Tropical soda apple, Solanum viarum Dunal (Solanaceae), is a 1.5-m-tall perennial shrub native to tropical regions of South America. First reported in Florida in 1988, tropical soda apple rapidly became a major weed in pastures and conservation areas across the southeastern United States (Mullahey 1996). In pastures, tropical soda apple competes with forages resulting in reduced stocking rates (Mullahey et al. 1998). Florida ranchers spent an average of $44 per acre on chemical and mechanical control costs on tropical soda apple in 2006 (Thomas 2007). Additionally, this plant is an alternate host of several diseases of solanaceous crops (McGovern et al. 1994; Adkins et al. 2007).
A biological control program of tropical soda apple was initiated in 1994, and several natural enemies were collected in Brazil, Argentina and Paraguay (Medal et al. 1996), including Gratiana boliviana Spaeth (Coleoptera: Chrysomelidae). This host specific beetle was first released into Florida in May 2003, and by 2008 approximately 180,000 beetles had been released (Overholt et al. 2009). Experiments conducted in central Florida demonstrated that beetle populations increased during the summer and remained very low during the coldest months of the year from Dec to mid-Mar (Overholt et al. 2010). Beetle populations were more abundant on plants located in open pastures compared to those in shaded hammocks (Diaz et al. 2011). In a four-year study, Overholt et al. (2010) demonstrated that tropical soda apple densities decreased by 90% two yr after beetle release. Survival from egg to adult in closed cages was 51% compared to 15% in open cages (Manrique et al. 2011), thus revealing the impact of biotic factors on G. boliviana populations. Because of the presence in Florida of many solanaceous plants, we inventoried the herbivores associated with tropical soda apple with the hypothesis that many would expand their host ranges to include the novel resource. Additionally, because of the importance of G. boliviana as a biological control agent of tropical soda apple, we inventoried its natural enemies in Florida.
Arthropods were collected from 2004 to 2011 at two G. boliviana mass rearing facilities in Fort Pierce, Florida and from several natural infestations on ranches or conservation areas in central and south Florida. Collection methods for insect herbivores and predators included hand catching, aspiration, rearing, and the use of beating cloths. Lepidopteran larvae found feeding on tropical soda apple were reared in the laboratory until adult emergence and then identified. Parasitoids were reared from G. boliviana pupae, and field observations of predation were made. Entomopathogens of G. boliviana were identified using light microscopy by Dr. Drion Boucias at the University of Florida, and arthropods were identified by personnel at the Florida Department of Agriculture and Consumer Services, Division of Plant Industry (DPI), Gainesville, Florida, and the Systematic Entomology Laboratory, United States Department of Agriculture, Beltsville, Maryland. All arthropods collected from tropical soda apple from 1994 to 2011 are included in the DPI database.
A total of seven mite species and 75 species of insect herbivores were collected from tropical soda apple in Florida (Table 1). The host specificity of these species ranged from Solanum specialists to generalists and included major pests of agricultural crops as well as ornamental plants. The high diversity of insect herbivores found in this study is explained in part by the presence of close tropical soda apple relatives in Florida, including 27 species in the genus Solanum and 31 species in other genera of Solanaceae (Wunderlin & Hansen 2008). Based on field observations, tropical soda apple is an attractive host for many agriculturally important insect pests such as Leptinotarsa decimlineata (Say) and L. juncta (Germar) (Chrysomelidae), Manduca sexta L. (Sphingidae), Bemisia tabaci (Gennadius) (Aleyrodidae), Aphis gossypii Glover (Aphididae) and Lineodes integra Zeller (Pyralidae) (Table 1), and therefore may serve as a reservoir on which pest populations may increase before moving into crops.
A total of one mite species, 19 species of spiders and 30 species of predatory insects were found on tropical soda apple (Table 2). Predators observed feeding on G. boliviana larvae and pupae included Geocoris punctipes (Say) (Lygaidae), Sinea sp. (Reduviidae), Perillis bioculatus (Fabricius), Stiretrus anchorago (Fabricius) (Pentatomidae), Tupiocoris notatus (Distant) (Miridae), Solenopsis invicta Buren (Formicidae), and the spider Peucetia viridans (Hentz) (Oxyopidae). The mirid species found in this study are facultative predators, and they comprised up to 95% of the predators found on tropical soda apple in central Florida (Manrique et al. 2011). Pupal parasitoids of G. boliviana included Conura side (Walker) (Chalcidae), Brasema sp. (Eupelmidae), and Aprostocetus nr. cassidis (Eulophidae). Because C. side also attacks lepidopteran larvae (Mitchell et al. 1997) and because of the taxonomic uncertainty of Brasema sp. and Aproctocetus nr. cassidis, we cannot conclude that any specialist natural enemies attack G. boliviana in Florida. The exploitation of G. boliviana by these parasitoids was reported three yr after its release in Florida (K. Hibbard, unpublished data). This relatively short time to host exploitation is similar to that which has been documented in other weed biological control programs (Hill & Hulley 1995; Kula et al. 2010, but see Christensen et al. 2011). Two parasitoids have been reported attacking the native Gratiana pallidula (Boheman) in Arkansas, i.e., a eulophid, Tetrastichus, and a chalcid, Conura sanguineiventirs (Cresson) (Rolston et al. 1965). However, these were not found attacking G. boliviana in Florida. Entomopathogens recovered from G. boliviana included Nosema sp. (Microspore: Nosematidae), Mattesia oryzaephili Ormières (Negregarinorida: Lipotrophidae), and a short gram-negative bacteria. The abundance of parasitoids and entomopathogens of G. boliviana was higher inside the mass rearing facilities compared to field conditions where predators (ants, spiders and mirids) were more abundant (Diaz et al. 2011).
HERBIVOROUS ARTHROPODS ASSOCIATED WITH TROPICAL SODA APPLE, SOLANUM VIARUM, IN FLORIDA.
Arthropods associated with the exotic weed tropical soda apple were collected in Florida. We found that tropical soda apple is a suitable host for several insect pests of agricultural and ornamental plants. Additionally, we report several predators, parasitoids and entomopathogens of Gratiana boliviana, a biological control agent of tropical soda apple.