Biological Control of Water Hyacinth (Eichhornia crassipes)

Water hyacinth was introduced from South America into the US in 1884. Since then it has spread into many lakes and rivers of the southern US. The first biocontrol insect released against water hyacinth in US was the mottled water hyacinth weevil (Neochetina eichhorniae). Its life cycle is 90 to 120 days, depending on temperature and other factors; both the adults and the larvae feed on various parts of the plant. This weevil was first released in Florida in 1972, and subsequently in Alabama, Arkansas, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee and Texas

It also has been established in Australia, Fiji, Honduras, India, Malaysia, Papua New Guinea, South Africa, Thailand and has been released in several other countries.

The second biocontrol insect released against water hyacinth in the US was another Neochetina species: the chevroned water hyacinth weevil (Neochetina bruchi), first released in Florida in 1974. Its life cycle is shorter than that of N. eichhorniae; its impact is similar.
Neochetina eichhorniae Mottled water hyacinth weevil
Neochetina bruchi Chevroned water hyacinth weevil

Another biological control insect introduced against water hyacinth is the Argentine water hyacinth moth (Sameodes albiguttalis). Its life cycle is only 30 days; the larvae are the only life state that feeds on the plant. It was released and is established in Florida, Louisiana and Mississippi, as well as in Australia, South Africa and Sudan. It may retard growth in the early stages of water hyacinth mat development.

Life History: Hyacinth Weevil

Neochetina eichhorniae and N. bruchi (Coleoptera: Curculionidae)

Neochetina bruchi (left) and N. eichhorniae (right) adults.

Members of the genus Neochetina are semiaquatic weevils that feed only on species of Pontederiaceae. Center (1994) reviewed the biologies of N. eichhorniae and N. bruchi. Adults of the two species (Fig. 5) are distinguished by the color and pattern of the scales on the elytra (Warner, 1970; DeLoach, 1975; O’Brien, 1976). Neochetina bruchi is typically brown with a tan band across the elytra. Neochetina eichhorniae is usually mottled gray and brown. Both species have two parallel tubercles on the elytra on either side of the mid-line, which are short and situated near mid-length on N. bruchi, but are longer and further forward on N. eichhorniae.

Late-stage Neochetina sp. larvae feed at the base of leaf petioles, often damaging subtending axillary buds.

The whitish, ovoid eggs (0.75 mm in length) are embedded in plant tissue. Larvae are whitish with a yellow-orange head (Fig. 6). They have no legs or prolegs, only enlarged pedal lobes bearing apical setae. Larvae can be distinguished by the presence (N. bruchi) or absence (N. eichhorniae) of setal-bearing protuberences on these pedal lobes (Habeck and Lott, unpub. report). Neonate larvae are about 2 mm and fully-grown third instar larvae are 8 to 9 mm in length. Pupae are white and enclosed in a cocoon that is attached to a root below the water surface.

Neochetina eichhorniae deposits eggs singly, whereas N. bruchi often deposits several in the same site. Neochetina bruchi prefers leaves with inflated petioles, especially those at the periphery of the plant (DeLoach and Cordo, 1976a), whereas eggs of N. eichhorniae are found in intermediate-aged leaves (Center, 1987a). Eggs hatch in seven to 10 days at 24°C.

The first instar larva excavates a sub-epidermal burrow and tunnels downwards. There are three instars and late-instar larvae are generally found near the crown where they often damage axillary buds. The entire larval period requires 30 to 45 days with N. bruchi developing somewhat faster than N. eichhorniae (Center, 1994). The fully developed larva exits the plant and crawls to the upper root zone to pupate. The pupal stage requires about seven days, but teneral adults may remain in cocoons for extended periods.

Emerging adults climb onto emergent plant parts to feed and mate, often aggregating within a furled expanding leaf or beneath membranous ligules. Females lay their first eggs soon after emergence (DeLoach and Cordo, 1976a, b). As many as 300 to 400 eggs are produced cyclically over a life span of up to 300 days (Center, 1994).

Both species of Neochetina undergo flight muscle generation and degeneration (Buckingham and Passoa, 1985), possibly reflecting alternating dispersive and reproductive phases. Center and Dray (1992) theorized that plant quality and phenostage influenced the weevil’s propensity to switch between phases, with N. bruchi being more sensitive to plant quality (see also Heard and Winterton, 2000) and more likely to disperse.

Adult feeding creates characteristic rectangular scars on the leaves, about 2 to 3 mm in width and of variable length, sometimes girdling the leaf petioles at the distal end and causing the blade to dessicate (see DeLoach and Cordo, 1983; Wright and Center, 1984; Center et al., 1999a). Moderate to severe weevil infestations cause plants to be shorter with smaller leaves, fewer offsets and flowers, lower tissue nutrient content, and reduced overall vigor (Fig. 7) than uninfested or lightly infested plants (Center and Van, 1989).

Waterhyacinth plants stressed by weevils tend lose buoyancy and to be of small stature.