Predicting parasitoid accumulation by potential Brazilian peppertree biological control agents from assessments in the native and invaded ranges

Abstract

During their initial releases, classical biological control agents may benefit from enemy-free-space as they are introduced to new habitats with relatively low attack rates by natural enemies. The benefits of classical biological control may be reduced by natural enemies that exploit new agents in the introduced range. Estimates of agent vulnerability to natural enemies prior to release could assist in predicting attack rates and prioritization of proposed agents. Additionally, release of vulnerable biological control agents could have unintended consequences that disrupt native food webs. Our goal was to predict the vulnerability of potential agents to attack by natural enemies by determining parasitism rates in the native range of the weed Brazilian peppertree, Schinus terebinthifolia. Furthermore, we conducted assessments of the rate of attack of ecological analogues in the invaded range in North America, where the agents are to be released, to assist in predicting post release vulnerability. Potential agents and analogues were assigned to four feeding niches, leaf folders, cryptic feeders, thrashers, and sap feeders. Cryptic members were generally most common in the invaded range. However, compared with the other niches, leaf folders were most common in at least one region of the native range. Surveys of potential agents of Brazilian peppertree in their native range of South America indicated parasitism rates were generally <20% for leaf folders (10.5 ± 6.3%; n = 485), cryptic feeders (17.6 ± 3.7%; n = 495), thrashers (12.1 ± 1.2%; n = 381), and sap feeders (2.5% ± 1.1%; n = 200). With exceptions, parasitism rates of the ecological analogues of North America were similar to those from South America for leaf folders (19.2 ± 7.9%; n = 19), cryptic feeders (16.5 ± 5.2%; n = 285), and sap feeders (0.2 ± 0.2%; n = 1247). Thrashers were not included in the analysis as a single parasitoid was found from few (n = 9) hosts recovered in North America. These results suggest that if species of these defoliating leaf folder or cryptic feeder niches are released for biological control in North America they will be parasitized at these same levels. However, if sap feeders are released, these results predict very low parasitism would result. These pre-release assessments of parasitism may assist in the prioritization of potential agent species for biological control of weeds and reduce the likelihood of indirect effects impacting native communities.