Crop dominance exerts specific effects on foliage‐dwelling arthropods in Bacillus thuringiensis cotton

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Evaluation of winter wheat as a potential relay crop for enhancing biological control of cotton aphids

A 2-year study was conducted to evaluate the role of winter wheat, Triticum aestivum L., as a potential relay crop to conserve arthropod natural enemies and suppress cotton aphids, Aphis gossypii Glover, in seedling cotton. The results suggested that the natural enemies that moved from the adjacent wheat fields to cotton fields with the maturity and harvest of wheat could keep the cotton aphid population at the edges (0--4 m) of cotton fields under the action threshold of 100 aphids/m². Data also suggested that the wheat strip served as a reservoir to conserve arthropod predators and relayed its predators to cotton when wheat matured and senesced.     

Efficacy of spider and ant predators on the cotton fleahopper [Hemiptera: Miridae]

The efficacy of predators of immature cotton fleahoppers,Pseudatomoscelis seriatus (Reuter), was calculated using field and laboratory cage confinement tests for consumption rate. The predators tested were the striped lynx spider,Oxyopes salticus Hentz; the black and white jumping spider,Phidippus audax (Hentz); the celer crab spider,Misumenops celer Hentz; and the red imported fire ant,Solenopsis invicta Buren. The spider predators were evaluated in a cotton field using predator-prey confinement cages on cotton plants. Average percent control (sensuAbbott 1925) of fleahoppers byO. salticus, P. audax, andM. celer were 42%, 66% and 32% respectively. The rate of fleahopper consumption by red imported fire ants was measured in the laboratory using various numbers of ants and fleahoppers. Daily percent control by ants ranged from 0.5% (single ant and fleahopper) to 100% (colony linked). The functional response of the 4 arthropod species to different prey numbers is illustrated and discussed as is the relative potential usefulness of natural enemies to suppress fleahoppers on cotton.      

Measuring gene flow in the cultivation of transgenic cotton (Gossypium hirsutum L.)

Transgenic Bt cotton NewCott 33B and transgenic tfd A cotton TFD were chosen to evaluate pollen dispersal frequency and distance of transgenic cotton (Gossypium hirsutum L.) in the Huanghe Valley Cotton-producing Zone, China. The objective was to evaluate the efficacy of biosafety procedures used to reduce pollen movement. A field test plot of transgenic cotton (6×6 m) was planted in the middle of a nontransgenic field measuring 210×210 m. The results indicated that the pollen of Bt cotton or tfd A cotton could be dispersed into the environment. Out-crossing was highest within the central test plot where progeny from nontransgenic plants, immediately adjacent to transgenic plants, had resistant plant progeny at frequencies up to 10.48%. Dispersal frequency decreased significantly and exponentially as dispersal distance increased. The flow frequency and distance of tfd A and Bt genes were similar, but the pollen-mediated gene flow of tfd A cotton was higher and further to the transgenic block than that of Bt cotton (χ² = 11.712, 1 degree of freedom, p<0.001). For the tfd A gene, out-crossing ranged from 10.13% at 1 m to 0.04% at 50 m from the transgenic plants. For the Bt gene, out-crossing ranged from 8.16% at 1 m to 0.08% at 20 m from the transgenic plants. These data were fit to a power curve model: y=10.1321x ^−1.4133 with a correlation coefficient of 0.999, and y=8.0031x ^−1.483 with a correlation coefficient of 0.998, respectively. In this experiment, the farthest distance of pollen dispersal from transgenic cotton was 50 m. These results indicate that a 60-m buffer zone would serve to limit dispersal of transgenic pollen from small-scale field tests.     

The dispersal and distribution of polyphagous predatory Coleoptera in cereals

Observations were made on the phenology of the dispersal of polyphagous arthropod predators from their overwintering habitats in field boundaries into adjacent farmland in cereal fields in southern England from 1981 to 1984. Agonum dorsale, Bembidion lampros and Demetrias atricapillus dispersed from overwintering habitats into adjacent cereal crops by crawling. B. lampros was fully dispersed by early May and the other two species by late May. Tachyporus spp. were thought to disperse mainly by flight, T. hypnorum being fully dispersed by mid-May and T. chrysomelinus by late May. A small proportion of A. dorsale marked in field boundaries in April before dispersal began were later recaptured up to 200 m into adjacent crops later in the season. Areas of a crop, immediately adjacent to field boundaries in which high numbers of predators had overwintered, were found to have significantly (P<0.01) higher numbers of predators that disperse by walking (A. dorsale, B. lampros and D. atricapillus) moving through them towards the centres of fields. By mid-summer, the mid-crop density of D. atricapillus was correlated with its overwintering density in surrounding field boundaries the previous winter, but this was not so in the other species. Mid-crop, mid-summer densities of A. dorsale were significantly (P<0. 02) correlated with mean percentage weed cover in fields. The densities of the other species were not correlated with weed cover. Analysis of data collected over a 10-yr period on a Sussex study area in late June revealed that significantly more D. atricapillus were found in fields surrounded by hedgerows than fields surrounded by fence-post and wire boundaries.     

