Studies On Effects Of Temperature And Phtotoperiod On Diapause Ragulation In Hippodamia Variegata (Goeze)

Variegated ladybird beetle Hippodamia variegata (Goeze) is known as an important natural enemy, which plays a key role in the biological control of pests owing to its long predation time and wide distribution. Numerous studies have been made on its biology and ecology at home and abroad. However, few studies are reported on the diapause of Hippodamia variegate.In this thesis population dynamics in multiple crop fields were invetstigated, and effects of temperature and photoperiod on adult diapause induction, duration and termination studied in the lab. The study provides data for diapause research of Hippodamia variegata, and technical supports for mass production and release for the biocontrol.. The main results and conclusions of the study are as follows:1.Adult overwintering and Seasonal population dynamics of Hippodamia variegate. In order to better understand the distribution and overwintering of the ladybird beetle on different crops, a periodical survey of the population was undertaken in wheat, cotton and corn fields. The results showed that population size varied with crops and other environment factors. A similar seasonal pattern in population was performed in these crop fields, first increasing and then decreasing in abundances. The peak time appeared on July19by75individuals per hour catch in the wheat field, August18by60in the cotton field, and Aug.28by43in the corn field, respectively. In addition, the survey in the winter showed that under natural conditions, the beginning of spawning adults and newly emerged adults to stop spawning time there are significant.Their time to stop oviposition is15d and3d,respectively.At the same time,we found that the overwintering state of the ladybird beetle is adult,the rate overwintering is35.6%.2. Diapause determination of Hippodamia variegata. So far, diapause of Hippodamia variegata has not been studied. In order to provide criteria for detecting diapause,in this experiment effects of temperature on the pre-oviposition period was studied, and differences in morphology between diapausing and non-diapausing females were examined. The results showed that female developmental progress was signifiantly affected by temperature underthe long photoperiod (14L:10D). Pre-oviposition period declined with the temperature. High temperature accelerated the ovarian development, shorten pre-oviposition period, but the low temperature caused opposite effects. The difference in ovarian morphology between diapause and non-diapause adults was significant. Diapause female’s ovarian was crystal, the ovarian tubule transparent and almost undeveloped, which is almost the same as the female upon emergence.The non-diapause female, however, contained a considerable amount of yolk sediment in ovary, and ovarian tubules with obvious segmentation and mature eggs. The results suggested that following females may be treated as being in diapause:without oviposition for40days at13℃, for30days at15℃, for20days at18℃, and for15days at21℃and24℃, respectively.3. Diapause-inducing sensitive stage of Hippodamia variegata. At15℃,imposing long photoperiod (14L:10D, with L represents) and short photoperiod (8L:16D, with S represents) treatment to various stages of H.variegata,we found that newly emerged adult is diapause-inducing sensitive stage. Only adult reared under specific temperature and specific light stimulation can be induced diapause.4. Effects of temperature and photoperiod on diapause induction in Hippodamia variegata. Lab experiments were conducted to investigate effects of photoperiod and temperature on diapause-inducing. Temperature, photoperiod and their interaction had significant influence on diapause incidence. Higher temperature treatments (21℃and24℃) did not induce diapause but increased the ovarian development. The lower temperature treatments (18℃,15℃and13℃) however, induced diapause in an increasing rate with decreasing temperature, as shown by slow development of the ovary. Under the temperature of18℃was the insect induced to diapause when light time was8h. Under15℃the proportion of diapausing individuals increased with decrease in light time, and reached to61.5%when the light time was8h. Under the temperature of13℃, more than50%of individuals entered into diapause under all photoperiod treatments, and reached to89.9%when the light time was8h. The results of this study suggest that temperature might be a dominant factor to induce diapause, and photoperiod can be a subordinate factor therein.5. Effects of photoperiod and temperature on diapause duration in Hippodamia variegata. In order to study effects of environmental factors such as temperature and photoperiod on this beetle diapause duration, experiments were made to examine adult diapause duration under different temperature and photoperiod combinations. The results showed that temperature and photoperiod have an impact on the diapause duration. At the same temperature, photoperiod had significantly effects on the female diapause duration. Diapause duration first increased then decreased with decreasing hotoperiod. The reaction of this beetle to photoperiod on the govering of diapause duration showed a quantitative photoperiodic response.Under photoperiod of8L:16D, diapause duration was99.05days; at10L:14D, diapause duration increased to141.90days; when photoperiod was12L:12D, diapause duration reduced to67.27days. Temperatures was very significantiy on effects on diapause duration, low temperature is conducive to the development of adult diapause. Atphotoperiod8L:16D,the mean adult diapause duration at15℃was99.05dayswhen the temperature drops to13℃, the mean extended to290.4days. Diapause induction temperature can regulate the speed of adult diapause development, thus affecting the adult diapause duration. Lower temperatures play a role on adult diapause maintaining, to extend the duration of the imaginal diapause.6. Effects of photoperiod and temperature on diapause termination. In order to study effects of environmental factors such as temperature and photoperiod on diapause termination of the beetle, trials were made to examine adult diapause termination under different temperature and photoperiod treatments. The results showed that temperature has an impact on the diapause termination of Hippodamia variegata at photoperiod8L:16D. Higher temperature accelerated the rate of diapause termination and shorten the time of diapause termination. At24℃, photoperiod did not significantly affect the time (3.5to4.5days) of diapause termination..The experiment suggested that temperature may be a dominant, and photoperiod a subordinate factor to terminate the diapause.