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云南切梢小蠹(Tomicus yunnanensis Kirkendall & Faccoli)是一种以危害云南松为特征的针叶树毁灭性害虫[1],该虫自20世纪80年代在云南中部大发生以来,已扩散至四川和贵州等地,累积因云南切梢小蠹危害致死的活立木蓄积量超过20万hm2,严重影响了云南松林的可持续发展和生态环境安全[2-7]。
云南切梢小蠹具有独特的危害特点:新羽化的成虫喜食新鲜嫩梢,一般仅选择健康松树补充营养,致树势衰弱;待性成熟后则只选择衰弱的云南松树干作为繁殖场所,阻碍树木水分和营养物质输送,最终导致树木死亡[2, 5, 7-8]。可见,云南切梢小蠹存在一个明显的蛀梢期和蛀干期,而转移期是相当短暂的,其绝大部分的生活史,如成虫取食、内生殖器发育、交配、产卵,幼虫生长、羽化等过程均在枝梢或树干内完成,这种隐蔽的生活方式为研究其产卵习性带来诸多不便。而另一方面,枝梢内补充营养和树干内繁殖的生活方式,与已知的黄杉大小蠹(Dendroctonus pseudotsugae)[9]、华山松大小蠹(D. armandi)[10]、十二齿小蠹(Ips sexdentatus)[11]、赤材小蠹(Xyleborus ferrugineus)[12]、咖啡果小蠹(Hypothenemus hampei)[13]等在树干或果内补充营养和繁殖的小蠹虫有着本质的区别,加之卵巢发育受环境温度的调控[14-15],意味着枝梢内补充营养的切梢小蠹的卵巢发育更易受到环境温度的作用,进而影响切梢小蠹生殖和种群繁衍。因此,本研究于2014年12月至2016年1月连续对在云南松枝梢内取食的云南切梢小蠹雌成虫卵巢进行解剖观察,并结合当地的环境温度和林间蛀干调查,借此分析云南切梢小蠹卵巢发育程度与温度间的关联性,以便了解云南切梢小蠹的种群数量动态和成灾机制,为后续开展预测预报和综合防治提供理论依据。
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云南切梢小蠹卵巢位于第4腹板消化道下方,由1对卵巢(Ovarioles)、2根短侧输卵管(Lateral oviduc)、1根中输卵管(Common oviduc)、储精囊(Spermatheca)、1对附腺(Accessory gland)和悬带(Terminal filaments)等组成,其中左右卵巢各有2条卵巢管,彼此平行排列,且表面附着大量的气管和微气管,而侧输卵的前端与卵巢小管交界处膨大成卵巢萼(Calyx)(图 1)。
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根据腹部外部特征,卵巢小管、侧输卵管、中输卵管、附腺、脂肪体形态和颜色,卵黄沉积状况,卵巢萼内卵粒有无、颜色及排列形式等将云南切梢小蠹卵巢发育分为透明期(Ⅰ级)、延伸期(Ⅱ级)、卵黄沉积前期(Ⅲ级)、卵黄沉积期(Ⅳ级)、产卵期(Ⅴ级)共5个等级,各等级的核心特征见表 1。
表 1 云南切梢小蠹卵巢发育分级标准
Table 1. Grading criteria of ovarian development in Tomicus yunnanensis
级别 腹部特征 卵巢 卵巢管 侧输卵管 储精囊 附腺 脂肪体 Ι级 棕黄色、略软 无色透明 纤细管状 略膨大、皱褶不明显 梨形、无色透明 肾形、无色透明 较少 Ⅱ级 渐棕褐色、较软 乳白色 梭形 膨大、皱褶不明显 梨形、乳白色 肾形、乳白色 少量 Ⅲ级 棕褐色、坚硬 乳白色 圆柱形 卵巢萼,具未成熟卵粒 梨形、淡褐色 肾形、淡黄色 较多 Ⅳ级 棕褐色、坚硬、略膨胀 乳白色 圆柱形 卵巢萼、皱褶明显,具成熟卵粒 梨形、淡褐色 肾形、杏黄色 大量 Ⅴ级 棕褐色、坚硬、明显膨胀 亮乳白色 圆柱形 卵巢萼、皱褶明显,大量成熟卵粒 梨形、淡褐色 肾形、杏黄色 大量 透明期(Ⅰ级):从迁飞蛀梢开始,持续15~26天,该时期腹部呈棕黄或渐棕褐色,略软;整个卵巢无色透明,卵巢管纤细,管状,管柄与侧输卵管黏连;侧输卵管略微膨大,包裹于管柄,皱褶不明显;中输卵管无色透明,末端与储精囊和附腺交界处略膨大,储精囊梨形,附腺肾形;卵巢表面布满气管和微气管,背面和腹面未见脂肪附着,但腹腔内已有少量脂肪体存在(图 2 A,A1)。
图 2 云南切梢小蠹雌成虫卵巢发育过程的形态变化
Figure 2. Processing-morphology Changes of ovarian development in Tomicus yunnanensis
延伸期(Ⅱ级):卵巢管延伸膨大阶段,持续45~62天,该时期小蠹腹部呈渐棕褐色,较硬;卵巢乳白色,卵巢管延伸明显,梭形,管柄与侧输卵管渐分离;侧输卵膨大,皱褶不明显,中输卵管略显淡黄褐色,短粗;附腺和储精囊增大,附腺乳白色;微气管与卵巢附着力强,剥离难度大,腹腔内脂肪体数量增加明显(图 2B,B1)。
卵黄沉积前期(Ⅲ级):卵巢管膨胀阶段,持续45~60天,该时期小蠹腹部坚硬,卵巢乳白色,卵巢管膨大,圆柱形,管柄分离明显;侧输卵管与卵巢管交界处开始膨大为卵巢萼,但没有成熟卵粒;中输卵管黄褐色,短粗,储精囊淡褐色,附腺淡黄色;卵巢表面附着气管和微气管,可剥离;有少量黄色脂肪附着,腹腔内也出现有大量的黄色脂肪体(图 2C)。
