橘小实蝇危害3种苹果的风险评估

郭腾达1,2,姜莉莉1,孙瑞红1*,宫庆涛1,叶保华2*

1山东省果树研究所,山东泰安 271000;2山东农业大学,山东泰安 271000)

摘 要【目的】探究橘小实蝇在‘金冠’‘新红星’‘富士’苹果上的产卵选择及幼虫发育特点,评估橘小实蝇对苹果的危害风险。【方法】观察成虫活动趋向,测定3种苹果果实生理指标,观测果皮和产卵器显微结构,统计橘小实蝇在苹果上的访问量、产卵孔数、幼虫数量和体重等,并分析其相关性。【结果】橘小实蝇对不同苹果访问规律不同,访问量与果肉硬度、含水量呈显著正相关。在3种苹果上的产卵孔数和单孔产卵数均存在显著差异,产卵孔数与淀粉含量呈显著正相关,每孔产卵数与可滴定酸含量呈显著负相关。产卵器最容易通过‘金冠’表皮裂缝进入果肉产卵,产卵孔数与果皮表面裂缝长度、宽度及蜡质层厚度有显著正相关性,与果皮细胞层数为极显著负相关。【结论】橘小实蝇选择苹果产卵会受到果实颜色、果皮结构、果肉硬度、内含物质等多因素影响。‘富士’果皮薄、表面裂纹多、成熟期晚,因此遭受夏秋季节来自南方的橘小实蝇危害风险最大。

关键词苹果;橘小实蝇;产卵选择;风险评估;产卵器

苹果是世界上种植范围最广的水果之一,也是我国产量最大的水果[1],主要分布在长江以北的山东、陕西、新疆、甘肃、河南、河北、辽宁等省份。山东省南邻江苏、河南,一直是苹果的主要产区,栽植面积居于所有果品之首。由于苹果属多年生植物,果园生态环境相对稳定,适合很多生物的栖居与繁衍,特别是一些影响苹果健康生长的病菌和昆虫,常导致苹果减产、降质、降效[2]。随着全世界物流业快速发展,一些有害生物也随之南北各地转移,不断侵害落叶果树,严重威胁北方果树产业持续健康发展[3]

橘小实蝇(Bactrocera dorsalis)属双翅目实蝇科、实蝇属,食性杂,可危害46 科250 多种水果和蔬菜,嗜好取食番石榴、杧果、杨桃、桃、石榴、苹果等水果[4]。橘小实蝇以雌成虫产卵于果皮下,幼虫孵化后直接取食果肉,从而导致果实腐烂、早落。该虫繁殖能力极强,单雌产卵量160~200粒,严重时田间水果受害率为80%~90%[5]。过去,该虫主要在南方发生为害,分布北界为苏南地区,在苹果上的危害极少报道。近年,橘小实蝇频繁在云南、四川、河南、新疆等苹果上发生危害,引起有关部门高度关注。为此,笔者以三大主栽苹果品种‘富士’‘新红星’‘金冠’为试材,研究了橘小实蝇在苹果上的产卵行为,幼虫发育与果实品质的相关性,产卵器与果皮结构的适合度等,旨在评价橘小实蝇对苹果的危害风险,为生产制定预警和防治方案提供参考。

1 材料和方法

1.1 试验材料

供试虫源:2019 年8 月份,从泰安城区桃树、枣树上采集虫果,带回密闭养虫室内让幼虫化蛹和羽化成虫,然后用人工饲料和水果进行连续继代饲养,建立起实验种群。从羽化后的同一批橘小实蝇内选用饥饿处理的产卵期雌成虫作为供试虫。

供试苹果:供试苹果品种为‘富士’‘金冠’‘新红星’,购自泰安市泰山区果品批发市场,‘富士’‘金冠’为套纸袋栽培生产的一级果,‘新红星’为不套袋的一级果。选择果实大小基本一致、果面洁净、颜色相同、无病虫和机械损伤的苹果供试,‘富士’果面呈粉红色,‘新红星’果面紫红色,‘金冠’果面浅黄色。

