| Cotton aphid was one of the main pests of Chinese wolfberry. The occurrence of aphid seriously affected the yield and quality of Chinese wolfberry, which restricted the development of Chinese wolfberry industry. To understand the population dynamics and its influencing factors of cotton aphid in Qinghai, we studied the seasonal dynamic of aphis gossypii by using the system investigation method, discussed the effects of the factors including overwintering sites, temperature, natural enemies, host, interspecific competition, intraspecific competition and so on, to the population of cotton aphids, to find out the cause of the changes of cotton aphid, Aphis gossypii Glover.The results were as follows:1. The population dynamic of cotton aphid and its alate.Cotton aphid began to appear in the field in mid-April and began to disappear in mid-September. Cotton aphid had two peaks; the first peak appeared at the end of June, this was a period that cotton aphid began to propagate massively and a small amount of alate aphids began to appear, preparing for the diffusion of cotton aphid. The second peak appeared in mid-August, the occurrence of the population of cotton aphid was the largest in this period, and the harm to Lycium barbarum was most serious, was the period that cotton aphid outbreak. Alate aphids had three peaks, appeared in the last ten day of June, the first ten day of September, the end of September, respectively.2. Study on the biological system of cotton aphid. Cotton aphids first fed on young leaves, then transferred to the buds, and transferred to the blades in the end. Cotton aphids were mainly in the form of eggs wintering. Chinese wolfberry was a major host that cotton aphids laying eggs overwinter, other hosts were mallow, quinoa and alfalfa. Eggs hatching rate of cotton aphid was very low. The highest occurring generations of cotton aphid was 14 generation in Nuo Muhong area. Natural enemies of the cotton aphid were lacewing flies, Hippodamia tredecimpunctata, starscream, and so on.3. The effect of temperature on cotton aphid and Myzus persicae. The developmental duration of each instar nymphs of cotton aphid shortened with the increasing of the temperatures, except for 30℃.The single fecundity of cotton aphid was high between the temperature 18 and 27, and was the optimum temperature area for breeding. With the increasing of the temperatures, the average litter size of Myzus persicae rised initially and then declined, reached a maximum at 18 ℃.4. Effects of interspecific competition on cotton aphid.When the cotton aphid and Myzus persicae existed at the same time, Myzus persicae didn’t outbreak as a result of the restrict of feeding range and temperature. Aceria macrodonis also had a certain impact on the population of cotton aphid.5. Effects of natural enemies on cotton aphid.With the increasing of the cotton aphids’ population, the number of predators increased. Laboratory research results showed that lacewing flies and Hippodamia tredecimpunctata had great control potential to cotton aphid. The largest predator of them was 135.14 and 434.78 head per day under ideal conditions, respectively. The interference of intraspecific competition also had some influences on searching efficiency. The distribution of cotton aphids also affect on the predation of natural enemies. With the increasing of cotton aphids’ population, the prey amount of lacewings increased.6. Effects of intercropping coverings on cotton aphid. The cotton aphids number on Chinese wolfberry tree is the largest in the Astragalus membranaceus intercropping row, is the minimum in the Vicia sativa intercropping row. The cotton aphids is the largest on the Astragalus membranaceus plant, is the minimum on the Vicia villosa plant.7. Effects of intraspecific competition on cotton aphid.Intraspecific density effect had a certain negative influence on cotton aphid; The density restriction effect of cotton aphid is relatively weak. |
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