UTTAR PRADESH JOURNAL OF ZOOLOGY

The Mango leaf cutting weevil, Deporaus marginatus (Pascoe, 1883) is a serious pest of mango (Mangifera indica L), which cuts the tender leaves of mango trees after oviposition. A study was conducted about the seasonal incidence of this pest, its biology and larval diapause in Kerala, India under laboratory and field conditions during the years 2015, 2016 and 2017. The adult weevil feeds on the epidermis of tender leaves, while the larva is a leaf miner. The appearance of adult weevils in the field show a strong positive correlation with the appearance of tender leaves on mango trees. Climatic factors like temperature, relative humidity and rainfall also affect the life cycle of the weevil. Under favourable conditions, the life cycle is completed in 18.50±1.64 days with an incubation period of 1.18±0.18 days, larval period of 5.76±0.19 days, pre pupal period of 3.76±1.09 days and pupal period of 7.79±0.91 days. After December the fully grown larva undergoes a resting period for 3-9 months under the soil, during which the minimum temperature also falls below 21°C and maximum temperature attains above 32°C. There was a sharp drop in afternoon relative humidity to 53% (average temperature and R.H. in the study area of Kasaragod District of Kerala for the months January 2016 and 2017) and the tender leaves mature and disappear from trees. These three factors induce the fully developed third instar larva to make earthen cocoon and undergoes larval diapause. This diapause was found to be terminated in very few larvae by the first onset of summer rain in April along with a fall in temperature to optimum of 25-28°C and simultaneous rise in rise in humidity with R.H. of 80-85% (for few days). However mostly the termination of diapauses happens during September-October with maximum temperature of 30.1°C and with mean afternoon R.H. of 76.5% and the rainfall below 180-200 mm. When reared in controlled conditions of laboratory, with the temperature kept at 30°C and humidity above 75%, the weevil showed a normal life cycle with development without any diapause even in unfavourable months and showed oviposition and leaf cutting behaviour. In the field in Kerala the pest population also shows two peaks in activity, one small peak in April along with summer rain and a comparatively large peak during November-December.