1.2 仪器设备

自制养虫笼,用铝合金框、100目纱网和透明玻璃板制作而成,长、宽、高分别为120、70、70 cm,其中上面和下面是透明玻璃板,其他4面是纱网,前面有闭合式开口。VEGA3 扫描电镜,捷克TESCAN公司生产。JJ-12J 脱水机,武汉俊杰电子有限公司。JB-P5包埋机,武汉俊杰电子有限公司。JB-L5冻台,武汉俊杰电子有限公司生产。RM2016 病理切片机,上海莱卡仪器有限公司。KD-P 组织摊片机,浙江金华科迪仪器设备有限公司。GFL-230 烤箱,天津市莱玻璃仪器设备有限公司。Eclipse E100正置光学显微镜,日本尼康公司。DS-U3成像系统,日本尼康公司。

1.3 试验方法

1.3.1 成虫访问试验 将3种供试苹果放置在一个养虫笼内,并在果柄上做好标记,每个品种放置4个果,混合均匀排列,其中2 个果柄向上,2 个果柄向下,果与果相距5 cm以上,3次重复。然后向笼内放入100头健康的橘小实蝇雌成虫,上午9:00放入,每隔1 h观察记录1次果实上的成虫数量。

1.3.2 产卵选择试验 把苹果和雌成虫一起放置在养虫笼内,方法同1.3.1。所有果实放入前称单果质量。经24 h 取出苹果,检查记录每个果实上的产卵孔数量。然后,把卵果放入人工气候箱内供虫卵孵化和幼虫发育,温度为(25.0±0.5)℃,相对湿度为60%~70%,光周期为16L:8D。待幼虫发育至3 龄时,剖开果实检查记录虫数,随机选12头3龄幼虫用万分之一电子分析天平称体质量。

1.3.3 果实品质测定 用GY-3 果实硬度计测定果肉硬度,用手持糖度计测定可溶性固形物含量。采用烘干法测定果肉含水量,酸碱滴定法测定可滴定酸含量。将果肉匀浆,提取可溶性糖后的沉淀物用于提取淀粉,淀粉的测定参考Wang 等[6]的方法。

1.3.4 果皮显微结构观察 果皮取样:用手术刀片从新鲜苹果的胴部直接切取两块相邻的果皮各0.5 cm2,一块用于制作石蜡切片,一块用于扫描电镜制片。

果皮显微结构观察:样品经过固定液浸泡24 h后,经过脱水、透明、浸蜡、包埋、切片、脱蜡、番红-固绿染色系列过程制成玻片,在Eclipse E100 正置光学显微镜下进行不同倍数观察拍照,3次重复。

果皮表面电镜观察:样品经过用2.5%(φ)戊二醇4 ℃固定,PBS 缓冲液冲洗3 次(每次10 min),1%(φ)锇酸4 ℃固定2 h,再用PBS缓冲液冲洗3次,依次放入30%(φ,后同)、50%、70%、90%、100%乙醇中进行梯度脱水10 min,样品临界点干燥、喷金等系列过程处理后,在VEGA3扫描电镜下观察拍照。

1.3.5 产卵器观察 取身体完好的橘小实蝇雌成虫4头,直接把雌虫腹部取下进行固定制片,产卵器扫描电镜观察方法同1.3.4。

1.4 数据处理与分析

所有试验数据均采用Excel进行统计与处理,采用SPSS 23.0软件进行单因素方差分析,采用S-N-K法进行显著性测定,并对各组数据之间进行双因素Person 相关性分析。利用Nano Measurer 软件进行显微镜图片的距离测量。

