QUANTIFYING THE ADVENTIVE GEOGRAPHIC DISTRIBUTION AND DISPERSAL RATE OF OXYOPS VITIOSA, A BIOLOGICAL CONTROL AGENT OF THE INVASIVE TREE MELALEUCA QUINQUENERVIA

Authors: Pratt, Paul; SLONE, DANIEL - USDA-FORESTRY SVC; FERRITER, AMY - SO. FL. WATER MGMT DIST.

Submitted to: Detecting Invasive Exotic Plants
Publication Type: Proceedings
Publication Acceptance Date: 2/12/2003
Publication Date: 2/28/2003
Citation: Pratt, P.D., Slone, D.H., Ferriter, A. 2003. Quantifying the adventive geographic distribution and dispersal rate of oxyops vitiosa, a biological control agent of the invasive tree melaleuca quinquenervia. Detecting Invasive Exotic Plants.

Interpretive Summary: The primary objective of most weed biological control programs is to suppress a pest population below an ecological threshold, ultimately resulting in the replacement of the target weed with more desirable vegetation. Although the realization of this objective has been described anecdotally for multiple biological control programs, rarely are impacts on the target weed quantified after the introduction of a natural enemy. The paucity of post release evaluations of biological control agents may be due, in part, to limited financial support, inadequate scientific know how or lack of a cohesive framework from which these evaluations can be made. With respect to the latter obstacle, ecological impacts of introduced species may be evaluated as a function of 1) the organism's geographic distribution, 2) its population densities and 3) the suppressive effect these populations have on the species of interest. Of the three parameters listed above, quantifying population densities of a biological control agent over time is fairly straight forward; however assessing the remaining parameters of this equation can be extremely complex. In early stages of a weed biological control program calculation of the first parameter, geographic distribution is generally limited to initial release localities of the natural enemy. However, as target weeds deteriorate or otherwise become unsuitable, the agent is forced to disperse and its distribution increases. The boundaries for the biological control agent's dispersal are delineated by the distribution of the host plant, which is dynamic and poorly understood for most invasive plant systems. Therefore, evaluating the biological control agent's rate of spread and quantifying the fluctuating distribution of the target weed are integral to assessing distribution in space and time. Similarly, the third component of the impact equation involves quantifying landscape level reductions in life history parameters of the target weed (i.e. flowering). Herein, we report our efforts at quantifying the first parameter of the impact equation (geographic distribution and rate of spread) for Oxyops vitiosa, a classical biological control agent of the invasive Australian tree Melaleuca quinquenervia.

Technical Abstract: Classical weed biological control involves reuniting an invasive plant with coevolved natural enemies from the weed's native range. The primary objective of most weed biological control programs is to suppress a pest population below an ecological threshold, ultimately resulting in the replacement of the target weed with more desirable vegetation. Although the realization of this objective has been described anecdotally for multiple biological control programs, rarely are impacts on the target weed quantified after the introduction of a natural enemy. The paucity of post release evaluations of biological control agents may be due, in part, to limited financial support, inadequate scientific know how or lack of a cohesive framework from which these evaluations can be made. With respect to the latter obstacle, ecological impacts of introduced species may be evaluated as a function of 1) the organism's geographic distribution, 2) its population densities and 3) the suppressive effect these populations have on the species of interest. Of the three parameters listed above, quantifying population densities of a biological control agent over time is fairly straight forward; however assessing the remaining parameters of this equation can be extremely complex. In early stages of a weed biological control program calculation of the first parameter, geographic distribution is generally limited to initial release localities of the natural enemy. However, as target weeds deteriorate or otherwise become unsuitable, the agent is forced to disperse and its distribution increases. The boundaries for the biological control agent's dispersal are delineated by the distribution of the host plant, which is dynamic and poorly understood for most invasive plant systems. Therefore, evaluating the biological control agent's rate of spread and quantifying the fluctuating distribution of the target weed are integral to assessing distribution in space and time. Similarly, the third component of the impact equation involves quantifying landscape level reductions in life history parameters of the target weed (i.e. flowering). Herein, we report our efforts at quantifying the first parameter of the impact equation (geographic distribution and rate of spread) for Oxyops vitiosa (Pascoe), a classical biological control agent of the invasive Australian tree Melaleuca quinquenervia (Cav.) S.T. Blake.