Studies On The Law Of Host Transferring For Aphis Gossypii Glover

The cotton aphid,Aphis gossypii Glover(Hemiptera,Aphididae),is a worldwide agricultural pest.It can cause losses seriously on important economic crops(cotton,cucumber,zucchini etc.)and ornamental plants(hibiscus,pomegranate,etc.)through direct feeding,secretion of honeydew and transmission of virus diseases.The polyphagous cotton aphid has been formed different host biotypes during the long-term feeding options.At present,the law of conversion for specialized aphids in laboratory has been covered in many literatures,but in the natural field is still unclear.In this study,we studied the law of host conversion for Aphis gossypii Glover on different host plants in Anyang area by setting field cage in natural field,and we combined with several other methods,included the population dynamics of insect,bioassay in laboratory,identification of biotypes,and the microsatellite methods.The results of this study may provide guidance for the management of actual field crops and provide new ideas for the comprehensive management of cotton aphids.The main conclusions are as follows:In the companion planting area of six summer host crops(cotton,cucumber,zucchini,kidney bean,cowpea and muskmelon)in cotton field,the result of record data showed zucchini have the highest density of cotton aphid.And the next were kidney bean,fewer amounts were found on other crops and their population dynamics were consistent.We set cages and investigated the population dynamics of cotton aphids on winter host plants in cotton field.The results showed that the peak of cotton aphid on pomegranate,hibiscus and Chinese prickly ash was delayed,and the density of insect on hibiscus was the highest.The dynamics of the population for cotton aphids on cotton,cucumber and zucchini at the seedling stage kept the rising trend.The field cage could delay the migration of cotton aphids,but could not change the migration habits of cotton aphids.We identified the biotypes of cotton aphids on different host plants in cotton field and field cages.The results showed that most of individuals on pomegranate,hibiscus and Chinese ash prickly were cotton-specialized biotype,fewer belonged to other types of aphids,and no cucurbit-specialized aphid was found on those winter hosts.So,we speculated that hibiscus,pomegranate and Chinese ash prickly may be the main winter host of cotton-specialized biotype,but not the main winter host of cucurbit-specialized biotype.The ratio of cotton aphids for the cotton-specialized biotype,cucurbit-specialzied biotype and other types of cotton aphids was changed on different sampling dates in cotton field.But in general,the percentage of cotton-specialized and cucurbit-specialized biotype was higher on cotton and cucumber,respectively.Both of the specialized biotypes were recorded on zucchini,and the cotton-specialized biotype occupied larger proportions.The other types of aphids were mainly found on cowpea and kidney bean.Few individuals were sampled on muskmelon and displayed higher percent of cucurbit-specialized biotype.There were significant differences in the cotton aphids on the summer hosts in the two cages that contained winter host plants,one of which only established the cotton-specialized population,and the other both of the cotton-specialized and cucurbit-specialized aphid species were established.The results of the next year in April observed outbreak of cotton aphids in the cage which both of the specialized biotypes were established,however,the other cage could not found any aphids.It can be seen that the coexistence of two specialized cotton aphids may enhance the wintering ability of cotton aphids.The effect of intermediate host plant zucchini or cowpea for cotton-specialized aphid was studied by insect population dynamics investigation,indoor bioassay and biotype identification in cotton field where planted cucumber,zucchini or cowpea.The results showed that the cotton-specialized aphids were able to reproduce and build the population through intermediate host zucchini.The fitness of cotton-specialized aphid had changed after transferring to zucchini,and the preference of specialized aphids for cucumber was stronger.While the intermediate host plant cowpea could not make the cotton-specialized aphid reproduce and establish populations on cotton successfully.The effect of intermediate host zucchini or cowpea on cucurbit-specialzied aphids was studied by the method of setting field cages.The results showed that the cucurbit-specialized aphid could not be propagated or established populations through intermediate host zucchini.The cucurbit-specialzied aphid could be transferred to cowpea to survive and build the population,but whether it could be survived and established populations successfully on cotton also needs further study(our test time was short relatively,and this may cause the failure of cucurbit-specialzied aphids to establish populations on cotton).We used 7 microsatellite locis(exploited by vanlerberghe)to study the genetic structure of cotton aphid on different seasons(summer,autumn and winter)in the field of Anyang.The results showed that the Fst of cotton aphid was mainly distributed between 0.040 and 0.080,and the Fst value of all microsatellite loci was 0.076.The results showed that the season was an important factor to affect the genetic structure of cotton aphid population,and Aphis gossypii Glover in Anyang had shown a certain degree of genetic differentiation.