2 结果与分析

2.1 橘小实蝇成虫对不同苹果的访问情况

试验结果(图1)表明,在雌成虫初放入时段10:00—11:00内,‘金冠’上的平均访问虫量最高,其次是‘富士’,对‘新红星’的访问量最低。成虫对‘金冠’的访问量在11:00到达最高峰,接着呈现下降,至16:00时降为最低,平均每果有虫仅1.9头。‘新红星’在前期时段的访问虫量最少,随后访问量逐渐上升,在16:00达高峰,之后开始下降。‘富士’的访问虫量在开始阶段少于‘金冠’,随后持续上升,到12:00时达到高峰,对‘富士’的访问量在白天都保持一个较高的水平,至17:00 开始下降。3 种苹果合计结果看,室内条件下橘小实蝇成虫对苹果的访问量在12:00、15:00和17:00各有1个高峰。但是,对于不同品种,访问量的变化规律不同,出现的高峰期也不一致,表明品种之间存在竞争。进一步比较橘小实蝇对3种苹果的选择几率,总选择几率以‘富士’最高,为50%,其次是‘金冠’,对‘新红星’的选择几率最低,仅为21.8%,远低于理论平均数33.3%。

图1 不同品种每个时间访问量动态变化
Fig.1 Dynamic changes of visits for different varieties

通过差异显著性分析,发现橘小实蝇对3 种苹果的全天访问总量存在显著差异(F=5.927,p <0.05)。其中,对‘富士’的全天访问总量显著高于其他2 个品种,全天访问总量为59.83 次,是‘金冠’访问量的1.77 倍,‘新红星’的2.29 倍。橘小实蝇成虫‘金冠’和‘新红星’的全天访问次数分别为33.75、26.08 次,对‘金冠’的访问量高于‘新红星’,但差异不显著(图2)。

图2 不同品种单个果实全天访问总量
Fig.2 Total daily visits for different varieties

表1结果表明,橘小实蝇对3种苹果的访问量与其单果内的幼虫数量呈显著正相关,与产卵孔数、单孔产卵数、百克果肉幼虫数和单头幼虫体重的相关性不显著。说明,雌虫访问果实的主要目的是寻找产卵场所和繁育后代。

表1 橘小实蝇雌成虫访问量与幼虫数量和果实品质的相关性
Table 1 Correlation between visits and larval numbers,fruit quality

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橘小实蝇对不同苹果的访问量与其果肉硬度、含水量呈显著正相关,与可溶性固形物含量呈显著负相关,与其他果实品质的相关性不显著。说明部分果实品质会影响橘小实蝇成虫的趋性。

2.2 橘小实蝇对不同苹果品种的产卵选择

图3表明,橘小实蝇在3种苹果内的幼虫数量由多至少依次为‘金冠’>‘富士’>‘新红星’,虫量分别为148.83、123.33、90.00 头·果-1。‘新红星’果内发育长大的幼虫平均体质量最高,为12.21 mg·头-1,‘金冠’的幼虫体质量略高于‘富士’,‘金冠’和‘富士’果内幼虫平均体质量分别为11.8、10.9 mg·头-1。3 个苹果品种间,其平均单果幼虫量及虫体重没有显著差异(F=1.197,p =0.365>0.05)(F=0.862,p =0.469>0.05)。

图3 在苹果不同品种果实中的产卵情况
Fig.3 Oviposition of different apple varieties

橘小实蝇在这3 种苹果上的产卵孔数、每孔产卵数和百克果肉虫数有显著差异(F=28.609,p <0.05)(F=5.113,p <0.05)(F=12.414,p <0.05)(表2)。其中,‘金冠’上的产卵孔数量显著高于其他两个品种,为12.17 孔·果-1,是‘富士’的1.92 倍,‘新红星’的5.61倍。‘富士’果上产卵孔数量显著高于‘新红星’,为6.33孔·果-1,‘新红星’为2.17孔·果-1

表2 产卵情况与幼虫的相关性
Table 2 Correlation between oviposition and larvae

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橘小实蝇在‘新红星’上的单孔产卵数显著高于另外两个品种,为48.65粒·孔-1,是‘富士’的2.42倍,‘金冠’的3.96倍。‘富士’和‘金冠’的平均单孔产卵数分别为20.08、12.28 粒·孔-1,差异不显著。

3种苹果的百克果肉虫数高低依次为‘金冠’>‘富士’>‘新红星’,分别为61.58、46.68、29.33 头,‘金冠’和‘富士’的百克果肉虫数显著高于‘新红星’的。

