| Summary: | 碩士 === 國立中興大學 === 昆蟲學系 === 89 === The developmental time of nymphal stage of cotton aphid, Aphis gossypii Golver, reared on three host plants, Psidium guajava L., Ageratum houstonianum Mill., and Bidens pilosa L., reduced with the increasing of temperatures at five constant temperatures of 10 ~30℃. The longest developmental time was 18.44 days at 15℃ and the shortest was 5.39 days at 25℃ on P. guajava, on A. houstonianum and B. pilosa the longest developmental time were 23.80 days and 22.51 days, respectively, both at 10℃, and the shortest was 4.63 days at 30℃ on A. houstonianum and 6.24 days at 25℃ on B. pilosa. The theoretical low developmental threshold and thermal summation of nymphal stage were 11.19℃ and 76.16 DD on P. guajava, 5.64℃ and 104.73 DD on A. houstonianum, and 4.52℃ and 133.73 DD on B. pilosa. The body length and body width of adults reared on various host plants were measured and compared in this paper. The adult longevities on various host plants were not significantly different at various temperatures. The highest fecundity was 36.43 offspring/ female observed at 25℃on P. guajava, and 48.93 and 48.07 offspring/ female, respectively, at 25℃ and 20℃ on A. houstonianum, and 35.27 offspring/female at 20℃ on B. pilosa. There were significantly different at each temperature for the fecundities of adult on three different host plants, except at 15℃. The population parameter of this species on various host plants showed that the hightest intrinsic rate of increase (r) and the finite rate of increase (λ) were at 25℃, of which r=0.3924/day and λ= 1.4800/day on P. guajava, r=0.5106/day and λ=1.6653/day on A. houstonianum, and r=0.3214/day andλ=1.3766/day on B. pilosa. The highest net reproductive rates (R0) were 36.40 offspring/female and 48.93 offspring, respectively, on P. guajava and A. houstonianum at 25℃, and 35.07 offspring/female on B. pilosa at 20℃. The generation times (T) on three host plants were reduced with an increase in temperatures, the shortest were 8.82 days on P. guajava, 6.99 days on A. houstonianum, and 9.69 days on B. pilosa, respectively, at 30℃. When alter the host plants by transferring the different nymphal instars and adults from the A. houstonianum and B. pilosa clones to P. guajava, the survival rate of the former was lower than 50%, and was more than 50% for the later, and the maximum fecundity of females transferred on new host plant was 2.19 to 3.85 offspring/day/female from A. houstonianum clone, and 2.82 to 4.00 offspring/ day/female from B. pilosa clone. From October 1999 to October 2000, the population fluctuations of A. gossypii were investigated on three host plants in the FTHES guava orchard. The populations occurred all year around, and reached the peak from December to the following February on P. guajava, and for the populations on A. houstonianum and B. pilosa the peak appeared in October to December, and at the end of January, respectively. The major factors affecting the population fluctuation of this aphid on P. guajava were the temperature, the nitrogen concentration, the number of aphid and the alatae on B. pilosa, and only the wind speed was positively correlated to the population on A. houstonianum.
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