Biological Control of the Leafminer

Identification

• Adult leafminers are typically identified as small, yellow and black flies (Diptera sp.) with clear wings, and are about the same size as a fruit fly. However, the larvae of some sawflies (Hymenoptera sp.), moths (Lepidoptera sp.) and beetles (Coleoptera sp.) are also considered leafminers because they follow the same pattern of mining and feeding on leaves.

Damage

• Female leafminers insert their eggs within the leaves of a wide range of host plants. They also puncture the leaf surface to feed on damaged plant tissue. Leafminer larvae develop within the leaves, forming large mines or blotches of dead tissue as they grow. Most leafminer larvae feed inside these mines for their entire larval period. Some larvae pupate within the leaf mine, while others cut their way out of the leaf when they mature to adults and drop to the ground to pupate in the soil. Even when leafminer populations are high, they rarely kill a plant, but their feeding can cause stippling of leaves and reduces the aesthetic appeal of your plants.

Parasitic Wasps

• There are many natural enemies that occur in your garden that naturally control leafminer populations, primarily parasitic wasps from the genus Diglyphus and the parasitoid Dacnusa sibirica. Both are commercially available at nurseries and greenhouses for control of leafminers. Dacnusa sibrica lays eggs within leafminer larvae and feeds on the tissues until the larvae pupate. It doesn’t prevent damage from occurring, but pupates with the leafminer larvae, reducing the next generation of leafminers. Diglyphus parasites, on the other hand, paralyze the leafminer larvae so they can't feed, and eventually kill the larvae.

Beneficial Nematodes

• Insecticidal nematodes (Steinernema spp., Heterohabditis spp.) are beneficial nematodes that can provide effective and fast control of leafminers. Nematodes are roundworms, and while many species are considered plant pests, insecticidal nematodes are beneficial because they attack specific insects and not plants. Nematodes infect leafminer larvae with symbiotic bacteria, typically killing them within 48 hours. Beneficial nematodes are available commercially, and are applied to irrigated soil.