由表2 可知,橘小实蝇在不同品种苹果上的单果幼虫数与百克果肉虫数呈显著正相关,与幼虫体重为显著负相关,说明多虫量共食一果必须有足量的果肉营养供给。不同品种上的产卵孔数与产单孔卵数呈显著负相关,与百克果肉虫数呈极显著正相关。

统计结果(表3)表明,橘小实蝇在苹果上的产卵孔数与其果肉淀粉含量存在显著正相关性,单孔卵数与可滴定酸含量呈显著负相关,其他产卵指标与果实品质的相关性不显著。幼虫体重与含水量成负相关,关联度较高。

表3 产卵情况与果实品质的相关性
Table 3 Correlation between oviposition and fruit quality

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2.3 橘小实蝇产卵器形态特征

产卵器是雌性成虫的外生殖器,实蝇类的产卵器属于伪产卵器,并非由附肢特化而成,而是腹部末端的几个体节逐渐变细并套接在一起,形成可以伸缩的产卵结构[6]

橘小实蝇产卵器自然状态下与腹部等长,产卵管回收进产卵器基节内,仅露出针突部分。从扫描电镜照片看,产卵器基节表面密被细毛,背腹扁平,向外端部渐尖细,类似漏斗状。产卵管尖端呈圆钝状,针突部分的上部宽度为40.12 μm,最尖端宽度小于11.05 μm(图4)。

图4 橘小实蝇产卵器宽度测定
Fig.4 Measurement of ovipositor width of Bactrocera dorsalis

产卵器上的感受器主要有3种(图5),分别为毛形感受器4(ST4)、毛形感受器5(ST5)和钟形感受器(CA)。ST4 主要分布在橘小实蝇产卵器的基节部分,具备一般毛形感受器的结构,顶端尖细。ST5主要分布在产卵管的针突部分,分为长形和短形两类,表面光滑,顶端尖细。CA外部形态如球状突出,凹陷在窝中,分布在产卵管针突部分[7]

图5 橘小实蝇雌成虫产卵器扫描电子显微镜
Fig.5 Scanning electron microscope picture of ovipositor of Bactrocera dorsalis

室内观察发现,橘小实蝇在产卵之前,会用产卵器轻轻“敲击”果实表面,在这个“敲击”的过程中,其上着生的感受器可以感知来自于寄主的气味、表皮结构、果肉硬度等。橘小实蝇产卵器上的毛形和钟形感受器在其接触寄主过程中可能是化学信息物质的接受者,也可能是产卵位置的丈量者,均有助于雌虫寻找到适宜的产卵场所。

2.4 不同苹果果皮显微结构比较

在扫描电镜下观察发现,‘新红星’果皮表面最为紧密,缝隙和皮孔稀少;‘富士’和‘金冠’的果皮表面有很多小裂缝,没有完整的皮孔(图6)。统计分析结果表明,不同苹果品种之间,它们的果皮表面的裂缝长度、宽度和蜡质层厚度均存在显著差异(F=358.459,p <0.05)(F=293.676,p <0.05)(F=164.215,p <0.05)。通过测量发现,‘金冠’果皮表面平均裂缝长度为100.07 μm,宽度为29.91 μm,蜡质层厚度为23.27 μm;‘富士’果皮表面裂缝平均长度为102.48 μm,宽度为22.05 μm,蜡质层厚度为14.99 μm;‘新红星’果皮表面裂缝平均长度为35.60 μm,宽度为7.12 μm,蜡质层厚度为16.8 μm。因此,‘金冠’和‘富士’的裂缝长度显著高于‘新红星’,且‘金冠’的裂缝宽度和蜡质层厚度都显著高于其他两品种;‘富士’的裂缝宽度显著高于‘新红星’,但蜡质层厚度显著低于‘新红星’(图7)。说明果面裂缝太多时,会把皮孔破坏,形成纵横交叉裂缝,更适合橘小实蝇产卵器刺入。

图6 不同品种苹果果皮扫描电子显微镜
Fig.6 Scanning electron microscope photographs of different apple varieties

A.金冠;B.富士;C.新红星。下同。
A.Golden Delicious;B.Fuji;C.Starkrimson.The same below.

