Simple SummaryThe ability to rapidly adapt to new environmental conditions is very important for the wide-scale invasion of pests or intentional introduction of beneficial insects. Diapause (i.e., a seasonal dormant state) formed in autumn in response to short days is a vital adaptation ensuring that the active development and reproduction of an insect population coincide with the favorable warm periods of the year. We conducted a laboratory study aimed to compare the induction of diapause in two invasive Caucasian populations of the brown marmorated stink bugHalyomorpha halys,which recently invaded two neighboring regions with subtropical (Sukhum, Abkhazia) and temperate (Abinsk, Russia) climates. Under the constant temperature of 25 °C and day lengths of 15.0 h and 15.5 h, the population from Abinsk showed a slower nymphal development and a stronger tendency to enter diapause than those from Sukhum. This finding agreed with the difference between the local dynamics of the autumnal temperature decrease. Similar interpopulation differences are known in other insects but our finding is distinguished by a very short adaptation time: the brown marmorated stink bug was first recorded in Sukhum in 2015 and in Abinsk in 2018. Thus, the differences between the compared populations evolved very quickly—during only several years.AbstractThe ability to rapidly adapt to new environmental conditions is a crucial prerequisite for the wide-scale invasion of pests or intentional introduction of beneficial insects. A photoperiodically induced facultative winter diapause is an important adaptation ensuring synchronization of insect development and reproduction with the local seasonal dynamics of environmental factors. We conducted a laboratory study aimed to compare photoperiodic responses of two invasive Caucasian populations of the brown marmorated stink bugHalyomorpha halys(Hemiptera: Heteroptera: Pentatomidae), which recently invaded neighboring regions with subtropical (Sukhum, Abkhazia) and temperate (Abinsk, Russia) climates. Under the temperature of 25 °C and the near-critical photoperiods of L:D = 15:9 h and 15.5:8.5 h, the population from Abinsk showed a slower pre-adult development and a stronger tendency to enter winter adult (reproductive) diapause compared to the population from Sukhum. This finding agreed with the difference between the local dynamics of the autumnal temperature decrease. Similar adaptive interpopulation differences in the patterns of diapause-inducing responses are known in other insect species but our finding is distinguished by a very short adaptation time:H. halyswas first recorded in Sukhum in 2015 and in Abinsk in 2018. Thus, the differences between the compared populations might have evolved over a relatively short span of several years.