Biological investigation of the mango leaf cutting weevil, Deporaus marginatus Pascoe, in laboratory and nursery

The biological investigations were made in the laboratory and mango nursery on the oviposition behaviour and development of different stages of life cycle of mango leaf cutting weevil, Deporaus marginatus Pascoe along with its natural enemies. Female weevils were mated with males for less than 30 minutes and eggs were deposited singly on the tender leaves manoeuvreing with snout at some egg to egg distance followed by cutting the leaves which dropped on the soil. The work was conducted through a series of field experiments in the nursery supported by laboratory experiments from January, 2006 to December, 2008. The experiments were conducted at the Fruit Research Station, Rajshahi, Bangladesh. Observations were made on the occurrence of predators, parasitoids and pathogens in the laboratory and nurseries. Investigations were also made on any biocontrol agents attacking weevil eggs, larvae, pupae and adults. Leaf cutting weevils of each life stage were examined daily after maintaining the collections in Petri dishes. Female laid 7.14 eggs per mango leaf, usually on the dorsal side of midrib. The developmental period from egg to adult was 435.37 hours (19.06 days), the egg stage lasted for 47.83 hours (1.99 days), the three larval instars lasted 144.97 hours (6.04 days) and the pre-pupa and pupal stage took 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 larval development occurred in fallen tender cut leaves. Deporaus marginatus was hibernated as final instar larva during winter months when its population was not observed in the nursery. Ants and spiders were found to feed on immature larva of this insect. Ants and spiders were found to feed on the immatures of mango leaf cutting weevil, the former being the most active on immature prey.