图7 不同品种苹果果皮比较
Fig.7 Comparison of skin of different apple varieties

从果皮石蜡切片照片(图8)可以看出,3种苹果外果皮结构比较完整,细胞排列清晰,细胞层数从多到少依次是‘新红星’>‘富士’>‘金冠’,蜡质层厚度从厚到薄依次是‘金冠’>‘新红星’>‘富士’。‘新红星’果皮的最外层细胞排列紧密、间隙少,细胞形态规整;‘富士’果皮细胞排列比较整齐、紧密;‘金冠’果皮外层细胞排列较为松散,形状不规则,因部分细胞凋亡出现间隙,进而导致果面产生较大裂缝。

图8 不同品种苹果果皮石蜡切片
Fig.8 Paraffin section photographs of different apple varieties

通过关联度分析(表4),橘小实蝇单果幼虫数、虫体重与果皮性质相关性不显著,但产卵孔数与裂缝长度、宽度和蜡质层厚度呈显著正相关,与细胞层数为极显著负相关。单孔卵数与裂缝长度呈显著负相关,与裂缝宽度呈极显著负相关,与细胞层数呈显著正相关。百克果肉虫数与裂缝长度和宽度均是极显著正相关,与细胞层数为极显著负相关。进一步说明,果皮结构影响橘小实蝇产卵。

表4 橘小实蝇在不同品种苹果的产卵情况与苹果果皮相关性
Table 4 Correlation between spawning behavior and skin of different apple varieties

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3 讨 论

昆虫选择寄主产卵是一个复杂过程,影响产卵的因素更是多种。已有研究表明,昆虫对寄主植物的产卵选择与寄主植物的种类、颜色、品种、成熟度等因素密切相关[8-10],且寄主体内的营养物质和次生化合物,可以直接或者间接影响昆虫的产卵选择性以及昆虫种群的生长动态[11],另外寄主植物体内的可溶性糖、蛋白质、氨基酸等物质都可以影响昆虫产卵选择性[12-13]。例如,橘小实蝇在切块甜橙果实上的产卵量大于在完整甜橙果实上的产卵量[14]。梨小食心虫对寄主的选择性与寄主体内蛋白质、游离氨基酸、可溶性糖和类黄酮等营养物质有关,蛋白质可对梨小食心虫产卵起到明显的抑制作用[15-16]

橘小实蝇的寄主多达250 余种果蔬,寄主种类之间对橘小实蝇的吸引力有显著差异,水果的气味、颜色和形态结构等因素也会影响橘小实蝇对寄主取食和产卵的选择性[17],该虫还具有对寄主果实的选择和嗅觉学习行为[18-19]。由于瓜果品种之间的外形和内含物质都存在很大差异,研究昆虫的产卵选择性主要是针对昆虫对不同寄主产卵的选择[20-21] ,以及对同一寄主的不同品种间的产卵选择[22]。苹果是国内生产的重要水果,也是橘小实蝇的寄主之一,随着南虫北移,必将存在很大受害风险。本研究表明,橘小实蝇对主栽苹果品种‘富士’‘金冠’‘新红星’均可为害,其危害程度与3 个品种的果实外观和内在品质有关,预示三者遭受橘小实蝇侵害的风险程度存在差异。

果实气味、颜色是影响橘小实蝇对寄主取食和产卵的第一步选择[23],因为气味和颜色可以让昆虫远距离感知,吸引昆虫靠近。从橘小实蝇雌成虫日间对3 种苹果的访问量次序看,首先访问了黄色的‘金冠’,其次是访问粉红色的‘富士’,最后是紫红色的‘新红星’。之后,随着访问时间延长,一些橘小实蝇成虫逐渐由‘金冠’转移到‘富士’果上。由此推测,橘小实蝇先通过视觉选择寄主,然后再通过嗅觉选择寄主,对黄色的趋性大于红色和紫色,这与任荔荔等[12]的研究结果一致。苹果气味物质很多,这些挥发性物质又与果实内的物质种类和含量有关,至于受何种物质影响,尚待进一步探究。

