to temperature stress were in soil with moisture contents above wilting point. There was no interaction between temperature and moisture.