The impact of a gall midge on the reproductive success of Ficus benjamina, a potentially invasive fig tree

Abstract

Fig trees (Ficus spp.) are popular ornamental trees that are entirely dependent on a mutalistic association with host-specific pollinating fig wasps for reproduction. They can become naturalized and invasive in countries where the associated pollinator is also established. Figs (syconia) are also also utilized by a diverse community of organisms that are potentially detrimental to the pollinators or seed production. Ficus benjamina is a widely-planted fig tree with the ability to establish outside its native range. We examined the impact of an undescribed gall midge species associated with F. benjamina within the plant’s natural range in Xishuangbanna, south-western China. Observations on the levels of abundance of the midge together with fig abortion and seed germination rates showed that the gall midge had a strong negative effect on reproduction. The gall midge reduced pollinator survival and at high densities eliminated all pollinators, due primarily to premature abortion of figs. Seed numbers were only reduced at high gall midge densities, but seed quality, as measured by germination success and root growth rates, was greatly reduced whenever the gall midge was present. Within its presumed natural range the gall midge appears to be host specific, and given its dramatic impact on host reproductive success, is a potential candidate for the biological control of F. benjamina.