江苏沿江棉区3代棉铃虫对棉花的为害及经济阈值

通过人工接虫为害,研究了3代棉铃虫对蕾铃脱落及结铃的影响,观察了不同年份棉铃虫卵和各龄幼虫的自然存活率及棉花蕾、幼铃的成铃率。结果表明,蕾铃的虫害脱落率对结铃的影响最大,直接通径系数达－0.8917,虫量和蕾铃脱落数主要通过接虫期间的虫害脱落率影响棉花结铃,其间接通径系数分别为－0.8894和-0.891,接虫期间的自然脱落率对结铃的直接和间接通径系数均很小,表明33代棉铃虫为害时棉花4的补偿能力已基本丧失,各龄幼虫的为害量观察表明,1－6龄幼虫的单虫为害当量分别为0.02、0.14、0.31、0.47、0.84和1.54个大铃,根据防治的直接和间接收益,得出3代棉铃虫的防治指标为百株累计卵量26粒。     

华北棉区棉铃虫种群动态与其为害特征分析

本文述及棉铃虫为害特性及其与为害后棉株的补偿作用关系。根据棉株生命表资料,蕾期棉株蕾花的脱落主要系由棉铃虫为害所致。而铃期蕾铃的脱落,则主要系由棉株的生理条件。在蕾期,前三周内蕾花被害脱落后,棉株的补偿作用是很高的,从第四周起补偿作用逐渐下降,而到铃期阶段时补偿作用降至很低水平。因此蕾期棉株遭受一定数量以内的棉铃虫为害,而使蕾花脱落后,反而可促使棉花增产。根据棉铃虫生命表资料,从卵期至三龄末幼虫期的累计死亡率占总死亡率的90%以上,结合幼虫死亡率与不同龄期为害水平分析,棉铃虫对棉株的主要为害阶段系在2—3龄期,其对果实的为害量占总为害的65%。而棉株被害蕾铃的田间空间分布型系遵从负二项分布,期公共K值为3.4626。     

叶型超补偿下棉花叶中保护酶活性的变化

研究了棉花在叶片损失后产生的超补偿现象和超补偿下棉叶中的保护酶活性的变化。在棉花盛蕾期,用剪刀剪除棉花标准叶面积的25%和50%,模拟田间害虫的食叶危害程度,结果显示：50%去叶处理可使棉花成铃数增加24.4%, 产生超补偿现象。25%去叶处理在短时间内对棉花的株高和叶中蛋白质含量都没有影响,植株株型亦无大的变化,表明25%叶面积属于生长冗余范畴。但25%去叶处理的植株叶中蛋白质含量最高点比对照推迟一周出现。50%去叶处理可增加单株棉花的冠叶面积,在处理后2周时使棉花株高减低14.5%,蛋白质含量增加7.7%,过氧化物酶活性增加14.1%。在处理后3天,不论是过氧化物酶比活力还是多酚氧化酶比活力,都是50%去叶处理的值较大。保护酶活性发生变化是棉花发生超补偿的前奏。而在处理后2周时过氧化物酶和多酚氧化酶的比活力,50%去叶处理的与对照最为接近,表明 50%去叶处理属于超补偿范畴。     

对于棉花早期蕾损失的补偿作用分析

1981—1984年在河北省饶阳县三种肥力水平地块上,以4个陆地棉Gossyium hirsutum L.品种为材料,进行了11次人工模拟第二代棉铃虫Heliothis armigera(Hübner)对棉蕾的为害试验,旨在确定受害株在繁殖器官水平上的补偿途径。每两天记录一次每处理各10株棉花各节位的发育状况。数据表明,每株去除8个左右的早期蕾的影响是:1)始花日推迟9.32天但不引起皮棉减产;2)有效花期缩短5.95天,这对产量有不利影响;3)现蕾总数(包括去除数)增加15.31％,合每株7.07个,这奠定了补偿的基础;4)开花速度加快17.21％,致使每株总花数比对照多0.43朵;5)幼铃脱落率降低9.85％;6)成铃数增加15.28％,合每株2.34个;7)果枝数、每铃籽棉重以及皮棉百分率都无显著变化。由此可以清楚看出,这些受害株能够基本上弥补损失的蕾数,同时开花速度显著加快,使得总花数略有增加,幼铃脱落率显著降低,结果成铃数显著增多。这些正作用的总效应远超出缩短有效花期造成的负作用。因此,遭受一定程度早期蕾损失的植株在一般情况下都能增产。这一认识动摇了华北棉区控制棉铃虫的通常对策,该对策把防治重点放在第二代上。     

