Bacterial phytopathogen infection disrupts belowground plant indirect defense mediated by tritrophic cascade

Plants can defend themselves against herbivores through activation of defensive pathways and attraction of third‐trophic‐level predators and parasites. Trophic cascades that mediate interactions in the phytobiome are part of a larger dynamic including the pathogens of the plant itself, which are known to greatly influence plant defenses. As such, we investigated the impact of a phloem‐limited bacterial pathogen, Candidatus Liberibacter asiaticus (CLas), in cultivated citrus rootstock on a well‐studied belowground tritrophic interaction involving the attraction of an entomopathogenic nematode (EPN), Steinernema diaprepesi, to their root‐feeding insect hosts, Diaprepes abbreviatus larvae. Using belowground olfactometers, we show how CLas infection interferes with this belowground interaction by similarly inducing the release of a C12 terpene, pregeijerene, and disconnecting the association of the terpene with insect presence. D. abbreviatus larvae that were not feeding but in the presence of a CLas‐infected plant were more likely to be infected by EPN than those near uninfected plants. Furthermore, nonfeeding larvae associated with CLas‐infected plants were just as likely to be infected by EPN as those near noninfected plants with D. abbreviatus larval damage. Larvae of two weevil species, D. abbreviatus and Pachnaeus litus, were also more attracted to plants with infection than to uninfected plants. D. abbreviatus larvae were most active when exposed to pregeijerene at a concentration of 0.1 μg/μl. We attribute this attraction to CLas‐infected plants to the same signal previously thought to be a herbivore‐induced plant volatile specifically induced by root‐feeding insects, pregeijerene, by assessing volatiles collected from the roots of infected plants and uninfected plants with and without feeding D. abbreviatus. Synthesis. Phytopathogens can influence the structuring of soil communities extending to the third trophic level. Field populations of EPN may be less effective at host‐finding using pregeijerene as a cue in citrus grove agroecosystems with high presence of CLas infection.     

Solar UV‐B radiation and ethylene play a key role in modulating effective defenses against Anticarsia gemmatalis larvae in field‐grown soybean

Solar UV‐B radiation has been reported to enhance plant defenses against herbivore insects in many species. However, the mechanism and traits involved in the UV‐B mediated increment of plant resistance are unknown in crops species, such as soybean. Here, we studied defense‐related responses in undamaged and Anticarsia gemmatalis larvae‐damaged leaves of two soybean cultivars grown under attenuated or full solar UV‐B radiation. We determined changes in jasmonates, ethylene (ET), salicylic acid, trypsin protease inhibitor activity, flavonoids, and mRNA expression of genes related with defenses. ET emission induced by Anticarsia gemmatalis damage was synergistically increased in plants grown under solar UV‐B radiation and was positively correlated with malonyl genistin concentration, trypsin proteinase inhibitor activity and expression of IFS2, and the pathogenesis protein PR2, while was negatively correlated with leaf consumption. The precursor of ET, aminocyclopropane‐carboxylic acid, applied exogenously to soybean was sufficient to strongly induce leaf isoflavonoids. Our results showed that in field‐grown soybean isoflavonoids were regulated by both herbivory and solar UV‐B inducible ET, whereas flavonols were regulated by solar UV‐B radiation only and not by herbivory or ET. Our study suggests that, although ET can modulate UV‐B‐mediated priming of inducible plant defenses, some plant defenses, such as isoflavonoids, are regulated by ET alone.     

Interactions between entomopathogenic nematodes and imidacloprid for rose sawfly control

Rose sawfly, Arge ochropus (Gmelin), is one of the most important pests of ornamental plants such as roses and wild rose bushes in Northern Iran. We investigated the interactions between the insecticides imidacloprid and the entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae as control agents of fifth-instar larvae in the laboratory. The larvae were very susceptible to S. carpocapsae (LC₅₀: 21 infective juvenile per larva) and H. bacteriophora (LC₅₀: 32). Combinations of two imidacloprid rates (LC₃₀ and LC₅₀) and four rates of each nematode species (LC₂₅–LC₇₅) were tested. Combinations with the lower imidacloprid rate except for that with the highest H. bacteriophora rate caused higher mortality than both respective single-agent treatments. In combination with the higher imidacloprid rate, only one combination with H. bacteriophora and two combinations with S. carpocapsae caused higher mortality than both respective single-agent treatments. Interactions were generally stronger at the lower imidacloprid rate and were stronger for S. carpocapsae (synergistic in seven combinations, additive in one) than for H. bacteriophora (synergistic in two, additive in six). Synergistic imidacloprid-S. carpocapsae combinations could be a useful tool for the control of A. ochropus larvae that would simultaneously control other common pests susceptible to imidacloprid.     

