Temperature effect on the growth of Buchnera endosymbiont in Aphis craccivora (Hemiptera: Aphididae)

Effect of temperature on the growth of the primary endosymbiont Buchnera aphidicola in the cowpea aphid Aphis craccivora was studied by measuring quantitatively the copy number of 16S rDNA of this endosymbiont. A 1.5 kb segment of eubacterial 16S rDNA amplified by PCR from total DNA of Aphis craccivora was confirmed by RFLP analysis and sequence BLAST as that of Buchnera aphidicola. No secondary endosymbiont was detected in the aphid population studied. The relative levels of Buchnera ratio, quantified by real-time PCR, were higher in old nymphs than in young ones at temperatures between 10-30 degrees C, and this age-dependent difference was more pronounced at lower temperatures. Throughout the entire reproductive stage of Aphis craccivora, the relative levels of Buchnera ratio were higher at 10-25 degrees C than at 30 degrees C and 35 degrees C. A close relationship was found between these levels and the net reproductive rate (R-0) of aphid, which was suppressed not only at 35 degrees C but also at 10 degrees C. The decoupling of Aphis craccivora and Buchnera response at low temperatures suggests that the cowpea aphid was more sensitive to low temperatures, while Buchnera was more sensitive to high temperatures.