Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/21/2011
Publication Date: 12/1/2011
Citation: Rodrigo, D., Aguirre, C., Wheeler, G.S., Lapointe, S.L., Rosskopf, E.N., Overholt, W. 2011. Differential performance of tropical soda apple and its biological control agent Gratiana boliviana (Coleoptera: Chrysomelidae) in open and shaded habitats. Environmental Entomology. 40:1437-1447. Interpretive Summary: Scientists at the University of Florida and ARS locations at Ft. Pierce and Ft. Lauderdale collaborated on a study of the effect of habitat on a noxious weed and its introduced natural enemy. The Tropical Soda Apple (TSA) is an exotic weed that has spread throughout the southeastern United States. TSA thrives in a variety of habitats from full sun to interior shade of forests. TSA reduces cattle stocking rates in pastures and can block access by cattle to shaded areas because of its sizeable thorns. In addition, TSA is a reservoir of disease of crops such as potato and tomato. The study showed that TSA leaves growing in the shade were less tough, had higher water and nitrogen content, lower soluble sugars, and less dense and smaller glandular trichomes compared with unshaded leaves. Plants grew slightly taller and wider under shaded conditions but total biomass was reduced compared with unshaded plants. A beetle that feeds on TSA leaves, Gratiana boliviana, was introduced starting in 2003 to control TSA. G. boliviana had higher survival, greater feeding activity, larger adults and higher fecundity when reared on shaded plants compared with unshaded plants. Sampling of field populations revealed that the overall abundance of G. boliviana was lower but leaf feeding damage was higher in shaded habitats. Eggs survivial was greater in shaded habitats. These results indicate that not only plant quality but also habitat structure are important for the performance of weed biological control agents.
Technical Abstract: The leaf feeding beetle Gratiana boliviana Spaeth has been released since 2003 in the southeastern United States for biological control of tropical soda apple, Solanum viarum Dunal. In Florida, G. boliviana can be found on tropical soda apple growing in open pastures as well as in shady wooded areas. The objectives of this study were to determine the effect of light intensity on the performance of tropical soda apple and G. boliviana under greenhouse conditions, and to determine the abundance and mortality of G. boliviana in open and shaded habitats. Leaves growing in the shade were less tough, had higher water and nitrogen content, lower soluble sugars, and less dense and smaller glandular trichomes compared to leaves growing in the open. Plants grew slightly taller and wider under shaded conditions and their biomass (leaves, stems and fruits) was drastically reduced compared to plants grown in the open. In the greenhouse, G. boliviana had higher immature survival, greater folivory, larger adult size and higher fecundity when reared on shaded plants compared to open plants. Sampling of field populations revealed that the overall abundance of G. boliviana was lower, but leaf feeding damage was higher in shaded habitats compared to the open habitats. Interestingly, the percentage of eggs surviving to the adult stage was greater in shaded compared to open habitats. The abundance of predators was higher in the open and positively correlated with the abundance of G. boliviana. These results indicate that not only plant quality but also habitat structure are important to the performance of weed biological control agents.