人工释放赤眼蜂对棉铃虫的防治作用及相关生态效应

1998～2000年在河北省南皮县棉区转Bt基因棉田及常规棉田中设置4种不同的组合处理,通过释放螟黄赤眼蜂控制棉铃虫的方法,减少化学农药的使用,达到提升和增强自然生物控制力的生态效应;并以不采取任何防治措施的常规棉田为常规棉对照田。研究表明：（1）转基因棉和常规棉棉田中自然寄生率随棉铃虫世代的增加而逐渐升高,2、3和4代棉铃虫卵被寄生率范围分别为13.3%～14.3%、26.7%～28.2%和60.8%～61.4%。（2）棉铃虫2代期,在常规棉综防田释放赤眼蜂2次,其寄生率为46.4%, 比未释放赤眼蜂的转基因棉棉田和常规棉对照田提高33.1%和32.1%; 3代期,转基因棉棉田释放赤眼蜂1次,其寄生率与常规棉综防田释放4次的效果相当,分别为73.7%和68.1%;但与转基因棉不放蜂田、常规棉化防田及对照田相比,分别提高45.5%、61. 8%和47.0%;4代期,无论放蜂与否,各处理棉田中的寄生率除化防田外（52.1%）均在60%以上。（3）常规棉化防田棉铃虫2代和3代期,分别使用农药2和3次,其自然寄生率分别为5.5%和11.9%,与对照田相比,分别降低8.8%和14.8%;与常规棉综防田相比,分别降低40.9%和56.2%;释放赤眼蜂的效果与施药时间有关,放蜂后1天内施药,寄生率仅为12.5%,施药后2天放蜂,寄生率达45.6%。（4）转基因棉棉田棉铃虫累计数和百株蕾铃被害数比常规棉综防田分别减少74.8%和73.8%,捕食性天敌增加63.0%;放蜂Bt棉田比不放蜂Bt棉田棉铃虫累计数、百株蕾铃被害数分别减少61.8%和33.3%;常规棉综防田棉铃虫累计数、百株蕾铃被害数、农药使用量比化防棉田分别减少29.7%、43.4%和60.0%,捕食性天敌数量增加63.0%。（5）转基因棉田和综防棉田的益害比（捕食性天敌/植食性害虫）分别为0.47∶1和0.30∶1, 而化防棉田为0.24∶1。上述结果表明释放赤眼蜂可弥补抗虫棉后期抗性减弱的不足,增加田间自然天敌的数量,提高对棉田害虫的自然控害功能。     

转Bt基因棉对非靶标害虫及害虫天敌种群动态的影响

2000～2001年,在湖北棉区系统研究了转Bt基因棉对棉田非靶标害虫及天敌种群动态的影响。试验设三个处理：转Bt化防田（使用化学农药控制害虫）、转Bt自控田（仅依靠田间自然天敌控制害虫）及常规对照棉田（利用综合防治措施控制害虫）。结果表明,在转Bt基因棉田中,除棉蓟马外,其它主要非靶标害虫（主要是刺吸性害虫）的种群发生数量呈明显的上升趋势。2000年棉蚜发生的总计值,化防田和自控田分别比常规对照田增加37.9%和71.4%,2001年则分别增加92.5%和134.9%;2000年朱砂叶螨发生的总计值,化防田和自控田分别比常规对照田增加181.1%和298.3%,2001年则分别增加69.9%和105.0%;转Bt基因棉对于斜纹夜蛾与烟粉虱这两种近几年来对棉花危害有加重趋势的害虫,在大田中没有表现出抗性。天敌的发生种类和数量也都远远高于常规对照棉田,几种主要天敌种群发生的总计值及高峰值都明显高于常规对照棉田。2000年蜘蛛类发生的总计值,化防田和自控田分别比常规对照田增加66.3%和112.1%,2001年则分别增加95.1%和111.7%;2000年龟纹瓢虫发生的总计值,化防田和自控田分别比常规对照田增加140.8%和135.4%,2001年则分别增加67.2%和109.5%;2000年在两块转Bt基因棉田中种群数量较大的大眼蝉长蝽在常规对照棉田的调查过程中没有发现,2001年在对照田中也仅记录到1头。试验表明,充分利用Bt棉田中天敌种类较丰富、种群数量较大的优势而加强生物防治,是湖北棉区转Bt基因棉田综防体系中的一个关键措施。     

