Behavior of Onion Maggot (Diptera: Anthomyiidae) In Commercial Onion Fields Treated Regularly with Parathion Sprays

Numbers of Delia antique (Meigen) adults captured in yellow water-traps in New York State indicated that fly activity remained crepuscular throughout each of three annual fly generations. Flies avoided onion crops during most of the day; they preferred to rest in the shade of surrounding foliage. Once active, flies were distributed more or less evenly through crops; most females were caught in the evening. Parathion sprays had to contact flies directly for mortality to occur. Data indicated that a single parathion spray applied at peak fly emergence in the spring is unlikely to contact >10–20% of the fly population. Sprays applied later in the year either to the entire crop or to just the surrounding hedgerows were unlikely to contact >4 or 0.2% of the fly population, respectively. These data suggest that application of parathion as an adulticide is unwarranted.