华北棉区第二代棉铃虫的经济阈值

1980—1983年在河北省饶阳县及安徽省濉溪县的不同的土壤肥力类型、不同的棉花品种和不同的栽培管理条件下进行了模拟为害和自然为害的试验,旨在确定第二代棉铃虫Heliothis armigera(Hübner)数量与棉花Gossypium hirsutum L.产量和质量的关系。试验结果表明,棉花对于第二代棉铃虫为害的补偿力很强,这种补偿力随着土壤肥力的提高而增强。棉花品种、年份以及栽培管理方法对补偿力的影响属于次要。通过组建的一个静态模型,收进了二代棉铃虫防治的直接收益与代价以及间接收益与代价,算得高、低肥力地的第二代经济阈值,百株累计卵量分别为332粒和34粒。产量水平在80—90斤的中等偏低肥力地,其阈值可定为60粒。     

华北棉区第三代棉铃虫的经济阈值

1980—1982、1984—1985年在河北省饶阳县的不同土壤肥力水平、不同棉花品种上进行了模拟为害和自然为害试验,旨在确定第三代棉铃虫 Heliothis armigera(Hubner)虫口密度与棉花产量之间的关系.结果表明,棉花对于第三代棉铃虫为害的补偿能力较弱.较好的土壤肥力亦不能促使棉株完全补偿三代期间的受害损失.每亩皮棉减产斤数Y与第三代百株累计卵量E₃的关系为:Y=-0.2801+0.0643E₃.根据防治的直接收益与直接代价,算出了第三代棉铃虫的经济阈值为百株累计卵量35粒,这一阈值可适用于不同肥力水平的地块.     

氮肥对棉田主要害虫种群密度及棉花产量的影响

通过2年的田间研究,分析了3种不同施氮水平对棉花主要害虫棉玲虫、棉蚜种群动态、棉花蕾铃脱落及棉花产量的影响。结果表明,增施氮肥的棉田棉铃虫和棉蚜数量比对照田要高,但它们之间的差异没有达到显著的水平。不同年份对棉铃虫种群密度有显著影响,但对棉蚜种群没有显著影响。蕾花期施肥可减轻棉铃虫为害造成的花蕾脱落和自然脱落,增加有效铃数和产量,但增加量没有达到显著水平。     

我国主要类型昆虫对CO_2升高响应的研究进展

大气CO2浓度增加已经受到国内外的极大关注。自2002年以来,在自行设计、组装的一系列密闭式动态CO2气室和开顶式CO2浓度控制箱基础上,研究了我国主要类型昆虫对CO2浓度升高响应的特征。结果显示,大气CO2浓度升高降低了棉铃虫Helicoverpa armigera的适合度和对棉花的危害作用,增加了棉花对棉铃虫为害的补偿作用,使以咀嚼式口器昆虫为代表的棉铃虫种群发生与危害下降;但大气CO2浓度升高改变了植物组织营养物质的组成与含量,提高了蚜虫Aphis gosypii对氨基酸营养的利用与补偿效率,降低了3种麦蚜的种间竞争,导致蚜虫种群发生与危害严重;而对烟粉虱Bemisia tabaci的种群特征影响较少。大气CO2浓度升高对天敌昆虫的影响存在种的特异性,表现出种群上升、下降和变化不大等特征。未来大气CO2浓度升高下,由于作物生长发育加快,生物量增加,蚜虫种群增多,导致吡虫啉农药防治效果下降,由此未来大气CO2浓度升高下农民将被迫使用更多的化学农药防治蚜虫类害虫,进而加重环境污染。     

蕾铃期繁殖器官的损失对棉花产量的影响——人工模拟为害试验

1994、1995连续两年在华北棉区第3代棉铃虫发生期间,通过一系列人工摘蕾模拟为害和人工接虫为害试验,研究了棉花对蕾铃期繁殖器官损失的补偿效应。试验结果表明：蕾、铃被害会诱导棉株产生补偿效应,即提高结铃数,增加生物产量。但棉花的补偿效应是有限的,蕾铃期单株被害蕾超过12个,被害铃超过4个,或被害超过2蕾2铃,都会导致皮棉显著减产。通过数学模型分析,1994年,单株被害0-11．80个蕾或0—2．26个铃都不会造成减产;1995年．单株损失0—10．58个蕾或0—3．8个铃,同样不会降低棉花产量。模型中各决策变量的边际产量表明,棉花蕾铃期铃的损失对皮棉产量的影响最大。     

具有疾病的棉铃虫—棉花SIS模型分析

棉铃虫是棉花蕾铃期重要钻蛀性害虫,也是中国棉区蕾铃期害虫的优势种,近年为害十分猖獗,给棉花生产带来了巨大的损失.由于棉铃虫依附于棉花生长,所以研究棉花与棉铃虫之间的依存制约关系对棉铃虫的防治有着重要意义.本文研究易感棉铃虫、感染疾病的棉铃虫和棉花之间的关系,构建"棉铃虫—棉花"的具有疾病的SIS模型,研究了系统的正平衡点和基本再生数R_0,利用了Hurwitz定理证明了正平衡点处渐进稳定性,通过构造Liapunov函数和Dulac定理说明了正平衡点的全局稳定性.数值模拟的结果也说明了所得结论的合理性,同时得出了当R_0 1时,棉铃虫和棉花的数量达到平衡.     

