Abstract
The bio-ecological investigations were made in the laboratory and in the mango nursery under an orchard on the development of different stages of life cycle of mango leaf cutting weevil, Deporaus marginatus Pascoe along with its population based on damage severity, susceptibility to mango varieties and management practices. The developmental period from egg to adult was completed in 435.37 hours (19.06 days) in which the egg stage lasted for 47.83 hours (1.99 days), the larva passed three instars through 91.22 hours (3.80 days) and the pre-pupa and pupal stage in 93.40 hours (3.89 days) and 171.17 hours (7.13 days) respectively. The adult longevity was 47.50 days in male and 36.50 days in female. The female laid 7.14 eggs per tender mango leaf singly by excavating a pouch usually on the dorsal side of midrib. The larval development occurred in fallen tender cut leaves. Deporaus marginatus hibernated as final instar larva during winter months when its population was nil in the nursery. This insect was found to attack mango grafts from March and heavy damage occurred in June to September. Temperature and relative humidity were significantly related to the damage severity. Ants and spider were found to predate on immatures of this insect pest. Out of 21 mango varieties, the most susceptible variety to mango leaf cutting weevil was BARI Aam-3 which caused 56.41 and 61.92 per cent leaf infestation in 2006 and 2007 respectively, and the tolerant varieties were BARI Aam-1 showing 20.78 and 17.67 per cent leaf damage in two years and Surmafazli and Kishanbhog with 21.04 and 21.35 per cent leaf damage in the first year. Apart from all other leaf characters midrib diameter significantly related to leaf infestation. The highest midrib diameter increased the infestation facilitating the oviposition of the female weevil and causing the varietal susceptibility of mango. Both macro and micronutrients such as N, P, K, S, Ca, Mg, B, Cu, Fe, Mn and Zn did not show any significant relationship between leaf infestation and mango varieties. Three types of bags such as mosquito net, perforated polythene bag and brown paper bag which provided a physical barrier against mango leaf cutting weevil for cutting tender leaves served as the most effective control measure. Sanitation in the nursery resulted almost one-third of the reduction of leaf infestation. The laboratory and field evaluation revealed that out of five insecticides 1ml/l of Ripcord and 2g/l of Sevin were highly toxic to the larvae of mango leaf cutting weevil and most effective in reducing as much as 85 to 89 per cent leaf infestation of mango plants in the nursery. The integration of sanitation and insecticides such as Ripcord (1 ml/l) and Sevin (2g/l) provided potential increase of the reduction of leaf damage by mango leaf cutting weevil and appeared to be promising IPM package for mango leaf cutting weevil.