5 WATERLETTUCE PEST STATUS OF WEED ... - Invasive Plants

Biological Control of Invasive Plants in the Eastern United States
waterlettuce (Mangoendihardjo and Nasroh, 1976;
Suasa-Ard, 1976; Habeck and Thompson, 1994).
Feeding and oviposition also were largely confined
to this plant. The acridid grasshopper Paulinia
acuminata (De Geer) feeds and develops on the
waterferns (Salvinia spp. and Azolla sp.) as well as
waterlettuce (Bennett, 1966; Vieira, 1989).
Releases Made
Only two insects have been released into the United
States as biological control agents against this weed,
the South American weevil N. affinis and the Asian
moth S. pectinicornis (Dray et al., 1990, 2001).
Figure 4a.
BIOLOGY AND ECOLOGY
OF KEY NATURAL ENEMIES
Neohydronomus affinis Hustache (Coleoptera:
Curculionidae)
Adult N. affinis (Fig. 4a) weevils are small (3 mm long)
and have a nearly straight rostrum that is strongly
constricted ventrally at the base. Neohydronomus
affinis ranges in color from uniform bluish gray to
reddish brown with a tan, chevron-like band across
the elytra. Further information on the identification
of this species may be found in DeLoach et al. (1976)
or O’Brien and Wibmer (1989). The following summary
of this weevil’s biology is based on DeLoach et
al. (1976) and Thompson and Habeck (1989).
Eggs are cream colored and subspherical (0.33
x 0.4 mm). Females chew a hole about 0.5 mm diameter
in the leaf (usually on the upper surface near the
leaf edge), deposit a single egg inside this puncture,
and close the hole with a black substance. Eggs hatch
within four days (at temperatures above 24 o C).
Young larvae (Fig. 4b), which are very small (head
diameter of 0.2 mm), burrow under the epidermis and
work their way toward the spongy portions of the
leaf at a rate of about 1.5 to 2.0 cm/day.
Larval mines (Fig. 4c) often are visible in the
outer third of the leaf where tissues are thin, but are
less apparent in the central and basal portions of the
leaf. The first molt occurs when larvae are about three
days old, the second molt occurs 3 to 4 days later.
The three larval stages last 11 to 14 days in total.
Figure 4b.
Figure 4c.
Figure 4. Adult (a) and larvae (left) and pupa
(right) (b) of the waterlettuce weevil
Neohydronomus affinis Hustache. Mining by
larvae produces characteristic tunnels (c).
(Photograph courtesy of USDA, ARS
Invasive Plant Research Laboratory.)
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