| The small brown planthopper, Laodelphax striatellus (Fallén)(Homoptera:Delphacidae) is widely distributed in the rice belt of China. This insect transmits variousvirus diseases of cereals, in addition to the damage it causes by sap sucking. However,detailed information of its biology and diapause are still lack. In the present study, weinvestigated the biological characteristics, diapause characteristics. Furtheremore, weanalyzed the relationship between the developmental rate and the mathematical model.Theresults are as follows.1. Life history, reproduction and overwintering biology of the small brownplanthopper, Laodelphax striatellus (Hemiptera: Delphacidae), in NanchangTo ascertain the biological characteristics of the small brown planthopper,Laodelphax striatellus (Fallén), in Nanchang, Jiangxi, East China, the annual life history,the influences of temperature on development and reproduction, sex ratio and itsoverwintering biology were systematically investigated under laboratory and naturalconditions. The results showed that this species exhibit mixed voltinism from4to7generations per year. Between18and32℃, and18and28℃, the egg duration and thenymphal duration gradually declined with increasing temperature, respectively. However,the nymphal duration was significantly longer at30and32℃than at28℃. The duration ofoverwintering nymphs ranged from143to187d. The lower development thresholds of eggand nymph were10.17℃and7.51℃, respectively. In the outdoors, the developmentalduration of the4th generation nymphs hatched at high temperature of mid-July hadsignificantly delayed, showing high-temperature induced summer quiescence. Between18and28℃, the pre-oviposition period gradually shortened with increasing temperature;however, the pre-oviposition period was longer at30℃than at26℃and28℃. Theoviposition period was the longest at22℃, and the shortest at30℃. The mean longevity ofadults was the longest at20~24℃. The number of nymphs produced per female washighest at28℃. Under both laboratory and natural conditions, the sex ratio is close to1:1.Between18and32℃, the number of long-winged adults (macroptery) was significantlyhigher than that of short-winged adults (brachyptery). In the outdoors, the number of thebrachytery was significantly more than that of the macroptery in the overwinteringgeneration and the6th generation, whereas the number of the macroptery was significantlymore than that of the brachytery in other generations. Under natural conditions, winter diapause had already occurred in some individuals that hatched in mid-September, and allindividuals that hatched after mid-October entered winter diapause. This planthopperoverwintered as1~5instar nymphs. In spring, overwintering nymphs began to emergeduring early March-late March when the mean daily temperature rose to10°C or higher,suggesting that early or late termination of winter diapause mainly depends on thetemperatures in March. This study provides the basic data for the prediction of Laodelphaxstriatellu occurrence and the effective prevention and control of this pest.2. Rice planthopper Research on mathematics model of relationship between growth rate andtemperature in Laodelphax striatellusPerformance-2model was used to fit these data of because this model can provide thelower and upper developmental thresholds simultaneously. The estimate of lowerdevelopmental thresholds of eggs(10.0℃) was different from that of nymphs (7.5℃). Andthe estimate of upper developmental thresholds of eggs (35.5℃) was also different fromthat of nymphs (30.2℃). However, for male and female nymphs, the difference in thelower developmental threshold is nonsignificant, and the difference in the upperdevelopmental thresholds is very small (95%confidence interval of the difference:[0.007℃,0.043℃]). The rate isomorphy hypothesis considers that the lowerdevelopmental thresholds of different stages for the same insect might be constant.However, the current study provides a counterexample of this hypothesis that the lowerdevelopmental threshold of eggs is different from that of nymphs. Thus, we demonstratethat the rate isomorphy hypothesis does not apply all insects. In addition, we used apopular nonlinear model, Lactin model, to fit the developmental rate data of ourexperiment. And we found that the estimates of lower and upper developmental thresholdsby using Performance-2model were very approximate to those by using Lactin model. Thecurrent study provides reliable estimates of thermal parameters for L.striatellus by usinglarge experimental samples at different temperatures. It would be useful for exploring therelationship of climate change and the outbreak of this insect on rice.3. Diapause induction and termination in Laodelphax striatellusThe small brown planthopper, Laodelphax striatellus, enters photoperiodic inductionof diapause as3rd or4th instar nymphs. Photoperiodic response curves in this mothshowed a typical long-day response type with a critical daylength of approximately11h at25°C,12h at22and20°C and12.5h at18°C. The third instar was the stage most sensitive to the photoperiod. The photoperiodic response curve at20°C showed gradual decline indiapause incidence in ultra-long nights, and DD resulted in100%development. Therequired day number for a50%response was distinctly different between short-andlong-night cycles, showing that effect of one short night was equivalent to the effect ofthree long nights at18°C. By transferring diapausing nymphs induced under LD11:13, LD12:12and LD13:11at18,20and22°C to25°C combined with LD15:9to terminatediapause the rearing day length of12h evoked weaker intensity of diapause than did10and11h. By transferring diapausing nymphs to a long photoperiod of LD15:9and a shortphotoperiod of LD11:13at18°C, the duration of diapause was significantly longer underthe short daylength of11h than under the long daylenth of15h. By transferringdiapausing nymphs to eight different temperatures of18,20,22,24,26,28,30and32°C, itshowed that the optimal temperature for diapause termination was26and28°C. Chillingat5°C for different times did not shorten the duration of diapause but significantlylengthened it when chilling period was included. In autumn,50%nymphs that hatchedduring late September-mid-October entered diapause in response to low temperaturesbelow20°C. The critical daylength in the field was between12h10min and12h32min(including twilight), being nearly identical to the critical daylength of12.5h at18°C. Inspring, overwintering nymphs began to emerge during early March-late March when themean daily temperature rose to10°C or higher, suggesting that early or late termination ofwinter diapause mainly depends on the temperatures in March. |
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