BASELINE STUDY OF COCONUT SCALE, ASPIDIOTUS DESTRUCTOR SIGNORET (HEMIPTERA: DIASPIDIDAE) AND ITS MANAGEMENT ON MANGO (MANGIFERA INDICA L.)

Abstract

Aspidiotus destructor Signoret (Hemiptera: Diaspididae) is a very serious insect pest in both tropical and subtropical regions. The pest causes chlorosis, defoliation and dieback on wide range of crops. In Pakistan, both early and late season mango cultivars are frequently infested by A. destructor from July to December each year. Despite heavy losses to mango crops, little information about the seasonal population fluctuation, general biology and management are known about this pest in Pakistan. This study was undertaken to (1) establish baseline information regarding population dynamics, efficiency of native parasitoids of A. destructor and biology; (2) physiological, biochemical and molecular changes in mango plant leaves under A. destructor infestation; and (3) use of gamma irradiation and insecticides for the control of various stages of A. destructor. In the first objective, I determined that the populations of A. destructor built up in July with peak in October to November and lowest from December to June and having a significant correlation with wind velocity and rainfall. Parasitism by Aphytis melinus DeBach (Hymenoptera: Aphelinidae) and an Anagyrus sp. (Hymenoptera: Encyrtidae) on A. destructor reached to peaks in November (13.6 and 16.3 %) and December (14.2 and 14.9 %) during 2011–12 and 2012–13, respectively. In developmental biology study, I determined that males had four immature stages and an adult stage and females had two immature stages with pre-oviposition and oviposition stages; and total developmental span for male and female was 27 and 39.5 days, respectively. Physiological parameters such as leaf area, leaf biomass, chlorophyll a, b and carotene contents as well as total soluble protein (TSP) decreased while proline accumulation increased with increasing A. destructor infestation period. Stress markers like malandialdihyde (MDA) and hydrogen peroxide (H2O2) as well as antioxidants enzymes such as superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and catalase (CAT) were determined as per their established protocols. Increasing trend in MDA contents indicated lipid peroxidation while up regulation of antioxidants enzymes revealed a well- defined defense response to scale insects infestation in the three mango cultivars. DNA (Deoxyribonucliec acid) damage study was conducted by random amplified polymorphic DNA (RAPD) technique using different markers. This technique confirmed that RAPD is a very effective tool in investigating genotoxicity caused by A. destructor in mango leaves. Co- 60 gamma irradiation was used to determine mortality of various stages of A. destructor at Nuclear Institute for Food and Agriculture (NIFA), Peshawar. I found egg stage as the most susceptible and 2nd instar nymphs as the most tolerant stage to gamma irradiation. In large- scale validation tests, a dose of 228 Gy provided quarantine security for all stages of A. destructor on exported commodities. Physiochemical analysis and sensory quality of irradiated and un-irradiated mango fruits were investigated. I determined that irradiation had no negative impact on mango fruit, but rather imcrease it’s shelf life as irradiated fruits retained its nutritional quality and were acceptable to consumer for long time on the basis of sensory quality scoring than un-irradiated fruits. I evaluated eight insecticides against A. destructor, in which highest percent mortalities was recorded with petroleum oil, imidacloprid and pyriproxyfen as compared to mineral oil, thiamethoxam, bifenthrin and profenofos against all life stage of the scale insect. Overall results of my dissertation suggest that management strategy plan for A. destructor may be designed in June-July with focus on crawler stage and insecticides application may be done in July or early August when there is least parasitoid ctivities in the field. I recommend irradiation dose of 228 Gy for 100 % mortality of A. destructor in mango fruits for export purpose. For future study predators, viruses and other parasitiods associated with A. destructor can be explored with quantification of irradiation stress to mango plant.