Biology of the Cottony Cushion Scale, Icerya purchasi Mask. (Hom.: Margarodidae) in Laboratory and It’s Seasonal Fluctuations in Citrus Orchards of Northern Khuzestan

The cottony Cushion Scale, Icerya purchasi Mask., is a polyphagous, cosmopolitan and destructive pest that infests more than 200 plant species apart from citrus. Laboratory studies were carried out on the orange at three temperatures, 17±1, 27±1 and 40±1°C 65±5% RH and 14:10 (L:D). The duration of nymphal stages, female longevity and the life cycle at 17±1°C were 85.8±3.83, 74.9±3.53 and 173.6±7.63 days and at 27±1°C were 62.6±4.40, 72.6±4.59 and 144.1±9.26 days, respectively. The duration of pupal stage and the life cycle of male at 27±1°C were 16.1±0.78 and 59.4±1.30 days, respectively. Field studies on the pest were conducted from July 2003 to September 2004 at Sharafabad region of Dezful. At 10-days intervals, five randomly selected orange trees in a citrus orchards (3ha) were sampled by taking 75 twigs, 15cm in length, at random. Number of eggs, nymphal stages and adults were recorded. From these observations I. purchasi had three generations in a year that were recorded as spring, summer and autumn-winter generation for I. purchasi. The autumn-winter generation developed in 6 months. I. purchasi overwinters as different developmental stages on different host plants with the 2nd nymphal stage was more abundant. Apart from different citrus cultivars, altogether 41 species of 22 different families of plants were recorded as the host plants of this scale in Khuzestan province.