Hemipteran Hopper Species Associated with Acid Lime Plants (Citrus aurantifolia L .) in the Sultanate of Oman: Candidate Vectors of Witches’-Broom Disease of Lime

Abstract

Regular monitoring of hemipteran hopper species (including psyllids) associated with small-fruited acid lime trees (Citrus aurantifolia L.) was conducted for four years using motorized insect suction to determine the possible vectors of witches’- broom disease of lime (WBDL). The study was done in two phases: monitoring was done in Habra village, Wilayat Wadi AlMaawal (Batinah region) for one year from June 2000 to May 2001; then monitoring was done in Maharah village, Wilayat AlMusannah (Batinah region), for a period of three years from May 2001 to April 2004. Twelve species of cicadellid leafhoppers and one delpahacid planthopper species were collected, while no psyllids were found. Hishimonus phycitis (Distant) (Cicadellidae) was the most abundant hopper (78.4 % of collected individuals). Next in abundance were Toya sp. (Delphacidae), Circulifera haematiceps? and a deltocephalin leafhopper, respectively constituting 10.4, 3.8 and 2.4 % of the total catches of the four years. Nine other species made up 5% of the total collection: Exitianus nanus (Distant), Cicadulina sp. (either chinai (Ghauri) or storeyi (China)), Emposca distinguenda (Paoli), Amrasca biguttula (Ishihara), Deltocephalus (Recilia) pruthii (Metcalf), Neolimnus aegyptiacus (Mutsumura) and three undetermined species (one Deltocephalinae, one Typhlocybinae and one undeterminable to subfamily). Catches of H. phycitis were highest from November to March and lowest from May to September. There was a significant linear relationship between number of H. phycitis and maximum and mininmum temperature. Relative humidity was not significantly correlated to number of H. phycitis. In Maharah, young lime trees were free from WBDL but the disease incidence increased with age. H. phycitis is the best candidate vector of WBDL. The potential of Toya sp., Circulifera haematiceps? and an undetermined deltocephalin as candidate vectors is discussed. Finally, it is suggested that regular sprayings of acid lime trees with effective systemic insecticides during November to March each year can greatly reduce the vector population and can prevent or delay the spread of the disease to a great extent.