当橘小实蝇雌虫落在寄主表面进行产卵活动时,雌虫会通过腹部上下移动与产卵管反复伸缩相结合的方式“敲击”果面,寻找适合产卵器刺入的位置,然后插入果皮内产卵。所以,果皮表面结构及果皮细胞间隙均对橘小实蝇的产卵产生很大影响,果面有裂缝和裂缝较大均有利于产卵管固定和插入。本研究发现,‘富士’和‘金冠’表面裂缝数量和大小均显著高于‘新红星’,并且多数裂缝的长度、宽度大于橘小实蝇产卵管的宽度,果皮细胞层薄等因素,导致雌虫喜欢在这两种果实上停留和产卵。果皮属于果实的保护层,由蜡质层和果皮细胞构成。果面裂缝的形成源于蜡质层破损和果皮细胞凋亡,凡是容易出现裂纹的苹果品种可能更适合橘小实蝇侵害。在供试的苹果中,‘金冠’和‘富士’果面的裂纹都比较多,实际被访问次数和产卵量也多,故其受害风险程度显著高于‘新红星’。

同时,昆虫对寄主植物的选择也包括为后代生长发育的选择[24]。本研究也发现,苹果内淀粉含量较高时有利橘小实蝇产卵和幼虫发育,表明适宜淀粉含量可为幼虫的生长发育提供充足营养。苹果的可滴定酸含量与幼虫数量呈显著负相关。一般情况下,苹果随着成熟度提高,可滴定酸含量逐渐降低,故橘小实蝇喜欢为害成熟期苹果。所以,橘小实蝇在选择寄主时兼顾了当代的产卵难易和后代的发育,这就是它在寄主表面长时间爬行和产卵器敲打的原因之一。

4 结 论

橘小实蝇产卵器细长,通过刺破果皮插入果肉内产卵。成虫选择苹果的产卵时间和位置会受到果实颜色、形状、果皮结构、成熟度、内含物质等多因素影响,充分发挥视觉、嗅觉、触觉系统的联动作用。对于苹果,橘小实蝇喜欢果皮薄、有裂纹的果实大于皮厚无缝果,在果肉硬度较低、淀粉和可滴定酸含量适中,最有利于幼虫生长发育。

根据研究结果推测,一旦橘小实蝇侵入长江以北和定殖后,会对苹果生产形成严重威胁,其中栽植面积最大的‘富士’苹果受害风险程度最高,必须严加防控。加强检疫监测,控制该虫侵入苹果主产区。对于橘小实蝇发生区域种植的苹果,实施果实套袋和理化诱控,在果实成熟期的脱袋前后,应及时喷洒低毒、低残留农药灭杀成虫,控制其产卵到果实上,影响果品产量、品质和对外贸易。

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Risk evaluation of three apple cultivars affected by Bactrocera dorsalis

GUO Tengda1,2,JIANG Lili1,SUN Ruihong1*,GONG Qingtao1,YE Baohua2*

(1Shandong Institute of Pomology,Taian 271000,Shandong,China;2Shandong Agriculture University,Taian 271000,Shandong,China)

