Seasonal adaptations of the scarce silver-lines Bena bicolorana (Fuessly, 1775) (Lepidoptera, Noctuidae)

Abstract

The influence of photoperiod and temperature on the growth and development of the scarce silver-lines Bena bicolorana (Fuessly, 1775) (Lepidoptera, Noctuidae) was studied in Belgorod Province, Russia (50°N, 36°E). At temperatures of 21 and 24°C, all photoperiodic regimes with 12 to 17 h of light per day induced diapause in the IV instar larvae. At 24°C, under long-day conditions with a photophase of 18 h, both diapausing and nondiapausing (i.e., directly developing) IV instar larvae were recorded in almost equal proportions; this photoperiodic regime may thus be considered as the threshold one. Diapause induction in B. bicolorana was associated with the larvae changing color from light green to brick-red. The larval growth rates, their weight dynamics, and timing of diapause induction are under photoperiodic control. Thus, seasonal development of B. bicolorana is controlled by two photoperiodic responses: the qualitative one that controls larval diapause induction, and the quantitative one that regulates larval growth parameters before diapause induction. In Belgorod Province B. bicolorana annually produces only one generation, what agrees well with the parameters of both of its photoperiodic responses. The results of the experimental eco-physiological studies support the separation of the monotypic genus Bena because it includes the only species in the subfamily Chloephorinae (B. bicolorana) that overwinters at the larval stage.