PACIFIC NORTHWEST NURSERY IPM
Honeylocust pod gall midge
Honey locust pod gall midge (Dasineura gleditchiae) is a major pest of honey locust (Gleditsia triacanthos). Feeding by the midge larvae causes leaflets of new growth to form pod like galls in which the larvae pupate. After the adult midge emerges from the pod, the leaf tissue dies and drops prematurely. Much of the new growth can be affected, reducing the aesthetic quality of the trees in nurseries and landscapes. All cultivars of G. triacanthos grown commercially are susceptible in both nursery and landscape situations.
Adult midges deposit eggs on new foliage along the rachis or on the edges of developing leaf buds. The eggs usually hatch in two days. The young larvae crawl along the leaf and begin feeding. Only one larva is required to initiate galling of the leaf. Leaf galls may be folded, partially podded, or the entire leaf may form a pod (Thompson, et al., 1998). The leaf gall dies and drops once the larvae pupate and emerge. Localized die-back is often associated with high infestation levels.
Midge Biology and Phenology
Research in California investigating over wintering and distribution of the pod gall midge indicates that the midge over winters as [late instar larvae or] pupae in cocoons in the soil mostly in the upper two inches near the base of the tree trunks (generally within one foot of the trunk) (Thompson, et al.,1998). In the Northwest, study of midge phenology has shown discrete egg laying events occurring very early in the maturation of the leaf buds (before they leaf out) in Oregon (Rosetta and Bell, 1996). Soon thereafter the populations appear continuous with many life stages present. The first pod gall midge eggs generally are found during the last week of March through the first week of April (Table 1). In 2000 the first evidence of oviposition occurred on April 7 and pod formation on April 13.
Table 1. Appearance of honey locust pod gall midge, Dasineura gleditchiae, egg deposition and pod formation at various Oregon sites from 1995 through 2000.
For more accurate application timing, monitor honey locust trees in nursery and landscape sites beginning in early spring and throughout the growing season to note appearance of eggs deposited on buds and new foliage by
A critical window for enhanced control of the midge is targeting the first two egg depositions beginning in late March or early April with horticultural oil or oil/insecticide applications. These targeted sprays suppress midge populations, reducing the frequency and intensity of pesticide applications necessary to achieve acceptable control.
Our research has investigated the efficacy of soil drenches of the over wintering stages of the midge. These drenches are applied shortly before emergence of the adult midges in the spring. Our trials have shown a well-timed drench can greatly reduce the number of pods on honeylocust trees. Once midges have emerged in the spring, they no longer pupate in the soil but rather within the leaf galls.
Thompson, P.B. and M.P. Parrella.1998. Distribution and Density of Over wintering Dasineura Gleditchiae (Osten Sacken)(Diptera: Ceciomyiidae).Pan Pacific Entomologist. 74(2):85-98.
Rosetta, R.L., P. Thompson and N. Bell. 1998. IPM of Honey Locust Pod Gall Midge.The Digger. 42(3):34-36.