| Aphids are one of the major insect pests with broad host range in agriculture, they not only cause direct damage to the plants, but also transmit many species of plant viruses which will result in more serious economic damage to a range of crops. Recently, with the development of greenhouse, the occurrence of aphids became more and more serious, so it is very important to manage aphid with effective and safe methods to protect the production of vegetables. Biological control is an ideal and important technique for controlling aphids for ensuring the safety of crops and managing the insecticide resistance. In this study, we isolated pathogenic microorganisms from field collected aphids and selected pathogenic microorganisms which have been isolated from other insect pests, then we detected the symbionts in Aphis gossypii Glover, and investigated whether symbionts in aphids has effect on the sensitivity of its host to pathogenic microorganisms. The results are as follows.We collected aphids from peach garden, wheat field et al, and investigated the infection of pathogens in lab, and we did not find dead aphids infected with microorganisms. Besides the investigation on field aphid, we tested the pathogenicity of two kinds of microorganism which has been kept in our lab, one was Paecilomyces fumosoroseus, a predominant fungus isolated from Bemisia tabaci in Nanjing, Jiangsu Province, China, the other was Serratia marcescens, a predominant bacteria isolated from Nilaparvata lugens in Nanjing, Jiangsu Province, China The above two microorganisms all successfully infected aphids, and the bacteria showed higher pathogenicity than the fungus.In order to improve the infectivity of S. marcescens against aphids, we purified the bacteria by serial passages in aphids. After three generations of passages, the infectivity and killing speed of S. marcescens were all not significantly improved.We established different clones of aphid, and tested their obligate and facultative symbiont infection status. The obligate symbiont, Bucherna was found in every individual tested from all clones. Two species of facultative symbionts were detected from the samples, they were Regiella and Spiroplasma. Based on the symbionts infection status, we built four lines of aphids with different symbionts. the four kinds of types were:Al (infected with Bucherna, Spiroplasma and Regiella). A2 (infected with Bucherna and Spiroplasma), A3(infected only with Bucherna), A4 (infected with Bucherna and Regiella). Bioassay of bacteria on the four lines showed that the sensitivity of aphids infected with Bucherna or Bucherna and Spiroplasma to 51. marcescens were significantly lower than that of the line infected with Bucherna. Spiroplasma and Regiella, which indicated that Regiella and Spiroplasma might has relation with the resistance to pathogenic bacteria in aphids. |