Predation of cotton leafworm first instar larvae,Alabama argillacea [Lep.: Noctuidae]

Natural predation first instar larvae of the cotton leafworm (CLW)A. argillacea was studied in cotton fields in Jaboticabal, Sao Paulo State, Brazil, during 1986. The presence of naturally occurring arthropod predators showed a first instar larvae predation rate of 78.6 and 88.9% after 24 h and 48 h of exposure, respectively. A predator prey ratio of 1∶1 (1 CLW key predator per 1 prey/plant) maintained a level of no more than 1 CLW small larvae per plant. The most evident arthropod predators in the studied fields were: beetles (Coleoptera: Coccinellidae), antsPheidole sp. andConomyrma sp.;Dermaptera Doru lineare (Eschs);Hemiptera Geocoris sp., andOrius insidiosus Say; and the spidersTheridion volubile, Chrysso pulcherrima, Misumenops sp.,Chiracanthium sp., andOxyopes salticus Hentz.      

A protein‐based approach to mark arthropods for mark‐capture type research

A series of studies was conducted to test methods for marking a wide variety of arthropods with inexpensive proteins for mark‐capture dispersal research. The markers tested included egg albumin protein in chicken egg whites and casein protein in bovine milk. The first study qualified the effectiveness of the two marks on more than 50 arthropod species inhabiting cotton via two application procedures. The application methods included: (1) a topical plus residue protein application, and (2) a residue‐only protein application. Both protein marks, regardless of the method of application, were readily retained on the arthropod assemblage over the duration of the study. The second study determined how rapidly insects acquire chicken egg albumin protein after contact exposure to cotton tissue sprayed with an egg whites solution. Under laboratory conditions, the vast majority of adult Hippodamia convergens Guérin‐Méneville (Coleoptera: Coccinellidae) and Lygus hesperus Knight (Heteroptera: Miridae) acquired the mark after 5 min, and immature Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) acquired the marker after 40 min. The third study determined how rapidly H. convergens and L. hesperus acquire bovine casein protein after contact exposure to either alfalfa, Medicago sativa L. (Fabaceae), or lesquerella, Lesquerella fendleri (Watson) (Brassicaceae), plants sprayed with a bovine milk solution. These insects rapidly acquired the casein mark from the plant residue under field conditions. A final study determined how long H. convergens retain casein protein after 24‐h exposure to alfalfa and lesquerella plants containing a 7‐day‐old residue of bovine milk. Approximately 95% of the H. convergens maintained the casein mark for 2 days after removal from each type of plant.     

Predation pressure in Ugandan cotton fields measured by a sentinel prey method

Pest suppression by natural enemies is an important ecosystem service, which is a valuable resource to poor smallholders in developing countries. Diverse natural enemy assemblages of arthropod predators and parasitoids are documented in various regions in Africa, but our knowledge of their impact on herbivores in agroecosystems remains limited. We conducted experiments in cotton, Gossypium hirsutum L. (Malvaceae), under typical local agronomic practices in Uganda to assess levels of predation pressure ascribed to natural enemies. We measured predation rates on artificial caterpillars made of plasticine glued to cotton plants. Predation pressure on cotton fields varied between 1.96 and 4.1% per day, but was not significantly influenced by cotton treatments (insecticide/no insecticide, monocropping/intercropping with Phaseolus spp.). Predation pressure in non‐crop habitats adjacent to cotton fields was up to 12× higher than in the fields. Marks left on the artificial caterpillars revealed that arthropods and birds were largely accountable for predation in cotton fields, whereas arthropods and small mammals were dominant in non‐cultivated habitats.     

