Field Colonization of the Melaleuca Snout Beetle ( Oxyops vitiosa) in South Florida Ted D. Center,* Thai K. Van,* Min Rayachhetry,† Gary R. Buckingham,* F. Allen Dray,* Sue A. Wineriter,‡ Matthew F. Purcell,§ and Paul D. Pratt* *Invasive Plant Research Laboratory, USDA-ARS, 3205 College Avenue, Fort Lauderdale, Florida 33314; †Fort Lauderdale Research and Education Center, University of Florida, 3205 College Avenue, Fort Lauderdale, Florida 33314; ‡Department of Entomology and Nematology, c/o Biological Control, University of Florida, P.O. Box 147100, Gainesville, Florida 32614; and §Long Pocket Laboratories, Division of Entomology, Commonwealth Scientific and Industrial Research Organization, Indooroopilly, Queensland 4068, Australia Received September 21, 1999; accepted June 13, 2000 The Australian melaleuca snout beetle, Oxyops vi- tiosa Pascoe, a biological control agent of Melaleuca quinquenervia (Cav.) S. T. Blake, was first released in south Florida during spring 1997. Field-emerged adults appeared 3 months later, which affirmed sur- vival of pupae despite occasional flooding. Releases at 12 other locations totaled more than 1500 adults and 6700 larvae by June 1998. Populations established at nine sites in Dade, Broward, Lee, Collier, Palm Beach, and Glades Counties. Habitats with short hydroperi- ods, intermediate stages of melaleuca invasion, and dry winter conditions engendered field colony devel- opment, whereas releases failed at aquatic sites. Even small releases (60 adults) produced populations at fa- vorable sites. Abundant young foliage facilitated es- tablishment, whereas soil type seemed unimportant: colonies developed at typical “glades” sites character- ized by organic soils and at pineland sites with sandy soils. Larvae predominated during October to May, coincident with flushes of plant growth. In contrast, only adults remained during summer, except at a site that was periodically mowed. The new growth induced by mowing supported a persistent year-round larval population. This demonstrated that population trends are influenced more by plant phenology than by cli- matic conditions, possibly reflecting adaptation to the nonseasonal climatic oscillations (El Nin ˜ o) of Austra- lia. Transect sampling estimated the population at more than 2000 adults and 22,000 larvae, 1 year after release of 3300 larvae. Numbers swelled to almost 80,000 adults and over 15,000 larvae by June 1999 and to nearly 83,000 adults and 137,000 larvae by January 2000. Weevils dispersed throughout the 8.1-ha site but remained concentrated near release plots during the first 18 months. Ease of establishment and slow dis- persal suggests an optimal strategy of many small re- leases at carefully selected but widely dispersed sites. Adults and larvae were subsequently relocated to other areas, and O. vitiosa is now widely established in southern Florida. © 2000 Academic Press Key Words: Everglades; invasive plants; Myrtaceae; bioagent establishment; classical biological control; weed control; dispersal; release strategies. INTRODUCTION Melaleuca quinquenervia (Cav.) S. T. Blake (Myrta- ceae), the broad-leaved paperbark (aka, melaleuca), is a large, native Australian tree (25–30 m tall). It occurs naturally within a 40-km-wide zone along the eastern coast of Queensland and New South Wales (11–34° S). It is the southernmost representative of the M. leuca- dendra complex composed of 15 closely related species with a center of diversity in tropical Queensland (Cra- ven, 1999). It occurs in coastal wetlands, typically in freshwater “paperbark swamps” which often occupy sandy soils behind heath-dominated headlands. It also occurs along streams and in brackish water behind mangrove swamps. Most melaleuca habitats are threatened by development in Australia, being located in highly desirable coastal areas of low topography, high rainfall, and mild climate (Turner et al., 1998; Boland et al., 1987). M. quinquenervia is a serious weed in south Florida (Laroche and Ferriter, 1992). Melaleuca invasion has transformed graminoid/herbaceous wetlands into closed-canopy swamp forests. These melaleuca swamp forests typically form dense monocultures character- ized by a sparse understory. Intermediate stages in this transformation include savannahs with scattered, individual trees and mature dense melaleuca heads surrounded by relatively pristine marshes that contain moderate to low levels of melaleuca (O’Hare and Dal- rymple, 1997). The increased structural diversity asso- Biological Control 19, 112–123 (2000) doi:10.1006/bcon.2000.0856, available online at http://www.idealibrary.com on 112 1049-9644/00 $35.00 Copyright © 2000 by Academic Press All rights of reproduction in any form reserved.