Posted by: David Green | January 27, 2010

Pests

Discussion at a recent meeting hovered on the subject of pests; a word that seems to mean different things to different people. To biologists, the term seemed generally to refer to an invasive alien species that damaged fragile ecosystems. It set me thinking about the insects and other animals that eat crops, and that led in turn to sawflies.

The Green Sawfly (Rhogogaster viridis) a common British species (which is not generally thought of as a pest)

Sawflies are common and attractive insects that are related to bees and wasps. Their name is derived from their saw-like ovipositors, which the females use to cut into the plants in which they lay their eggs. Here’s how:

The larvae, which look like small caterpillars, have a voracious appetite and can cause substantial damage to plants. A few specialize in crops.

Sawfly larvae commonly feed in groups.

One species, Nematus ribesii, has a particular fondness for gooseberries. The females cut delicately into the edge of the gooseberry leaves and lay a single egg. Hidden in their leafy envelope, the larvae hatch and begin to eat. Working in concert they can defoliate large bushes in a matter of days. It is easy to see how a process that is fascinating to a naturalist with an interest in gardening could be a threat to a farmer whose livelihood depended on a good crop. For those who prefer gooseberries to sawflies some suggestions for organic control can be found here.

Thousands of sawflies, including most of the British species, are neatly arranged in the museum entomology collections. Most are quite small and identification can be difficult. The spectacularly coloured green sawfly fades on mounting to a less attractive yellow-brown. To see the insect in its true colours look carefully in a garden in the Summer…

David Green

Phil Rispin

Dmitri Lugonov

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