SEASONAL CYCLES OF NOCTUID MOTHS OF THE SUBFAMILY PLUSIINAE (LEPIDOPTERA, NOCTUIDAE) OF THE PALAEARCTIC: DIVERSITY AND ENVIRONMENTAL CONTROL
The analysis of data on seasonal development of the 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 diver- 23 sity of the seasonal patterns of Plusiinae species from different regions. The ho-modynamic type of seasonal development has been found in Trichoplusia ni and Ctenoplusia agnata of the Argyrogrammatini, and in Autographa gamma of the Plusiini. Seasonal development of these southern noctuids is accompanied by regular inter-zonal migrations of flying adults. When spreading northwards, they can produce different number of annual generations depending on the local climatic conditions and establish temporary local populations whose longevity is limited by the available warmth resources. Adults of some species can probably fly back southwards; however, 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 surviving in the regions with pronounced seasonality of climate. This type of seasonal development includes univoltine, multivoltine and semivoltine seasonal cycles. Univol-tine seasonal cycles with obligate diapause are known in Autographa buraetica, Au. excelsa and Syngrapha ain (Plusiini). Diapause provides tolerance to both low temperature and prolonged period when food is not available. In Syngrapha ottolenguii (Plusiini), the same result is achieved by inclusion into life cycle of two photoperiodically controlled diapauses (winter larval and summer adult diapauses). Semivoltine seasonal cycle has been reported only in one Plusiinae species, namely Syngrapha devergens. Larvae of this moth overwinter twice before they become pupae. Multivoltinism is widely distributed in the tribe Plusi-ini. Depending on latitude, different species from this tribe can produce up to four generations per year and overwinter as middle-instar larvae in the state of facultative diapause. However, characteristics of diapause differ substantially between species: diapause can be deep and stable (as in Diachrysia chrysitis, Plusiini) or labile and unstable, thus, not insuring successful overwintering and steady population growth (as in Macdunnoughia confusa, Plusiini). Among seasonal adaptations of Plusiinae, we know 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 systematic position of particular taxa. Only tribe Abrostolini stands apart from other Plusiinae taxa: moths of this tribe differ not only in morphology but also in peculiarities of their seasonal development, because all species of this tribe overwinter as pupae which makes their seasonal cycles different from those of other Plusiinae species.