Rapid responses are essential: adaptive temporal variation in cold tolerance of the invasive fall armyworm

Overwintering presents an ecological challenge to insects given highly contrasting environments between native versus invaded environments. The capacity for in situ adaptation through tracking temporal changes in ambient conditions through phenotypic plasticity is thus ecologically important. The fall armyworm is a tropical invasive economic pest of cereals that has become a major biosecurity threat globally. While reports suggest fall armyworm overwinter in tropical environments, little is known on how it survives the environmentally-divergent invaded environments. Here, we tested whether fall armyworm critical low temperature activity limits adaptively tracked prevailing temporal ambient environments. Using field collected populations over 2 years, we show that fall armyworm low temperature responses tracked environmental ambient temperatures. Summer 2020 collected larva had significantly lower cold tolerance (high critical thermal minima [CT_min] and chill coma recovery time [CCRT]) than those from winter seasons. However, winter collected larva had the highest cold tolerance (lower CT_min and CCRT). These results show adaptive fall armyworm responses to ambient temperature environments suggesting that both long-term and short-term responses may shape pest thermal traits and overall ecology.