Seasonal dynamics and spatial distribution of the lettuce aphid, Nasonovia ribisnigri Mosely (Hem.: Aphididae) in Ahvaz

Nasonovia ribisnigri Mosely, is considered as a key pest of lettuce and was reported for the first time from southern part of Khuzestan province in 2008. Increasing population and covertly feeding habit of the pest in the central part of lettuce heads causes severe damage in most parts of the fields. To approach the purpose of seasonal dynamics and spatial distribution of lettuce aphid, numerous samples were randomly taken from lettuce field twice a week during 2010-2012. The activity of this pest began in mid and end of December in the first and second year of sampling, respectively. In 2010- 11 and 2011-12, population reached a peak on 9 March (116) and 12 March (62) aphids per plant, respectively and then aphid number declined in the mid April. The population increased slowly in the second year compared with the previous year and there was a significance different between the years (p<0.05). Based on estimation of aphid's population on head, wrapper and frame leaves, 50% of the aphids colonized on head leaves and nymphs were the most abundant stage. The data of spatial distribution with both Iwao’s Patchiness regression and Taylor’s Power Law methods indicated that Taylor's Power Low showed a better fit than Iwao's model and distribution of different stages of aphid population were aggregated. Based on results of this study, despite of difference in population dynamics of lettuce aphids during two years of sampling, counting of nymphs with aggregated distribution pattern on the head leaves can provide a good index to estimate the population and management of this pest.