Argidae - Arge berberidis-001 by Hectonichus (CC BY-SA 4.0)
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Arriving in the UK about 20 years ago, Berberis sawfly is an insect that's closely related to wasps. These sawflies have short stumpy antennae and are completely black. A female will have 2 generations of offspring. However, this can vary with summer conditions. They lay eggs in Berberis, which hatch into white-spotted larvae that look very similar caterpillars. They feast on the leaves of the host plant from the outside in, consuming the whole leaf. They can defoliate plants when infestations are severe, but healthy plants can recover.
Larvae defoliate Berberis plants.
Adult sawfly are pollinators.
Adult: The adult sawfly has a small black body, light brown legs, transparent wings and short-stumpy black antennae. They can vary from 7-9mm. Larvae: The larval stage of berberis sawfly resembles a caterpillar. They can reach as long as 18mm. They are creamy-white with black heads. Two lots of yellow circles run down the centre of the body, with the whole body being covered in tiny black dots. Pupae: Once fully grown, larvae burrow beneath the soil, they pupate and overwinter within a silken-spun cocoon. Eggs: Adults lay the eggs in the leaves so it can be quite difficult to detect this pest this early on.
Severe defoliation of plants. Branches can be depleted of leaves. Small, green caterpillar larvae on leaves. Healthy plants will recover.
Check plants regularly and remove insects by hand. Cultivate the ground surrounding plants so that pests are disturbed and come to the surface of the soil. Move to a nearby bird table or fence for the birds to eat! Attract natural garden predators into the garden by providing spots of cover. Wild patches and strips of native wildflower/ grass can provide cover for predatory insects. Climbing plants such as ivy is excellent habitat for small songbirds. Likewise, bird tables and ponds are an excellent resource for attracting wildlife.
If there are too many larvae to pick off, pesticides may be used as an alternative measure. There are organic pesticides that incorporate natural pyrethrins available for use in the UK. Some more persistent chemicals can also be purchased from garden centres. It's advised to research and read labels carefully before applying products. Many pesticide treatments are non-specific and can hurt wildlife coming into contact with it.