抄録
Survivorship and fertility schedules of two phytophagous lady beetle species, Epilachna vigintioctopunctata (hereafter abbreviated as EV) and E. enneasticta (EN), were studied under laboratory conditions in a Sumatran highland (Sukarami, 928 m altitude), Indonesia. In the study area, both species commonly occur together on the same solanaceous host plants such as egg plant and a weed, Solanum torvum. EV frequently reached a high density to deplete the plants, while EN remained at low levels. Duration of immature stages was 32.1 days (EV) and 35.3 days (EN). The mean longevity of EV (125.7 days and 90.8 for males and females, respectively) was much shorter than that of EN (149.6 and 124.4). Females of both species laid eggs until day 120 (EV) and 158 (EN) after emergence. Compared to EV, EN had a lower fertility (472.7 eggs per female vs. 787.2) and longer mean length of generation (T) (92.6 days vs. 72.9). The intrinsic rate of increase (r) of EV (0.082) was higher than that of EN (0.059), resulting from the faster developmental times (immature stages and female pre-reproductive period) and the larger fertility of EV than those of EN. The different r-values between the two species corresponded to the difference in the density levels in the field. We also compared the demographic traits of EV populations between the highland (present study) and lowland (previous study in Padang), and found that the former had longer developmental times than those of the latter but both had similar magnitude of fecundities. The r-value of the former was much smaller than that of the latter because of the longer developmental times due to lower temperature condition.
