| The pine caterpillar Dendrolimus punctatus Walker(Lepidoptera: Lasiocampidae)is considered to be one of the most destructive and periodically outbreak forest insect pests around southern of China.Since 1950 s,researchers carried out many studies on this pest and obtained many significant research achievements from their work.This caterpillar has a short life span and mating only once in their lifetime,and is so called monogamous insect species.Previous studies showed that many external factors influence the population dynamics of this pest,such as biological factors,including host plants and natural enemies,and environmental factors,including temperature,humidity and photoperiod.However,there have no systematic reports on how these factors affect their mating behavior and reproductive fitness.In this thesis,we investigated the influence of environmental factors,host plants,and inbreeding on larval growth and development,adult mating behavior and reproductive fitness consequences using this pine caterpillar as model insect.The results showed as follows: 1.Effects of environmental factors on mate behavior and reproductive fitness in D.punctatus.To test whether the environmental factors affect the population dynamics of this pine caterpillar,the mating behavior and reproductive fitness of D.punctatus had been observed under five constant temperatures,three constant humidity and five constant photoperiods respectively.The results showed that: 1)in the temperature trial range from 22 to 34?,the mating success was the highest at 25-28?,with the shortest mating latency and the longest mating duration.The oviposition period and adult longevity decreased with increasing of temperature.When the temperature was up to 31?,the fecundity and fertility decreased,the remnant fecundity in female abdomen increased dramatically,and the relative expected reproduction decreased over 85% than 28?.The relative reproductive expectation also fell by more than 5% when the temperature is down to 25?.This result indicated that the population growth of this pine caterpillar inhibited by either high or low temperature.2)In the relative humidity trial range from 25% to 75%,there was no difference in the mating success among three humidity treatments,but the mating latency was shorter and the mating duration was longer at RH 75%.Fertility and female longevity significant influenced by relative humidity,but there were no differences in terms of oviposition period,fecundity,remnant fecundity and male longevity.However,these fitness consequence parameters exhibited higher values at RH 75%,and the relative reproductive expectation increased by 23% than RH 25%,indicating that higher relative humidity are favorable for population growth of this insect.3)Under five photoperiod conditions,we found this caterpillar did not mating in L0: D24,and there were no difference in the parameters of mating behavior among other four photoperiods although the mating success was the highest,the mating duration was the shortest and mating duration was the longest in L14: D10.The parameters of reproductive fitness showed that the oviposition period,fecundity and fertility were significantly lower in L0: D24 than those in other photoperiod treatments.The relative reproductive expectation was the highest in L14: D10,indicating scotophase was essential for the reproduction success of this insect species.All results mentioned above indicated that the mating behavior and reproductive fitness of D.punctatus significantly influenced by environmental factors such as temperature,relative humidity and photoperiod,and the optimal conditions was 28?,RH 75% and L14: D10 for reproduction success of D.punctatus.2.Effects of host plants on mating behavior and reproductive fitness in D.punctatus.To investigate the role of host plants on mating behavior and reproductive fitness,we analyzed the effects of host plant species and host age on the life history traits,adult morphology,mating behavior and reproductive fitness through feed on D.punctatus using old and young needles of P.massoniana,old and young needles of P.elliottii at larval stage.The results showed that: 1)In the pre-adult stage,the life history traits in terms of larval and pupal survivorship,larval and pupal development duration,percentage of adult emergence and adult growth index influenced by host species and needles age of the host.The highest values in life history traits obtained when larvae feed on old needles of P.massoniana,and the lowest values when larvae feed on young needles of P.elliottii.The sex ratio did not influence either by the species or by needles age of the host.Old needles of P.massoniana were favorable to pupal morphological development.A strong effect of host species and needles age found in terms of male pupal weight and body size.However,male head width and female morphology influenced by host species but not by needles age of host.2)In mating behavior trial,mating success was not affected by host plant,while mating latency and mating duration was affected by species but not by needles age of host,showing the shortest mating latency and the longest mating duration when their larvae feed on old needles of P.massoniana.3)In reproductive fitness trial,the parameters including female fecundity,remnant fecundity,first-day fecundity,fitness index and adult longevity but not oviposition period and fertility significantly influenced by larval host plants.Further analysis showed that female fecundity influenced by either host species or needles age,while remnant fecundity and adult longevity affected by host species but not by needles age.The reproductive fitness index when their larvae feed on old needles of P.massoniana(53.66%)was significantly higher than that when their larvae feed on young needles of P.massoniana and old needles of P.elliottii(23.80% and 3.57%,respectively).These results suggested that host plant species and needles age play an important role in larval development,adult mating behavior and fitness consequence,and a strong evidence supported that old needles of P.massoniana is the preferred host plants for D.punctatus.3.Effects of inbreeding on mating behavior and reproductive fitness in D.punctatus.To ascertain whether inbreeding of D.punctatus result in inbreeding depression,inbreeding and outbreeding trials were conducted for three successive generations to analysis the development of offspring,adult mating behavior and reproductive fitness.The results showed that: 1)in individual development trial,the larval and pupal survivalship,percentage of adult emergence significantly decreased,larval and pupal development duration significantly prolonged,and male and female pupal body weight reduced in inbreeding treatment than those in outbreeding treatment.This difference significantly enhanced with successive generations of inbreeding.However,the sex ratio was lower in in inbreeding treatment than in outbreeding treatment but there was no significant difference.2)In mating behavior trial,inbreeding resulted in significantly lower mating success,longer mating latency and shorter mating duration compared with outbreeding.In mate choice trial,female and male preferred to mate with non-sibling partners when they had an opportunity to choose the sibling and non-sibling partners respectively,showing non-sibling partners obtained significantly higher mating success than sibling partners.3)In reproductive fitness trial,there were significantly shorter in oviposition period and adult longevity,lower in fecundity,first-day fecundity and fertility,and higher in remnant fecundity in inbreeding than those parameters in outbreeding.These differences also significantly enhanced with successive generations of inbreeding.All of these results indicated that inbreeding had adverse effects on the larval growth and development,adult mating behavior,and reproductive fitness in D.punctatus,and these adverse effects were significantly enhanced with successive generations of inbreeding in this caterpillar,which strongly support our hypothesis that inbreeding has adverse effects on mating and fitness-related traits in monogamous insect. |
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