There are 18 species in the weevil genus Gerstaeckeria in North America, north of Mexico. Of these, only G. hubbardi (LeConte) and G. fasciata Pierce, feed on cacti of the genus Opuntia in Florida.
Gerstaeckeria hubbardi (LeConte)
Acalles dilatatus Casey, 1895
Acalles hubbardi LeConte, 1880
Gerstaeckeria fasciata Pierce, 1912
(from O'Brien 1970)
The genus is known from Cuba, Guadeloupe, Guatemala, Haiti, and Mexico (Arnett 1962, Kissinger 1964). In the U.S. and Canada, the genus is known in all regions except in eastern Canada, the northeast U.S., and states in the Great Lakes region (Arnett 2000). G. hubbardi and G. fasciata are the only species found in the eastern U.S. (O'Brien 1970).
G. hubbardi is known in Alabama, Georgia, and Florida (Peck and Thomas 1998). It probably occurs throughout peninsular Florida.
G. fasciata was originally described from Buck Key, Florida. All known localities are in Monroe County, and the species may be confined to the Florida Keys, associated with one or more of the southern species of Opuntia.
These are medium sized weevils with G. hubbardi 7.5 to 9.5 mm, and G. fasciata 5.0 to 5.8 mm in length (O'Brien 1970). Beaks are concealed in a groove. Surfaces are coated with minute scales that vary in color from white through shades of brown to black. These scales can be rubbed off, and the pattern is somewhat variable. The general pattern of white humeral angles and a broad light colored apical band is similar in many species, including the two Florida ones.
All members of this genus are known to breed in Opuntia cacti, although there has been little specific data published on their life histories. Brief notes on western species were published by Pierce (1907, 1912), and Hunter et al. (1912).
The adults feed externally on the pads, often hiding beneath those on the ground during the day. Both Florida species appear to be more active at night. When disturbed they drop to the ground, fold up the legs, and feign death. They are difficult to distinguish from their surroundings.
The larva of G. hubbardi feeds within the pads, producing semicircular scars, leaving the epidermis intact. The single pad is usually killed and sometimes separates from the main plant. Hunter et al. (1912) suggested that the weevil appears "to follow the work of Melitara prodenialis Walker." This is a moth of the family Pyralidae, the larvae of which feed on Opuntia in Florida.
The pupal cell of G. hubbardi is formed near the base of the pad and is composed of sand grains cemented around a chamber of larval feces and decaying cactus. The adult may remain in the cell for some time before emerging. Adults have been collected in Florida every month except January, July, August, September, and October. Most of the records are for April, May, and June.
Key to the Florida Species of Gerstaeckeria
1. Elytral color pattern predominantly black and white; length 7.5 to 9.5 mm; elytra nearly twice as wide as pronotum; peninsular Florida . . . . . hubbardi
1'. Elytral color black with white humeral spots and caramel or tan subapical band; length 5.0 to 5.8 mm; elytra about 1.5 times wider than pronotum; Florida Keys (Monroe County) . . . . . fasciata
All known species are associated with cacti of the genus Opuntia (sens. lat.). G. hubbardi was listed by Pierce (1912) from Opuntia vulgaris. However, Small (1925) did not list this species from Florida, although he does list approximately 13 other species of Opuntia from within the range of G. hubbardi. At Gainesville, the author found it on the "joe jumper," probably O. tracyii. The localities where G. fasciata was found are within the distribution of at least three species of Opuntia (dillenii, keyensis, stricta).
The genus Opuntia is a large and taxonomically confusing one, with the status of several Florida forms somewhat in doubt. However, it is likely that G. hubbardi feeds on several species. It is possible that G. fasciata, with its restricted distribution, is more host specific.
Since most members of the genus Opuntia are considered weeds or undesirable plants, these weevils are, therefore, beneficial. However, their damage has not been noted severe enough to suggest their usefulness in biological control. Additional life history studies may suggest their value in combination with other cactus-feeding insects.
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Hunter WD, Pratt FC, Mitchell JD. 1912. "The principal cactus insects of the United States." USDA Bureau of Entomology Bulletin 113: 1–71.
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Peck SB, Thomas MC. (1998). Family Curculionidae. A Distributional Checklist of the Beetles (Coleoptera) of Florida. (18 August 2015).