昆虫病原线虫液体培养研究概况

综述昆虫病原线虫液体培养的研究概况。包括液体培养的研究历史,不同培养基组分对昆虫病原线虫产量的影响,营养源的选择,培养参数在昆虫病原线虫液体培养过程中的作用,感染期昆虫病原线虫脂肪酸含量,以及昆虫病原线虫应用前景等。     

Factors limiting short-term persistence of entomopathogenic nematodes

Abstract:  Entomopathogenic nematodes are commonly applied to soil and crops for biocontrol of insects. Typically, when nematodes are applied, recoverable numbers decline quickly. Because ultra-violet light is known to kill entomopathogenic nematodes in the laboratory, many researchers blame poor field persistence on the action of ultra-violet light. We conducted a field experiment to test this hypothesis, using Heterorhabditis bacteriophora applied to turf as a model system. We compared persistence of surface-applied nematodes with subsurface-applied nematodes and found no difference in persistence. Numbers of potential nematode antagonists (mites and collembola) were also monitored. Poor persistence was positively correlated with numbers of mites and collembola in plots where nematodes were surface-applied, but not in plots where they were subsurface-applied.     

昆虫病原线虫对烟苗的保护效果

小地老虎Agrotis ypsilon是危害烟草的重要害虫.为了实现该害虫的绿色防控,本研究测定了小地老虎幼虫对不同食物(小白菜、蕹菜、人工饲料和麸皮)取食的偏好性,评价添加鲜叶类诱食剂时昆虫病原线虫Steinernema carpocapsae All粉剂、S.feltiae SN虫尸剂、绿僵菌Metarhizium anisopliae和化学农药敌杀死(溴氰菊酯)对小地老虎的防控而实现对移栽期烟苗的保护效果.结果表明,尽管不同时间不同食物吸引的小地老虎幼虫数量有差异,但是这些幼虫对鲜叶类蔬菜(小白菜和蕹菜)具有偏好性.当每株烟苗存在2头小地老虎4龄幼虫时,未添加幼虫诱食剂的情况下,昆虫病原线虫粉剂处理后的烟苗死亡率为56.7％,显著低于绿僵菌处理的74.2％、昆虫病原线虫虫尸剂处理70.0％和对照78.3％,但高于敌杀死(溴氰菊酯)处理的烟苗死亡率37.5％;添加诱食剂后,昆虫病原线虫粉剂处理后烟苗的死亡率为40.8％,显著低于绿僵菌62.5％和昆虫病原线虫虫尸剂67.6％处理和对照62.5％,但与敌杀死(溴氰菊酯)处理的烟苗死亡率39.2％,差异不显著.当每株烟苗存在3头小地老虎4龄幼虫时,不论是否添加小地老虎幼虫诱食剂,昆虫病原线虫粉剂处理后的烟苗死亡率显著低于绿僵菌、昆虫病原线虫虫尸剂处理和对照,但与敌杀死(溴氰菊酯)处理的烟苗死亡率差异不显著.同样,添加幼虫诱食剂后,昆虫病原线虫粉剂处理的烟苗死亡率为36.7％,显著低于未加入小地老虎幼虫诱食剂的处理71.7％.因此,烟苗周围存在2头或3头小地老虎4龄幼虫的情况下,S.carpocapsae All线虫粉剂对刚移栽烟苗具有明显保护作用,在烟苗周围添加小地老虎幼虫诱食剂能显著降低烟苗的被危害率,为烟田小地老虎幼虫防控提供了有效的方法.     

昆虫病原线虫对草原毛虫幼虫的致病力

草原毛虫Gynaephora alpherakii是青藏高原草原的主要害虫。国家明令禁止使用化学药剂防控这一害虫。因此,有必要以生物农药控制这种害虫。本试验室内测定5种昆虫病原线虫（Steinernema longicaudum X-7,S. carpocapsae All,S. feltiae SN,Heterorhabditis bacteriophora H06和H. indica LN2）对草原毛虫的致病力。结果表明,S. carpocapsae All、S. feltiae SN两种线虫对草原毛虫的侵染效果较好。适宜S. carpocapsae All、S. feltiae SN线虫的侵染活动的环境温度为25℃;低温环境下两种线虫随着剂量的提高,对草原毛虫的致病力均有着显著地增长（P<0.05）,且S. feltiae SN线虫的活性高于S. carpocapsae All线虫。因此,昆虫病原线虫S. feltiae SN品系具有效防治青藏高原高寒草地草原毛虫的应用潜力。     