The red imported fire ant,Solenopsis invicta,modifies predation at the soil surface and in cotton foliage

Red imported fire ants, Solenopsis invicta, are generalist predators that can have major impacts on foliar arthropod communities in agricultural systems; however, their effects as predators at the soil surface have not been adequately characterized. We examined the contribution of fire ants to predation at the soil surface and in cotton foliage at two sites and over the course of two field seasons in Georgia, using egg masses of the beet armyworm, Spodoptera exigua. To assess interactions between fire ants and other arthropod species, we also measured the densities of edaphic predators and honeydew‐producing hemipterans at both sites. The sites occurred in different growing regions (Piedmont and Coastal Plain), and allowed us to characterize the importance of fire ants as predators under different climatic and soil conditions. Fire ant suppression decreased egg predation at both field sites, and predation by fire ants at the soil surface was equal to if not greater than that in cotton foliage. However, the impact of fire ants on predation varied between sites, likely due to differences in climate and the composition and activity of the extant arthropod communities. Our study also indicates that fire ant suppression is associated with decreases in the density of honeydew‐producing insects, and increasing abundance of whiteflies on the plants coincided with a decrease in egg predation at the soil surface. This finding suggests the mutualism between ants and whiteflies may lead to a shift in predation intensity from edaphic towards plant‐based food webs.     

Insectivorous bats selectively source moths and eat mostly pest insects on dryland and irrigated cotton farms

Insectivorous bats are efficient predators of pest arthropods in agroecosystems. This pest control service has been estimated to be worth billions of dollars to agriculture globally. However, few studies have explicitly investigated the composition and abundance of dietary prey items consumed or assessed the ratio of pest and beneficial arthropods, making it difficult to evaluate the quality of the pest control service provided. In this study, we used metabarcoding to identify the prey items eaten by insectivorous bats over the cotton‐growing season in an intensive cropping region in northern New South Wales, Australia. We found that seven species of insectivorous bat (n = 58) consumed 728 prey species, 13 of which represented around 50% of total prey abundance consumed. Importantly, the identified prey items included major arthropod pests, comprising 65% of prey relative abundance and 13% of prey species recorded. Significant cotton pests such as Helicoverpa punctigera (Australian bollworm) and Achyra affinitalis (cotton webspinner) were detected in at least 76% of bat fecal samples, with Teleogryllus oceanicus (field crickets), Helicoverpa armigera (cotton bollworm), and Crocidosema plebejana (cotton tipworm) detected in 55% of bat fecal samples. Our results indicate that insectivorous bats are selective predators that exploit a narrow selection of preferred pest taxa and potentially play an important role in controlling lepidopteran pests on cotton farms. Our study provides crucial information for farmers to determine the service or disservice provided by insectivorous bats in relation to crops, for on‐farm decision making.     

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

Field studies were carried out to evaluate the effect of two transgenic cotton varieties (SGK321 carrying Cry1A+CpTI and DP99B carrying Cry1Ac) and the conventional variety (shiyuan321‐parental line of SGK321) on spider mites, Tetranychus spp. from 2002 to 2004. In 2002, this experiment included three treatments: Bt cotton field (SGK321) treated with acaricides against spider mites, untreated non‐Bt cotton field (Shiyuan321), and untreated Bt cotton field (SGK321). In 2003–2004, there are four types of treatments after a new transgenic Bt cotton variety, DP99B (non‐chemical control), was added into the experiments. The results showed that there were no significant difference in densities of spider mites among Bt without acaricides and non‐Bt without acaricides cotton fields, nor was there a significant difference in damage of spider mites to cotton among these treatments (P > 0.1). However, there are significant differences (P < 0.05) in densities of spider mites and damage caused by spider mites between cotton fields with and without acaricides. Acaricide significantly reduced the densities of spider mites in Bt cotton (P < 0.05). These results suggest that Bt cotton has no effect on spider mites populations. However, spider mites have the potential for severe damage in Bt cotton fields. Acaricides are essential tools in controlling cotton spider mites in northern China.     

Using the stable isotope marker 13C to study extrafloral nectar uptake by parasitoids under controlled conditions and in the field

Parasitic wasps are prominent natural enemies of crop pests. They usually feed on floral resources during the adult stage (nectar, pollen, or honeydew). Extrafloral nectar is an alternative source of sugar easily accessible to adult parasitoids. We developed an original method of nectar labelling based on the injection of labelled sugar solution into the plant stem in order to analyse the nectar uptake by parasitoids (cotton wick method). This method was used to artificially enrich extrafloral cornflower, Centaurea cyanus L. (Asteraceae), nectar with the stable isotope ¹³C. We analysed (1) the transfer of ¹³C from the sugar solution into extrafloral nectaries, (2) the uptake of labelled nectar by parasitoids under laboratory conditions, and (3) the ability of the method to discriminate, in an oilseed rape (Brassica napus L., Brassicaceae) field, between labelled parasitoids (i.e., those who have fed on labelled cornflowers located adjacent to the field) and unlabelled parasitoids to track parasitoid movements from the margin into the field. The extrafloral nectar of all test plants was ¹³C‐labelled. Most (66%) of the parasitoids were identified as marked after 96 h of exposure to labelled plants in the laboratory. We could also detect labelled parasitoids inside the field, but the detection rate was only 1%. The experiments clearly demonstrate that the cotton wick method is appropriate to label extrafloral nectar and parasitoids feeding on this labelled nectar. Further research is needed on the amount of labelled extrafloral nectar required to obtain a sufficient marker level to track parasitoid movements in the field.     

