tenebrosus

We tested the flower-bud weevil, Anthonomus tenebrosus (Boheman) (Coleoptera: Curculionidae) as a biological control agent of TSA in Florida. It was first collected by the late Daniel Gandolfo (Argentina USDA-ARS Laboratory) and Julio Medal from TSA in Rio Grande do Sul, Brazil in April 2000. The identity of A. tenebrosus was confirmed by Drs. Wayne Clark (Auburn University, AL) and Germano Rosado Neto (Universidade Federal do Paraná in Curitiba, Brazil). This species does not have a common name in Brazil. According to Borror, Triplehorn, and Johnson (1989), and White (1983) the ‘true’ weevils or snout beetles contains 18 subfamilies of Curculionidae worldwide with more than 60,000 species in over 400 genera described worldwide, becoming the largest of the beetle families. Taxonomists disagree on the number of subfamilies and other taxonomic categories.
TAXONOMY AND GENERAL BIOLOGY
The genus Anthonomus is in the Anthonominae, a subfamily with approximately 200 species found in North America, with over 100 of them in the genus Anthonomus (Borror, De Long, and Triplehorn 1981). Clark and Burke (1996) described 51 species of Anthonomus from the neotropics with thirty-two of them associated with plants in the family Solanaceae mostly non-crops. Few species of Anthonomus known as significant pests include the cotton bollweevil Anthonomus grandis Boheman and the pepper weevil Anthonomus eugenii Cano. The known host plants of A. tenebrosus in Brazil are: Solanum viarum and Solanum aculeatissimum Jacq., with Solanum mauritianum Scop. as a minor host (Medal unpublished data). The biology of this weevil was studied by B. Davis and J. Medal at the quarantine facility in Gainesville, Florida.
Eggs are inserted individually into TSA flower-buds. Incubation of the egg takes 3-5 days.
Larvae are cream with a yellowish brown head capsule. They feed on the contents of the flower-bud, with all larval developmental stages occurring within the flower-bud. This larval feeding prevents the flower-bud from opening. There is usually one larva per flower-bud, but occasionally two larvae can be found in a single flower-bud. As larval feeding progresses, the flower-bud senesces and drop from the plant. The three larval instars are completed in 7-13 days. Pupae resemble the adult in form. They are cream colored but darken shortly before emergence as an adult. The pupa stage is completed in 3-7 days inside the flower-bud. Emerging adults chew their way out of the flower-bud.
Development from egg to adult stage lasts 11-69 days. Long developmental times are not associated with seasonal differences as they happened at all times of the year. Adults can live up to 210 days under laboratory conditions.
Sex determination can be done without dissection of the genitalia. The female is often larger than the male in many insects genera but this character proved not to be accurate for A. tenebrosus. Size appears to be related to food abundance during development as opposed to differences due to sex. Similar to Anthonomus pomorum L. and A. grandis, sexes can be distinguished by separating the elytra and examining the last two abdominal tergites. The last abdominal tergite of the male is about one-third the size of the last abdominal plate of the female (Duan et al., 1999, Agee 1964). Copulation has been observed a few hours after adult emergence and throughout the oviposition period. At least 7-8 generations per year can occur under optimum environmental (temperature 24° ± 3 C, relative humidity 50-70%) conditions.