Reproductive Biology In The Pine Caterpilar, Dendrolimus Punctatus Walker (Lepidoptera:Lasiocampidae)

The pain caterpillar Dendrolimus punctatus Walker (Lepidoptera:Lasiocampidae) is broadly distributed across southern of China. This moth is considered to be one of the most destructive insect pests, with populations that frequently reach outbreak status and cause significant damage to pine forests in China. The larvae seriously damage pine needles of Pinus massoniana. In the field, this species can complete 2-3 generations per year, and overwinters as third to fourth instars of the second and third generations in the region near 30°N in China. From1950s, numerous studies about this moth were conducted in terms of the biological characteristics, population dynamics, outbreak mechanism, control strategy etc, and obtained a serious of achievements.In this thesis, we investigated the nature of emergence and mating behavior, the effect of copulation duration, mating frequency, delayed mating and temperature on mating behavior and reproductive success in this pine caterpillar. The results are as follows.1. Circadian emergence and mating rhythms in the pine caterpillar.At 28℃, female and male moth eclosed from the beginning of scotophase (18:00) to 1 h before the scotophase terminating (5:00). The peak of emergence of male moth appeared at 2 to 4 h after scotophase starting (from 20:00 to 22:00), whereas the peak of emergence of female moth appeared at 4 to 5.5 h after scotophase starting (from 22:00 to 23:30). When paired with newly emergence moth as 1:1 (female and male sex ratio), we found that the calling and mating behavior of this moth occurred in midnight (1:30), copulated immediately after terminating calling behavior. The peak of mating occurred 0.5 h before the beginning of photophase (5:30) to 3 h after the next scotophase starting (21:00). Female and male moth could mate 4 consecutive days, but most (80.6%) of pairs occurred at night in that day and the next day after their emergence. Based on our observation, the average number of matings is 1.23±0.76 times, with 77.4% moth mated one time, and only 22.6% individuals mated two times. The average copulation duration was 16.94± 0.46 h in once mating pairs and 24.71±3.98 h in twice mating pairs. These results suggest that the pine caterpillar D. punctatus is belonging to the species of protandry and monogamy.2. Effects of copulation duration and mating frequency on female fitness consequences in pine caterpillar.The effects of copulation duration and mating frequency on female fitness consequences in pine caterpillar D. punctatus were investigated under 28℃, LD16:8. Copulation durations experienced 0 h,0.5 h,1 h,3 h,5 h,10 h and free mating (more than 10 h) showed that mean longevity of unmated females (copulated 0 h) was significantly longer than that of mated females, but there had no difference in female longevity when copulated different durations. The copulation durations and lifetime egg production did not show significant difference among different copulation durations, while the copulation durations mainly effected the daily egg production, showing the daily egg production in first day significantly increased with increasing in copulation duration. Virgin female laid infertile eggs, and the hatching rate of eggs laid by females significantly positively related to the copulation durations. Comparing the mating frequency, which were allowed to mate for 1 and 2 times, we found that two copulation treatments resulted in a slightly shorter in male and female life span, higher in lifetime fecundity and egg hatching rate than one copulation treatments, but there were no significant differences between these two treatments. However, the later daily egg-hatching rate positively related to mating frequency. These results suggest that the pine caterpillar D. punctatus accrued significant fertility benefits from prolonged copulation durations and increased mating frequency.3. Effects of delayed mating on mating behavior and reproductive fitness in pine caterpillar.The effect of delayed mating on mating behavior and reproductive performance of pine caterpillar, D. punctatus, were investigated under laboratory conditions. When virgin male and female were allowed to mate soon after emergence or 1,2 and 3 days after emergence, the proportion of mating and copulation duration were significantly decreased with increasing age at mating. When both males and females delayed mating, the female and male longevity were significantly prolonged. Female lifetime fecundity and fertility were also significantly decreased with increased age at mating. Males delayed from mating for 3 d after emergence were unable to inseminate females. The moth age was negatively correlated with those variables. These results indicated that delayed mating had a significant negative impact on reproduction in this pine caterpillar, and disrupt mating may be effective behavioral strategies for managing this important forestry pest.4. Effects of temperature on mating behavior and reproductive fitness in pine caterpillar.Temperature is one of the most important climatic factors that may influence different traits of insect species. In order to determine the effects of temperature on the mating behaviors and fitness consequence of the pine caterpillar D. punctatus, we subjected pairs of male and female to five temperatures from 22℃ to 34℃ at an interval of 3℃ in a controlled laboratory conditions. Results indicated that at 28℃, the proportion of mating was highest, the mating latency was shortest and the copulation duration was longest. Above or below this temperature, these behavior variables exhibited some significantly opposite results. Female and male longevity declined significantly with increasing temperature. The lifetime fecundity and egg fertility increased gradually with increasing temperature within the range of 22～28℃, whereas declined gradually with increasing temperature within the range of 28～34℃ and there had a significantly difference in fecundity and fertility among temperature treatments. Further analysis indicated that there were no significant differences in these behavior variables and reproductive fitness parameters between 25℃ and 28℃. These results suggest that the mating behaviors and reproduction success of this pine caterpillar were significantly influenced by environmental temperature and the optimal temperature was between 25～28℃.