Ministry of Agriculture
Grape Insect and Mite Pests
Snailcase Bagworm
(Apterona helix Siebold)
- Identification
- Life Cycle and Damage
- Monitoring and Spray Thresholds
- Biological Control
- Cultural Control
- Chemical Control
Prepared by D. Thomas Lowery, Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland.
Identification
This introduced moth (Family Psychidae) remains throughout most of its life within a snail-like case made from particles of soil and sand bound together with silken threads. When fully grown the coiled case is approximately 4 mm in diameter. There are no males and the wingless female moths remain inside the case to deposit their eggs without having mated (parthenogenetic reproduction). Large aggregations often form on posts, tree trunks, or vine trunks in late summer.
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| Snailcase bagworm larvae on wires | Snailcase bagworm larvae on post |
Life Cycle and Damage
Young caterpillars overwinter within the case formed by the mother. They drop to the ground in spring, form C-shaped cases, and begin to feed on a wide range of weeds, native plants and cultivated crops. Damage consists of small excavated holes on the leaf surface. As the larva grows it eventually expands its case into the typical snail-like, helical shape. In mid-summer the fully grown larvae will climb vines, posts or buildings, attach themselves firmly with silk, and pupate within the case. Several weeks later the females emerge, lay eggs, and then exit the case to die. The eggs hatch in late summer and the small first instar larvae spend the winter within the protective cases. There is only one generation per year.
Monitoring and Spray Thresholds
Larvae of the snailcase bagworm cause minimal feeding damage to leaves and they are not considered economic pests of wine grapes. The large aggregations are easily detected on buildings, posts, wires, and the trunks of vines. If contamination of table grapes is a concern, inspect vines and apply control measures before the overwintering aggregations form in late summer. The non-feeding overwintering stage, secure within the case, is not susceptible to insecticides.
Biological Control
Because it has not yet been adequately studied, natural enemies of this pest of grapes in British Columbia are unknown. The protective case would provide some protection from certain generalist predators, but predators, parasites and diseases undoubtedly take their toll.
Cultural Control
Snailcase bagworm prefer moist areas with thick vegetation. Avoid excessive irrigation and drain areas that puddle or remain damp. Proper drainage will also help reduce grapevine root diseases. Occasional discing or mowing of areas of the vineyard where bagworm are a problem can help reduce infestations.
Chemical Control
Dipel™ (Bacillus thuringiensis) is registered for snailcase bagworm control on grapes. Sprays applied for the control of other insects will provide some protection. For this reason, they are more common in organic vineyards or conventional vineyards with low chemical inputs.September 2010
