In 2021, a surprising outbreak of Spodoptera frugiperda (fall armyworm, FAW) occurred in alfalfa fields in temperate regions, sparking two key questions: How are FAW able to survive into late September despite periods of cold? And which insecticides provide effective control in these systems? Traditionally associated with warm climates, FAW’s persistence in cooler environments suggests an ability not only to tolerate cold, but to withstand and recover from fluctuating temperatures. At the same time, little is known about effective chemical control of FAW in forage crops like alfalfa. This study combines two objectives prompted by that outbreak: (1) to evaluate the effect of constant and oscillating temperature regimes on FAW larval development, and (2) to assess the residual efficacy of seven insecticides commonly used in alfalfa. Temperature trials revealed that larvae survived and developed under cold oscillating temperatures, despite developmental delays under field-like conditions. In the insecticide trial, third-instar larvae were exposed to treated leaves collected at intervals up to 21 days post-application. Mortality, feeding cessation, and growth inhibition were evaluated at 12 and 36 hours. Together, these studies provide practical insight into how FAW can persist under environmental stress and how growers might respond with effective chemical control, offering new guidance for integrated pest management in non-traditional hosts like alfalfa.
.png)
