Investigation on seasonal population dynamics of dominant citrus aphids on Thomson Navel orange and Satsuma mandarin in West of Mazandaran province

Seasonal population dynamics of the aphids on two important commercial citrus species, Thomson navel orange (TNO) and Satsuma mandarin (SM) were investigated in the west of Mazandaran province, Ramsar, during 2015-2016. Samplings were performed biweekly from April 2015 to July 2016. In each sampling date, four young shoots were randomly selected from each main geographical direction of each tree and the number of aphids was counted under a stereomicroscope. The Pearson correlation coefficient was used to determine the relationship between aphid density and temperature and relative humidity as variables. For both species of citrus, the results showed that the first and second population peaks of the aphids occurred in May and October, respectively. Furthermore, there was a significant difference between the infestations of both citrus host plants by the aphids, with Satsuma mandarin showing more infestation. There was a significant difference among the population densities of different aphid species on both citrus species. Aphis spiraecola, Aphis gossypii, and Toxoptera aurantii had the highest population abundances, respectively. A positive and significant correlation was observed between these citrus aphid population densities and temperature (r= 0.689, n=49, P=0.04), however, the correlation was not significant for relative humidity (r= 0.661, n=49, P=0.53). In total, seasonal population dynamics of the citrus aphids were affected by the host plant species and different species showed different population fluctuation trends.