不同类型棉田棉铃虫天敌功能团的组成及时空动态

比较分析Bt基因棉棉田、常规棉综防棉田棉玲虫天敌功能团的组成、数量、时空和多样性的发生动态。主要结果为：Bt棉田比常规棉综防棉田和化防棉田天敌种类分别增加16.3%和54.1%;百株累计捕食性在敌数量分别增加52.8%和176.3%,棉铃虫幼虫寄生蜂数量分别降低42.9%和52.9%;天敌功能团多样性分别增加10.1%和24.1%。常规棉棉田二代、三代棉铃虫幼虫寄生率分别为11.1%－65.0%和4.1%-66.2%,Bt棉田为0.0%-5.0％。就不同类型天敌功能团来说,Bt棉田瓢虫和草蛉的数量比综防棉田分别减少8.4%和5.8%,比化防棉田分别增加34.1%和206.3%;Bt棉田食虫蝽和蜘蛛的数量比综防棉田分别增加180.6%和71.2%,比化防棉田分别增加329.1%和483.7%。棉铃虫捕食性天敌空间生态位发生动态在各类棉田相似。分析认为：Bt棉田有利于保护瓢虫和草蛉,有利于食虫蝽类和蜘蛛类天敌的增殖;Bt棉田棉铃虫天敌群落依次比常规棉综防棉田和化防棉田稳定。不同时期、不同类型棉田的棉铃虫天敌功能团数量和所起的作用不同。6月下旬棉铃虫捕食性天敌控制作用存在“空缺”,7月下旬化防棉田出现天敌控制“空缺”。不同时期捕食性天敌功能团恢复能力有差异。6月底－7月初天敌恢复能力最强,7月下旬,天敌恢复能力最弱。天敌功能团中,瓢虫恢复能力最强,食虫蝽类和蜘蛛类天敌次之。     

转Bt基因棉田节肢动物群落营养层及优势功能团的组成与变化

1998年在河北南皮棉区转Bt基因棉棉田和常规棉综防田的生物群落变化的研究表明,与常规棉综防田相比,转Bt基因棉棉田的节肢动物种类增加30.7%,功能团多样性增加66.9%,天敌类和中性节肢动物类的丰富度分别增加97.6%和158.0%,害虫类的丰富度减少45.7%。就功能团的种群数量来看,主要害虫棉铃虫、蚜虫和蓟马种群数量分别减少98.9%、69.0%和72.6%;而次要害虫害蝽、粉虱、叶蝉类昆虫的种群数量分别增加了2.2、3.2和14.8倍,棉花生长中期,转Bt基因棉棉田中的基位物种丰富度大于中位和顶位物种;常规棉田中的差异则更大,出现天敌控制“空缺”。综合分析表明,转Bt基因棉棉田生态系统比常规棉综防田稳定;转Bt基因棉棉田的中性节肢动物和次要害虫在害虫－天敌的营养链中起到了重要的调控作用。     

棉花叶螨对三氯杀螨醇和氧乐果的抗性动态

对棉花叶螨（优势种朱砂叶螨）抗三氯杀螨醇和氧乐果的系统监测表明,棉田化防前期是当年棉花叶螨抗性最低点,大面积化防后抗性水平明显上升。化防停止后至下年春季,抗性呈下降趋势,反映在系统监测动态上,棉花叶螨抗性水平曲折性上升。对三氯杀螨醇和氧乐果的抗性分别由1986年的5．28～6．65倍和9．24～11．26倍上升到1992年的8．55～15．57倍和19．23～28．48倍。     

