Studies On Biology And Diapause Characteristic Of Ostrinia Furnacalis (Guenée)

The Asia corn borer, Ostrinia furnacalis (Guenée)(Lepidoptera, Crambidae), isserious pest in corn. Ostrinia furnacalis, enters facultative diapause as fully grown larvaein response to short-day conditions during the autumn, and is widely distributed in Chinadue to its adaptation to diverse environmental conditions. Photoperiod is a major factorcontrolling diapause induction and termination.1. Biology of theAsian corn borer Ostrinia furnacalisThe results showed that this moth can produce3-5generations per year. Someoverwintering individuals that emerged at the earliest in spring produce5generationsannually. Same overwintering individuals that emerged at the latest in spring produced on3generations. Most individuals completed4generations. There were overlappinggenerations in the field due to the differences of diapause intensity of overwintering larvaeand individual differences of larval duration. Between20and28℃, developmentalduration was7-4days in the egg stage，42.68-23.80days in the female larval stage，45.70-23.39days in the male larval stage,14.06-5.63days in the female pupal stage and14.12-5.72days in the male pupal stage. The lower development threshold of O. furnacaliswas9.24℃for egg,9.85℃for the female larva,11.90℃for the male larva,12.02℃forthe female pupae and11.93℃for the male pupae. According to laboratory observation for20pair adults, under the photoperiod of LD16:8at25℃,the pre-oviposition period was3.23±0.87days, oviposition period was10.45±1.95days, the egg production was500.9±66.77, the longevity of female was13.68±2.06days and12.50±2.92days for male.In the field, winter diapause had already occurred in some individuals that hatched at thebeginning of the late August,50%individuals that hatched at the end of August entereddiapause and all individuals that hatched after September3entered diapause.Overwintering larvae began to pupate in the mid-April and pupation ended in late May.Adult emergence from overwintering generation exceeded more than one month from lateApril to early June. Development duration for overwintering larvae ranged from220to268days. 2.24h and non-24h light-dark cycles photoperiodic response in Ostrinia furnacalisThe24h light-dark cycles photoperiodic response curves for diapause induction in O.furnacalis at various temperatures indicated that the photoperiodic response curves showeda typical long-day response type at the ecologically relevant daylengths (11–15h), with astable critical daylength of about13.5h at25,28and30°C and14.5h at22°C.Interestingly, the incidence of diapause began to decline when the daylength was shorterthan12h, especially in DD, most or almost all individuals developed without diapause(68.6%development at22°C;80-100%development at25,28and30°C). Maximumincidence of larval diapause (>98%) was observed in non-24h light-dark cycles containingthe long night of12h. With scotophases of4,8,16,20,22, and24h, most of theindividuals developed without diapause independent of the length of the photophase.Theresults suggest that the dark period is of central importance to determine the incidence ofdiapause.3. The most sensitive stage to photoperiod in Ostrinia furnacalisThe required day number (RDN) for a50%response differed significantly betweenshort-and long-night cycles at different temperatures, showing that effect of one shortnight was equivalent to the effect of3long nights at25and28°C. When a long night ofLD9:15(a diapause-inducing photoperiod) was systematically interrupted by a1-h lightpulse at1h interval at25°C, one broad trough of light sensitivity appeared in thephotoperiodic response curves, i.e. light pulses commencing3–11h after the onset ofdarkness averted diapause effectively (73.6-100%). Similar results were also found in theinterrupting experiment at LD12:12, light pulses commencing3–7h after the onset ofdarkness resulted in development of54.3-98%individuals. The third instar was the stagemost sensitive to the photoperiod.4.The photoperiodic clock of diapause induction in Ostrinia furnacalisThe Nanda-Hamner and Bünsow experiments in O. furnacalis did not show anyrhythmic fluctuations with a period of about24h in their photoperiodic response curves;the incidence of diapause was very low when the length of scotophase exceeded16h.