| Buchnera aphidicolia is the primary intracellular symbiont of the aphids. The symbiosis of Aphid-Buchnera is probably the most perfect and harmonious one. Buchnera-free aphids grow poorly and produce few or no offspring. The mutualism between Buchnera and the aphid is so obligate that neither one could live and exist independently. A great deal of investigations in this field have raised the possibility that the elimination of the symbiotic bacteria may develop the new ways in controlling aphid pests and the virus diseases transmitted by the vector aphids. Meanwhile, this type of research will help us to better understand the principle of co-evolution in microbe-host . Up to now, there is still no one working on this particular field in China. This research focused on the following four aspects. 1 The effect of symbiont on growth and reproduction of the black bean aphid, Aphis craccivora KochObtaining aposymbiotic aphids is key to study the relationship between the aphid and Buchnera. Using antibiotics to treat the aphids is the major method to obtain aposymbiotic aphids. Most researchers used rifampicin to obtain aposymbiotic aphids. In this study, we treated the black bean aphids Aphis craccivora with five kinds of other antibiotics and five different methods. The first method is to use 2mg/ml antibiotics to spray Vicia faba plants, inoculated with 0-day-old aphids. The second method is to use 2mg/ml antibiotics to spray Vicia faba plants, and 24 h after spraying, 0-day-old aphids were transferred on it. The third method is to spray antibiotics on 0-day-old aphids body directly. The forth method is soak the plant in a 0.2mg/ml solution containing antibiotics. The last method is to administrate the antibiotics via the synthetic diet with a concentration of 0.05 mg/ml. The results are shown in the following. In the first and second methods used terramycin, aphid larval development was prolonged for 2-3 days, and the adults had a smaller size, and were unable to reproduce. Treated with chloromycetin or aureomycin, the larval development were prolonged for 1-2 days, and the adults had a smaller size too, but were able to produce a few offsprings. Treated with penicillin or streptomycin, the larval development and adult size were similar to the control, the reproduction rate was significantly lower than that in control. Spraying the aphids with antibiotics had little effect on aphids. The aphids cannot live normally. These results indicate that the forth method using the antibiotic, terramycin was the optimal treatment. 2 Molecular diagnosis of aposymbiotic black bean aphid, Aphis craccivora Koch It is important to develop a simple and accurate method to diagnose the effect of the antibiotic on aphids. Based on the unique organization of the ribosomal RNA operon and the close proximity of aroE (gene coding for arginyl-tRNA synthase) upstream of rrl (gene coding for 23S rRNA) ,the PCR was conducted using synthetic oligonucleotide primers designed according to the sequence of aroE-rrl. The results indicated that 5 days after the treatment with antibiotics, all the samples showed the expected fragment of 0.8Kb. The possible reason is that the symbionts in aphid body cavity were not injured. However, 10 days later after the treatment with oxytetracycline and rifampicin, the fragment disappeared,indicating that the symbionts in aphid body cavity were disrupted completely. The observation by transmission electron microscopy showed that the aphids treated with streptomycin for 7 days, the symbiont Buchnera was normal, but the symbionts from the aphids treated with rifampicin for 7 days were disrupted almost completely. This is consistent with the diagnosis by PCR. These results indicate that using the unique sequence and PCR can diagnose the existence of Buchnera.3 The impact of aposymbiosis on the total protein and amino acid metabolism of the black bean aphid Aphis craccivora KochTo evaluate the role of bacterial symbionts in the black bean aphids, we treated aphids with the antib...
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