Ecology and management of stone weevil

Abstract

Mango stone weevil, (MSW) Sternochetus mangiferae (Fabricius) (Coleoptera: Curculionidae) is an important monophagous pest of mango, its ecology and ethology have escaped the attention of entomologists, but its effects as a pest of mango fruit is highly pronounced affecting yield and exports. In order to understand the insect better, for better management, there is a need to follow the insect, into its niches like seed and bark in an intensive manner. Hence, the present study was conducted at the laboratory and fields of Indian Institute of Horticultural Research (IIHR), Bangalore (12o58’N; 77o35’E) during 2001-2005. The different linear and non-linear models employed could explain the variability in infestation at harvest due to the infestation in fallen fruits to the extent of 57 to 83% in different varieties. Further, per cent infestation at harvest was predicted using polynomial model order 2 equation in Alphonso and Banganpalli, and polynomial model order 3 in Totapuri. An adult infested by Beauveria bassiana (Balsamo) Vuillemin was found. The natural occurrence was < 1%, but under laboratory conditions, the fungus gave 100% mortality of adults in 2-7 days when sprayed at 1.3 x 109 spores per ml concentration. Carbaryl, acephate and deltamethrin with 3.33, 6.67 and 8.15% infestation, respectively were effective. Ethofenprox with 14.82% infestation gave intermediate control. Fish oil rosin soap and azadirachtin were not effective. The study clearly brought out for the first time that infestation begins on fruits of 2-4 cm diameter. This is the time to initiate management interventions. The discovery that majority of the adults eventually rest in junctions of main trunk and primary branches augur well to target spot application of insecticides on the main trunk prior to fruiting, thus obviating full canopy sprays. The fact that older trees harboured more MSW is also crucial in being vigilant to MSW infestation. This is environment friendly cost effective and time saving, as trunk spot application requires only 1/5th of spray liquid. The study showed that prediction of weevil infestation in a variety is possible. As stretches of mango of one variety are common in India, this will be useful in forecast and surveillance. The efficacy of B. bassiana demonstrated that the eco-friendly IPM is a potential future venture.