Timing of Insecticide Application Against Larval Invasion of Spring Sown Onion Bulb by Stone Leek Leafminer, Liriomyza chinensis in Hokkaido

Abstract

In the onion fields of Hokkaido, a major northernmost island of Japan, outbreaks of stone leek leafminer (Liriomyza chinensis) infestation have been occurring since 2013. In fields where heavy leaf damage occurred, a proportion of the harvested bulbs showed damage from larval mines, in addition to evidence of larval remains. The capture rate of adults in yellow sticky traps indicated that leafminers produce three generations annually. The peaks include the hibernating generation (late May to early June), first generation (mid-July to late July), and second generation (mid-August to late August). The position of the damaged scales and the timing of leaf emergence indicated that bulb damage from oviposition occurred after mid-June.However, the most effective time to implement control measures against larval invasion was in early August,when two applications of effective insecticide reduced onion damage by 1/10.