Abstract
ABSTRACTClassical biological control agents fail to achieve an impact on their hosts for a variety of reasons and an understanding of why they fail can help shape decisions on subsequent releases. Ornamental Ficus microcarpa is a widely planted avenue fig tree that is invasive in countries where its pollinator (Eupristina verticillata) is also introduced. This tree also supports more than 20 species of non-pollinating fig wasps (NPFW) that feed in the figs and have the potential to reduce the plant’s reproduction. Odontofroggatia galili, one of the most widely introduced NPFW, has larvae that develop in galled ovules that might otherwise develop into seeds or support pollinator larvae. We examined the distribution and relative abundance of the pollinator and O. galili on F. microcarpa in China, towards the northern limit of the tree’s natural range, and in Italy where the two species have been introduced. Where they co-existed, we also recorded the impact of varying densities of O. galili on F. microcarpa seed and pollinator production. O. galili and E. verticillata displayed contrasting habitat preferences in China, with O. galili almost absent from warmer sites. O. galili abundance and sex ratios varied between the natural and introduced ranges. Figs with more O. galili contained fewer seeds and pollinator offspring, but reproduction was rarely inhibited totally. Additional species with a greater impact in the figs they occupy are needed if biocontrol of F. microcarpa is to be effective.
Highlights
Classical biological control attempts to control weeds that have become invasive using plant-feeding insects or diseases that originate in the plant’s natural range (Culliney 2005).Most biological control agents that are released become established, but only a proportion of these have any significant impact on their hosts (Julien, and Griffiths 1998; McFadyen2003) and an understanding of why established species have little impact can help shape decisions on subsequent releases (Myers 2000)
To determine whether the sex ratio of O. galili varied according to the numbers of offspring individuals sharing a fig, we modeled the effects of O. galili abundance on the proportion of males produced in China and Italy using binomial generalized linear mixed models (GLMM) with logit links
Our results confirm that O. galili has a detectable impact on female and male reproductive functions of F. microcarpa in both its natural and introduced ranges, and that it rarely suppresses reproduction entirely
Summary
Classical biological control attempts to control weeds that have become invasive using plant-feeding insects or diseases that originate in the plant’s natural range (Culliney 2005).Most biological control agents that are released become established, but only a proportion of these have any significant impact on their hosts (Julien, and Griffiths 1998; McFadyen2003) and an understanding of why established species have little impact can help shape decisions on subsequent releases (Myers 2000). Most biological control agents that are released become established, but only a proportion of these have any significant impact on their hosts Fig trees (Ficus, Moraceae) are a species-rich group distributed in warmer countries throughout the Old and New Worlds (Harrison 2005). They are of great ecological significance because of the many animals that feed on their figs (syconia) (Shanahan, So, Compton, and Corlett 2001), but this wide range of seed dispersal agents results in the rapid dispersal of any ripe figs produced by fig trees growing outside their natural range (Simberloff, and Von Holle, 1999). Because fig crops are often synchronized within trees, this usual means that they must fly between trees, which can be tens or even hundreds of kilometers apart
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