转Bt基因棉和转Bt+CpTI双价基因棉对棉田主要害虫及其天敌种群动态的 影响

2002年4～10月,在北京西北旺中国农科院实验园区系统研究了单价转基因棉GK321（CryIAc）和双价转基因棉SGK321CryIAc+CpTI）对棉田主要害虫及其天敌种群动态的影响。试验设三种处理：单价转基因棉田（单价棉田）、双价转基因棉田（双价棉田）和常规对照棉(石远321)田（常规棉田）。在棉花的整个生育期系统调查棉田主要害虫及其天敌的种群数量。结果表明,单、双价棉田棉铃虫的发生数量都显著低于常规棉田;双价棉抗虫性在棉铃虫第2代发生期和单价棉无差异,但第3代发生期双价棉田内棉铃虫幼虫百株累计量比单价棉田减少了36.6%,抗虫性明显优于单价转基因棉。两种转基因棉田内非靶标害虫的发生量明显高于对照棉田的发生量,每种非靶标害虫在双价棉田和单价棉田发生数量多少因种类而异。双价棉田和单价棉田相比,棉蚜、棉叶蝉和棉粉虱的累计发生数量分别减少了33.0%、50.6%和22.7%,前两种差异极显著,后一种差异不显著;棉蓟马和绿盲蝽分别增加了208.9%和18.4%,前者差异显著,后者差异不显著。大多数天敌（包括捕食性和寄生性）在转基因棉田内发生数量显著低于常规棉田的发生数量。双价棉田内的龟纹瓢虫、棉蚜茧蜂和卵形异绒螨比单价棉田分别减少30.4%、42.8%和46.8%,差异均显著;草蛉卵和蜘蛛比单价棉田分别减少20.0%和27.4%,但差异不显著;双价棉田内的中华草蛉和小花蝽分别比单价棉田增加了27.0%和8.9%,前者差异显著,后者差异不显著。所以,单、双价转基因棉相比,对不同天敌的影响差异较大。     

湖北棉区转Bt基因棉对棉铃虫的控制作用

2000-2001年通过田间系统调查,表明转Bt基因棉（品种为GK19）在湖北江汉平原棉区对棉铃虫抗性稳定。试验设3个处理：转Bt基因棉化防田（使用化学农药控制害虫）、转Bt基因棉自控田（依靠天敌控制害虫）及常规棉对照田（利用综合防治措施控制害虫）。从棉铃虫的第2代到第5代整个发生期内,即使在不进行化学防治的情况下,棉铃虫在Bt棉田的发生量也保持在极低的水平(最高百株虫量为12头)。室内饲养结果表明,转Bt基因棉对棉铃虫的生长发育（幼虫体重、蛹重）有较为明显的影响,使6龄幼虫体重减少25.6%,蛹重减少18.2%。棉铃虫幼虫取食转Bt基因棉组织后,发育迟缓,相对于常规棉喂养的整个发育历期延长17 d,使棉铃虫在田间的危害减少至少一个世代。另外,接虫试验表明,棉铃虫幼虫在常规棉上的取食时间是转Bt基因棉株上的6.1倍,极大地减轻了棉铃虫的危害程度。     

转基因棉对土耳其斯坦叶螨生命参数的影响

为了研究转基因棉花对北疆叶螨优势种土耳其斯坦叶螨Tetranychus turkestani(Ugarov et Nikolskii)种群生命参数的影响,本实验以常规棉中棉49作为对照,构建了叶螨在单价转基因棉新棉33B(Bt)、双价转基因棉中棉41(Bt+CpTI)上的室内种群生命表。结果表明,单双价转基因棉对叶螨的生长发育历期及生殖参数并没有明显影响;且取食常规棉的叶螨种群参数净生殖率、内禀增长率、平均世代周期、种群加倍时间、周限增长率、存活曲线也与单双价棉无显著差异,这说明转基因棉对棉叶螨的生长发育、繁殖及种群增长并无显著影响。     

边缘效应对棉田害虫和天敌种群的影响

比较了棉田中间棉株与边缘棉株上害虫、天敌的种群动态,分析了边缘效应对棉株-害虫-天敌能量动态的影响。结果表明,棉田边缘棉株上第2代棉铃虫幼虫发生量比其中间棉株高出1．94倍;第3代棉铃虫发生量比棉田中间要低62．12％;第4代棉铃虫比中间棉株高12．5％。棉田边缘棉株上苗蚜发生量比棉田中间要高出1．09倍,伏蚜和秋蚜的数量比棉田中间分别低97．73％和37．70％。棉田边缘棉株上捕食性瓢虫、蝽类、蜘蛛和寄生性天敌的种群数量低于棉田中间的数量,分别为棉田中间的73．81％、35．79％、52．90％和39．11％;棉田边缘棉株上害虫群落多样性高于棉田中间,而天敌群落的多样性低于棉田中间;棉田边缘的光能利用率和生产力比棉田中间的值要高。     