Abstract:【Objective】In order to evaluate the risk of Bactrocera dorsalis to apples and to provide a reference for the early warning and control scheme of apple production,the oviposition behavior of B.dorsalis on apples was studied.The correlation between larval development and fruit quality,the suitability of ovipositor and pericarp structure of three main apple varieties,‘Fuji’,‘Starkrimson’and‘Golden Delicious’were observed.【Methods】Four fruits of each variety were placed in the same cage, and marked on their petioles.Among them, two fruit stalks were upward and two downward.The distances among fruits were more than 5 cm.All fruits were weighed in advance.100 healthy female adults of B.dorsalis were put in the cage at 09:00.And the number of adults on the fruits was recorded per hour.The numbers of spawning holes on each fruit were recorded 24h later.Then,the fruits were put in an artificial climate box for observing the larva hatching and development, under the condition of(25.0±0.5)℃,with 60%-70%RH,and at 16 L:8 D.The numbers of larvae were recorded at 3 instars,and 12 mature larvae were weighed randomly.Then the microstructure and surface of fruit skin were observed under an electron microscopy, and the ovipositor of adult B. dorsalis was observed under a scanning electron microscopy.【Results】Under indoor conditions, the female adults of B. dorsalis exhibited two visiting peaks on fruits,both at noon and afternoon during the day.For different apple varieties,the visiting patterns were different.Further comparing the female selection probability on three apple varieties by B.dorsalis,‘Fuji’was the highest, accounting for 50%, followed by‘Golden Delicious’, and‘Starkrimson’was the lowest, only accounting for 21.8%, far below the theoretical average of 33.3%.Visit volume was significantly positively correlated with the number of larvae in single fruit,flesh firmness and water content,indicating that some fruit quality would affect the attacking tendency by B.dor-salis adults.The number of B.dorsalis larvae in three apple varieties was in descending order:‘Golden Delicious’>‘Fuji’>‘Starkrimson’. There were significant differences among the number of spawning holes, the number of spawning per hole and the number of larvae in 100g pulp for three varieties,the number of spawning holes was in descending order:‘Golden Delicious’>‘Fuji’>‘Starkrimson’,the number of spawning per hole was in descending order:‘Starkrimson’>Fuji >‘Golden Delicious’,and the number of larvae in 100 g pulp was in descending order:‘Golden Delicious’>‘Fuji’>‘Starkrimson’.There was a significantly negative correlation between the number of single fruit larvae and the weight of larvae on different apple varieties, which indicated that the nutrition supply of fruit was insufficient when the number of larvae was too large.There was a significantly positive correlation between the number of spawning holes and the content of starch, and a significantly negative correlation between the number of spawning per holes and titratable acid content.Larval weight was negatively correlated with water content,and the correlation degree was higher.There were significant differences in crack length, width and waxy layer thickness on the skin surface among different apple varieties.The crack lengths of‘Golden Delicious’and‘Fuji’were significantly higher than those of‘Starkrimson’,and the crack width and wax layer thickness of‘Golden Delicious’were significantly higher than those of two other varieties. In the microscopic state, the surface of‘Starkrimson’skin was the most compact,almost no gaps could be seen,and the skin holes on the surface were scarce.The ovipositor of B.dorsalis was the most likely to enter the flesh through the surface cracks of‘Golden Delicious’,followed by‘Fuji’.It is difficult to find the position of spawning on‘Starkrimson’because of its few and thin cracks.The number of spawning holes was positively correlated with crack length,width and waxy layer thickness, and negatively correlated with the number of cell layers. It was further demonstrated that the skin structure could affect the oviposition of B.dorsalis.【Conclusion】The ovipositor of B.dorsalis was slender and inserted into the flesh to lay eggs. The oviposition time and position of adult on apple fruit would be affected by many factors, such as fruit color, shape, pericarp structure, maturity,and starch contents, etc., which can give full play to the interaction of vision, smell and touch system.For apples,B.dorsalis preferred the fruit with thin and cracked skin than the fruit with thick and seamless skin. It is most beneficial for larval growth and development when flesh hardness was low and starch and titratable acid contents were moderate.According to the results,once the B.dorsalis invaded and colonized to the north of the Yangtze River,it would cause a serious threat to apple,especially‘Fuji’,which had the largest planting area,and must be strictly controlled.Strengthening quarantine monitoring, implementing fruit bagging and physicochemical trapping were necessary. In the attacking area by B. dorsalis, appropriate pesticides must be applied before and after bagging of‘Fuji’to prevent B.dorsalis adults from laying eggs on fruits,which would affect fruit yield,quality and marketing.

Key words:Apple;Bactrocera dorsalis;Oviposition selection;Risk assessment;Ovipositor

中图分类号S661.1

文献标志码:A

文章编号:1009-9980(2021)02-0231-11

DOI:10.13925/j.cnki.gsxb.20200387

收稿日期:2020-09-11接受日期:2020-11-09

基金项目:山东省重点研发计划(2017GNC13101)

作者简介:郭腾达,男,硕士,主要从事果树昆虫研究。Tel:17569611415,E-mail:kobe7911@126.com

*通信作者Author for correspondence.Tel:13793805182,E-mail:1366847074@qq.com;Tel:0538-8266607,E-mail:srhruihong@126.com