Night-interrupting light inhibits diapause induction in the Kanzawa spider mite, Tetranychus kanzawai Kishida (Acari: Tetranychidae) Maqsood Shah a,⇑ , Takeshi Suzuki b,c , Noureldin Abuelfadl Ghazy a , Hiroshi Amano d , Katsumi Ohyama a,b a Graduate School of Horticulture, Chiba University, Matsudo 648, Matsudo, Chiba 271-8510, Japan b Center for Environment, Health and Field Sciences, Chiba University, Kashiwa-no-ha 6-2-1, Kashiwa, Chiba 277-0882, Japan c Japan Society for the Promotion of Science, Japan d Graduate School of Agriculture, Kyoto University, Kitashirakawa-Oiwake, Sakyo, Kyoto 606-8502, Japan article info Article history: Received 5 March 2011 Received in revised form 12 May 2011 Accepted 17 May 2011 Available online 14 June 2011 Keywords: Critical dark period Diapause LED Night-interruption Photoperiodism Tetranychus kanzawai abstract The inhibitory effects of the timing, intensity (I I ) and period (I T ) of night-interrupting light on diapause induction of the Kanzawa spider mite (Tetranychus kanzawai) were investigated in a series of laboratory experiments. During a light and dark period of 8 and 16 h d À1 , respectively, a single 1-h night-interrupt- ing light was applied at early (E), middle (M), and late (L) parts of the dark period: i.e., at 3, 7.5, and 12 h after the start of the dark period, respectively. No interrupting light was applied in the control treatment. The incidence of diapause was significantly lower in the M treatment (63%) compared to the control treatment (100%). In the E and L treatments, more than 90% of females entered diapause, which was com- parable to the control treatment. Since the longest consecutive dark period during the E and L treatments was longer than the critical dark period (CDP) of 10.5–11 h d À1 , during which 50% of females entered dia- pause, the night-interrupting light probably failed to prevent diapause induction. However, in the M treatment, the longest consecutive dark period was shorter than the CDP; therefore, the night-interrupt- ing light inhibited diapause induction. Moreover, the inhibitory effects of night-interrupting light in the M treatment increased as I I and I T increased. The dose of night-interrupting light (I I Â I T ) was significantly negatively related to the incidence of diapause. The median effective dose for 50% disturbance of dia- pause induction was 2.5 kJ m À2 at wavelengths between 350 and 1050 nm. Our results suggest that the longest consecutive dark period and the dose of night-interrupting light should both be considered when a lighting-based physical control is applied to inhibit diapause induction and consequent overwin- tering of T. kanzawai in commercial agricultural fields. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Insects and mites often perceive periodic physical environ- ments such as photoperiod and thermoperiod and consequently change their physiological conditions to prepare for the approach- ing favourable and/or unfavourable seasons. Because photoperiod is considered the most accurate calendar in nature, it has fre- quently been reported as the sole factor responsible for adjust- ments by insects and mites to the changing seasons (Tauber et al., 1986). Such seasonal adjustments help insects and mites to increase population growth rates during favourable seasons and to overcome unfavourable seasons. Diapause is one major seasonal adjustment that is dependent on photoperiod as well as on ther- moperiod and food sources. Diapause is defined as a hormonally mediated state of low metabolic activity that induces an increase in resistance to environmental stresses, changes in behavioural activity and the suppression of morphogenesis (Tauber and Tauber, 1981). Denying pest insects and mites an ecological refuge in the form of diapause can expose them to severe environments, result- ing in a failure to survive. Disruption of this ecological refuge can be achieved either by preventing or promoting diapause induction under artificially altered photoperiods (Barker et al., 1964). Such a scenario can offer an alternative and attractive option for pest con- trol with comparatively fewer problems than those associated with chemical control measures (Denlinger, 2008). Controlling the pho- toperiod has been attempted for management of the European corn borer Ostrinia nubilalis (Hayes et al., 1970), the tortricid moth Adoxophyes orana (Berlinger and Ankersmit, 1976), the Indian meal moth Plodia interpunctella (Kikukawa and Masaki, 1984), and the cabbage moth Mamestra brassicae (Kimura and Masaki, 1992). The Kanzawa spider mite, Tetranychus kanzawai Kishida, is one of the most common and serious pest mite species in Japan (Takafuji et al., 2000). Females of T. kanzawai as well as many other Tetranychidae enter diapause in the adult stage when they experi- ence long dark periods during immature stages. Diapause 0022-1910/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jinsphys.2011.05.018 ⇑ Corresponding author. Tel.: +81 80 3483 0657. E-mail address: entomologist13@yahoo.com (M. Shah). Journal of Insect Physiology 57 (2011) 1185–1189 Contents lists available at ScienceDirect Journal of Insect Physiology journal homepage: www.elsevier.com/locate/jinsphys