BIOLOGY AND MANAGEMENT OF DUBAS BUG, OMMATISSUS LYBICUS ON DATE PALM IN BALOCHISTAN (PAKISTAN)

Abstract

Dubas bug, Ommatissus lybicus (Homptera: Tropiduchidae) is a major sap sucking insect pest of date palm in district Panjgur of Balochistan province, Pakistan. This study was undertaken to know the biology, comparative efficiency of four monitoring techniques on population dynamics of dubas bug, and quantification of chlorophyll loss and honeydew production by dubas bug feeding on three date palm cultivars. Functional response of predators Coccinella septempunctata and Chrysoperla carnea, and efficacy of plant oils (neem, castor and mustard oil) were also studied for the management of dubas bug. Studying biological performance of dubas bug for four generations under semi field conditions on Kehraba Cv. of date palm it was found that in both the years’ fecundity of first (spring) generation was significantly lower than that of second (summer) generation. Corresponding values for spring and summer generations (2009-10) were as: Egg laying frequency (4.9 and 5.3 eggs/female/day), adult longevity (19.5 and 21.8 days), incubation period (147.6 and 62.7 days) and post ovipositional period (3.6 and 4.5 days). Total life cycle (average value) of 1 st and 2 nd generation completed in 217.25 and 136.35 days, respectively. Eggs distribution density had highly significant difference among the frond rows and within the frond. Second experiment included comparison of sampling techniques for dubas bug population, viz. absolute sampling (visual count, VC) and relative monitoring techniques viz., water-sensitive papers (WSP), yellow sticky traps (YST) and water traps (WT). Count of each sampling techniques varied significantly over the season. Relative sampling methods were positively correlated with absolute method. In the third experiment chlorophyll loss index of date palm cultivars was found highly dependent on dubas bug density level. Among cultivars, chlorophyll loss in/on the infested leaflet of Jan sore and Kehraba was 9.30 % and 9.07%, which was statistically higher than that from Mozavati (8.43 %). Honeydew production excreted by different life stages of dubas bug on individual xxvibasis were non significant among tested date palm cultivars. However, honeydew production (mm 2 /WSP) by dubas (population), on Kehraba ranked first (32.3 mm 2 /WSP) followed in order by Jan Sore (28.8) and Mozavati (20.0). Results of 4 th experiment indicated that predation rate of C. septempunctata and C. carnea was prey density dependent and both predators consumed significantly more number of first instar nymphs than 3 rd instar nymphs of dubas bug. Evaluated predators (both species) displayed type II functional response on 1 st and 3 rd instars prey; however, handling time and attack rate of predators varied significantly to prey stage. Results of 5th experiment revealed that percent mortality of first instar nymphs and adult stage of dubas bug was dose and time dependent. The highest mortality percentages of nymphs after 72 hour exposure time were 84.80, 86.21 and 76.57 % with 3 mL/liter each of neem, castor and mustard oil treatments, respectively. For first instar nymph the LD 50 values of treatment with neem, castor and mustard oils after 72 hours of exposure time were estimated as 2.18, 2.06 and 2.39; and for adult stage 2.23, 2.24 and 2.88 ml/liter, respectively. Field efficacy of imidacloprid and average of oils (in bracket) was assessed based on percent mortality of dubas bug and reduction of honeydew droplets was 32 (26.8) and 35.5 (34.8), respectively. Shade within date palm canopy significantly affects the eggs distribution of dubas bug, and monitoring techniques with relative sampling methods is rapid and efficient. Further, C. septempunctata (female adult) is more voracious than 4 th instar larvae of C. septempunctata and 3 rd instar larvae of C. carnea. Therefore, removal of 2-3 lower frond rows before eggs hatching, installation of YST at position I and the use of plant oils can serve as an alternate to chemical pesticides and thus be the part of dubas bug IPM in date palm plantation.