Differential performance of tropical soda apple and its biological control agent Gratiana boliviana (Coleoptera: Chrysomelidae) in open and shaded habitats.

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 with leaves growing in the open. Plants grew slightly taller and wider under shaded conditions but total biomass was significantly reduced compared with 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 with 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 with the open habitats. The percentage of eggs surviving to adult was greater in shaded compared with open habitats. The abundance of predators was higher in the open pasture and was 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.

Temperature-dependent development and potential distribution of Episimus utilis (Lepidoptera: Tortricidae), a candidate biological control agent of Brazilian peppertree (Sapindales: Anacardiaceae) in Florida.

The invasive Brazilian peppertree (Schinus terebinthifolius Raddi), native to South America, is widely established throughout central and south Florida. The defoliating leaflet-roller Episimus utilis Zimmerman was selected as potential biocontrol agent of this invasive species. The objectives of this study were to determine development rate and survival of E. utilis at seven constant temperatures (10, 15, 20, 25, 30, 33, and 35 degrees C) and generate prediction maps of the number of generations per year this species may exhibit in the United States. The rate of development of E. utilis as a function of temperature was modeled using linear regression to estimate a lower developmental threshold of 9.6 degrees C and the degree-day requirement of 588. The Logan nonlinear regression model was used to estimate an upper developmental threshold of 33 degrees C. Cold tolerance of E. utilis was examined using all insect stages, and each stage was exposed to three constant temperatures (10, 5, 0 degrees C) for 0.5, 1, 2, 4, and 8 d (or until all insects died). The pupal stage was the most cold tolerant with 100% mortality after 12 d at 0 degrees C. The pupal lethal times at 5 (Ltime50 = 10 d, Ltime90 = 28 d) and 0 degrees C (Ltime50 = 5 d, Ltime90 = 9 d) were used to generate isothermal lines to predict favorable regions for E. utilis establishment. A GIS map was generated to predict the number of generations of E. utilis (range, 0.5-9.8) across all Brazilian peppertree range in the United States. The potential for establishment of E. utilis and its probable distribution in the continental United States was examined.

Chloroplast and microsatellite DNA diversities reveal the introduction history of Brazilian peppertree (Schinus terebinthifolius) in Florida.

Brazilian peppertree (Schinus terebinthifolius) is a woody perennial that has invaded much of Florida. This native of northeastern Argentina, Paraguay, and Brazil was brought as an ornamental to both the west and east coasts of Florida at the end of the 19th century. It was recorded as an invader of natural areas in the 1950s, and has since extended its range to cover over 280 000 ha. Our goals were to understand the history of this invasion, as one step toward understanding why this exotic was so successful, and ultimately to improve development of biological control agents. We sampled plants from the native and exotic ranges, particularly Florida, and genotyped these individuals at nuclear and chloroplast loci. Nuclear microsatellite and cpDNA loci reveal strong genetic population structure consistent with limited dispersal in the introduced and native ranges. Bayesian clustering of microsatellite data separates the east and west coast plants in Florida into distinct populations. The two chloroplast haplotypes found in Florida are also concordant with this separation: one predominates on the east coast, the other on the west coast. Analysis of samples collected in South America shows that haplotypes as distinct as the two in Florida are unlikely to have come from a single source population. We conclude that the genetic evidence supports two introductions of Brazilian peppertree into Florida and extensive hybridization between them. The west coast genotype likely came from coastal Brazil at about 27 degrees south, whereas the east coast genotype probably originated from another, as yet unidentified site. As a result of hybridization, the Florida population does not exhibit low genetic variation compared to populations in the native range, possibly increasing its ability to adapt to novel environments. Hybridization also has important consequences for the selection of biocontrol agents since it will not be possible to identify closely co-adapted natural enemies in the native range, necessitating more extensive host testing.