Preliminary Studies On The Host Biotypes And Formation Mechanism Of Cotton Aphid In Cotton Areas Of North China

The cotton aphid, Aphis gossypii Glover, is a common species with a worldwide distribution, and it can demage varous crops including cotton by directly feeding and spreading the virus diseases. Cotton aphid, a polyphagous insect, has formed different host biotypes in the long-term feeding and evolutionary process. The cotton cultivation systems are complex and there are various host plants for cotton aphid and the host biotype of cotton aphid has good representativeness in cotton areas of north China. In this paper, the integrated theory and method of insect ecology, biochemistry and molecular biology were used in order to study the host biotypes of cotton aphid in cotton areas of north China, molecular method for distinguishing the two biotypes, host transfer rule of the two biotypes, the fitness of the two biotypes on various summer plants, and we also measured the free amino acids and secondary compounds for cotton, cucumber and zucchini and analysed their effects on the formation of Aphis gossypii host biotypes. This study can help to elucidate the interaction relationship between cotton aphid and its hosts and explore new technology to provide scientific basis for the cotton aphid ecological prevention and control.The main research conclusions were as follows:1. The bioassay experiments of host transfer for A. gossypii were conducted and results showed that survival rate and body weight of adult aphids had a significant reduction, the survival and fecundity of offspring declined dramatically and could not establish a population when their hosts were exchanged that from cotton and cucumber, while transferred to zucchini, the aphids could survive, reproduce and establish a population. That is, there are two host biotypes: cotton biotype and cucumber biotype in cotton areas of north China, and zucchini is the common host for the two host biotypes aphid.2. The complete mitochondrial genomes of two host biotypes of apterous A. gossypii were sequenced and aligned. There were five single nucleotide polymorphisms in this fragment, and they were T, A, A, T, and T in the sequence of cotton biotype aphid and C, G, G, C, C in the sequence of cucumber biotype aphid. A molecular technology for identifying the two host biotypes aphid was developed using that difference.3. The host transfer rule of the two host biotypes A. gossypii was studied using the method of establishing life tables and molecular method. The results showed that hibiscus, pomegranate, Chinese prickly ash were the overwinter hosts for cotton biotype aphid and the fitness were hibiscus, pomegranate, Chinese prickly ash in turn, but the three plants were not the overwinter hosts for cucumber biotype aphid.4. The A.gossypii host biotypes of the alate aphids on various summer hosts in Anyang, Henan province and apterous aphids on cotton plants in the province of Henan, Hebei and Shandong were identified using molecular method. Results showed that different plants had different fitness for the two host biotype aphids. There were two host biotypes aphid on cotton and cucumber, but the proportion of cotton biotype was larger than cucumber biotype on cotton, the proportion of cucumber biotype was larger than cotton biotype on cucumber. There were two host biotypes aphid on zucchini and the proportion of cucumber biotype was higher than cotton biotype. Cotton aphids from muskmelon were cucumber biotype aphid; and the proportion of cotton biotype was higher than cucumber biotype on kidney bean. There were not the two host biotypes aphid on potato and cowpea.5. Host choice experiments were conducted for cotton and cucumber biotype aphid, and results showed the selectivity of cotton biotype aphid to cotton was significantly higher than cucumber, selectivity of cucumber biotype aphid to cucumber was significantly higher than cotton and there were no significant choice difference for the two biotypes to zucchini.6. There was a big difference in the content of secondary compounds and the species and content of free amino acid among cotton, cucumber and zucchini. The contents of 4-aminobutyric acid, succinic acid, caffeic acid, putrescine, 5-methoxytryptamine, epigallocatechin,(+)-catechin and salicin were different between the leaves of cotton and cucumber. The species and total content of free amino acid were the most in zucchini leaf, followed by in cotton and the least in cucumber; The content of Ser, γ-Aba and Pro in zucchini and cotton leaf were significantly higher than those in cucumber leaf. The content of Cys in zucchini leaf was significantly higher than that in cucumber leaf, while that was not detected in cotton leaf.