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.
