Diapause And Life-history Traits In The Cabbage Butterfly,Pieris Melete

The cabbage butterfly,Pieris melete Ménétriés,is a serious pest of crucifers.In the field,there are two distinct infestation peaks per year,one in spring and a second in autumn.Almost all progenies produced by the overwintering generation enter summer diapause as pupae under conditions of the relatively low daily mean spring temperatures(< 20 ?)and gradually increasing daylengths.Normally,there is only one generation in spring.The aestivating individuals emerge between the end of August and early November.The early emerged individuals can produce three generations in autumn under conditions of higher temperatures and intermediate daylengths.The late emerged individuals produce only one generation because of the lower temperature and short daylength occurring in late autumn.In the present study,The induction and termination of summer diapause and the life-history traits between diapause and direct development individuals of the cabbage butterfly,P.melete have been investigated under constant temperatures(16?19?22?25?)combined different photoperiods(LD10:14,LD 12.5:11.5 and LD 14:10)and naturally changed temperature conditions(for 7 different mean daily temperatures).The results are as follows.1.The induction and termination of diapause at constant temperaturesPhotoperiodic responses at constant temperatures combined different photoperiods showed that expression of diapause induction depended on temperature and photoperiod.At the lower temperature of 16 ?,most pupae entered diapause without showing significant difference in diapause induction among photoperiods.At 16 ?,95% individuals entered diapause under short and long photoperiods,whereas only 54.3% individuals entered diapause under intermediate photoperiod,being significantly lower than short and long photoperiods.At 22 ?,diapause incidence declined under all photoperiods.Diapause incidence under intermediate photoperiod was significantly lower than under short and long photoperiods.At25?,diapause incidence was positively related to photoperiod.The incidence of diapause under short photoperiods was significantly lower than those under intermediate and long photoperiods.It needs to note that diapause incidences at25 ? under intermediate and long photoperiods(36.5 % and 49.2 %)were higher than those at 22 ?(21.9 % and 36.6 %),suggesting that long photoperiod still displayed a role in diapause induction at higher temperature.Termination of Diapause pupae induced by different photoperiods under long photoperiod LD 15:9 at 18? showed the duration of diapause induced by the intermediate photoperiod combined with 16 ? was quickest,significantly quicker by short and long photoperiods;whereas the duration of diapause induced by shortphotoperiod combined with 19 ? was shortest,significantly shorter those diapause pupae induced by intermediate and long photoperiods.The duration of diapause induced by 25 ? combined with intermediate and long photoperiods was shortest,significantly shorter those diapause pupae induced by 16,19 and 22 ?.There were no significant differences in diapause duration when larvae fed on Chinese cabbage,Suzhouqiu,Brassica chinensis,radish Raphanus sativus L.var.longipinnatus and stem mustard Brassica juncea(L.)var.tumida2.The incidences of diapause for seven generations in an outdoor screened insectaryThe incidence of diapause for seven generations in an outdoor screened insectary showed that high summer temperature combined with relatively long daylengths averted diapause incidence effectively;autumn relatively higher temperature or intermediate temperature inhibited diapause incidence most effectively.The results suggest that the butterfly has a cryptic ability to reproduction in summer.The adult emergences form aestivating and hibernating pupae were observed under natural conditions.The result showed that the butterflies which emerged as adults in the spring had a tightly synchronized emergence,while the butterflies whose emergence occurred in autumn had much longer and less synchronized emergence.3.Life-history traits at the constant temperaturesLarval and pupal development times were significantly influenced by photoperiod,development pathway and temperature and their interactions.However,Larval and pupal development times were not affected by sex.Larval development times for the direct developing individuals significantly decreased with increasing rearing temperature under different photoperiods.Diapause pupae induced by intermediate photoperiod had the lowest pupal period.Larval development time was shorter in diapause individuals than in direct developing individuals.Pupal weight was significantly affected by photoperiod,temperature and sex.Pupal weight for both diapause and direct developing individuals significantly decreased with increasing rearing temperature under different photoperiods.There was significant difference in pupal weight between diapause and direct developing individuals.Male pupae were heavier than female pupae for both diapause and direct developing individuals.Growth rate was significantly affected by photoperiod,development pathway,temperature and sex.Growth rate was positively correlated with rearing temperature.Growth rate was higher in males than females for both diapause and direct developing individuals.Photoperiod,temperature and sex had significant influences on adultweight but not on weight losses.Adult weights decreased with increasing rearing temperature under different photoperiods for diapause and direct developing individuals.Male adults were bigger than females.Male pupae lose significantly more weight at metamorphosis compared to females at most cases.The sexual size dimorphism(SSD)varies with photoperiod.SSD for the direct developing individuals was higher at high temperatures under the photoperiods of LD10:14 and LD12.5:11.5.SSD for diapause pupae was highest at 19 ? under LD 10:14,lowest at 22 ? under LD 12.5:11.5,highest at 22 ? under LD 14:110.SSD for diapause adults tended to increase with increasing temperature.SSD was greater in adults than in pupae.4.Life-history traits under naturally changed temperature conditionsDevelopment pathway and temperature had significant influences on larval and pupal development times.But there were no significant differences in larval and pupal development times between sexes.Larval development time for direct developing individuals gradually decreased with increasing the mean daily temperature.Pupal time for diapause individuals induced by high temperature was lowest.Temperature and sex had significant influences on pupal weight.Pupal weight for both diapause and direct developing individuals significantly decreased with increasing rearing temperature.Male pupae were bigger than female pupae for both diapause and direct developing individuals but without showing significant differences.Growth rate was significantly influenced by temperature and sex.Growth rate was positively correlated with the mean daily temperatures.Growth rate was higher in males than females.Adult weights tended to decrease with increasing rearing temperature.Male adults were bigger than female adults.Weight losses varied among temperatures without showing a regular change.SSD tended to decrease with increasing temperature.SSD was greater in adults than in pupae.Our results indicate that most life-history traits were similar when the cabbage beetles were reared at constant temperatures and naturally changed temperatures.The main difference was the SSD.SSD tended to increase with increasing temperature,without fitting the Rensch's rule at constant temperature conditions,whereas SSD tended to decrease with increasing temperature,following the Rensch's rule.