Population fluctuation and spatial distribution of cynipid oak gall forming wasps (Hymenoptera: Cynipidae) in Kermanshah, Iran abstract
Oak trees form the major elements of the Zagros forests at western part of Iran. The activity of cynipid gall wasps (Hymenoptera: Cynipidae) greatly affects survival and fertility of these trees, by inducing formation of various galls on a certain part of the oak trees (Quercus spp.). In this study, population fluctuation and spatial distribution of four common species, Andricus asetivalis (Giraud), Aphelonyx persica (Melika), Neuroterus lanuginosus (Giraud)and Neuroterus saliens (Kollar) were studied in Kermanshah province from the early February to the late December of 2011. The galls that formed on the 100 cm end of branches from the four cardinal directions were sampled in two different heights of 1.5 and 2.5 m on each tree every 7-10 days throughout the season. To estimate the spatial distribution patterns, data were analysed through regression models. According to the Taylor's power model, in the height of 1.5 m, the slope of regression line was not significantly different from 1, indicating a random pattern for all gall wasp species. Also the spatial distribution pattern of N. lanuginosus and N. saliens was determined as random in the height of 2.5 m. Using Iwao's patchiness regression, similar patterns were distinguished for all species in two different heights except for A. aestivalis and N. lanuginosus in the height of 1.5 m which regression between Lloyd’s mean crowding and mean density was not significant. At early season, just sexual galls of A. aestivalis and A. persica were observed and the first asexual galls of N. lanuginosus and N. saliens were formed on the branches starting in early August. Combining data of both heights of 1.5 and 2.5, the peaks of gall density of A. aestivalis, A. persica, N. lanuginosus and N. saliens were observed on 23 May, 27 June, 4 September and 15 September as 2.85 ± 1.60, 34.40 ± 22.17, 159.27 ± 40.01 and 4.50 ± 1.38, respectively. Overall, the most observed galls belonged to N. lanuginosus. The activity period of N. saliens was clearly shorter than other species and lasted only less than two months.