转Bt基因抗虫棉田棉铃虫消长规律及危害特点

通过对转 Bt基因抗虫棉田棉铃虫的系统调查研究表明 :(1)转 Bt基因抗虫棉对棉铃虫蛾、卵无抗性表现 ,田间落卵量与常规棉田无明显差异 ,相反 ,二代棉铃虫百株累计卵量倒比常规棉处理区增加了 2 16～ 2 74粒 ,增长幅度为 30 %～ 38% ;(2 )转 Bt基因抗虫棉对二代棉铃虫幼虫的抗性及控制作用较强 ,基本不用进行药剂防治 ,但对三代棉虫幼虫的抗性控制效果明显下降 ,田间 3龄以上幼虫平均达2 0～ 4 0头 /百株 ,多者达 6 0头以上 ,仍需进行必要的药剂防治 ;(3)棉铃虫在转 Bt基因抗虫棉株上的危害特点与常规棉株有明显的差异 ,表现在幼虫和危害症状均较隐蔽 ,不易被发现。     

Positive association between thrips and spider mites in seedling cotton

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Impact of transgenic Bacillus thuringiensis cotton on a non-target pest Tetranychus spp. in northern China

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With the wide adoption of transgenic Bacillus thuringiensis (Bt) cotton, the incidence of bollworm has reduced significantly, but secondary pests such as cotton spider mites have become serious problems in Bt cotton fields. The objective of the present study was to investigate the underlying mechanism of increased incidence of secondary pests in Bt cotton. Two transgenic cotton varieties, sGK321 and Bt-C12, and their non-transformed counterparts, SY321 and C12, were used to study differences in the incidence of spider mites in relation to secondary metabolites. Plants of each cotton cultivar were infested with five female adult spider mites and then isolated. Leaf samples with a pair of adult mites of the same age were transferred individually into Petri dishes for examination of egg laying and duration of development stages. The number of spider mites on Bt-C12 and sGK321 was more than that on C12 and SY321. The cotton spider mites feeding on Bt-C12 laid significantly more eggs than those feeding on C12; those feeding on sGK321 laid significantly more eggs than those feeding on SY321. The generation time of spider mites feeding on Bt-C12 was greatly reduced relative to those feeding on C12. Also, the generation time of mites feeding on sGK321 was shorter than those feeding on SY321. Gossypol and tannin contents in leaves of Bt-C12 were substantially lower than those in C12, and the contents in leaves of sGK321 were significantly lower than those in leaves of SY321. The occurrence of spider mites was more serious on Bt than non-Bt cotton, and the fitness of the mites on Bt cotton was higher than on non-Bt cotton. Reductions in gossypol and tannin contents in Bt cotton decreased the generation time and increased the number of eggs of cotton spider mites.     

From the laboratory to the field: contrasting effects of multi-trophic interactions and agroforestry management on coffee pest densities

Only few factors influencing pest populations can be studied in the laboratory, but many population‐driving factors interact in the field. Therefore, complementary laboratory and field approaches are required for reliable predictions of real‐world patterns and processes. Laboratory and field experiments with the red spider mite, Oligonychus ilicis McGregor (Acari: Tetranychidae), and the coffee leaf miner, Leucoptera coffeella Guérin‐Méneville (Lepidoptera: Lyonetiidae), on coffee plants, Coffea arabica L. (Rubiaceae), were combined to study the relative importance of biotic interactions, including resource preferences and natural‐enemy impact, and habitat factors, such as agroforestry type and management intensity, on coffee pest densities. In the laboratory, leaf discs cut from undamaged coffee plants were significantly preferred by red spider mites over those from plants infested with conspecific mites, leaf rust pathogens [Hemileia vastatrix Berkeley & Broome (Uredinales)], or coffee leaf miners, resulting in higher reproductive success. Similarly, undamaged plants were preferred by coffee leaf miners over red spider mite‐infested plants. However, in the field, red spider mite densities were positively correlated with coffee leaf miner and leaf rust densities, thereby contrasting with laboratory predictions. Hence, our study suggests that the importance of resource preferences and fitness expected based on laboratory experiments was suppressed by environmental conditions in the field, though other unassessed biotic interactions could also have played a role. Furthermore, intensified agroforestry was characterized by higher red spider mite densities, whereas densities of its major natural enemy, the predatory mite Amblyseius herbicolus Chant (Acari: Phytoseiidae), were not related to agroforestry management. Densities of coffee leaf miner and its main natural enemy, a eulophid parasitoid (Hymenoptera), were not affected by management practices. In conclusion, patterns found in the laboratory did not hold for the field, emphasizing the difficulties of extrapolating small‐scale experiments to larger spatial scales and the need to combine both approaches.     

