| Summary: | 碩士 === 國立屏東科技大學 === 熱帶農業暨國際合作研究所 === 94 === Cycad aulacaspis scale, Aulacaspis yasumatsui Takagi, is an invasive species, which threatens a native cycad, Cycas taitungensis Shen et al., to a verge of extinction. This study was to obtain basic data on the biology and ecology of Cybocephalus nipponicus, introduced from Thailand in 2003 to aid in the control of A. yasumatsui. Studies were conducted to determine life history parameters; including life cycle, fecundity, sex ratio and longevity, of C. nipponicus and using these parameters to develop its life table. Also studied were the predator-prey interactions, such as functional response and mutual interference, and the population fluctuations of A. yasumatsui before and after the release of C. nipponicus in the field. A female C. nipponicus laid its eggs under the scale cover of a mature female scale or in an empty male armor. The eggs measured 0.41 ± 0.02 mm in length and 0.19 ± 0.01 mm in width. The mean width of the head capsules of 1st instar larva was 0.164 ± 0.008 mm, 2nd instar larva was 0.238 ± 0.013 mm and 3rd instar larva was 0.33 ± 0.015 mm. At 26 ± 1 ºC and 60 ± 10 % RH, the average incubation period of eggs of C. nipponicus was 6.24 ± 1.45 days and its larval period, consisting of three instars, was 9.47 ± 2.9 days. Its pupal period was 15.05 ± 1.27 days. At 17 ºC and 60 ± 10 % RH, the egg stage was twice as long as that of 26 ºC. The mean development time of its larval and pupal periods was longer at 17 ºC than at 26 ºC. At 29 ºC and 60 ± 10 % RH, the durations of its egg, larval and pupal periods were considerably shorter than that of 26 ºC. The duration of the life cycle of C. nipponicus, in a descending order, was 62 days (17 ºC) > 31 days (26 ºC) > 24 days (29 ºC). The longevities of an adult male and female C. nipponicus were not significantly different at about 81 days. The pre-ovipositon period of a female C. nipponicus was 5.18 days and its mean fecundity was 109.47 ± 68 eggs. The sex ratio of females to males was 0.8: 1. Analysis of its life table revealed that the highest mortality occurred in the larval stage. Its net reproduction rate (Ro) was 46.53; its mean generation time (T) 62.05 days; its intrinsic rate of increase (r) 0.06 and its finite rate of increase (λ) 1.06. The functional response of male and female C. nipponicus adults at different densities and stages of A. yasumatsui showed that the females consumed more cycad scales than the males at all the temperatures tested. C. nipponicus adults consumed less cycad scales of older stages. Temperature significantly influenced the mean daily number of cycad scales of different stages consumed by both males and females C. nipponicus. The 1st instar larvae were the preferred prey of C. nipponicus adults followed by the male pupa. In general, a Type II functional response was demonstrated by C. nipponicus adults in preying on 1st instar larvae and male pupae of A. yasumatsui. At 26 ºC, the handling time for a male and a female C. nipponicus adult was 0.015 days and 0.016 days, respectively. At 17 ºC, the handling time for a female C. nipponicus was longer (0.033 days) than that of a male (0.023 days), indicating that the female was more sensitive to the low temperatures than the male. However, at 29 ºC, the handling time of the female was 0.008 days, which was shorter than that of 0.013 days for the males, indicating that the males were more sensitive to high temperatures than the females. The discovery of a morphologically different A. yasumatsui indicated that it may be undergoing a genetic change, which could be important to the efforts being made to place it under control and to minimize its damage to C. taitungenesis in Taiwan.
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