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Classical Biological Control of Tropical Soda Apple in the USA1
J. Medal, W. Overholt, P. Stansly, L. Osborne, A. Roda, J. Chong, R. Gaskalla, E. Burns, K. Hibbard, B. Sellers, K. Gioeli, S. Munyan, D. Gandolfo, S. Hight, and J. Cuda 2
Introduction
Tropical soda apple, Solanum viarum Dunal (Solanaceae), is an invasive nonnative weed of pastures and woody areas in the southeastern United States. This perennial prickly shrub, native to South America, has been spreading at an alarming rate during the last decade. Tropical soda apple was first discovered in Glades County, Florida, in 1988, and has since been reported in Alabama, Georgia, Louisiana, Texas, Mississippi, North Carolina, South Carolina, Tennessee, Pennsylvania, and Puerto Rico. In Florida, over 1 million acres are currently estimated to be infested with tropical soda apple. Cattle and wildlife feed on the mature fruits of tropical soda apple and are primarily responsible for spreading the weed by passing the undigested seeds in their droppings ( Figure 1 ).
CREDITS: Julio Medal, University of Florida
Figure 1. Cattle feeding on tropical soda apple fruits. Field surveys in South America for potential biological control agents were initiated in 1994 by researchers from the University of Florida in collaboration with the Universidade Estadual Paulista Jaboticabal campus, Sao Paulo state, Brazil, and the USDA-ARS South American Biological Control Laboratory, Buenos Aires province, Argentina.
South American insects identified as potential biological control agents of tropical soda apple include the defoliating leaf beetles, Gratiana boliviana Spaeth, Gratiana graminea Klug, Metriona elatior Klug (Chrysomelidae), and the flower bud weevil, Anthonomus tenebrosus Boheman (Curculionidae).
The Tropical Soda Apple Leaf Beetle Gratiana boliviana
Host-specificity studies (choice & no-choice feeding & oviposition tests) conducted in Argentina and in the USA, and field surveys in South America, confirmed the high degree of specificity and damaging effect of G. boliviana on the foliage of tropical soda apple. A petition to release this insect from quarantine was approved by the USDA-APHIS-PPQ in May 2003. Initial field releases of this beetle began in August 2003 at Mr. Joe Costine's ranch in Polk County, Florida. Since then more than 75,000 beetles have been released in 21 counties in Florida, 2 counties in Georgia, 2 counties in Alabama, and 1 county in South Carolina. The beetles have established at all sites where they were released in 2003 and 2004. They are causing extensive defoliation on tropical soda apple (20-100%), and are spreading from 1 to 10 miles/year from the initial release sites. Three years post-release, no nontarget effects have been observed on closely related plants growing in close proximity to tropical soda apple.Larvae ( Figure 2 ) and adults ( Figure 3 ) of G. boliviana feeding on tropical soda leaves reduce the vigor, growth rate, and fruit production of the plants. The feeding damage is reducing the competitive advantage this invasive weed has over native vegetation and forage grasses in improved pastures.
CREDITS: Julio Medal, University of Florida
Figure 2. Larva of Gratiana boliviana.
CREDITS: Jeff Lotz, FDACS-DPI
Figure 3. Adult of Gratiana boliviana. The life cycle of G. boliviana begins when females deposit eggs individually on tropical soda apple leaves and petioles. Females produce an average of 300 eggs. The egg stage lasts 5-6 days at 25°C. The larval stage is completed in 15-18 days, and there are five instars. The pupa stage usually lasts 6-7 days. In total, 26 to 31 days are required for the insect to develop from the egg to the adult stage.
The Tropical Soda Apple Leaf Beetle Gratiana graminea
Plant host-specificity tests with G. graminea adults and first instar larvae were conducted from September 2000 to August 2004 at the FLDACS-DPI quarantine facility in Gainesville, FL, and an open field risk assessment with solaneceous crops was concluded at the Universidade Regional de Blumenau, Santa Catarina state, Brazil, in June 2006. A request for field release was submitted in August 2006 to UF-IFAS for internal review and will be submitted to the Technical Advisory Group (TAG) for Biological Control Agents of Weeds. Field release of this insect in Florida is anticipated in the summer-fall of 2007.Leaf feeding by the adults ( Figure 4 ) and larvae ( Figure 5 ) of G. graminea reduce the plant growth and fruit production of tropical soda apple similar to G. boliviana already established in Florida. However, this Gratiana species is more cold tolerant than G. boliviana and remains active during the winter season in southern Brazil when other insects are not present.
