The Florida Everglades have been invaded by an exotic weed fern, Lygodium microphyllum. Across its native distribution in the Old World tropics from Africa to Australasia it was found to have multiple location-specific haplotypes. Within this distribution, the climbing fern is attacked by a phytophagous mite, Floracarus perrepae, also with multiple haplotypes. The genetic relationship between mite and fern haplotypes was matched by an overarching geographical relationship between the two. Further, mites that occur in the same location as a particular fern haplotype were better able to utilize the fern than mites from more distant locations. From a biological control context, we are able to show that the weed fern in the Everglades most likely originated in northern Queensland, Australia/Papua New Guinea and that the mite from northern Queensland offers the greatest prospect for control.

A gall‐making fly, Fergusonina sp., is under study as a potential biological control agent of Melaleuca quinquenervia (Cav.) S. T. Blake, an invasive weed in Florida, USA. The seasonal phenology of Fergusonina sp. and its host M. quinquenervia was studied over 2 years in northern New South Wales and south‐eastern Queensland. Fergusonina sp. populations followed an annual cycle, with gall numbers peaking in August/September. Gall density was strongly correlated with leaf bud density and temperature, but not rainfall. Comparison of climates in Australia across the native range of Fergusonina sp. with the climate of Miami, Florida, predicts that climate should not be a limiting factor in its establishment. The fly/nematode complex of Fergusonina/Fergusobia sp. is compared with other gall‐making agents used in biological control programs. Galls are formed from primordial leaf bud and reproductive structures of the plant and have many of the attributes of a moderately powerful metabolic sink. High gall densities could potentially suppress seed production and reduce the vigour of the tree, which would make this insect species an effective biological control agent of M. quinquenervia.

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