|
Nanophyes marmoratus Goeze
Order: Coleoptera
Family: Brentidae (see Note below)
Common name: Loosestrife flower weevil
Nanophyes marmoratus is a minute, dark brown weevil, measuring 0.06-0.08 inches (1.4-2.1 mm) in length (Figure 18). It was introduced from Germany and first released in New York and Minnesota in 1994.
|
Adult loosestrife flower weevils overwinter in the leaf litter, and emerge from sites in late May to early June to feed on young purple loosestrife leaves. As soon as flower buds develop, weevils move to the flower spikes, where they feed on the buds, mate, and begin to lay eggs. Females continue to lay eggs throughout the peak flowering period of purple loosestrife.
Eggs are laid singly into the tips of flower buds before petals are fully developed (Figure 19). Larvae feed on developing
|
Figure 18. Adult Nanophyes marmoratus on purple loosestrife flowers. (UGA0021100) |
ovaries, hollowing out the bud in the process. As a result, attacked buds never flower. All attacked buds senesce and most drop off the inflorescence before new adult weevils emerge. Mature larvae 1use frass to form pupation chambers at the bottom of the bud (Figure 20).
The new generation loosestrife flower weevils emerge from dried, hollowed out buds in July and August and feed on the remaining green leaves of purple loosestrife before seeking overwintering sites in leaf litter. Holes chewed in the buds when the loosestrife flower weevils emerge from their pupation chambers provide evidence that the weevil is present at the site bud. (UGA1291019) at the site (Figure 21) Most damaged buds drop from the plant. The loosestrife flower weevil has one generation per year. Complete development from egg to adult takes about one month (Figure 22). loosestrife flower bud. (UGA1291020)
Figure 19. Nanophyes marmoratus egg in a purple loosestrif flower bud. (UGA1291019) |
Figure 20. Nanophyes marmoratus larva in a purple loosestrife flower bud. |
Impact:
|
Bud feeding by adults causes premature flower bud drop; attack by larvae kills the bud, thus preventing flowering and seed production. At high loosestrife flower weevil densities, larval feeding can reduce seed output of a purple loosestrife plant by about 60 percent.
The effectiveness of the loosestrife flower weevil may be reduced where it occurs with the loosestrife beetle (Galerucella). This is because high levels of dead purple
|
Figure 21. Nanophyes marmoratus (Galerucella). adult exit hole in a dead purple loosestrife bud. |
loosestrife defoliation by the loosestrife beetle prevents purple loosestrife from flowering, and consequently limits activity of the flower weevil. Initially, the loosestrife flower weevil should only be released where the beetles do not occur or where their densities are low.
Figure 22. Schematic lifecycle of Nanophyes marmoratus. Solid colored bars represent the length of activity for each of the life stages, with adult overwintering represented in the patterned bars. This weevil produces one generation per year. |
Note:
The taxonomic placement of the genus Nanophyes is in transition, and thus you may find it listed under three different family names. The genus was historically in the weevil family Curculionidae, and was reclassified in 1995 into the weevil family Brentidae. It was later moved to the family Apionidae (1999). However, the latest classification (2002) returns Nanophyes and all species formerly in the family Apionidae to the family Brentidae. For the purpose of this manual, this classification system is followed. All three families are commonly known as weevils. For more information, key references are provided in the Selected Reference section.glossary.html
Another species, N. brevis, was tested and approved for importation but was never released in North America because of problems with parasitism.
Summary:
Four species of beetles are established in the United States and Canada for the biological control of purple loosestrife. For a quick reference to the beetles, Table 4 compares the adult beetles and their damage, and Table 5 compares the larvae and pupae, and their damage. Figure 23 is an illustration of a purple loosestrife plant showing which parts of the plant are attacked by each of the biocontrol beetles.
Table 4. Comparison of adult purple loosestrife biocontrol beetles and their damage.
| Scientific Name |
Galerucella calmariensis and G. pusilla |
Hylobius transversovittatus |
Nanophyes marmoratus |
| Common Name |
Loosestrife beetle |
Loosestrife root weevil |
Loosestrife flower weevil |
| Adult Description |
Light brown leaf beetles |
Large reddish-brown weevil with white spots, large snout |
Small, shiny, dark brown weevil |
| Life Cycle |
One generation per year, may have a partial second generation |
Long lived, often more than two years. |
One generation per year |
| Body Shape/Size |
Cylindrical body shape, 0.15 to 0.3 inches (4 -6 mm) in length |
Ovoid body shape, 0.4 to 0.6 inches (10 to 14 mm) in length |
Round-ovoid body shape, 0.06-0.08 inches (1.4 to 2.1 mm) in length |
| Eggs |
Lays eggs in clusters on leaves and stems, covered with fecal strands |
Lays eggs (one or more) in soil or stem near base |
Lays eggs singly inside flower bud |
| Damage |
Adults feed on foliage causing a 'shothole' damage pattern in the leaves |
Adults feed on edge of leaves |
Adults feed on young leaves and flower buds |
Table 5. Comparison of larvae and pupae of purple loosestrife biocontrol beetles and their damage.
| Species |
Larval Description and Feeding Characteristics |
Effects |
| Galerucella calmariensis and G. pusilla |
Larva is yellow with brown cross markings and a dark brown head capsule; larva feeds on foliage, window-paning the leaves (top layer of leaf cuticle and epidermis is intact); pupates in soil or aerenchyma (on flooded plants). |
Reduces shoot height, root mass, generally stresses plant. |
| Hylobius transversovittatus |
Larva is C-shaped, white with light brown head capsule; larva feeds and pupates inside root. |
Reduces shoot height, root mass, root storage reserves, and generally stresses plant. |
| Nanophyes marmoratus |
Larva is C-shaped, white with light brown head capsule; feeds in bud on developing ovary, killing bud; pupates inside hollowed bud. |
Reduces flowering and seed production. |
Figure 23. Purple loosestrife biological control agents and the plant parts they attack (drawing adapted from Thompson et al. 1987): a) Nanophyes flower weevil adult (UGA0002035); b)and c)Galerucella leaf beetle adult (UGA1291023) and larva (UGA0022078); d) Hylobius root weevil adult on leaf (UGA0021099), and e) emerging from root (UGA0002034). |
[ Contents ]
[ Previous ]
[ Next ]
[ Home ]
|
