Effect of mango mealybug and sooty mould attack on mangoand the impact of the released Gyranusoidea tebygi Noyes on yield

Abstract

Introduction. The mango mealybug Rastrococcus invadens is a pest of horticultural crops, especially mango. Though this fact has been demonstrated and its parasitoid, Gyranusoidea tebygi, released for its control in many countries, quantitative information on the damage inflicted by the mealybug and post-release mango fruit production are still scanty. This study was therefore undertaken to investigate the damage caused by mango mealybug and its associated sooty mould on mango plants and to assess mango fruit production after the release of G. tebygi in 1989. Materials and methods. Laboratory experiments were set up to determine the effect of different populations of mango mealybug (0, 5, 10, 20, and 40 adults/cage) on the chemical constituents of mango leaves. The mould associated with the mango mealybug was identified and its effect on leaf temperature was studied. A mango orchard was studied for fruit production from the time of fruitlessness in 1990 to 1998 when fruit yield peaked. The resultant effect of the parasitism of mango mealybug by G. tebygi was monitored on the chemical composition of mango leaves during this period. Results. Protein, fat, carbohydrate, ash, crude fibre and moisture contents were depleted with increase in mealybug population. The isolated mould fungus Capnodium mangiferae was found to raise leaf temperature of infected mango seedlings. The population density of G. tebygi was found to be negatively but significantly correlated with mango mealybug population and positively correlated with mango fruit yield. Parasitism was highly correlated with mealybug population and yield, and was considered a major factor in the control of the pest and the subsequent increase in mango fruit yield. Rainfall did not have a significant impact on yield, mealybug population or sooty mould score. Discussion. The injury inflicted by R. invadens and its associated mould, and the enhancement of mango fruit production by the activities of G. tebygi on the mealybug were discussed.