韭菜田中常用化学农药对昆虫病原线虫

本文研究了韭菜Allium tuberosum Rottle ex Spreng田常用化学农药辛硫磷、毒死蜱、高效氯氰菊酯、阿维菌素、敌敌畏、三唑酮、菌核净、多菌灵在田间推荐使用浓度及高一倍浓度条件下对Heterorhabditis bacteriophora H06和Hindica LN2线虫存活及感染力的影响,测定了农药与昆虫病原线虫施用间隔时间对线虫感染力的影响。结果显示,高效氯氰菊酯、三唑酮、菌核净和多菌灵对Hbacteriophora H06和Hindica LN2的存活及感染力无显著影响,可与这两种线虫共同使用;敌敌畏对两种线虫有显著致死作用,应严禁使用;辛硫磷、毒死蜱和阿维菌素对Hbacteriophora H06的存活无显著影响,对Hindica LN2具有一定的致死作用,但影响这两种线虫的感染力,这三种农药分别施用10 d、10 d、20 d后则对线虫感染力没有影响,可施用线虫。     

Efficacy of two entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae for control of the leopard moth borer Zeuzera pyrina (Lepidoptera: Cossidae) larvae under laboratory conditions

The biological traits of the entomopathogenic nematodes (EPNs), Steinernema carpocapsae and Heterorhabditis bacteriophora, against the larvae of the leopard moth, Zeuzera pyrina were evaluated in the laboratory. The traits included pathogenicity, penetration potential as well as foraging behaviour. Plate assays were performed using a range of EPN concentrations (5, 10, 20, 50 and 100 infective juveniles (IJs) per larva). The LC₅₀ values for S. carpocapsae and H. bacteriophora were 6.4 and 8.4 IJs larva^?1 after 72 h. Both EPN species caused high mortality in branch experiments. Significantly higher mortality rates occurred in the larger larvae after exposure to S. carpocapsae. Both EPN species successfully penetrated the Z. pyrina larvae as well as larvae of Galleria mellonella L. (Lepidoptera: Galleridae).The proportional response of H. bacteriophora to host-associated cues was strongly higher than S. carpocapsae in Petri dishes containing agar 1, 12 and 24 h after EPN application. These results highlight the efficiency of EPNs for the control of Z. pyrina larvae. However, due to the cryptic habitat of Z. pyrina larvae in their galleries in the trees, field trails need to be conducted to further evaluate this potential.     

Extracellular protease production fromXenorhabdus nematophilus, a symbiotic bacterium of entomopathogenic nematodes

Effects of nutrients and growth temperature on the production of an extracellular protease fromXenorhabdus nematophilus, a symbiotic bacterium of entomopathogenic nematodes were studied for batch culture. Tryptone and fructose were most effective nitrogen and carbon sources to produce high level of the protease within 24–28 hr of incubation. The stability of protease was poor during the incubation of the bacteria. The protease activity increased in parallel with cell growth then decreased significantly for extended culture periods of the bacteria over 48 hr at 22–30°C. Autolysis of the protease was not a major cause for the decreased protease activity since no decrease in the protease activity was observed for the whole culture broth of the bacteria which was stored up to 80 hr at 4°C.     

水杨酸、茉莉酸和乙烯介导的防卫信号途径相互作用的研究进展

乙烯、水杨酸和茉莉酸是植物体内主要的几个防御信号途径,也是研究比较多的几个信号途径。很多试验证明不同的防御信号途径相互间存在相互作用,他们或相互抑制,或相互促进。从这三种信号途径相互间的作用,及作用的联系点进行综述。     

Susceptibility of cockroaches (Gromphadorhina portentosa,Nauphoeta cinerea and Blaptica dubia) exposed to entomopathogenic nematodes

