Seasonal cycles of noctuid moths of the subfamily Plusiinae (Lepidoptera, Noctuidae) of the Palaearctic: Diversity and environmental control

Abstract

Analysis of data on seasonal development of noctuid moths of the subfamily Plusiinae shows that the control of their seasonal cycles is poorly understood. At the same time, the available data demonstrate considerable diversity of the seasonal patterns of Plusiinae species from different regions. The homodynamic type of seasonal development has been found in Trichoplusia ni and Ctenoplusia agnata of the tribe Argyrogrammatini and in Autographa gamma of the Plusiini. The seasonal development of these southern noctuids is accompanied by regular interzonal migrations of flying adults. When spreading northwards, they can produce a different number of annual generations, depending on the local climatic conditions, and establish temporary local populations whose longevity is limited by the available thermal resources. Adults of some species may fly back southwards, but it is more likely that individuals from temporary local populations cannot survive long winters and are destined to die. The heterodynamic type of seasonal cycles allows insects to survive in the regions with pronounced seasonality of climate. This type of seasonal development includes univoltine, multivoltine, and semivoltine seasonal cycles. Univoltine seasonal cycles with obligate diapause are known in Autographa buraetica, A. excelsa, and Syngrapha ain (Plusiini). Diapause provides tolerance to both low temperatures and a prolonged period when food is unavailable. In Syngrapha ottolenguii (Plusiini), the same result is achieved by inclusion of two photoperiodically controlled diapauses (winter larval and summer adult ones) into the life cycle. The semivoltine seasonal cycle has been reported in only one species of Plusiinae, namely Syngrapha devergens. Larvae of this moth overwinter twice before pupation. Multivoltinism is common in the tribe Plusiini. Depending on the latitude, different species of this tribe can produce up to four generations per year and overwinter as middle-instar larvae in the state of facultative diapause. However, the characteristics of diapause vary substantially between the species: diapause can be deep and stable (as in Diachrysia chrysitis, Plusiini) or unstable and thus not ensuring successful overwintering and steady population growth (as in Macdunnoughia confusa, Plusiini). The seasonal adaptations known in Plusiinae include migrations, winter and summer diapauses, photoperiodic control of larval growth rates, and seasonal polyphenism of larval body coloration. In general, seasonal adaptations of Plusiinae are determined by local environmental conditions and only loosely associated with the systematic position of particular taxa. Only the tribe Abrostolini stands apart from other taxa of Plusiinae: moths of this tribe differ not only in morphology but also in peculiarities of their seasonal development, because all the species of this tribe overwinter as pupae and their seasonal cycles are therefore different from those of the rest of Plusiinae.