POPULATION FLUCTUATION, BIOLOGICAL FEATURES OF DUBAS BUG (Ommatissus lybicus DeBerg (HOMOPTERA :TROPIDUCHIDAE ) ATTACKING DATE PALM TREES (Phoenix dactylifera L.) AND ITS BIOLOGICAL CONTROL BY Chrysoperla carnea (Steph.) LARVAE.

Abstract

The Palm trees, attacking by many insect pests and among the most important of these insect pests Dubas bug Ommatissus lybicus DeBerg (Homoptera: Tropiduchidae). The study of the population fluctuation of Dubas bug O. lybicus was carried out in Helwan on date palms in correlation with studying associated natural enemies. Field studies were carried out during two successive seasons (2010/2011 and 2011/2012) by fortnightly visits to examine the fronds of the selected palms. The data showed that there are two generations per every year (spring and autumn generations) on Date palm trees. There was a negative correlation between Dubas numbers and each of temperature and relative humidity. There was no significant differences between the two seasons. The most widely spread predators were Chrysoperla carnea (Steph.), Coccinella undecimpunctata L., Sphodromantis sp. As respect to biological studies on dubas bug, O. lybicus were carried out in 2009. The obtained results showed that the insect pest had two annual generations (spring and autumn generations) and the adult passed through five nymphal instars before maturity. The spring generation lasted 166.5±12.85 days, while autumn generation lasted 145±6.20 days. The nymphal stage lasted 53.5±1.87 days for the spring generation and 51.5±1.87 days for the autumn generation. Adult females lived 63±5.6 days and 91.4±13.6 days in spring and autumn generations, respectively. The respective figures for males were 33.5±6 and 76±9 days. The number of deposited eggs ranged from 146.5±8.23 eggs/female for the spring generation to 146.5±2.45 eggs/female in autumn generation. The incubation period of the egg stage reached 117.5±1.87 days and 60±3.32days for spring and autumn generations, respectively. Statistical analysis showed that there were significant differences between developmental time means of eggs and adults for both generations. Results also showed that there were significant differences between spring and autumn life span periods (235.5±16.30 and 164±9.09 days, respectively). Nymphal stage of dubas bug showed five developmental instars with five moulting, with significant differences recorded among means of developmental periods among nymphal instars (8.5±1.29, 10.5±1.29, 13±1, 11.5±1.29, 14±1 and 8±1, 8.5±1.29, 12±1, 13±1, 13.5±1.29 days) for spring and autumn generations, respectively. The results showed significant differences between male and female longevities for both generations. The biological control of dubas bug by Ch.carnea Larvae, showed that the Ch. carnea larvae has the ability to consume average 16.4±6.9 nymphs of the first nymphal instar of dubas bug during 24 hours.