THE IMPACT OF TEMPERATURE ON BIOLOGICAL ASPECTS AND LIFE TABLE OF RHOPALOSIPHUM PADI (HEMIPTERA: APHIDIDAE) FED WITH SIGNAL GRASS

The impact of temperature was evaluated on Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Nymphs, 12-h-old, were placed individually in cylindrical plastic dishes (2.5 x 2.5 cm), with a layer of 1% agar in which leaf disks of signal grass had been placed. The nymphs were reared at 12, 16 20, 24, 28, and 32 degrees C +/- 1 degrees C, RH of 70 +/- 10% and 12-h photophase. We evaluated number of instars, duration of each instar and the nymphal period, survival of instars, duration of the reproductive period, daily and total production of nymphs, and longevity of the nymphal and adult phases. To construct the life expectancy table and fecundity, daily observations were made of 70 nymphs at each temperature, from birth to death. Development of R. path was faster with increased temperature, but they did not complete the last nymphal instar at 32 degrees C. The same pattern occurred for the pre-reproductive, reproductive, and post-reproductive periods. The highest fecundity rates were between 16 degrees C and 24 degrees C. The highest fertility (4 nymphs/female/day) was recorded at 12 degrees C and 20 degrees C. The highest net reproduction rates were at 24 degrees C and 28 degrees C, and the time interval between each generation (T) and the population doubling time (DT) diminished as temperature increased. The finite rate of increase (lambda = 1.9 nymphs/female/day) and the intrinsic rate-of increase (r(m) = 0.64) were greatest at 24 degrees C and 28 degrees C, respectively. There was a negative impact on the biology and life table of R. padi at 32 degrees C, but the range of 12 degrees C to 28 degrees C, despite some fluctuations, was favorable for survival and reproduction.