The density seasonal dynamics of Bemisia tabaci MED were evaluated over two years in a cotton-growing area in Langfang, Hebei Province, northern China on cotton （Gossypium hirsutum L.） and six other co-occurring common plants, common ragweed （Ambrosia artemisiifolia L.）, piemarker （Abutilon theophrasti Medicus）, sunflower （Helianthus annuus L.）, sweet potato （Ipomoea batatas L.）, soybean （Glycine max L.）, and maize （Zea mays L.）. The whitefly species identity was repeatedly tested and confirmed; seasonal dynamics on the various host plants were standardized by the quartile method. B. tabaci MED appeared on weeds （the common ragweed and piemarker） about 10 days earlier than on cotton, or the other cultivated plants. The peak population densities were observed over a span of 2 to 3 weeks on cotton, starting in early （2010） or mid-August （2011）. The common ragweed growing adjacent to cotton supported the highest B. tabaci densities （no. on 100 cm2 leaf surface）, 12-22 fold higher than on cotton itself. Sunflower supported more B. tabaci than the other plants, and about 1.5-2 fold higher than cotton did, Our results indicate that weeds （esp. the common ragweed） around cotton fields could increase the population density of B. tabaci MED on cotton, while sunflower could act as a trap crop for decreasing pest pressure on cotton.
ZHANG Xiao-mingYANG Nian-wanWAN Fang-haoGabor L Lvei
桨角蚜小蜂体型小,个体差异小,传统的形态学鉴定方法难以快速准确鉴定。本研究以海氏桨角蚜小蜂,古桥桨角蚜小蜂及两个本地桨角蚜小蜂未知种群为研究对象,利用线粒体DNA细胞色素C氧化酶亚基I(mitochondrial cytochrome oxidase subunit I gene,mt DNA COⅠ)基因序列分析和相似种种间杂交方法,鉴定了桨角蚜小蜂属的两个本地种群(河北廊坊和新疆吐鲁番种群)。通过对靶标片段剪辑序列的测序及比对分析,以最大简约法(Maximum parsimony,MP)和最大似然法(Maximum likelihood,ML)分别构建系统发育树,并以Kimura双参数模型计算种内和种间遗传距离,进而利用种群间杂交手段分析相似种间生殖隔离情况。结果显示:桨角蚜小蜂廊坊种群与古桥桨角蚜小蜂聚为一支,两者的种群内遗传距离分别为0.0029和0.0173,种群间遗传距离为0.011;桨角蚜小蜂新疆种群和海氏桨角蚜小蜂聚为一支,两者的种内遗传距离分别为0.0023和0.000,种间遗传距离0.024,进一步的种间杂交试验表明,新疆种群与海氏桨角蚜小蜂间无生殖隔离现象,证明两种群属于同一物种。桨角蚜小蜂属新疆吐鲁番种与海氏桨角蚜小蜂可能属于同一物种。结合COⅠ基因序列分析和种间杂交试验来共同鉴定未知桨角蚜小蜂不仅可以提高鉴定准确度,更能一定程度上弥补分子鉴定手段可能存在的缺陷。
海氏桨角蚜小蜂Eretmocerus hayati(Zolnerowich and Rose)原产于巴基斯坦,是B型烟粉虱Bemisiatabaci(Gennadius)的一种有效天敌。本文报道了不同温度条件(20、22、26、30、34℃,RH65%±5%,光周期14L∶10D)和饲养在不同寄主植物——番茄、黄瓜、甘蓝上(26℃,RH65%±5%,光周期14L∶10D)烟粉虱对海氏桨角蚜小蜂生物学特性的影响。结果表明,在20℃和30℃恒温条件下,该蜂寄生在番茄上饲养的烟粉虱的发育历期分别为31.7d和12.4d,完成发育的有效积温为247日.度,发育起点温度为11.9℃。在26℃恒温条件下,该蜂寄生番茄、黄瓜和甘蓝上的烟粉虱若虫时,卵至成蜂羽化的发育历期分别为15.7、16.1和15.2d,相应存活率分别为74.6%、72.1%和78.7%,雌蜂寿命分别为7.4、7.6和8.1d,平均繁殖量分别为67.2、62.3和74.7粒卵。本研究结果对海氏桨角蚜小蜂的大量饲养和田间释放具有指导作用。
The parasitoids in the genera of Encarsia and Eretmocerus （Hymenoptera： Aphelinidae） are important biological control agents of whiteflies, and some of them not only parasitize hosts but also kill them with strong host-feeding capacity. Two whitefly parasitoid species, Encarsia sophia and Eretmocerus melanoscutus were examined to determine if mating and host density affected their host feeding and parasitism. The whitefly host, Bemisia tabaci, was presented to these two wasp species in densities of 10, 20, 30, 40, 50 and 60 third-instar nymphs per clip cage. Mated whitefly parasitoid females fed on more hosts than unmated females under a range of host densities （under all six host densities for En. sophia; under the densities of 40 nymphs or more for Er. melanoscutus）. Meanwhile, mated females parasitized more whitefly nymphs than unmated females under all host densities for both species. With increase of host density, mated or unmated Er. melanoscutus females killed more hosts by host feeding and parasitism. Mated En. sophia females killed more hosts by host feeding with increase of host density, whereas unmated females did not parasitze whitefly nymphs at all. Our results suggest that only mated female parasitoids with host-feeding behavior should be released in crop systems to increase their bio-control efficiency.
Lian-Sheng ZangTong-Xian LiuFan ZhangShu-Sen ShiFang-Hao Wan