Intercrop movement of convergent lady beetle,Hippodamia convergens (Coleoptera: Coccinellidae), between adjacent cotton and alfalfa

A 2‐year study was conducted to characterize the intercrop movement of convergent lady beetle, Hippodamia convergens Guerin‐Meneville (Coleoptera: Coccinellidae) between adjacent cotton and alfalfa. A dual protein‐marking method was used to assess the intercrop movement of the lady beetles in each crop. In turns field collected lady beetles in each crop were assayed by protein specific ELISA to quantify the movement of beetles between the crops. Results indicated that a high percentage of convergent lady beetles caught in cotton (46% in 2008; 56% in 2009) and alfalfa (46% in 2008; 71% in 2009) contained a protein mark, thus indicating that convergent lady beetle movement was largely bidirectional between the adjacent crops. Although at a much lower proportion, lady beetles also showed unidirectional movement from cotton to alfalfa (5% in 2008 and 6% in 2009) and from alfalfa to cotton (9% in 2008 and 14% in 2009). The season‐long bidirectional movement exhibited by the beetles was significantly higher in alfalfa than cotton during both years of the study. The total influx of lady beetles (bidirectional and unidirectional combined) was significantly higher in alfalfa compared with that in cotton for both years. While convergent lady beetles moved between adjacent cotton and alfalfa, they were more attracted to alfalfa when cotton was not flowering and/or when alfalfa offered more opportunities for prey. This study offers much needed information on intercrop movement of the convergent lady beetle that should facilitate integrated pest management decisions in cotton utilizing conservation biological control.     

板蓝根田节肢动物群落的结构与多样性研究

为了解河南省板蓝根田节肢动物群落的结构组成及物种多样性,该研究采用5点随机取样,通过网捕法和目测法调查并记录了板蓝根植株及地面上的节肢动物种类和数量。结果表明:河南省板蓝根田节肢动物群落物种丰富,共采集到2 613头,隶属于2纲10目39科61种。其中,植食性种类和捕食性种类均为24种(各占39.34%),寄生性种类4种(占6.56%),中性种类9种(占14.75%)。蜘蛛的种类占群落总种数的比例最高(为21.31%),表明田间的蜘蛛种类最丰富。鳞翅目物种的个体数量远大于其他的目,占群落个体数的43.78%。菜青虫和小菜蛾的相对丰盛度最高,分别为0.184 8和0.162 6,说明二者是河南省板蓝根田的优势害虫。捕食性集团的均匀度指数最高,寄生性集团的优势度指数最高,其中小菜蛾幼虫的寄生性天敌菜蛾盘绒茧蜂的数量最大。     

Geographic variation in a facultative mutualism: consequences for local arthropod composition and diversity

Geographic variation in the outcome of interspecific interactions may influence not only the evolutionary trajectories of species but also the structure of local communities. We investigated this community consequence of geographic variation for a facultative mutualism between ants and wild cotton (Gossypium thurberi). Ants consume wild cotton extrafloral nectar and can protect plants from herbivores. We chose three sites that differed in interaction outcome, including a mutualism (ants provided the greatest benefits to plant fitness and responded to manipulations of extrafloral nectar), a potential commensalism (ants increased plant fitness but were unresponsive to extrafloral nectar), and a neutral interaction (ants neither affected plant fitness nor responded to extrafloral nectar). At all sites, we manipulated ants and extrafloral nectar in a factorial design and monitored the abundance, diversity, and composition of other arthropods occurring on wild cotton plants. We predicted that the effects of ants and extrafloral nectar on arthropods would be largest in the location with the mutualism and weakest where the interaction was neutral. A non-metric multidimensional scaling analysis revealed that the presence of ants altered arthropod composition, but only at the two sites in which ants increased plant fitness. At the site with the mutualism, ants also suppressed detritivore/scavenger abundance and increased aphids. The presence of extrafloral nectar increased arthropod abundance where mutual benefits were the strongest, whereas both arthropod abundance and morphospecies richness declined with extrafloral nectar availability at the site with the weakest ant–plant interaction. Some responses were geographically invariable: total arthropod richness and evenness declined by approximately 20% on plants with ants, and extrafloral nectar reduced carnivore abundance when ants were excluded from plants. These results demonstrate that a facultative ant–plant mutualism can alter the composition of arthropod assemblages on plants and that these community-level consequences vary across the landscape.     