Cockroaches are major pests, vectors of pathogenic bacteria and induce allergies. Current control methods use chemical pesticides, but they can be ineffective and costly and there are reports of resistance in the field; hence new control methods are needed. There are conflicting reports about the susceptibility of cockroaches to entomopathogenic nematodes (EPNs); so we investigated if EPNs could kill several diverse cockroach species, including the Madagascan hissing roach (Gromphadorhina portentosa), the Lobster roach (Nauphoeta cinerea) and Blaptica dubia. Female adult cockroaches were exposed to either commercial products containing Steinernema kraussei or a combination of Heterorhabditis spp. and Steinernema spp. at 50 and 150 nematodes per cm² for 21 days. We also monitored feeding and the numbers of infective juveniles that were produced from each cockroach corpse. We found that S. kraussei were harmless to all cockroach species (at both doses) but when exposed to a mixture of Heterorhabditis spp. and Steinernema spp. B. dubia died after 6 days and its feeding was strongly inhibited. We also found that the mixture of Heterorhabditis spp. and Steinernema spp. could proliferate in the cadavers of B. dubia whilst S. kraussei could only reproduce in G. portentosa and B. dubia but not N. cinerea. In conclusion, S. kraussei was harmless to all three cockroach species but B. dubia was killed when exposed to Heterorhabditis spp. and Steinernema spp., highlighting the differences in the host range of EPNs.     

昆虫病原线虫共生菌Tc毒素研究进展

来自昆虫病原线虫共生菌的Tc毒素是一类多亚基组成的高分子蛋白复合物,对多种农业害虫具有广谱的胃毒活性,这类毒素与目前已知的其它杀虫蛋白同源性非常低,有可能成为新的杀虫资源。本文对来自昆虫病原线虫共生菌的Tc毒素的特性、作用模式等方面的国内外研究进展进行了综述。     

Factors affecting the natural occurrence of entomopathogenic nematodes in turfgrass

We conducted a study to determine the relationship between turfgrass management intensity and natural occurrence of entomopathogenic nematodes (EPNs). We surveyed for EPNs on putting greens, fairways, and rough areas—three distinct surface types on golf courses that are managed with different intensities. We collected 159 soil samples from putting greens, contiguous fairways, and rough areas from 19 golf courses in Ohio, USA. Nematodes were recovered from soil samples using the insect baiting technique. We also analyzed the soil samples for texture, organic matter, pH, phosphorus, calcium, magnesium and potassium. We used principal components analysis and Pearson correlation to determine the relationship between nematode occurrence and the measured parameters. Surface type was the most important factor in predicting EPNs occurrence. Putting greens differed significantly from fairways and rough areas in the number of EPN-positive sites. No EPNs were recovered from putting greens but were recovered from 43% of the fairways and 57% of the rough areas. Putting greens also differed significantly from fairways and rough areas in organic matter, pH, calcium, and phosphorus. The fairways and rough areas did not however differ in number of EPN-positive sites and measured soil parameters. Presence of EPNs correlated significantly, although weakly, with sand, silt, phosphorus, organic matter, and magnesium content, but not with clay, pH, calcium, and potassium. Nematode isolates were identified as Heterorhabditis bacteriophora, Steinernema carpocapsae, and S. glaseri. This suggests that EPNs are more likely to occur in less intensively managed sites that receive fewer inputs and have relatively high sand, and moderate silt, organic matter, phosphorus, and magnesium content.     

Habitat associations of two entomopathogenic nematodes: a quantitative study using real-time quantitative polymerase chain reactions

1. Despite nematodes being the most abundant animals on earth, very few animal ecologists study them, probably because of the difficulties of identifying them to species by morphological methods. 2. A group of nematodes that are important both ecologically and economically is the entomopathogenic nematodes, which play a key role in regulating soil food webs and are sold throughout the world as biological insecticides, yet for which very little is known of their population ecology. 3. A novel detection and quantification method was developed for soil nematodes using real-time polymerase chain reaction (PCR), and the technique was used to estimate numbers of two closely related species of entomopathogenic nematodes, Steinernema kraussei and S. affine in 50 soil samples from 10 sites in Scotland representing two distinct habitats (woodland and grassland). 4. There was a high degree of correlation between our molecular and traditional morphological estimates of population size and our data clearly showed that Steinernema affine occurred only in grassland areas, whereas S. kraussei was found in grassland and woodland samples to a similar degree. 5. Real-time PCR offers a rapid and accurate method of detecting individual nematode species from soil samples without the need for a specialist taxonomist, and has much potential for use in studies of nematode population ecology.     

