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The production of extrafloral nectar is thought to represent an indirect plant defense, as it allows plants to recruit natural enemies which can protect the plant against herbivore attacks. In previous work we demonstrated that plants may show a strong increase in extrafloral nectar secretion in response to herbivory. Here we address the question of whether this induction is herbivory-specific, or simply a general response to tissue damage. We compared the level of induction in Gossypium herbaceum (L.) (Malvaceae) following either herbivory by Spodoptera littoralis (Boisduval) (Lepidoptera; Noctuidae) or mechanical damage with and without the addition of S. littoralis regurgitate. Both herbivore feeding and mechanical damage significantly raised nectar production. No difference in volume or pattern of nectar secretion was found between natural and mechanical damage, nor between artificially damaged plants treated with regurgitate or water. Our findings indicate that the induction of extrafloral nectar secretion constitutes a general response by the plant to tissue damage, rather than representing a herbivory-specific mechanism. The costs and benefits of such a non-specific strategy for the plant are discussed.

In 1990, a broadleaf weed growing on a cattle ranch in Hendry County in southwest Florida was identified as tropical soda apple (Solanum viarum Dunal), a species native to Argentina and Brazil (5) (Figure 1). Tropical soda apple (TSA) was apparently collected in Florida from Glades County in 1988 (University of Florida Herbarium) but was observed on the Hendry County ranch as early as 1987. Having foliage unpalatable to livestock, this noxious weed can infest a pasture or rangeland within one to two years resulting in lower stocking rates (animals per hectare). However, livestock and wildlife (feral hogs, deer, raccoons) will eat the fruit and disseminate the seed via feces. Fruit production occurs throughout the year (primarily September through May) thus providing high numbers (40000 to 50 000 per plant) of viable seed (75% germination) for seed dispersal. Our objectives are to alert those concerned with weed control of the presence of TSA in subtropical regions of the U.S., to discuss the ecology and taxonomy of this weed, and to indicate areas for future research.

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