This was something I had never considered until reading this article by Koptur and colleagues. These researchers studied the epiphytic fern Pleopeltis crassinervata in cloud forest of Veracruz, Mexico. This species is related to our ngārara wehi (Pyrrosia eleagnifoia) and was found to employ bodyguards to keep nasty herbivores away!
Pleopeltis crassinervata on host tree. Insert: foliage with scale bar = 1cm. Photos: J. Morales & Koptur et al. (2013).
Pleopeltis crassinervata is one of many plants that produces nectar in glands outside of flowers (click here for more info). Nectaries on the leaves of this fern produce nectar that attracts ants.
Nectar droplet on the upperside of a Pleopeltis crassinervata leaf. Scale bar = 1 mm. Photo: Koptur et al. (2013).
The ants then repay their host for this tasty meal with defence services against hungry caterpillars. Koptur et al. (2013) found that plants with healthy, functioning nectaries had fewer caterpillars browsing on their leaves and that the bodyguard ants were often responsible for attacking, removing or killing them.
One species of caterpillar that has to contend with the ants that protect Pleopeltis crassinervata: Leptophobia aripa. Photo: Koptur et al. (2013).
So that is how it is done in Mexico, now I wonder if any of New Zealand's epiphytes have similarly clever tactics?
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