Partitioning of Symbiotic Bacteria between Generations of an Insect: a Quantitative Study of a Buchnera sp. in the Pea Aphid (Acyrthosiphon pisum) Reared at Different Temperatures

The population of symbiotic Buchnera bacteria in parthenogenetic females of the pea aphid Acyrthosiphon pisum was determined by quantitative hybridization of a DNA probe (groESL) to aphid homogenates. The aphids bore 1 x 10(sup7) to 2 x 10(sup7) bacterial cells per mg (fresh weight). In teneral aphids (i.e., aphids that had moulted to adulthood but that had not initiated reproduction), >75% of the bacteria were in the embryos, and the density of bacteria in the embryos was consistently greater than that in the maternal tissues. The bacterial density in teneral aphids increased from 1.3 x 10(sup7) to 2.0 x 10(sup7) cells mg (fresh weight) of aphids(sup-1) with temperature between 15 and 25(deg)C. This variation could be attributed to a temperature-dependent increase in both the density of bacteria in the embryos and embryo content of the aphids.