Effects Of Temperature And Photoperiod On Regulation Of Diapause And Post-diapause Biology In Coccinella Septempunctata

Seven spot lady beetle Coccinella septempunctata was known as an important natural enemywhich had played a key role in the biological control of aphids in numerous plants such as vegetables,fruiters and crops. Because of its high fecundity, short generation cycle, good adaptability, broad hostrange and easily mass rearing, it was widely utilized both at home and abroad and made a significantecological and economic contribution to the production of agricultural commodities. But in the actualproduction and application of this beetle, there were a lot of choke points, such as short period of massrearing, time limits for storage and releasing, low propagation efficiency because the adults underwentdiapause, and so on. Thought the adult diapause affected the production of this beetle, it could be usedas a method for the development regulation. The development progress regulation is one of the coretechnologies in propagation and application of natural enemy insects including C.septempunctata. Withthis technology, the goal of annual production, products storage, timely application and other practicedemands in propagation and release of natural enemy insects could be reached. Development progressregulation just based on the knowledge of how the environmental factors, primary photoperiod andtemperature, on the governing the induction, duration and termination of diapause in insects. At present,although there were many studies in biology, ecology, and application of large-scale breeding etc., nodetailed study on diapause of C.septempunctata has been reported. Knowledge of diapause inC.septempunctata not only could be helpful for promoting the large-scale propagation, increasing theshelf-life and prevention-time of this species used in biological control, but also could contribute tolearn the developmental characteristics and dynamics of natural enemy insects, enhancing the efficiencyof pest control. Furthermore, it helps to understanding the developmental mechanisms of natural enemyinsects deeply, and exploring the adaptation mechanism and evolution paths of insects.C.septempunctata overwintered or overaestivated as adult. In the paper, the sensitive stages tostimulus for diapause induction, the effects of photoperiod and temperature on diapause induction,diapause duration and diapause termination of this beetle were further discussed. Meanwhilepost-diapause life-traits were explored as well. These provide references for diapause research ofC.septempunctata, and supply a technical support for large-scale propagation and application. Theresearch results as follows:Preoviposition period of C.septempunctata was significantly affected by temperature under L16:D8. The higher the temperature was, the faster the ovarian matured. While low temperature deceleratedthe ovarian developmet and increased the preovipostion period. Preovipostion period was a good markerfor identification of diapause in C.septempunctata. Females didn’t lay eggs in40days,30days,15daysat18°C,24°C,30°C respectively were thought to be diapause induced. Anatomic differences betweendiapause induced and non-diapause female were quite obvious. Ovarian of the former were transparentand there was no signs of vitellogensis in the ovarioles. Besides fat body fulfilled the abdomen wasobserved. However, non-diapause female showed a reproductive state which was indicated by the presence of vitellinized oocytes in the ovarioles, even the mature eggs were observed. And the fat bodywas just a little.Newly emerged adults and newly oviposited females were sensitive to the short-day length. Adultstage was the key development period for diapause induction. Only adult reared under short-day lengthcould diapause be induced at18°C. Photoperiodic response in C. septempunctata showed that it is along-day species. Temperature, photoperiod and their interaction all had significant influence ondiapause incidence of this beetle. Temperature played the key role in diapause induction; while theeffect of photoperiod on diapause induction depended on temperature. Diapause rate of this beetledeclined when temperature increased. Incidence of diapause was significantly lower under24°C than18°C. Critical photophase for diapause induction was greatly shifted with temperature. Photoperiodicresponse curve showed that critical day length was between14hr/d and16hr/d at18°C. But no criticalday length was got under photoperiod of L10: D14, L12: D12, L14: D10, L16: D8at24°C.Theinduction of diapause in this beetle was mightily based on a quantitative photoperiodic response. Effectsof photoperiod on the induction of diapause differed with the day length the adult experienced. Shortdaylight induced more adults into diapause than long daylight under18°C and24°C.Diapause duration of C. septempunctata showed depended on the day length and temperature.Duration of diapause female showed a negnective relationship with day length. The reaction of thisbeetle to photoperiod on the governing of diapause duration also showed a quantitative photoperiodicresponse. Short day length induced longer diapause duration compared with long daylength at the sametemperature. This suggested that adult of this beetle could measure the accurate diapause inducing daylength. Diapause inducing temperature could modify the diapause development speed and influenceddiapause duration. Diapause speed slowed down at low temperature so the duration of diapause lastedlong; while high temperature accelerated diapause development speed and promoted the oviposition.Diapause duration at24°C was significantly shorter than at18°C under L12: D12.Temperature and photoperiod the adults reared also governed the diapause termination of thediapause induced beetle when environmental factors changed. Diapause female were still sensitive tophotoperiod, with the long day photoperiod promoted diapause termination. Preoviposition period of thediapause induced female adults were significantly shorter than long day photoperiod at the sametemperature. While short day length extended preoviposition period and the duration of diapausetermination for the diapause induced female was much longer under short day length than that underlong day length. Moderately increasing of temperature could speed up the diapause termination ofdiapause induced female. Duration of diapause termination of diapause female induced to diapauseunder L12: D12or L10: D14was significantly shorter at24°C than at18°C under the test twophotoperiods. Diapause could be terminated very quickly under long day length even under short daylength. This suggested that temperature played a key role in diapause termination in diapause induced C.septempunctata adults. Effect of photoperiod depended on temperature. Short day length and lowtemperature enforced the adult diapause state and ensured diapause development. Incidence of diapause significantly affected the life-trait parameters of the diapause induced adults;there was a trade-off between diapause and longevity, fecundity and some other life-history traits.Longevities of both the post-diapause female and male adults were significantly shorter than the adultsthat didn’t experienced diapause at24°C. Oviposition period, total number of eggs laid per female in theinitial30days and hatching rate of the post-diapause females decreased significantly compared with thenon-diapause females reared at24°C. At24°C, longevity of both the females and males, ovipositionperiod, total number of eggs laid per female during the initial30days and hatching rate of post-diapauseadults had no significant difference between under L16：D8and under L10：D14．Post-diapause femalescould lay eggs tile they died. These suggested that photoperiod had no observable inferences onpost-diapause female.