DIVERTING DELIA-ANTIQUA (DIPTERA, ANTHOMYIIDAE) OVIPOSITION WITH CULL ONIONS - FIELD STUDIES ON PLANTING DEPTH AND A GREENHOUSE TEST OF THE STIMULO-DETERRENT CONCEPT

Microplots (2.5 m long) of sprouting onion bulbs planted 5 cm deep received an average of 2,300 Delia antiqua (Meigen) eggs during 3 wk in a field trial. Plots with bulbs resting on the soil surface, planted with their neck at the soil surface, or at 12-cm depth, received 280, 1,530, and 980 eggs, respectively. In the laboratory, damage to sprouting bulbs caused by slicing, maggot infestation, or both did not enhance or diminish D. antiqua oviposition compared with intact bulbs. Egg laying was equivalent for all treatments as long as green, moist foliage was present. The simultaneous use of an ovipositional deterrent (cinnamaldehyde) and diversionary cull onions to protect seedling onions from D. antiqua was tested using a factorial experiment in the greenhouse. The interaction between deterrent and culls was consistent with a multiplicative model where the probability of an onion maggot fly accepting seedlings was reduced independently by the presence of deterrent or culls. Collectively, these experiments suggest that insect control by stimulo-deterrent diversion is a valid concept, albeit not yet practical for D. antiqua.