Min B. Rayachhetry

Regeneration Potential of the Canopy-Held Seeds of Melaleuca quinquenervia in South Florida

Melaleuca quinquenervia produces and maintains extensive seed reservoirs in the forest canopy. We collected capsules from different infructescences (clusters; Cluster I is the youngest, located at the most distal position, and Cluster VII is the oldest, located at the most proximal position) on branches from dry, seasonally flooded, and permanently flooded habitats. Extracted seeds were soaked for 10 d in sterile deionized water and/or 2,3,5,-triphenol tetrazolium chloride (TTC) stain to assess viability. Microscopic inspections revealed that only 15% of the seeds were embryonic (filled), 50% of embryonic seeds were viable (stained red with TTC), and 73% of viable seeds were germinable after 10 d. The remaining 27% of viable seeds may have been dormant or, possibly, required special conditions for germination. A higher percentage of seeds were embryonic on trees at permanently flooded habitats (18%) when compared to dry (14%) or seasonally flooded (14%) habitats. Overall seed viabilities and germinabilities were comparable among the three habitat types. Proportions of filled seeds were constant among infructescence positions within each habitat. Both viability and germinability of seeds varied with infructescence age, both being highest in Clusters II-V and lowest in Cluster VII.

Characteristics of the Fusicoccum anamorph of Botryosphaeria ribis, a potential biological control agent for Melaleuca quinquenervia in South Florida.

Eight isolates of the Fusicoccum anamorph of Botryosphaeria ribis (six from Melaleuca quinque? nervia; two from Hhizophora mangle) were obtained from South Florida. Morphological characteristics of these isolates were studied on various culture media

MORPHOLOGY AND LIFE HISTORY CHARACTERISTICS OF PODISUS MUCRONATUS (HETEROPTERA: PENTATOMIDAE)

Abstract Podisus mucronatus Uhler is a generalist predator found in Florida and the islands of the Caribbean. Adult P. mucronatus were observed preying on larvae of the Australian weevil Oxyops vitiosa (Pascoe), a biological control agent of Melaleuca quinquenervia (Cav.) S.T. Blake. To facilitate field-based identification of this predator, we present descriptions of eggs, nymphal stages, and adults. Life history traits of P. mucronatus when held with no food or either of two prey species (O. vitiosa and Tenebrio molitor (L.) larvae) are also reported. The potential use of this species as a biological control agent of arthropods and its interference with weed biological control are discussed.

Histopathology of Botryosphaeria ribis in Melaleuca quinquenervia: Pathogen Invasion and Host Response

The histopathology of Botryosphaeria ribis invasion and Melaleuca quinquenervia response was studied under laboratory and greenhouse conditions. Infection of excised leaves in a moist chamber occurred through wounds and stomata, and tissue discoloration followed. Development of callus tissue on wounded stems was more pronounced after spring inoculations than after fall inoculations and, likewise, more on nonstressed ramets than on stressed ramets. Callus ridges on B. ribis-inoculated wounds were surrounded by two-to-three-celled suberized layers, which were also present on callus ridges of noninoculated wounds and healthy bark. Cells in callus ridges of B. ribis-inoculated wounds had lignified cell walls and contained tanninoid substances that were invaded by hyphae. Invasion of callus tissue occurred through the interface between the callus ridges and the sapwood. Invasion and discoloration of phloem, cambium, and xylem occurred beyond the margins of callus ridges. In noncallused wounds, hyphal colonization was extensive in the cambium and phloem regions. In both callused and noncallused stems, hyphae grew inter- and intracellularly in the cortex, cambium, xylem, and pith. Callus did not limit fungal invasion of newly formed tissues or the tissues formed prior to wound inoculation. Stem girdling by the fungus appeared to be delayed by callus formation.

FIELD-BASED RATES OF POPULATION INCREASE FOR OXYOPS VITIOSA (COLEOPTERA: CURCULIONIDAE), A BIOLOGICAL CONTROL AGENT OF THE INVASIVE TREE MELALEUCA QUINQUENERVIA

Melaleuca quinquenervia (Cav.) S. T. Blake (melaleuca) is a large (-30 m tall) broad-leaved tree indigenous to eastern Australia and was introduced into south Florida as an ornamental plant in 1906 (Meskimen 1962). Since introduction, melaleuca has aggressively invaded >200,000 ha of natural areas in southern Florida, including ecologically sensitive habitats such as the Everglades National Park (Turner et al. 1998). Instigated by ecological damage resulting from the melaleuca invasion, a classical weed biological control program was initiated in 1986 (Balciunas et al. 1994). Of the >400 herbivores associated with melaleuca in Australia, the weevil Oxyops vitiosa Pascoe became the first candidate introduced into US quarantine facilities for host specificity screening (Balciunas et al. 1994). After extensive testing the weevil was approved for release into south Florida, where it subsequently established at 9 of 13 initial release sites (Center et al. 2000). Once established, populations of a classical weed biological control agent are expected to increase rapidly in response to the seemingly ubiquitous resource (Grevstad 1999), resulting in eventual suppression of the target plant (Marohasy 1997). Therefore, an important component of post-release evaluations of biological control agents includes an assessment of population increase in the introduced habitat. The intrinsic rate of increase and the finite rate of population increase are commonly used to quantify growth rates of insect populations (Carey 1993, Price 1997). These estimates of population growth are typically calculated from fecundity bioassays conducted under controlled environmental conditions. While estimating population growth rates under laboratory conditions is useful for inter and intraspecific comparisons (Evans 1982), the extrapolation of these data to the field is limited because environments in nature continuously vary. Therefore, laboratory based estimates may not describe the actual rates of increase in heterogeneous (realistic) environments. Herein we quantify population growth rates for 0. vitiosa under environmental conditions experienced in its adventive range and compare these estimates with those of other successful weed biological control agents. Ultimately, these data will be used in the development of mathematical models to describe population dynamics of the weevil in south Florida. For this study, the finite rate of population increase for 0. vitiosa was defined as the multiplication factor that converts one population size to another, one time step later or: