Rhythmicity in Life Events of an Aphidophagous Ladybird Beetle, Cheilomenes Sexmaculata
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J. Appl. Entomol. 131(2), 85–89 (2007) doi: 10.1111/j.1439-0418.2007.01148.x Ó 2007 The Authors Journal compilation Ó 2007 Blackwell Verlag, Berlin Rhythmicity in life events of an aphidophagous ladybird beetle, Cheilomenes sexmaculata Omkar and K. Singh Ladybird Research Laboratory, Department of Zoology, University of Lucknow, Lucknow, India Ms. received: June 28, 2006; accepted: December 20, 2006 Abstract: The present laboratory experiments have been carried out to investigate rhythms in various life events, viz. mating, oviposition, hatching, moulting, pupation and eclosion, of an aphidophagous ladybird beetle, Cheilomenes sexmaculata under laboratory conditions. Incidences of mating and eclosion occurred mostly (66% and 73% respectively) in photophase. While oviposition, hatching, moulting and pupation occurred during scotophase with the peaks of the former two distributed between time intervals 12:00–15:00 h and 21:00–00:00 h respectively. Confinement of life events that are associated with vulnerable stages in scotophase might be an adaptation to prevent their exposure to natural enemies. Key words: Cheilomenes sexmaculata, Coccinellidae, eclosion, hatching, mating, moulting, oviposition, pupation, rhythmicity 1 Introduction More such studies elucidating the spatial and tem- poral occurrence of life events and identifying the Rhythms in organisms have evolved as adaptive underlying patterns will enhance understanding of strategies for successful survival with their phases basic ecology along with providing cues that may changing in response to important environmental and facilitate mass multiplication and utilization of lady- temporal cues, such as daily light and temperature bird beetles in biocontrol of target insect pests. Thus, cycles. The rhythms may be free running with a period the present investigation has been carried out to study of about 24 h under constant conditions and are and analyse rhythmicity in various life events, viz. regulated by endogenous clocks or oscillators. Many mating, oviposition, hatching, moulting, pupation and internal clocks forming a complex circadian system emergence, of a ladybird beetle, Cheilomenes sexmac- provide synchronization of life events of an organism ulata (Fabricius) under laboratory conditions. Cheil- with environmental variables (Plautz et al. 1997; Gie- omenes sexmaculata is a native predator of aphids in bultowicz 1999; Edery 2000; Myers 2003). Oriental and Palaearctic regions and found abundantly Rhythmicity in life-events, viz. mating, oviposition, almost throughout the year in areas around Lucknow, hatching, moulting, pupation, emergence, foraging, and India (Hussein 1991; Omkar and Bind 1993; Omkar flight activity is well known in insects (Saunders 1982; and Pervez 2004). Its high reproductive and predatory Schotzko and O’Keeffe 1986, 1990; Zinov’eva et al. response on many aphid species (Omkar and Bind 1996; Jimenez-Perez et al. 2002; LiJuan et al. 2002). 2004; Omkar et al. 2004b) and better performance in Those pupating above ground are likely to be more competitive environment (Agarwala and Yasuda 2000; sensitive to daily changes in light than temperature and Omkar et al. 2005) has been the criterion for its hence more synchronized to the former. Amongst such selection as an experimental model. insects, predatory ladybird beetles (Coleoptera: Coc- cinellidae) are of pragmatic value being potential biocontrol agents of several insect and mite pests of agricultural and horticultural crop plants. Although 2 Materials and Methods ample literature exists on the ecology and behaviour 2.1 Stock culture of coccinellids (Hodek and Honeˇ k 1996; Dixon 2000), the rhythmicity of life events has been meagerly studied. Adults of C. sexmaculata were collected from agricul- A few previous studies reveal prominent diurnal peri- tural fields adjoining the city of Lucknow (26°50¢N, odicity in foraging and feeding patterns of ladybird 80°54¢E), India and brought in the laboratory to beetles (Hull et al. 1977; Mack and Smilowitz 1978; establish stock culture in Environmental Test Chamber Miura and Nishimura 1980; Nakamuta 1987). Some (ETC) (at 25 ± 2°C, 65 ± 5% RH; 10L: 14D; white recent attempts have also been made to provide light) along with prey Aphis craccivora Koch infested on information on the biorhythms of predaceous ladybirds Dolichos lablab Linnaeus. They were paired and allowed (Mishra and Omkar 2004; Omkar et al. 2004a). to mate in transparent Petri dishes (9.0 · 1.5 cm). Eggs 86 Omkar and K. Singh were collected daily and hatched instars reared till 2.6 Moulting, pupation and eclosion rhythms pupation in glass beakers (11.0 · 9.0 cm) on daily Ten first instars of C. sexmaculata were placed in a replenishment of ad libitum prey. Beakers containing beaker (6.5 · 9.5 cm) with prey and conditions as pupae were inspected every 4 h and emerging new adults above and observed every 2 h through their inter were sexed and isolated in Petri dishes (space and prey as developmental period for the incidence of moulting, above) for further use in experiments. pupation and eclosion. The experiment was replicated 10 times, thus in a total of 100 individuals. 2.2 Experimental setup The experimental ladybird beetles were kept in beakers 2.7 Data analysis in ETC provided with the above prey. The lights for The data on number of incidences of various life- maintaining the desired photophase were kept events, viz. mating, oviposition, hatching, moulting, switched on between 00:00 and12:00 h (photophase) pupation and eclosion, at different time intervals were and switched off between 12:00 and 00:00 h (scoto- subjected to two-way anova taking time interval as row phase) with experimental conditions similar to those factor and days as a column factor followed by for stock culture. For recording data in scotophase the post hoc test for comparison of means. The percent ladybird beetles were exposed to brief duration of red data on total incidences of life-events in the photo- light (under 3.8 V red light bulb having light inten- phase and scotophase over different days were subjec- sity 190–200 lux; measured by an EP628 digital lux ted to chi square analysis. All statistical analyses were meter by Eurisem technics (Eurisem technics, Leice- performed on PC using computer software minitab ster, Leicestershire, UK)). (Minitab Inc., State Coltege, Pennsylvania, USA). 2.3 Mating rhythm For the study of mating rhythms over a 24-h period, 3 Results 10-day-old ladybird beetle pair (n ¼ 10) was selected 3.1 Mating rhythm and placed in a Petri dish under suitable abiotic and biotic conditions (as above). Each pair was observed at In a diel cycle, mating occurred mostly throughout an interval of 3 h for the incidence of mating and its photophase (66%; v2 ¼ 20.48; P < 0.001; fig. 1) and occurrence recorded. The recordings were made for early scotophase, and was relatively reduced during late five consecutive days. scotophase as lower percentages (1% and 3%) of mating were recorded between 18:00–21:00 and 21:00–00:00 h respectively (fig. 2). The differences in means of mating 2.4 Ovipositional rhythm incidences at 3-h interval were statistically significant To record the ovipositional rhythm an unmated (F ¼ 10.13; P < 0.001; d.f. ¼ 7, 399). However, the mating pair after being subjected to single mating rhythm was not found to change significantly between was observed after every 3 h from 10th day of days (F ¼ 0.63; P > 0.05; d.f. ¼ 4, 399). The interac- oviposition for two consecutive days. The observations tion between days and time intervals was statistically were taken in 10 replicates. significant (F ¼ 1.77; P < 0.05; d.f. ¼ 28, 399). 2.5 Hatching rhythm 3.2 Ovipositional rhythm One hundred eggs were selected from the above In the diel cycle, peak of oviposition (62%) was experiment and hatching was recorded at an interval attained during early scotophase (12:00–15:00 h). Rel- of 3 h. The experiment was replicated 10 times, thus atively lower percentages of eggs (1–15%) were laid hatching in a total of 1000 eggs was recorded. during rest of the day and none during 0600–0900 h Scotophase 120 Photophase 20.48 92.48 72.00 32.00 15.68 42.32 100 80 60 Incidences (in%) 40 Fig. 1. Incidence of various 20 life events in photophase and scotophase; chi square test 0 values, given above the bars Mating Oviposition Hatching Moulting Pupation Eclosion significant at P < 0.001 Life events level Ó 2007 The Authors Journal compilation Ó 2007 Blackwell Verlag, Berlin, J. Appl. Entomol. 131(2), 85–89 (2007) Rhythmicity in a ladybird, Cheilomenes sexmaculata 87 30 b b b b 20 b b 10 a ab Mating (%) 0 100 b 50 a a a a aa a 0 Oviposition (%) c 60 40 b ab ab 20 a a a a 0 Hatching (%) 30 b b b b 20 b ab 10 ab a Moulting (%) 0 50 c 40 c 30 20 b ab ab ab 10 a Pupation (%) a 0 40 b 30 b 20 ab ab aa 10 aa Eclosion (%) 0 Fig. 2. Diel rhythms of various life events; different 0000– 0300– 0600– 0900– 1200– 1500– 1800– 2100– letters denote data signi- 0300 0600 0900 1200 1500 1800 2100 0000 ficant at P < 0.001 Time interval (h) (fig. 2). Overall oviposition was significantly higher scotophase. Differences in means of incidences of (82%; v2 ¼ 92.48; P < 0.001; fig. 1) in the scotophase. hatching within 24 h were statistically significant The differences in means of oviposition at 3-h interval (F ¼ 13.61; P < 0.001; d.f. ¼ 7, 159). Differences in were statistically significant (F ¼ 5.93; P < 0.001; means of incidences of hatching in between different d.f. ¼ 7, 159). However, the rhythm did not change days (F ¼ 31.07; P < 0.001; d.f.