Seasonal phenology of Amauromyza karli (Diptera: Agromyzidae) in quinoa in San Luis Valley of Colorado.

Amauromyza karli Hendel (Diptera: Agromyzidae) has recently emerged as a damaging stem-boring pest of quinoa in Colorado and other quinoa-producing regions of the United States. Severe infestations have been associated with substantial yield losses, highlighting the need for improved understanding of the pest's seasonal dynamics to support integrated pest management (IPM) strategies. The objective of this study was to characterize the seasonal phenology of A. karli in quinoa production systems in the San Luis Valley of Colorado. Adult flight activity was monitored using yellow sticky traps over 4 growing seasons, and larval incidence and stem exit holes were quantified across 2 years. Our results indicated that larval densities peaked in early June with infestations reaching over 90% by mid-July. An ordinal-day, 2-parameter logistic model based on cumulative trap captures was the most parsimonious model and predicted that 50% of adult activity occurred around late June. In addition, a negative binomial mixed-effects model showed no significant association between quinoa field size and adult captures, suggesting that variation in pest pressure is driven by field-level heterogeneity and temporal factors. These findings provide a framework for improving monitoring and management of A. karli. Aligning the timing of biological or chemical control measures with periods of peak adult activity, as well as adjusting planting dates to reduce exposure of vulnerable crop stages, may help mitigate damage caused by this pest. Overall, this study contributes foundational phenological information that can be used to inform IPM decision-making and reduce economic losses in quinoa production.