Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2001
Publication Date: 4/1/2002
Citation: vol.31, no.2 pgs. 339-347
Interpretive Summary: The blueberry gall midge is a native North American fly now introduced and becoming a blueberry pest in Mediterranean Europe. In warmer temperate climates eleven or more generations of the gall midge can be completed with larvae infesting buds and reaching very destructive population densities. Blueberry plants grown in the southeastern U.S. and likely those in Europe possess no obvious natural immunity to gall midge attack and plant-growth regulators intended to enhance leafing also spurred blueberry gall midge reproduction. A safe method for controlling blueberry gall midges is the preservation and possibly augmentation of natural enemies that eat blueberry gall midge larvae. Three species of tiny wasps paralyzed, developed inside and eventually killed gall midge larvae. Predatory maggots of hover flies were reared in the laboratory; each can eat about 400 gall midge larvae during their 22-day life span. Wasps and hover flies became active in commercial blueberry fields during and after late bloom. Thus, insecticides may be needed to reduce damaging levels of gall midges before the onset of bloom. Pre-bloom applications of pesticides were effective, but post-bloom applications killed natural enemies and actually increased gall midge infestation. No insecticides were sprayed during blueberry bloom for fear of injuring and killing pollinators.
Technical Abstract: Integrated pest management for a little understood, blueberry bud-infesting gall midge, Dasineura oxycoccana (Johnson) (Diptera: Cecidomyiidae) can help reduce an estimated 15-80 percent crop loss due to this insect in the southern United States. Newly discovered parasitoids and predatory flies form a natural enemy complex whose dominant species either internally parasitize gall midge larvae or voraciously eat them. These natural enemies rely on bloom for initiating reproduction and become effective biocontrol agents after bloom when blueberry plants begin leafing out. Later post-bloom emergence of these natural enemies increases their compatibility with chemical control. Pre-bloom insecticides can be effectively and safely applied for gall midge control when an action threshold of 0.25 larvae per flower bud is attained in late winter and before flower buds fully open. Many blueberry cultivars and clones grown in Mississippi do not show any obvious patterns of bud resistance to D.oxycoccana. Additionally, the continuing use of plant growth regulators such as the dormancy-breaking compound, hydrogen cyanamide, could also have a deleterious side-effect: boosting gall midge populations and spurring greater infestation of D. oxycoccana larvae in rabbiteye blueberry buds.