Limiting Onion Fly (Delia antiqua) and Onion Thrips (Thrips tabaci) Damage to Onions by Combined Use of Environmentally Acceptable Control Methods: Fact or Fantasy?

In a two-year study (2023-2024), field experiments were conducted at a location where onion fly (<i>Delia antiqua</i> [Meigen]) and onion thrips (<i>Thrips tabaci</i> Lindeman) are permanent pests. The objective of the study was to investigate independent and combined application (synergistic effect) of environmentally acceptable methods (biological and biotechnical control methods) of controlling these pests on onions. Seven treatments were tested, including a positive control (chemical control) and a negative control (untreated plots), as well as various combinations of environmentally friendly approaches, such as entomopathogenic fungi and nematodes, white clover intercropping, and colored sticky boards with lures. The onion fly caused greater damage and subsequent bulb loss than the onion thrips in both years, despite white clover (as independent application) as an intercrop, and the combined application of white clover and entomopathogens proved to be most effective against thrips and fly damage, ultimately resulting in a suboptimal onion yield of less than 7 tons per hectare annually. It is evident that environmentally acceptable control methods were experiencing challenges in either reducing the extent of damage caused by both pests or increasing the yield of healthy bulbs. It is unfortunate that, despite observing an increased yield of healthy bulbs in certain treatments, a significant quantity of bulbs was also lost due to onion fly.