No abstract

No abstract

No abstract

No abstract

Interspecific competition between phytophagous insects using the same host plant occurs frequently and can strongly affect population densities of competing species. Competition between gallmakers and stemborers could be especially intense because both types of herbivore are unable to avoid competition by relocation during their immature stages. For apical meristem gallmakers the main result of competition is likely to be the interruption of resources to the gall by the stemborers' devouring of stem contents. The proximate effect of such competition could be to reduce gall size, thereby increasing the number of chambers per gall unit volume, and reducing the size and potential reproductive output of the gallformer. In addition, smaller galls may be more susceptible to attack from size‐limited parasitoids, resulting in a second indirect effect of competition. Using a community of galling and stemboring insects on the saltmarsh shrub Iva frutescens L. (Asteraceae), we measured for indirect effects of competition. We examined the primary indirect effect of competition on gall midge crowding and the secondary effects on parasitism rates and parasitoid guild composition. Results indicated that galls co‐occurring with stemborers were smaller, crowding of gall inhabitants was 22% greater, and the composition of the parasitoid guild was altered relative to galls on unbored stems. The overall parasitism rate was not different between galls on bored vs. unbored stems. These results show that competition resulting from the presence of stemborers has the potential to affect the gall midge Asphondylia borrichiae Rossi & Strong (Diptera: Cecidomyiidae) and secondarily to affect its guild of hymenopteran parasitoids.

The St. Johns River is one of the premiere waterways in the southeastern United States, but it is increasingly affected by anthropogenic disturbances and influences such as excessive loading of nutrients. In the current pilot project, small native plant communities ("garden sites") were established along sections of riparian corridors of five first-order tributaries in residential-commercial areas that drain into the lower St. Johns River in north Florida. In addition, four "non-garden" (control) tributaries were monitored for comparison. Garden sites included five species native to the area; 20 plants of each species on both banks (200 total plants). These sites were used to assess the ability of partially restored riparian areas to ameliorate nutrient loading and water quality and determine their impact on local biodiversity in disturbed suburban drainage systems. Partially restored sites showed a significant reduction in both NO 3 -and P concentrations in both soil and water samples compared to control sites. For instance, soil NO 3 -levels were reduced by 14% in garden sites, while water samples were 30% lower. Moreover, both plant species richness and Shannon diversity (H') were significantly higher at partially restored sites, 33 and 19% respectively, compared to control streams after two years. Garden sites also had significantly higher terrestrial and invertebrate diversity than non-restored tributaries. Intermittent patches of partially restored habitat along suburban riparian corridors may provide a practical cost-effective technique for improving ecosystem function, water quality and increasing biodiversity along these frequently disturbed lotic habitats. Trends detected in the current study may have general implications for riparian restoration and reduction of nutrient loading in these small tributaries and, ultimately, effect water quality of the lower St. Johns River basin.

No abstract

Schinus terebinthifolia is a dioecious tree native to South America that has become an invasive weed in Florida, southern California, southern Arizona, Texas and Hawaii and has been naturalised in over 20 countries. Biological control is considered a viable long‐term control option for S. terebinthifolia because release from natural enemies appears to be at least partly responsible for its success in Florida. We examined leaf phenology of S. terebinthifolia over a period of 15 months at five sites in central and southern Florida to provide information that may help in predicting the impacts of potential biocontrol agents for this weed. We documented leaf lifespan, the seasonality of leaf development and abscission and the survivorship of leaves that emerged during either spring, summer or autumn. Average leaf lifespan was >4.5 months at all sites, and leaf phenology followed the seasons closely. Although S. terebinthifolia possesses leaves throughout the year, leaf production was greatest from April to September, and most leaves were abscised in February and March. Spring‐ and summer‐emerging leaves were also longer‐lived than leaves produced during autumn. These results suggest that leaves of S. terebinthifolia would be most vulnerable to herbivory during the spring and summer months when newly growing leaf tissue is most plentiful. Biocontrol agents capable of damaging these tissues during spring/summer might be an effective means of controlling this invasive weed.