Trichoplusia ni, also known as the cabbage looper moth, is a significant crop pest throughout the world. Larvae cause severe defoliation of cole crops and other vegetables including beet, lettuce, peas, snap beans, and spinach. The species is highly vagile and migratory. It is presumed that T.ni overwinters in southern latitudes and reinvades the United States and Canada each spring. However, activity is known to be erratic; some years experience a true outbreak level of adult moths, while activity in other years is abnormally low. These shifts are likely influenced by natural enemy activity, including a nucleopolyhedrovirus that causes larval mortality, in combination with abiotic environmental factors. This study uses T. ni activity trends from a long-term pest monitoring dataset from Oregon and compares it to climate variables from established weather stations throughout the region. Statistical analysis of temperature, rainfall, and ENSO patterns from 1996-2024 suggest that the arrival of cabbage looper moths in Oregon varies widely per year and may be attributed to changes in climate patterns occurring in southern latitudes. Understanding the environmental factors that contribute to T. ni activity fluctuations will help refine models so that growers and researchers can better predict pest pressure. Additionally, findings will be incorporated into the Oregon Pest Monitoring Network’s pest forecast tool, a publicly available digital platform that combines phenology models and estimated life stage to better aid scouting efforts.
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