Condensed tannins of cotton leaves

Some primitive races of cotton (Gossypium hirsutum) are almost immune to spider mites. These strains contain condensed tannins of about 20% of dry wt. The tannins accumulate in leaves and their concentration increases in successive leaves until about the 10th true leaf. The upper leaves maintain this quantity until early fall. The condensed tannins give a moderate astringency to the leaf, and are mixed polymers hydrolysing in acidic digests to 1 part cyanidin and 4 parts delphinidin.     

Induced resistance against spider mites in cotton: Field verification

Cotton plants that had been damaged by spider mites (Tetranychus spp.) or by mechanical abrasion at the cotyledon stage were less likely to develop infestations of spider mites compared to controls early in the season. These are the first field results to demonstrate that induced resistance can reduce pest populations in an agricultural system. Differences in mite populations early in the season caused by induced resistance did not translate into differences in plant growth or cotton yield at harvest.

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Vérification au champ de la résistance du coton induite par les acariens

Résumé Les plants de coton qui ont été endommagées, au stade cotylédons, par des acariens ou par une abrasion mécanique, ont moins de chance que les témoins, de présenter ultérieurement des dégats dus aux acariens. C'est la première fois que des résultats montrent qu'une résistance induite peut réduire les populations dans un agrosystème. Les différences ultérieures dans les populations d'acariens, ne transparaissent pas au niveau de la croissance du coton ou de la production au moment de la récolte.

     

Interactions in a tritrophic acarine predator-prey metapopulation system III: effects of Tetranychus urticae (Acari: Tetranychidae) on host plant condition

Spider mites are serious pests on many economically important plant species, because they may reduce plant productivity and, at high mite densities, overexploit and even kill the host plants. We have conducted a series of greenhouse experiments to quantify the effects of two-spotted spider mites (Tetranychus urticae) on host plants (Phaseolusvulgaris). The average amount of chlorophyll per cm² leaf area was used as a measure of plant condition. It was shown that chlorophyll concentration decreases with plant age and intensity of spider mite feeding. Damage caused by spider mites was assessed visually, using the Leaf Damage Index (LDI) defined by, and a mathematical relationship between the visual measurements and the amount of chlorophyll/cm² was fitted to data. The relationship may serve as a short-cut to estimate overall plant injury, expressed as the relative loss of chlorophyll/cm² leaf area caused by spider mites (D). D takes values between 0 (no injury) and 1 (all leaves dead). A highly significant positive relationship between the instantaneous spider mite density and D was found, even though D is expected to reflect the cumulated density of mites (mite-days). A model of plant growth incorporating information about plant age and D predicts that plant area has a maximum when plant age is about 60 days, and that plant area decreases exponentially with an increase in D. This revised version was published online in July 2006 with corrections to the Cover Date.     

Agroforestry management affects coffee pests contingent on season and developmental stage

1 Management of vegetational diversity in agroecosystems is a potentially regulating factor of pest population dynamics and may affect developmental stages in different ways.
2 We investigated the population dynamics of red spider mites, coffee leaf miners, and coffee berry borers in three management types of coffee agroforests: increasing plant diversity from a few shade tree species (simple-shade agroforests), intermediate-shade tree species (complex-shade agroforests) to high-shade tree species (abandoned coffee agroforests) in Ecuador. Furthermore, we studied how changes in agroforestry management affect population stage structure of each coffee pest.
3 Our results show that agroforestry management affected seasonal patterns of coffee pests in that higher densities of red spider mites were observed from August to December, coffee leaf miners from December to February, and coffee berry borers from May to July. Moreover, specific developmental stages of red spider mites, coffee leaf miners, and coffee berry borers differed in their responses to agroforestry management. During all stages, red spider mite reached higher densities in simple-shade agroforests compared with complex-shade and abandoned agroforests. Meanwhile, coffee leaf miner densities decreased from simple-shade to complex-shade and abandoned agroforests, but only for larvae, not pupae. Similarly, only coffee berry borer adults (but not eggs, larvae and pupae) demonstrated a response to agroforestry management. Environmental variables characterizing each agroforestry type proved to be important drivers of pest population densities in the field.
4 We emphasize the importance of considering seasonal differences and population structure while investigating arthropod responses to different habitat types because responses change with time and developmental stages.