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Hosts

Recorded hosts of the orchid weevil include these genera of Orchidaceae: Dendrobium, Vanda, Phalaenopsis, Renanthera, Angraecum, Saccolobium, Cymbidium, Spathoglottis (Swezey, 1945).

Distribution

Orchid weevils were first observed in Hawaii at an orchid house in Honolulu in 1910. Accidentaly introduced from Asia, the orchid weevil occurs on Kauai, Oahu, Maui and Hawaii. Asian locations include Singapore, Philippines, Thailand, Indonesia and Japan. Because of plant movement and glasshouse orchid culture, it occurs in temperate regions as well (Swezey, 1945; Mau, 1983).

Damage

Orchid weevil larvae and adults have chewing mouthparts. They feed on orchid flowers and on tender tissues at the growing points of orchid plants. These tissues can be stems, leaves, and exposed roots. The adult females chew feeding holes into pseudobulbs or other plant parts, crawl in, and deposit eggs. After hatching, the grubs continue feeding, creating frass/fiber chambers suitable for pupation. Pupae do not feed. adults eventually eat their way out of the pseudobulb. While feeding may not kill the pseudobulbs, bulbs often stop growing and fail to produce flowers. Color break, a white streaking of Vanda flowers, is associated with larval infestation of pseudobulbs or stems (Mau, 1983; Hara & Mau, 1988).

Biology

Orchid weevils lay eggs inside pseudobulbs, in leaves (Dendrobium)and in leaf axils (Vanda). In the laborabory, eggs hatch in 11 days. Larvae feed for about 4 months, molting at least 4 and maybe 5 times. Pupation, or the transformation from larva to adult, lasts 16 days. Total development time from egg to adult is about 5 months. Adults live 9 months to a year (Mau, 1983).

Eggs

Eggs are tiny (1/32 in) ovals. At first they are white, but during the last few days the jaws of the grubs are visible as triangular brown spots. The last day before hatching the heads of the grubs are visible (Mau, 1983).

Larvae

The legless body is white to yellow-white, with a light brown head which darkens during development. Mature larvae are 3/8 in long by 1/4 in wide. Larvae feed immediately after hatching from the egg (Mau, 1984).

Pupae

When fully grown, larvae enter the pupal stage. This is the stage of transformation to adult. In preparation, larvae construct chambers of frass and fibers. Development of pupae usually occurs inside pseudobulbs. The total time for transformation from a white, legless grub to a dark weevil with legs, antennae, and wings is a little over 2 weeks (Mau, 1984).

Adults

After hardening and before emergence from the pseudobulb the adult is totally black. About 2 weeks after pupation, adults chew holes about 1/16 in across and crawl out of the pupation site. (Mau, 1984). Adults have long, curved snouts typical of weevils (Marsden, 1979) The hard wingcovers have distinct, longitudinal grooves. It is not easy to tell males from females. Males are, on the average, larger than females, but small features identifiable in the lab are the only sure means of sexing the weevils (Mau 1984). Orchidophilus aterrimus is the largest of the so-called orchid weevils in Hawaii. They range from 3.5 to 6 mm (1/8 - 1/4 in) long. The lesser orchid weevil overlaps the lower end of the size range (Buchanan, 1935).

Behavior

Feeding and reproductive behavior occur more in light than in darkness (Mau, 1983). When disturbed, weevils immediatelly drop from the plant and play dead.

Management

Biological control-Parasites

Information lacking 

Biological control-Predators

Information lacking. Generalist predators such as spiders, toads, and birds can be expected to feed on orchid weevils.

Sanitation

Plants with feeding damage should be immediately destroyed. This may prevent spread of an infestation if done soon enough.

Preharvest

In bioassays, organophosphates and synthetic pyrethroids were effective against orchid weevils. Synthetic pyrethroids had greater residual activity, and some were superior to others in their effectiveness (Hata & Hara, 1991; Hata & Hara, 1992; Hara & Hata, 1994). Consult the University of Hawaii Cooperative Extension Service for effective, currently registered chemicals. An effective spray progam may last as long as 144 days, the average life cycle of the weevil. Contact sprays must reach the insect, or the insect must encounter the residue. In the field, sprays tested were only effective against adults. Control was effective after 4 months of spraying every 3 weeks. (Hara & Mau, 1988). 

Postharvest

A pyrethroid dip will help eliminate adults harbored in leaf axils but will probably not affect eggs, larvae and pupae inside stems or leaves. Material with feeding holes should be discarded.

References

Buchanan, L. L. 1935. A new Genus and Species of Orchid Weevils (Coleoptera, curculionidae, Barinae). Proc. Haw. Ent. Soc. 9: 45-48.

Hansen, J. D., A. H. Hara & V. L. Tenbrink. 1992. Insecticidal dips for disinfesting commercial tropical cut flowers and foliage. Tropical Pest Management 38: 245-249.

Hara, A. H. & R. F. L. Mau. 1988. The orchid weevil, Orchidophilus atterimus (Waterhouse): insecticidal control and effect on vanda orchid production. Proc. Haw. Ent. Soc. 26: 71-75.

Hara, A. H. & T. Y. Hata. 1994. Residual activity of insecticides on dendrobium for control of orchid weevils, 1993. Insecticide and Acaricide Tests, 19: 369-370.

Hata, T. Y. and A. H. Hara. 1991. Control of Orchid Weevils on Dendrobium, Hawaii, 1990. Insecticide and Acaracide Tests, 16: 252.

Hata, T. Y. and A. H. Hara. 1992. Control of Orchid Weevils on Dendrobium, Hawaii, 1991. Insecticide and Acaracide Tests, 17: 348.

Marsden, D. A. 1979. Orchid Weevils. Insect Pest Series no. 11. University of Hawaii at Manoa College of Tropical Agriculture and Human Resources Cooperative Extension Service: Honolulu.

Mau, R. F. I. 1984. Development of the orchid weevil, Orchidophilus atterimus(Waterhouse). Proc. Haw. Ent. Soc. 24: 298-297.

SEPT/1994.

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