The rhododendron gall midge (Clinodiplosis rhododendri) damages the new buds and leaves of rhododendron shrubs. As adults, the tiny flies do no damage, but their larvae voraciously feed until they pupate to adulthood. Several generations of the rhododendron gall midge can do extensive damage over the course of spring and summer. In severe infestations the leaves of the shrub may completely die.
The adult rhododendron midge is very small and often difficult to see. They measure only 1/16 of an inch. The insects resemble tiny flies in their adult stage. The males have light fur on their body and are brown in color. The male's antenna is quite long and often measures 1 1/2 their body length. The females antenna is much shorter. In the insects larva stage they are a tiny, white speck that is flat in appearance and barely discernible to the naked eye.
History and Distribution
The rhododendron gall midge has been reported in New Jersey, North Carolina, Pennsylvania and New York, according to North Carolina State University. It is also known to frequent Connecticut. The insect was first described and written about in 1939.
Spring and Winter
During the winter months the rhododendron gall midge winters in the soil in the form of a pupa as it transforms into an adult. During the early spring it emerges from the its pupa stage and crawls out of the soil onto the rhododendron where it breeds and lays eggs. The eggs are laid in clusters, predominately on the underside of newly emerged leaves. If the leaf has not completely unfurled the insect will lay the eggs along the outer edge of the leaf.
The eggs hatch into larvae which spend seven days of their lives feeding on the leaves and buds of the shrub. The leaves appear to curl inward as they sustain damage from the feeding insects. Once the larvae have fed they drop to the ground beneath the shrub to burrow into the soil and pupate into an adult so the cycle can begin all over again.
Apply diazinon, isazofos or chlorpyrifos to the soil around the rhododendron in the fall, according to University of Connecticut Integrated Pest Management. The fall application will kill the pupas that overwinter. A soil drench in April of chlorpyrifos will also help break the insects spring and summer life cycle. The larvae and adults on the shrubs foliage can be controlled by applying dimethoate in May to the leaves of the shrub.