Efficacy of spot-spray applications of protein bait-insecticide combinations to roosting hosts of melon fly (Zeugodacus cucurbitae) in Hawai’i

Over the past decade, resistance to GF120^® Fruit Fly Bait (Dow AgroScience), which contains the insecticide Spinosad, has been increasing in Hawaii populations of melon fly, Zeugodacus cucurbitae (Coquillett), leading to the need for alternative bait and insecticide combinations. Field experiments were conducted to determine the effectiveness of Nu-Lure^® Insect Bait (Miller Chemicals and Fertilizer Co.) with two insecticides, malathion (Malathion 5EC, Drexel Co.) and abamectin (Agri-Mek^® SC, Syngenta), in the control of melon fly. These combinations were previously found effective in lab bioassays. Field trials were conducted on Oahu and Maui to test the combination of Nu-Lure^® and Agri-Mek^® SC applications as spot-sprays to known roosting hosts of the melon fly. Fly counts were made using Cuelure bottle traps, which capture males, and torula yeast multi-lure traps, which capture both sexes. Trapped flies were counted at one-week intervals for four weeks (two pre-treatment counts, two post-treatment counts). Two treatment sprays were, conducted one week apart: at the label rate to roosting hosts and not to the cucurbit crops. Oahu farm was over 300 acres and the Maui farm was under 30 acres. On Oahu, spot-sprays were applied every twenty feet to uniform windbreaks of jackfruit (Artocarpus heterophyllus) that were 2000-2400 ft in length, where Z. cucurbitae were seen roosting. This led to a small reduction in population numbers. On Maui, spot-sprays on known roosting hosts, mainly false koa (Acacia koa), led to a significant drop in fly trap captures.