Honeylocust Podgall Midge
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'"`UNIQ--btaxobox-00000000-QINU`"' Compiled by Whitney Cranshaw, Colorado State University:
Dasineura gleditschiae (Osten Sacken)
Diptera: Cecidomyiidae
Hosts
Honeylocust (Gleditsia triacanthos)
Damage and Diagnosis
Larvae feed on developing leaves causing the production of thickened pod-like galls. Inside currently infested leaf galls, small white maggots can be found. The galls darken, dry and drop a few weeks after adults emerge. This defoliation gives a thin appearance to the plant, particularly when most of the leaflets on a leaf are affected. Injury is usually of minor cosmetic importance but can constitute a further stress and may contribute to twig dieback. In extreme cases, attacks can be so intense that all emergent buds are killed which results in a thickened club-like swelling of the twigs.
Associated Species
Another gall midge, Neolasioptera brevis (Gagne) is reported to induce twig swellings and bushy growth on honeylocust. It has not been confirmed from Colorado but similar symptoms have been observed in Mesa and Morgan counties.
Life History and Habits
Honeylocust podgall midge spends the winter in the adult stage under protective cover around previously infested honeylocust plantings. The adults are tiny, delicate gray-brown flies that move to emerging honeylocust buds as they first start to break. Eggs are laid among the emerging leaves and the larvae feed on the leaflets causing them to curl and thicken into the characteristic pod gall. Larvae are cream-colored maggots that become full-grown in about 3 to 4 weeks. Pupation occurs within the gall. As the adults emerge the old pupal skin is often pulled partially out at the gall opening.
There are typically about three generations per year, with populations usually declining by early July. Later infestations may extend for additional generations where sprout growth continues to be produced or in highly fertile, irrigated sites, such as nurseries.
Management
Several natural controls are present for this species. A tiny parasitic wasp can be an important natural enemy late in the season and the predatory plant bug Deraeocoris nebulosus feeds on many larvae within galls. However, competition with the honeylocust plant bug has been even more important. Honeylocust plant bug competes with the honeylocust podgall midge, killing the new growth needed by the developing midges. Finally, when populations of honeylocust podgall midge get extremely high, excessive egg laying and larval feeding on the new growth can cause leaves to prematurely abscise, killing the larvae. Pyrethroid insecticides have been the most effective chemical controls. They should be timed for periods when adults are actively laying eggs. The presence of fresh pupal skins sticking from the galls is a good indication of a recent emergence.
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