Susceptibility of Oriental armyworm,Mythimna separata (Lepidoptera: Noctuidae) larvae and pupae to native entomopathogenic nematodes

The Oriental armyworm, Mythimna separata Walker (Lepidoptera: Noctuidae) is a major pest of cereal crops, and its outbreaks result in complete crop loss. In this study, we tested the pathogenicity and reproductive potential of indigenous entomopathogenic nematodes (EPNs), Heterorhabditis indica Poinar, Karunakar, & David NBAIIH38, Steinernema abbasi Elawad NBAIISa01, S. carpocapsae Weiser NBAIISc05 and S. siamkayai Stock, Somsook and Reid NBAIRS92 against larval and pupal stages of M. separata under laboratory conditions. Steinernema carpocapsae caused significantly greater mortality in second- and fourth-instar larval stages than other EPNs species. Steinernema carpocapsae caused greatest mortality 100% in larval stages and 75% in pupal stages. Significant differences were observed in the lethal concentration values (LC₅₀ and LC₉₀) of EPNs species against different stages of M. separata. Differences in penetration and multiplication in the fourth-instar larval stages of M. separata were observed amongst the EPNs species. However, further studies are needed to reveal the field performance of EPN isolates tested to be included in the IPM programme of M. separata.     

Efficacy and persistence of entomopathogenic nematodes for black cutworm control in turfgrass

Field experiments were conducted in turf maintained under golf course fairway conditions in May, June, and August 2009 and in August and September 2010 to evaluate the ability of entomopathogenic nematodes to control larval populations of the black cutworm, Agrotis ipsilon, on golf courses. Commercial products containing the entomopathogenic nematodes Heterorhabditis bacteriophora, Steinernema carpocapsae, S. feltiae, and S. riobrave were applied at 1.0 or 2.5×10⁹ infective juveniles per ha against fourth-instar black cutworms. Larval mortality and turf damage were evaluated at 4 and/or 7 days after treatment (DAT). Steinernema carpocapsae was the best performing species due to a combination of high control rates (average 83%), most consistent results (70–90% range), high speed of kill (average 68% at 4 DAT), and prevention of significant turf damage despite very high larval densities at 0 DAT. Efficacy of S. feltiae and H. bacteriophora was often similar to that of S. carpocapsae but overall less consistent. Short-term persistence of the nematodes was evaluated in four turfgrass sites maintained under golf course putting green, fairway, or rough conditions in June and August 2009 by baiting soil samples at 0, 4, 7, and 14 DAT. Relative to recovery immediately after application, at least 50% of S. feltiae and 25% of S. carpocapsae consistently persisted up to 4 days in one of the greens and up to 7 days in some trials. Our finding suggests that S. carpocapsae and S. feltiae may provide adequate black cutworm control in golf course turf under moderate summer temperatures.     

昆虫病原线虫防治烟草小地老虎技术优化研究

小地老虎Agrotis ipsilon是烟草Nicotiana tabacum移栽期主要的切根害虫,严重危害烟草生产。为研判烟草生产中符合双减（减肥、减药）要求的生物和生态防控技术,集成适合推广的虫害综合治理模式,本研究在云南玉溪华宁县以昆虫病原线虫（EPN）Steinernema carpocapsae All粉剂和化学药剂敌杀死（溴氰菊酯）处理,配合2种幼虫食诱方法（传统引诱剂、人工引诱剂）以及2种增效助剂（激健1、2）组合,调查移栽后烟草幼苗受小地老虎危害死亡率,评价生物药剂、食诱剂和助剂对烟草幼苗的保护效果。结果表明,无论是否存在食诱剂,移栽4 d各施药处理均能显著降低烟草幼苗死亡率,随时间的推移,所有处理的烟草幼苗死亡率均显著上升;无食诱剂情况下,EPN+激健1和敌杀死于移栽7 d仍具显著保苗效果;传统的糖醋酒液食诱法本身具备一定保苗效果,配合施药,初期效果最好,4 d时,烟草幼苗危害率最低达0.83%±0.008%（传统食诱剂+昆虫病原线虫）;人工食诱剂持效性最好,移栽10 d时配合EPN、EPN+激健2和敌杀死仍具明显保苗效果。施用化学药剂时,食诱剂本身对保苗效果无显著贡献;使用EPN时,传统食诱法较空白具有显著保苗效果,但与人工食诱法间差异不显著。移栽4 d时,EPN+激健1较单独施放EPN具显著保苗效果,之后调查中添加助剂小区与EPN小区无显著差异。综上所述,EPN粉剂配合人工食诱剂和激健助剂,可长期较好地抑制小地老虎对烟草幼苗危害,为集成烟草全程绿色生态治理模式提供了有效参考。