June 2017 – Oil palm plantations: a beginner’s guide to invertebrate interactions

 

A blog post from Amy Eycott, a Postdoctoral Research Associate in the Insect Ecology Group

Left: The Golden silk orb weaver, Nephila, was cause for some excitement. Photo credit: Ed Turner.

I’ve just joined the Insect Ecology Group as a postdoc studying oil palm biodiversity as part of the El Niño project, but until three weeks ago I’d never been to an oil palm plantation, or even Southeast Asia, before. So when I took a two-week trip in May to meet the project staff and see the sites, there was the potential for everything to be a little overwhelming. Fortunately, after a few days relaxing in Bogor I arrived at the BEFTA site in Sumatra at a time when pretty much the whole Cambridge team were there.

Now, as well as having no experience of Southeast Asia, I also had rather limited experience with insects. So it was an intense but a very fun two weeks, as I got to ask as many silly questions as I wanted, the team always ready with a patient reply. Here’s a potted summary of the main things I learnt which I think might be interesting for people as uninformed as I was. I’m interested in interactions, so the focus is on ecology rather than taxonomy!

There are lots of grasshoppers, crickets and bush crickets (katydids) in oil palm plantations. If you hold a bush cricket badly, it can give you quite a nip for such a peaceful herbivore. Rhino beetles are a big pest in oil palm plantations because the adults can damage young palms. They don’t bite but instead pinch you between two sections of leg that have spines, which can puncture your skin. They also make a strange hissing sound by rubbing their wings against their wing-cases (elytra). The other main pest is a moth called a bagworm; they have caterpillars which live in little cases made of dead leaves to protect them from predators.

The main invertebrate predators of these pests in the plantations are ants, assassin bugs and parasitic wasps. The number and diversity of ants is pretty impressive and some of them have crazy jaws – BEFTA PhD student Millie works on how useful ants are. Assassin bugs are ‘true bugs’ with sucking mouthparts and while many true bugs are sap-sucking, assassin bugs use their very extended mouthparts to stab the soft bodies of invertebrate prey and suck them to death from the inside out. The parasitic wasps lay eggs on or inside their hosts. They must be effective at pest control because the plantations have started planting nectar-rich flowers to give the adults an energy boost, which should help them to live longer and produce more eggs – see work by Julie Hinsch to find out more.

Of course, this is a simplified version of what goes on, even in oil palm monocultures. There are praying mantids, scorpions, aphids, dragonflies sporting funky 1980s looks, and spiders including the very cool Golden silk orb weaver, Nephila. I look forward to writing more informed contributions as the year goes on!

 

 

80s style for the Orthetrum sabina dragonfly. Photo credit: Amy Eycott.

This little planthopper caught my eye. It’s a derbid planthopper, a pest of palms. Photo credit: Amy Eycott.

These eye-catching grasshoppers were everywhere. Yellow and black seems to be a common warning colouration in tropical grasshoppers. Photo credit: Amy Eycott.

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