Assessment of cotton aphids, Aphis gossypii, and their natural enemies on aphid-resistant and aphid-susceptible wheat varieties in a wheat–cotton relay intercropping system

The cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae), is an important cotton pest in northern China, especially in the seedling stage of cotton. After large scale commercial use of transgenic Bt cotton, cotton aphids became one of the most important cotton pests. A 2‐year study was conducted to evaluate the role of four winter wheat varieties that were resistant or susceptible to wheat aphid, Sitobion avenae Fabricius (Homoptera: Aphididae), in conserving arthropod natural enemies and suppressing cotton aphids in a wheat–cotton relay intercropping system in northern China. The results indicated that wheat–cotton intercropping preserved and augmented natural enemies more than a monoculture of cotton. The density of natural enemies in cotton was significantly different among relay‐intercropping fields with different wheat varieties. The highest density of natural enemies and low cotton aphid populations were found in the treatment of cotton in relay intercropped with the wheat variety Lovrin10, which is susceptible to wheat aphid. The lowest density of predators and parasitoids associated with high cotton aphid populations were found with the wheat variety KOK1679, which is resistant to wheat aphid. The results showed that wheat varieties that are susceptible or moderately resistant to wheat aphid might reduce cotton aphids more effectively than an aphid‐resistant variety in the intercropping system by enhancing predators to suppress cotton aphids during the cotton seedling stage.     

玉米秸秆还田量对黑土区农田地面节肢动物群落的影响

为考察玉米秸秆还田量对黑土区农田地面节肢动物群落的影响,2016年6—9月在内蒙古兴安盟扎赉特旗研究了0(CK)、9000(SR1)、10500(SR2)、12000(SR3)、13500(SR4) kg/hm25个梯度对农田地面节肢动物群落影响。结果表明:共捕获地面节肢动物1820只,隶属于16个类群; SR4处理显著提高了地面节肢动物个体数(P0.05),SR3处理显著提高了地面节肢动物类群数(P0.05)。各处理样地地面节肢动物个体数最高值均出现在8月,类群数则出现在7月; SR4处理显著提高了地面节肢动物多样性指数和丰富度指数(P0.05),SR1处理显著提高了地面节肢动物优势度指数(P0.05),对照CK的均匀度指数最高(P0.05)。相关分析表明:农田地面节肢动物的个体数与土壤有机质呈极显著相关(P0.01),与平均入渗率呈显著正相关(P0.05),与土壤容重呈显著负相关(P0.05);类群数与土壤温度呈显著正相关(P0.05);丰富度指数与平均入渗率和土壤含水量呈显著正相关(P0.05)。主成分分析表明:地面节肢动物的个体数、多样性指数、蟋蟀总科、跳甲科和步甲科5个特征指标对玉米秸秆还田最为敏感,初步认为是衡量黑土区土壤玉米秸秆还田后肥力状况的评价指标。     

不同邻作作物对玉米田节肢动物多样性的影响

为探明不同邻作对云南普洱地区玉米田节肢动物多样性的影响.采用目测法和粘虫板等多种诱集法对邻作咖啡、水稻、李树及单作的玉米田节肢动物群落进行系统调查,分析不同邻作作物对玉米田节肢动物群落的影响.结果表明:不同邻作玉米田天敌亚群落主要为双翅目和膜翅目,其中玉米单作田赤池信息量准则(AIC)值最低为-16.858,最优模型为...     

Infection of Sentinel Cotton Aphids (Homoptera: Aphididae) by Aerial Conidia ofNeozygites fresenii(Entomophthorales: Neozygitaceae)

Uninfected adultAphis gossypii(Homoptera: Aphididae) apterae (sentinel aphids) on cotton leaves were exposed for 8 h to the air over a commercial cotton field in Louisiana during the night of 1–2 July 1995. At 0015 h there were 90,437 primary conidia/m³air of the fungusNeozygites fresenii(Entomophthorales: Neozygitaceae) at the midfield position as determined from Rotorod samples. Forty-eight percent (n = 106) of the sentinel aphids exposed for 8 h at midfield were infected by aerial conidia ofN. fresenii.Exposure of sentinel aphids outside the cotton field, at 10 and 100 m downwind and 10 m upwind, resulted in 34.8% (n = 131), 24.0% (n = 129), and 17.4% (n = 146) infected aphids, respectively. These data demonstrate that wind-dispersed aerial conidia ofN. freseniiare infective and rapidly and efficiently disperse the pathogen throughout aphid populations within and between fields.