Biology and biometry of Neochetine elchhorniae warner (Curculionidae: Coleptera)and the nature of damage caused by it on Eichhornia crassipes (mart)

Abstract

The biology, morphology, biometrics and dispersal pattern of the weevil Neochetina eichhorniae Warner and the nature and extent of damage caused by it on water hyacinth (Eichhornia crassipes (Mart.) were studied. An indirect method of estimating the field population was also attempted. The insect laid the eggs beneath the epidermis of plant parts. Incubation period was 6.6 days and the hatching percentage was 93.2. The larvae fed by tunnelling, and the first, second and third larval instars were completed in 8-10, 13-16 and 13-17 days, respectively. The cocoon was attached to the live roots of the plant and the pupation was just below the water surface. The pupal period was 16.6 days. Adult female longevity was 75.3 days while that of the male was 172.3 days. Pre-oviposit iona I period was 49 days and the total number of eggs produced during the whole life period was 462.5. The head capsule width of first, second and third instar larvae were 0.3, 0.488 and 0.693 mm respectively. In adult males, the average distance between the antennal socket and the tip of the rostrum was 0.259 mm and it was 0.487 mm in females. This character helps in the identification of sexes. No microbes or mites were recorded as natural enemies. The predators were the common non-specific aquatic insects like dytiscid beetle, giant water bug, dragon fly naiads and back swimmers.