Biology
Forno et al. (1983) report the biology of this weevil studied
in the native habitat of South America. They found that adults
are light brown when they first emerge but darken to black
in 5 days. Adults are sub-aquatic and can be found beneath
young leaves, within leaves or in the roots of salvinia. Adults
of this tribe, Bagoini, respire, when resting or feeding below
the water surface, with the aid of air bubbles or air tapped
from plant stems. The preoviposition stage is 6-14 days. Eggs
are laid singly in stem cavities produced by the adult feeding.
Oviposition took place only when salvinia was in contact with
the water. Females laid one egg every 2-5 days over a 60 day
study period. Larvae feed on young terminal buds and enter
the leaf bud tunneling inside after 3-14 days of surface feeding.
Three larval instars are completed before development is complete.
The average developmental time for larvae is 23 days at 25.5EC.
Pupation takes place in a cocoon in contact with living plants.
Most cocoons are found below the leaves or within the root
mass. Prepupae and pupae are found in cocoons and average
12.6 days at 25.5EC. Temperature extremes of 19EC and 37EC.
decrease oviposition and reduce longevity.
History
This weevil was collected in Brazil and Argentina for the
biological control of the giant salvinia. Studies in Australia
(Room et al. 1981), Sri Lanka (1986), South Africa (Cilliers
1991), and Papua, New Guinea (Mitchell and Rose 1979) proved
to be an effective biological control agent for Salvinia
molesta. This weevil is established in Florida where a
resident population feeds on Salvinia minima when S.
molesta is not available. The introduction into Florida
was probably accidental.
Status
This weevil has been released in Texas since the discovery
of Salvinia molesta.
Weeds Affected
This weevil prefers to feed on Salvinia
molesta but can feed and reproduce on Salvinia
minima. Many other plants were tested and determined not
to be a suitable host for this weevil (Forno et al. 1983).
Literature
Cilliers, C. J. 1991. Biological control of water fern,
Salvinia molesta (Salviniaceae), in South Africa. Agri.
Ecosystems Environ. 37: 219-224.
Forno, I. W., D. P. A. Sands, W. Sexton. 1983. Distribution,
biology, and host specifity of Cyrtobagous singularis
( Coleoptera: Curculionidae) for the biological control of
Salvinia molesta. Bull. Ent. Res. 73: 85-95.
Mitchell, D. S., and D. J. W. Rose. 1979. Pest. Agric. News
Summary. 27: 171-177.
Room, P. M., K. L. S. Harley, I. W. Forno, and D. P. A.
Sands. 1981. Successful biological control of the floating
weed salvinia. Nature, Lond. 294: 78-80.
Sands, D. P. A. 1983. Identity of Cyrtobagous sp.
(Coleoptera: Curculionidae) introduce into Australia for Biological
Control of Salvinia. J. Aust. Ent. Soc. 22: 200.
Links
