Extrafloral nectaries as a deterrent mechanism against seed predators in the chemically protected weed Crotalaria pallida (Leguminosae)

Abstract

In several plants, extrafloral nectaries (EFN) are located close to the reproductive structures, suggesting that ants may act as a defence against specialized seed predators that overcome chemical defences. Alternatively, ants may also deter herbivores in a generalized manner, thereby protecting the whole plant. In this work, we examined the relationship between the chemically protected weed Crotalaria pallida Ait. (Leguminosae) that bears EFN, its specialized seed predator, the larvae of the arctiid moth Utetheisa ornatrix L. (Arctiidae) and ants. We tested two hypotheses related to the type of deterrence caused by ants. The Seed Predator Deterrence Hypothesis predicts that ant deterrence is directed primarily towards herbivores that destroy seeds and other reproductive structures, without attacking herbivores on vegetative structures. The General Deterrence Hypothesis states that ants are general in their effects, equally deterring herbivores in vegetative and reproductive structures. Our results supported the predictions of the Seed Predator Deterrence Hypothesis, namely, that (i) ant activity on EFN was related to the vulnerability of reproductive structures to attack by U. ornatrix; (ii) ant patrolling was restricted almost entirely to racemes; (iii) ants removed termites used as baits more frequently on racemes than on leaves; and (iv) U. ornatrix larvae were often expulsed from the racemes. These results indicate that EFN can act as another deterrent mechanism in chemically protected plants by promoting the expulsion of specialist seed predators.

Soil organisms associated to the weed suppressant Crotalaria juncea (fabaceae) and its importance as a refuge for natural enemies

“…(Jones & Coppedge, 2000, Jackson & Harrison, 2008, N. clavipes (Ferro et al, 2006), O. insidiosus (Erlandson & Obrycki, 2010), Phyllophaga spp. (Lewis et al, 2003), and U. ornatrix (Iyengar & Eisner, 2002;Guimarães et al, 2006) were abundant in C. juncea and/or other Fabaceae. 2.52 ± 0.18 a 0.00 ± 0.00 a 0.00 ± 0.00 a Gryllus assimilis/1.08 m 3 soil 0.84 ± 0.06 a 0.00 ± 0.00 a 0.00 ± 0.00 a Tylenchida Heteroderidae adults Meloidogyne incognita 19.27 ± 2.47 a 0.00 ± 0.00 b 0.00 ± 0.00 b Nematodes/1.08 m 3 soil 6.42 ± 0.82 a 0.00 ± 0.00 b 0.00 ± 0.00 b Coleoptera Scarabeidae larvae Phyllophaga sp.…”

Local adaptation in a plant herbivore interaction depends on the spatial scale

“…PAs are assumed to serve as protective chemicals against herbivores (Hartmann, 2004), and the toxic effect of PAs on a generalist herbivore has recently been demonstrated (Narberhaus, Zintgraf & Dobler, 2005). Crotalaria pallida also has extrafloral nectaries that attract ants, which positively affect plant fitness by decreasing herbivore activity (Heil & McKey, 2003; Ferro, Guimarães & Trigo, 2006; Guimarães et al. , 2006).…”

Chemical defence of the warningly coloured caterpillars of Methona themisto (Lepidoptera: Nymphalidae: Ithomiinae)

“…It is interesting to note that pyrrolizidine alkaloids, widespread mainly in adults of Ithomiinae and Danainae butterflies and caterpillars and adults of Arctiidae moths (see Trigo, 2008 for a review) are sometimes reported to be ineffective against birds (Ritland, 1991;Yosef et al, 1996). Caterpillars of Utetheisa ornatrix contain pyrrolizidine alkaloids but are eaten by ants (Ferro et al, 2006;Guimarães et al, 2006). Tropane alkaloids are effective against monkeys but not spiders .…”