Annual Occurrence and Population Dynamics, of Cotton Aphids, Aphis gossypii Glover on Specific Host Plants at Sharkia Governorate, Egypt

This study was conducted at Zagazig region, Sharkia Governorate during the period extended from the end of November, 2013 till early December, 2015 to determine host plants list of Cotton Aphid, Aphis gossypii Glover, occurrence on hosts, in addition to figure its annual population dynamic on the important economic and weeds/wild plant hosts to employ these information in preparing effective integrated aphids management program. The obtained results revealed that the cotton aphid colonized wide range of 37 economic host plant species and 23 weeds/wild plant species follow 22 plant families. The highest occurrence ratio of 38.9 %, was recorded on the family Malvaceae plants while, the lowest one of 0.069 % recorded on the family liliaceae (garlic plants). The mean numbers of A. gossypii were varied as host plant variation where the highest occurrence ratio of 16.81 % was recorded on cotton plants; Gossypium barbadenc L. followed by okra plants, Hibiscus esculentus L. presented 11.456 %; while the lowest ratio of 0.043 % was recorded on aellen-wild beet, Beta vulgaris Perennis. In regarded to the weed/wild plants the highest harboring ratio of 5.023% was recorded on purslane, Pertulaca oleracea while the lower ratio of 0.079 % was recorded on yellow weed sorrel, Oxalis corniculata plants.
The cotton plants, G. barbadenc found harbored A. gossypii with longest periods extended from early April till early October during growing season of 2014 and from early- may till mid-October 2015, with the highest peak of 320 individuals / leaf  recorded at 15^th   August, 2014; followed by the peak of 270 individuals / leaf  recorded at 30^th July, 2015 on lantana plants. 
In regarded to the general annual population dynamic, there were two critical activity periods, where the aphids recorded on limited number of plant hosts and with low numbers, the 1^st period extended from 6^th Feb., till 5^th Apr., 2014 with 16 hosts only and the population density ranged 1 individual/leaf on scarlet pimpernel, Anagallis avensis to 47 individual/leaf on little mallow, Malva  parriflora . The 2^nd activity period from 2^nd Jan., till 20^th Feb., 2015  with 14 host only and the population density ranged from 1 individual/leaf on shepherd purse, Capsella bursa-pastoris  to 66 individual/leaf on little mallow, M. parriflora. That means the obvious hosts play important role in the annual dispersal and dynamic of A. gossypii inter between its main and alternative hosts throughout the activity periods.