卵黄沉积期(Ⅳ级):该时期持续120~135天,此时切梢小蠹腹部略微膨胀,坚硬;卵巢小管内的卵黄形成乳白色未成熟的卵粒排列于卵巢萼内,侧输卵管和附腺继续膨大且皱褶明显,中输卵管短粗,黄褐色,附腺杏黄色,光滑饱满。卵巢表面附有黄色脂肪,腹腔内黄色脂肪体数量众多(图 2D)。
产卵期(Ⅴ级):持续时间20~45天,腹部明显膨胀,坚硬;卵巢管亮乳白色,端部到末端依次可见到未成熟卵粒和成熟卵粒,呈念珠状排列,而卵巢萼内充满大量的成熟卵粒;储精囊发育成熟,梨形,附腺杏黄色;卵巢萼、附腺、储精囊均附着大量的黄色脂肪,腹腔内黄色脂肪体略少于卵粒形成期(图 2E,E1,F)。
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云南切梢小蠹卵巢管长度在Ⅰ~Ⅳ级时增长较为缓慢,Ⅳ~Ⅴ级增长快速(χ2=23.103, P=0.000 12;图 3),如由Ⅳ级的2.05±0.12 mm显著增长到Ⅴ级的2.26±0.17 mm(t=3.120, P=0.016)。卵巢宽度有两个快速增加期(χ2=32.549, P < 0.000 1),一是由Ⅰ级的0.105 ± 0.038 mm显著增加到Ⅲ级的0.179 ± 0.011 mm(t=2.825, P=0.040),二是由Ⅳ级的0.206±0.027 mm显著增加到Ⅴ级的0.256±0.041 mm(t=2.791, P=0.042)。卵巢体积呈幂指数级增长(y=0.05e0.4x, R2=0.948)。
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环境温度对云南切梢小蠹卵巢发育有明显的影响(图 4),当环境均温大于10℃时,羽化的云南切梢小蠹从树干进入枝梢开始补充营养,此时卵巢为透明期(Ⅰ级),占比为100%,随后比例逐步降低,而延伸期(Ⅱ级)和卵黄沉积前期(Ⅲ级)开始增加,至10月温度开始降低才逐渐进入卵黄沉积期(Ⅳ级)和产卵期(Ⅴ级)。当环境最低温低于5℃时,即从12月份至翌年1月份,Ⅴ级卵巢比例逐步增加到100%,蛀干产卵开始。相关性分析表明卵巢体积相对增加量与环境均温差呈正相关(r=0.556, P=0.016;图 5),而蛀干产卵数量与月最低温为负相关(r=-0.828, P=0.022;图 6)。
图 4 不同月份云南切梢小蠹不同时间卵巢发育级别与温度的关系
Figure 4. Relationship between ovarian development and environment temperature on the grading ovary of T. yunnanensis in each month
云南切梢小蠹雌成虫卵巢发育程度的分级研究
Processing-morphology Change and Grading Criteria for Ovarian Development in Tomicus yunnanensis (Coleoptera, Scolytidae)
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摘要:
目的 探究卵巢发育与环境温度在云南切梢小蠹生殖和种群繁衍中的作用,进而加深对其种群数量动态和成灾机制的认识。 方法 采用随机抽样法,于2014年12月-2016年1月解剖正在云南松枝梢内取食的云南切梢小蠹雌成虫。 结果 云南切梢小蠹雌成虫卵巢位于第4腹节消化道侧下方,由1对卵巢、2根短侧输卵管、1根中输卵管、受精囊和附腺构成;卵巢包括四根管状的卵巢管,每个卵巢管前端延伸出端丝并集合成悬带,附着于体壁或脂肪体上。根据卵巢发育形态特征的变化,分为透明期(Ⅰ级)、延伸期(Ⅱ级)、卵黄沉积前期(Ⅲ级)、卵黄沉积期(Ⅳ级)、产卵期(Ⅴ级)共5个等级,卵巢发育过程与蛀梢补充营养密切相关,每一级别可持续1~4月不等;Ⅰ-Ⅳ级卵巢管长度增长较慢,Ⅴ级增长快速,而卵巢管宽度Ⅱ级和Ⅴ级增加快,卵巢面积呈幂指数级增长。结合环境温度和林间蛀干调查,发现云南切梢小蠹卵巢发育与温度呈正相关,而蛀干产卵与温度负相关。 结论 云南切梢小蠹雌成虫卵巢发育主要集中在Ⅲ~Ⅴ级,且温度影响该蠹虫的蛀梢和蛀干产卵,研究可为云南切梢小蠹产卵期的预测预报提供理论依据 Abstract:Objective To investigate the role of ovarian development associated with environmental temperature in reproduction and population growth of Yunnan shoot borer Tomicus yunnanensis for further understanding the basic mechanism of its population fluctuation. Method The females of T. yunnanensis were randomly obtained from the shoot of Pinus yunnanensis, and