An-Najah Staff

Despite the importance of arthropods in grassland ecosystems, few studies have examined how grassland arthropods have been impacted by disturbances especially in the Wadi Alfara’a area, West Bank. This work was aimed at studying the effects of animal grazing on arthropod diversity, including species composition, species richness and species diversity, in a semi-arid Mediterranean grassland ecosystem at Alfara'a area in the Palestinian West Bank. The field work was conducted at the Tallouza village, located in the north-eastern part of the West-Bank. The experiment was established in 2006 in an area of about 2000 donums of a mainly grassland ecosystem usually used for grazing sheep and goats herds, under different land use management systems: recently fenced grassland, undisturbed natural grassland, and recently reclaimed agricultural land. Terrestrial arthropod communities were sampled seasonally at the three sites using pitfall traps, over the period of Apr 2006 to Apr 2007. Arthropods communities were found to be sensitive to livestock grazing. Overall population levels of arthropods were highest in the undisturbed natural grassland, followed by grazed grasslands, and the recently fenced grassland. Certain insect orders (Coleoptera and Hymenoptera) were generally, negatively impacted by livestock grazing. However, members of the family (Carabidea, ground beetles) (order Coleoptera) especially Carabus impressus, were richer in grazed sites. On the other hand families of Hymenoptera like (Sphegidae, Cephidea and Apiddae) were not detected in the grazed grassland. On the other hand the unidentified species (Form 5) of the family (Formicidae) found only in the grazed grassland. A significant seasonal variation pattern was detected for total arthropod populations (P<0.05) at the different study sites, with the highest population levels detected in summer and early autumn, and lowest population levels detected in  winter. The fluctuation patterns were comparable in the three sites. Comparable fluctuation patterns were also found for Hymenoptera and Coleoptera.  Higher arthropod population levels in summer months coincided with higher air temperatures and lower soil moisture content, whereas, lower arthropod population levels in winter, coincided with lower temperatures and higher soil moisture content. Grazing has a considerable impact on the biodiversity of grassland arthropods in Alfara’a area. Some of the insect components, especially Carbus impressus, are well adapted to grazing disturbance, and therefore can be used as bioindicators of habitat disturbance such as grazing. 

Soils from 100 irrigated fields (95 under vegetables, 5 under citrus) in different geographical locations in the West Bank (Palestinian Autonomous Territory) were surveyed for hymexazol-insensitive (HIS) Pythium species using the surface soil dilution plate (SSDP) method with the VP3 medium amended with 50 mg/L hymexazol (HMI) (VP3H50), over a period of 12 months. HIS Pythium species were isolated from 37% of the soils surveyed, with mean population levels ranging from 4.3–1422 CFU g−1 dry weight. Eight HIS Pythium taxa were recovered on the VP3H50 medium, the most abundant of which was P. vexans (found in 29% of field soils surveyed). Seasonal variations in population levels of HIS Pythium species were studied in four fields over a period of 12 months. Significant seasonal variations in HIS population levels were detected in the four fields, with the highest population levels of HIS Pythium spp. encountered in spring and the lowest population levels in winter in three of the fields surveyed. Effects of HMI on linear growth and colony morphology of 149 Pythium ssp. isolates were examined on CMA amended with HMI at five concentrations. Pythium vexans isolates responded differently from those of the other Pythium species. Isolates of this important pathogen were more insensitive to HMI at high concentrations than the other main species tested. A large proportion of the P. ultimum isolates was either insensitive or weakly sensitive to HMI. Furthermore, a few isolates of other Pythium species were insensitive to the fungicide at various concentrations. The colony morphology of P. vexans isolates was not affected by HMI, whereas colonies of the other species showed sparse growth on the HMI amended medium relative to the control. The pathogenicity of P. vexans and P. ultimum isolates to cucumber seedlings was examined in growth chambers. Insensitive isolates of both species were found to be more virulent damping-off pathogens than the sensitive isolates. The present study demonstrates that HMI can not be used effectively in controlling Pythium spp. in soil inhabited with high densities of HIS Pythium spp. pathogens.