CREDITS: Jeff Lotz, FDACS-DPI
Figure 4. Adults of Gratiana graminea.
CREDITS: Jeff Lotz, FDACS-DPI
Figure 5. Larvae of Gratiana graminea. Females produce from 112 to 325 eggs during a period of 3 to 4 months. Eggs are laid individually on tropical soda apple leaves and petioles. Larvae undergo five instars and it may take from 14 to 20 days to reach the pupa stage, which lasts from 6 to 9 days attached by the last abdominal segment to the underside of the leaf. At least 4 to 6 generations/year can occur under optimum environmental conditions.
The Tropical Soda Apple Leaf Beetle Metriona elatior
Feeding-oviposition tests with M. elatior adults and first instar larvae were conducted from January 1997 to May 2001 at the FLDACS-DPI quarantine facility in Gainesville, FL. Open field risk assessments with Solaneceous crops were conducted during 2002 in Argentina, and from August 1998 to March 2006 in Brazil. A request for field release was submitted for internal review in May 2006 to UF-IFAS and will be submitted to the Technical Advisory Group (TAG) for Biological Control Agents of Weeds in 2006. Field release of this insect in Florida is anticipated in the summer-fall of 2007.Most of the life-cycle of this beetle was studied at the Universidade Estadual Paulista, Jaboticabal campus, Brazil. Leaf feeding by the adults ( Figure 6 ) and larvae of M. elatior reduce plant growth and vigor of tropical soda apple similar to G. boliviana already established in Florida. However, M. elatior prefers to feed on tropical soda apple plants growing in woody areas or under shady conditions contrary to G. boliviana that prefers semi-shady to sunny conditions.
CREDITS: Jeff Lotz, FDACS-DPI
Figure 6. Adult of Metriona elatior. Females laid from 32 to 98 egg-cases, and each case contains between 1 to 21 eggs (mostly from 4 to 8 eggs). Larvae undergo five instars and a non-feeding pre-pupae stage. As in many other tortoise beetles in the Cassidini tribe, the larvae have spiny-form processes or anal forks that carry fecal material and exuviae. Pupation lasts from 7 to 10 days. Females live from 94 to139 days while males are short lived, surviving only from 56 to 90 days.
The Tropical Soda Apple Flower Bud Weevil Anthonomus tenebrosus
Feeding and oviposition tests with the flower bud weevil A. tenebrosus were conducted in South America and at the Florida quarantine facility. The results obtained indicated a narrow host range for this insect. The life cycle of the weevil is currently being investigated.Larvae of A. tenebrosus develop inside the flower buds and inhibit fruit production by causing the flowers to abort prematurely. Efforts were initiated in the summer of 2002 to develop an artificial diet for mass rearing this insect; these studies are currently ongoing. Screening tests (laboratory and open-field) were concluded in 2006. A request for field release will be submitted to UF-IFAS and TAG committee in 2006.
CREDITS: Daniel Gandolfo, USDA-ARS
Figure 7. Egg and feeding scars of the flower-bud weevil, Anthonomus tenebrosus.
CREDITS: Stephan McJonathan
Figure 8. Adult flower-bud weevil Anthonomus tenebrosus. Expected Impacts of Host Specific Insects on Tropical Soda Apple
The impact that the released and established leaf beetle G. boliviana is having on tropical soda apple in Florida will be complimented by the introduction of other insects (e.g., the leaf-beetles G. graminea, M. elatior, and the flower bud weevil A. tenebrosus) that damage the leaves, flowers, and seeds of the target weed. These insects will reduce the competitive ability of tropical soda apple. The establishment of a complex of host specific insects attacking different plant parts will contribute to the permanent restoration of grasslands and conservation areas currently infested with tropical soda apple.Financial support for this project is being provided by the USDA-APHIS.
Footnotes
1. This document is ENY-824 (IN457), one of a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Published: September 2002. Revised: August 2006. Please visit the EDIS Website at http://edis.ifas.ufl.edu.2. J. Medal, W. Overholt, P. Stansly, L. Osborne, B. Sellers, K. Gioeli, S. Munyan, and J. Cuda, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida; A. Roda, J. Chong, USDA-APHIS; R. Gaskalla, E. Burns, K. Hibbard, FDACS-DPI; S..Hight, USDA-ARS, and the late D. Gandolfo, USDA-ARS South American Biological Control Laboratory, Hurlingham, Argentina.
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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
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