Study On The Diapause Induction And Diapause Characteristics Of Eocanthecona Furcellata(Wolff)

Diapause is an essential strategy for insects to copy with harsh environmental conditions.This paper try to distinct the environmental factors for diapause induction of Eocanthecona furcellata?Wolff?,an important biological agent in agriculture in south China,as to contribute to the biological control for pest and the use of E.furcellata.By using behavioral,ecological and biochemical theories and technologies to study the diapause mechanism of E.furcellata,this paper focused on the photoperiodic and thermal aspects for E.furcellata diapause induction,confirming the diapause stage and sensitive stage and studying diapause-mediated morphological,physiological and behavioral characters of E.furcellata in diapause induction,maintenance and termination.The results of these researches provided theoretical evidences for the seasonal adaptation mechanism of E.furcellata.And in practice,it provided technical supports for the mass propagation and field releasing of E.furcellata by using diapause induction or termination acknowledge.The main results of this paper were showed bellow:1.The diapause induction of E.furcellata.Photoperiod?temperature was 26±0.5??had significant effects on development and fecundity of E.furcellata.Especially,short photoperiod at the nymphal stage could significant prolong the duration of nymphal phase and pre-oviposition,as well as decline the fecundity.Throughout the experiment,all the different stages combined with different photoperiods treatments could not induce E.furcellata entering diapause.All the survived E.furcellata could finish their generation and eventually laid eggs,and these eggs developed normally and hatched without any delay.But when different stages of E.furcellata were subjected to high temperature,they showed varied response to high temperature.No individual survived to adult stage when eggs and younger nymph were subjected to 35:33?,whereas high portion of elder nymph and adult could survive and the 5^th instar nymph showed the highest endurance to high temperature,and finally laid high portion of delay-developed diapausing eggs.By observing the morphological characters of diapausing eggs,we found diapausing eggs showed different morphological characters from nondiapausing eggs.Diapausing eggs developed slowed,they showed“black circle”in 23-24 h after laying and“red spots”appeared in the 4^th day after diapause termination.Diapausing eggs started developing rapidly after appearance of“red spots”and hatched in the 13^th day after transferred to26?.Nondiapausing eggs developed rapidly after laying and showed“black circle”and“red spots”in 1-2 h and 4^th day respectively.Nondiapausing eggs hatched in the 8^th day after laying.Through SEM,aero-micropylar projections on the diapausing eggs showed a supine position,they have large opening,thin wall and large vacant cavity.While on nondiapausing eggs,they were up-right,had small opening,thick wall and a narrow vertical channel inside the projection.By further researching the diapause induction of E.Furcellata,high temperature could induce the 5^th instar and young female laying diapausing eggs,and the 5^th instar nymph was the most sensitive stage for diapause induction.For female E.furcellata,the younger they subjected to high temperature,the larger portion of diapausing eggs they laid.The threshold thermoperiod was 34:32?,and the optimal thermoperiod for egg diapause induction was 35:33?.Thermoperiod bellow 34:32?resulted small portion of diapausing egg and higher than 36:34?declined the diapausing rate.3.Diapause maintenance and termination of E.furcellataHigh temperature maintained egg diapause of E.furcellata,the longer diapausing eggs held at high temperature,the longer diapause maintaining.Diapausing eggs held at high temperature for 1 d?3 d?6 d?9 d and 12 d,the diapause duration were longer than12 d,especially held for 6 d?9 d and 12 d,the diapause duration were longer than 20 d,significantly longer than nondiapausinng eggs?egg duration was 5-9 d?.Exposure time of high temperature affected the hatch rate of diapauding egg,Mostly,the intensity of high temperature held for diapausing eggs also influence the hatch rate.The longer and higher temperature exposure decline the hatch rate of diapausing eggs however longer but relative lower temperature exposure showed little impact.This result indicated that though high temperature could maintain egg diapause of E.furcellata,it also reduced the fitness of diapausing eggs.4.Postdiapause development and the fitness of E.furcellataAll post-diapausing nymph showed faster development,shorter duration of pre-oviposition and increased feeding and laid more eggs per female.But Nymphal survival rate and eclosion rate was not sinificant than nondiapausing individual.5.Diapause-meidated oviposition behavior of E.furcellata and its relation to the fitness of diapausing eggHigh temperature diapause induction influenced the behavior and egg location of E.furcellata.After inducing at high temperature,the 5^th instar nymph and female tended to disperse on the plants,they were inactive and female laid most portion of eggs on the leaves.Egg location had no significant influence on the diapause rate of eggs,but influenced the viability of diapausing eggs.Diapausing eggs on the wooden frame or net failed to hatch or hatch in a little number.However,the viability of diapausing eggs on leaves was above 70%,which suggested that the behavioral and egg location changed in favor of the survival of diapausing eggs.6.Physiological characteristics of E.furcellata in the process of diapause induction,maintenance and terminationHigh temperature influenced the trehalose content and trehalase activity of E.furcellata.Before oviposition,trehalose content increased as the age of E.furcellata increased,however,E.furcellata reared at normal temperature was opposite.trehalase activity was also relative to mature degree of E.furcellata.After inducing at high temperature,trehalase activity maintained at a stable and higher degree but then declined when approached oviposition,but it raise again when female laid diapausing eggs.Both diapausing and nondiapausing eggs contained lower DNA content when they were first laid,but slowly increased as development.Diapausing eggs contained lower RNA content during diapause maintenance but gradually raised after terminating diapause.Sorbitol content in diapausing eggs kept at a higher level during diapause maintenance.After diapause termination,sorbitol content raised up and then fell down.Nondiapausing eggs contained relative lower sorbitol content compared to the same stages of diapausing eggs.In nondiapausing eggs,sorbitol dehydrogenase still maintained at a low activity during diapause maintenance,however it suddenly increased and remained at a high level after diapause termination.