Response of cotton to prebloom square loss

In 1996 and 1997, various intensities of prebloom square removal were applied to three cultivars of cotton grown in Mississippi. With the exception of one cultivar in 1997, all cultivars were B. thuringiensis (Bt)-transgenic cotton. At harvest, the number of bolls and seed cotton weight was recorded for all plants in each square removal treatment. All cultivars responded similarly to square loss. A yield increase (overcompensation) was observed in the treatment where all squares were removed from the plant one week after squaring began. Only the treatment where all squares were removed before bloom significantly reduced yield and caused a large (>7 d) delay in crop maturation. Otherwise, moderate levels of square removal (approximately 20-50% of prebloom squares) had little impact on overall lint production. However, the patterns of cotton production on the plants were significantly influenced by the square removal treatments. The removal of relatively more or larger squares increased seed cotton production in late-season fruiting cohorts and on 'vegetative' branches. Compensation for square loss occurred by increasing the relative number and weight of bolls produced subsequent to early-season square removal. Typically, early-season square loss increased the value of later-season fruiting cohorts, especially the midseason cohorts and bolls on vegetative branches. The implications of prebloom square loss, including the compensatory ability of the cotton plant, on insect management are discussed.     

Effects of kaolin particle film on oviposition,larval mining,and infestation of cotton by pink bollworm (Lepidoptera: Gelechiidae)

We tested effects of kaolin particle film on oviposition, larval mining, and infestation of cotton by pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), in the laboratory, greenhouse, and field. In laboratory choice tests, females laid seven times more eggs on untreated bolls than on bolls treated with kaolin. When neonates were put on bolls in the laboratory, each boll with a treated and untreated half, larvae and mines were found 24 h later on the untreated half but not on the treated half. In oviposition choice tests with whole plants in the greenhouse, females laid four times more eggs on untreated plants than on treated plants and the number of eggs on bolls was five times higher for untreated plants than for treated plants. Kaolin treatments altered the distribution of eggs among plant parts, with untreated bolls receiving a higher percentage than treated bolls, whereas the opposite occurred for petioles. In field tests, treatment with kaolin alone reduced the proportion of bolls infested with pink bollworm, but a mixture of kaolin and the pyrethroid lambda-cyhalothrin was most effective. The results suggest that kaolin particle film may be useful against pink bollworm, particularly in conjunction with other control tactics.     

Reducing boll weevil populations by clipping terminal buds and removing abscised fruiting bodies

Cotton pests damaging fruiting bodies (squares and young bolls) are difficult to control and their damage results in direct yield loss. Small growers, with low technological inputs, represent a large portion of cotton growers worldwide comprising more than 76 countries; they rely mainly on cultural practices to counteract pest attack in their crops. Boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), oviposition involves puncturing cotton squares and young bolls, causing abscission. We examined the impact on boll weevil population of collecting abscised cotton fruiting bodies and clipping plant terminals at 50% boll maturation in the field during two cotton‐growing seasons and under field cage conditions. Greatest numbers of damaged squares occurred ca. 117 days after planting and clipped plants resulted in reduction of abscised structures and adult boll weevils compared with non‐clipped plants, irrespective of cotton variety. Damaged young bolls were found ca. 128 days after planting in 2009 and 2011, but clipping had no effect. Numbers of boll weevils found in plants of the varieties BRS 201 and BRS Rubi (both in 2009) and BRS Rubi (in 2011) were, respectively, 13‐, 17‐, and 20‐fold greater when clipping plus collecting abscised fruiting bodies were not practiced. Furthermore, the average percentage of the boll weevil parasitoid Bracon vulgaris Ashmead (Hymenoptera: Braconidae) emerging from abscised and collected structures was similar between clipped and non‐clipped plant terminals in both seasons. Clipping plant terminals did not result in yield reduction and reduced adult boll weevil production. Collecting abscised reproductive structures, clipping plant terminals, and using both practices together reduced boll weevil populations by as much as 63, 57, and 79%, respectively, in cage trials. Thus, these practices cause significant impact on boll weevil populations and are feasible of adoption, especially for smallholder cotton growers.     