dissected on a paraffin plate. Result The female reproductive system of Yunnan shoot borer is located in the inferior toward the lateral part of alimentary canal at the fourth abdominal segment. It consists of a pair of ovaries and two short lateral oviducts, a common oviduct, a spermatheca and two accessory glands. The ovaries have four tubular ovarioles. The terminal filaments extended from the anterior end of each ovariole can adhere to the internal tegument or fat body. According the morphological changes, the ovarian development was divided into five grades, including transparent period (grade Ⅰ), terminal elongation period (grade Ⅱ), previtellogenic (Ⅲ grade), vitellogenic eggs (grade Ⅵ), and ovipositing period (grade Ⅴ). Each grade of ovarian development can last less than 1 to 4 month, and show a closely relation to the nutrient acquisition. The length of ovariole grows slowly in the previous and middle and rapidly in late grades, but the width of ovariole grow rapidly in the previous and late grades. The whole size of ovary increase rapidly with a power-law dependence. Using Kendall's tau-b correlation analysis, it was found that the correlation between ovarian development and temperature was positive, and a negative relationship was found between oviposition and temperature. Conclusion The ovarian devel-opment of female adults of T. yunnanensis focuses mainly on the middle and late grades. The environment temperature has a significant effect on the life style of shoot and stem, respectively. The results can help to further deepening the theoretical basis for the prediction of oviposition of Yunnan shoot borers. -
Key words:
- Tomicus yunnanensis
- / ovarian morphology
- / ovarian development
- / grading criteria
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表 1 云南切梢小蠹卵巢发育分级标准
Table 1. Grading criteria of ovarian development in Tomicus yunnanensis
级别 腹部特征 卵巢 卵巢管 侧输卵管 储精囊 附腺 脂肪体 Ι级 棕黄色、略软 无色透明 纤细管状 略膨大、皱褶不明显 梨形、无色透明 肾形、无色透明 较少 Ⅱ级 渐棕褐色、较软 乳白色 梭形 膨大、皱褶不明显 梨形、乳白色 肾形、乳白色 少量 Ⅲ级 棕褐色、坚硬 乳白色 圆柱形 卵巢萼,具未成熟卵粒 梨形、淡褐色 肾形、淡黄色 较多 Ⅳ级 棕褐色、坚硬、略膨胀 乳白色 圆柱形 卵巢萼、皱褶明显,具成熟卵粒 梨形、淡褐色 肾形、杏黄色 大量 Ⅴ级 棕褐色、坚硬、明显膨胀 亮乳白色 圆柱形 卵巢萼、皱褶明显,大量成熟卵粒 梨形、淡褐色 肾形、杏黄色 大量 -
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