Acquired natural enemies of the weed biological control agent Oxyops vitiosa (Colepotera: Curculionidae)

Abstract

The Australian curculionid Oxyops vitiosa Pascoe was introduced into Florida in 1997 as a biological control agent of the invasive tree Melaleuca quinquenervia (Cav.) S. T. Blake. Populations of the weevil increased rapidly and became widely distributed throughout much of the invasive tree's adventive distribution. In this study we ask if O. vitiosa has acquired natural enemies in Florida, how these enemies circumvent the protective terpenoid laden exudates on larvae, and what influence 1 of the most common natural enemies has on O. vitiosa population densities? Surveys of O. vitiosa populations and rearing of field-collected individuals resulted in no instances of parasitoids or pathogens exploiting weevil eggs or larvae. In contrast, 44 species of predatory arthropods were commonly associated (>5 individuals when pooled across all sites and sample dates) with O. vitiosa. Eleven predatory species were observed feeding on O. vitiosa during timed surveys, including 6 pentatomid species, 2 formicids and 3 arachnids. Species with mandibulate or chelicerate mouthparts fed on adult stages whereas pentatomids, with haustellate beaks, pierced larval exoskeletons thereby bypassing the protective larval coating. Observations of predation were rare, with only 8% of timed surveys resulting in 1 or more instances of attack. Feeding by the pentatomid Podisus mucronatus Uhler accounted for 76% of all recorded predation events. Podisus mucronatus numerically responded to fourth instars but no response was observed for other life stages. Damage to M. quinquenervia plants from feeding by O. vitiosa, however, was not influenced by P. mucronatus densities, indicating that predation does not alter plant suppression.