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。     

华北棉区第三代棉铃虫对棉花为害损失与经济阈值的研究

通过在华北棉区棉花蕾铃期阶段,连续５ａ的田间蕾铃脱落原因的观察,明确了在第三代棉铃虫的中常发生年份,影响蕾铃期蕾铃脱落的主要因素是棉株本身的自然脱落其脱落率占总脱落的９０％以上,而因第三代棉铃虫为害造成的脱落率在５％以上。根据田间棉铃虫Ｈｅｌｉｃｏｖｅｒｐａ ａｒｍｉｇｅｒａ（ｈｕｂｎｅｒ）３龄幼虫虫量与为害力的关系研究,结合多年第三代棉铃虫田间生命表,文中提出了三代棉铃虫的经济阈值为百株累计卵量     

A facultative mutualism between aphids and an invasive ant increases plant reproduction

1. The consequences to plants of ant–aphid mutualisms, particularly those involving invasive ants, are poorly studied. Ant–aphid mutualisms may increase or decrease plant fitness depending on the relative cost of herbivory by ant‐tended aphids versus the relative benefit of increased ant suppression of other (non‐aphid) herbivores. 2. We conducted field and greenhouse experiments in which we manipulated the presence and absence of cotton aphids (Aphis gossypii) on cotton plants to test the hypothesis that a mutualism between cotton aphids and an invasive ant, the red imported fire ant (Solenopsis invicta), benefits cotton plants by increasing fire ant suppression of caterpillars. We also manipulated caterpillar abundance to test whether the benefit of the mutualism varied with caterpillar density. 3. We found that more fire ants foraged on plants with cotton aphids than on plants without cotton aphids, which resulted in a significant reduction in caterpillar survival and caterpillar herbivory of leaves, flower buds, and bolls on plants with aphids. Consequently, cotton aphids indirectly increased cotton reproduction: plants with cotton aphids produced 16% more bolls, 25% more seeds, and 10% greater seedcotton mass than plants without aphids. The indirect benefit of cotton aphids, however, varied with caterpillar density: the number of bolls per plant at harvest was 32% greater on plants with aphids than on plants without aphids at high caterpillar density, versus just 3% greater at low caterpillar density. 4. Our results highlight the potential benefit to plants that host ant–hemipteran mutualisms and provide the first experimental evidence that the consequences to plants of an ant–aphid mutualism vary at different densities of non‐aphid herbivores.     

Relationships of abscised cotton fruit to boll weevil (Coleoptera: Curculionidae) feeding, oviposition, and development

Abscised cotton, Gossypium hirsutum L., fruit in field plots planted at different times were examined to assess adult boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), use of squares and bolls during 2002 and 2003 in the Lower Rio Grande Valley of Texas. Although boll abscission is not necessarily related to infestation, generally more bolls abscised than squares and abundances of fallen bolls were not related to the planting date treatments. During 2003, fallen squares were most abundant in the late-planted treatment. Although large squares (5.5-8-mm-diameter) on the plant are preferred for boll weevil oviposition, diameter of abscised squares is not a reliable measurement because of shrinkage resulting from desiccation and larval feeding. Fallen feeding-punctured squares and bolls were most abundant in late plantings but differences between fallen feeding-punctured squares versus fallen feeding-punctured bolls were found in only one treatment in 2003. During the same year, fallen oviposition-punctured squares were more numerous in the late-planted treatment than in the earlier treatments. Treatment effects were not found on numbers of oviposition-punctured bolls, but fallen oviposition-punctured squares were more common than bolls in the late-planted treatment compared with earlier treatments each year. Dead weevil eggs, larvae, and pupae inside fallen fruit were few and planting date treatment effects were not detected. Living third instars and pupae were more abundant in fallen squares of the late-planted treatment than in the earlier treatments and bolls of all three treatments. This study shows that fallen squares in late-planted cotton contribute more to adult boll weevil populations than bolls, or squares of earlier plantings.     

Influence of cotton fruit stages as food sources on boll weevil (Coleoptera: Curculionidae) fecundity and oviposition

Boll weevil, Anthonomus grandis grandis Boheman (Coloeoptera: Curculionidae), populations in the Lower Rio Grande Valley of Texas increase strongly during the squaring stage, and preemptive insecticide sprays at the pinhead square stage were designed to capitalize on that association. Laboratory assays showed that cotton plant volatiles, or leaves as a food source, do not elicit egg production in wild weevils. Boll weevils fed on large (5.5-8-mm diameter) squares for 7 d resulted in > or = 3.8-fold more gravid females that developed 4.8-fold more chorionated eggs per female than weevils fed on match-head-sized squares, or postbloom, young (5-10-d-old), or old (3-5-wk-old) bolls. When presented with a choice, nongravid females preferred to feed on young and old bolls 4.7- and 8.4-fold more, respectively, than on large squares. In the field, large squares had 7.8- and 25-fold more feeding punctures than match-head-sized squares and bolls, respectively. Oviposition increased > or = 2.7-fold when females fed on large squares compared with match-head-sized squares and bolls. Greater feeding on large squares during squaring and the associated greater fecundity explain rapid weevil population buildups shortly after large squares become well established.