Life Table of Aphis craccivora and Quantitative Study of Its Endosymbiont Buchnera 16S rDNA

Abstract

The development, longevity, fecundity and population parameters of the cowpea aphid, Aphis craccivora, were studied at six constant temperatures (10, 15, 20, 25, 30 and 35℃) on the asparagus bean, Vigna sesquipedalis, in the laboratory. The results showed that the development time of immature stage shortened from 28.1 days at 10℃ to 4.2 days at 30℃. According to the linear regression analysis of development rate and temperature between 10 and 30℃, the overall immature development required 97.2 day-degrees above 7.4℃. The adult longevity shortened from 42.2 days at 15℃ to 6.2 days with increasing temperature to 35℃. At 15 to 25℃, the fecundity was more than 82 (offspring/♀/life). The intrinsic rate of increase (r) and the finite rate of increase (λ) were the lowest at 10℃ (r = 0.0437/d, λ= 1.0447/d), and highest at 30℃ (r = 0.4330/d, λ= 1.5419/d). The population reared at 25℃ had the highest net reproductive rate (R0 = 97.1 offspring/♀/generation). The mean generation time (T) shortened as the temperature increased from 41.1 days at 10℃ to 8.3 days at 35℃. The sequence of bacterial 16S rDNA of A. craccivora revealed that it belongs to primary symbionts, Buchnera sp. According to the RFLP maps of Buchnera 16S rDNA, cowpea aphid seems not to have secondary symbionts. We designed specific primers, AcPS128F and AcPS453R, based on non-conserved regions of 16S rDNA, to quantify the Buchnera 16S rDNA of A. craccivora by real-time PCR technique. The result indicated that the related contents of Buchnera 16S rDNA of older nymphs were higher than those of young nymphs at 10 to 30℃. When temperature was lower, the tendency of such phenomenon was more obvious. In the whole reproduction stage of A. craccivora, the related contents of Buchnera 16S rDNA was higher at 10-25℃than at 30℃ and 35℃.

以長豇豆 (Vigna sesquipedalis) 飼育黑豆蚜 (Aphis craccivora)，於實驗室中觀察六個不同定溫處理 (10、15、20、25、30及35℃，光週期12L：12D) 對若蚜發育時間、成蚜壽命及繁殖、族群介量之影響。結果顯示若蚜的發育時間由10℃的28.1天縮短至30℃的4.2天。根據10-30℃的發育速率與溫度的直線迴歸分析，估算未成熟期的發育臨界低溫為7.4℃，總積溫為97.2 DD (day-degree)。成蟲壽命由15℃的42.2天縮短至35℃的6.2天，而繁殖率在15-25℃下可達82 (子代/♀/生) 以上。最小內在增殖率 (r) 為10℃的0.0437/天，最大為30℃的0.4330/天；終極增長率 (λ) 由10℃的1.0447/天增加至30℃的1.5419/天。在25℃下的族群具有最高之淨增殖率 (R0) 為97.1 (子代/♀/世代)。平均世代時間 (T) 隨著溫度升高而由10℃的41.1天縮短至35℃的8.3天。黑豆蚜的內共生菌16S rDNA定序結果顯示其為初級共生菌Buchnera sp.所有，由Buchnera 16S rDNA之RFLP圖譜初步判別黑豆蚜可能未具有次級共生菌。我們在該序列與其他次級共生菌有明顯差異的區域設計了專一性引子對AcPS128F/AcPS453R，利用real-time PCR技術進行不同溫度及不同齡期下，黑豆蚜體內Buchnera 16S rDNA之定量。結果發現除35℃外，若蚜體內Buchnera 16S rDNA的相對含量以老熟若蚜較年輕若蚜多且愈低溫愈明顯。整個黑豆蚜繁殖期的Buchnera 16S rDNA相對含量，在10-25℃時明顯較在30℃及35℃時為高。