Cold tolerance in nematodes

Summary The nematodesTrichostrongylus colubriformis (J3),Ditylenchus dipsaci (J4) andPanagrellus silusae (adults) are freezing-susceptible but can avoid freezing by supercooling. Their mean supercooling points were –30.0±0.7°C forT. colubriformis, –21.7±0.7°C forD. dipsaci and –20.7±0.84°C forP. silusae. T. colubriformis andD. dipsaci could prevent seeding by external ice butP. silusae could not. The glycerol concentrations of these nematodes are considered to be too low to have a significant antifreeze effect.Abbreviations J3 3rd-stage juvenile - J4 4th stage juvenile - SEM standard error of the mean - T ₅₀ 50% survival temperature     

昆虫病原线虫的耐寒性

昆虫病原线虫可开发成生物农药,广泛应用于多种地下及钻蛀害虫的安全防治。但昆虫病原线虫货架期较短,对寒冷等极端环境的耐受性较差,影响了其在生物防治方面的商业开发。本文介绍了寒区的昆虫病原线虫资源,总结了昆虫病原线虫耐寒性的测定方法及增强方法、耐寒性差异的研究进展,并对其耐寒的生理生化机制及分子机理进行了综述。研究昆虫病原线虫的耐寒性,对于解释种群动态,指导昆虫病原线虫的低温保存,以及拓展其在生物防治方面的应用具有重要意义。     

Susceptibility of Delia radicum to steinernematid nematodes

Isolates of different Steinernema species (S. affine, S. bicornutum, S. feltiae and Steinernema C1) were used in mortality assays with third instar larvae of Delia radicum (L.) (Diptera: Anthomyiidae). The nematode isolates had been obtained by baiting soil regularly grown with cabbage. One isolate (S. feltiae) was the result of a natural infection of a D. radicum puparium. The highest mortality (77%) was obtained with an isolate of S. feltiae (DK1). The isolate DK1 was also used in tests with all larval stages of D. radicum. Mortality around 60% was observed for second and third instar larvae, while first instar larvae showed very low or no susceptibility. Maximum mortality of second and third instar larvae was reached applying only 25 nematodes per larva. Observations of larvae that pupated revealed that some of these puparia contained nematodes. Experiments with hatching puparia showed that a high proportion was infected by nematodes if the flies were prevented from leaving nematode-containing soil. In addition to mortality, the ability of the nematodes to successfully reproduce in the insects was studied. It was found that the species S. feltiae and S. bicornutum reproduced in D. radicum larvae and adults with S. feltiae being the most successful.     

Directional movement of steinernematid nematodes in response to electrical current

Steinernematid nematodes are parasites that are important natural regulating agents of insect populations. The infective juvenile nematodes respond to a variety of stimuli that aid in survival and host finding. Host finding strategies among steinernematids differ along a continuum from ambush (sit & wait) to cruiser (search & destroy). In this paper we describe directional movement in response to an electrical current, which was generated on agar plates. Specifically, Steinernema glaseri (a cruiser) moved to a higher electric potential, whereas Steinernema carpocapsae, an ambusher, moved to a lower electric potential. Thus, we hypothesize that steinernematids may detect electrical currents or electromagnetic fields in nature, and these stimuli may be used differentially among species for host finding or enhancing other fitness characters.     

Mutualistic association of Photorhabdus asymbiotica with Japanese heterorhabditid entomopathogenic nematodes

Gram-negative bacteria, Photorhabdus luminescens and P. temperata, form a mutualistic association with entomopathogenic heterorhabditid nematodes while P. asymbiotica is known as an opportunistic human pathogen that causes disseminated bacteremic spread on two continents, the United States and Australia. In the course of our phylogenetic study of Photorhabdus bacteria associated with Japanese Heterorhabditis nematodes, we found two Photorhabdus isolates (Photorhabdus sp. Cbkj163 and OnIr40) whose partial 16S rRNA gene sequence showed high similarities to clinical isolates of this pathogen from Heterorhabditis indica. The phylogenetic study, based upon the gyrase subunit B gene sequences of the two isolates, revealed clustering with these clinical isolates of P. asymbiotica from both the United States and Australia but not with other Photorhabdus bacteria associated with nematodes. The two bacterial isolates were also found to share microbiological and biochemical characteristics with clinical and entomopathogenic Photorhabdus strains. Moreover, not only the two novel Photorhabdus isolates but also an Australian clinical isolate of P. asymbiotica formed mutualistic association with H. indica isolates. These data suggest that the bacteria isolated from H. indica CbKj163 and OnIr40 are a novel subspecies of P. asymbiotica, and that some clinical isolates of P. asymbiotica could have originated from bacteria associated with entomopathogenic nematodes.     

Latent infection: a low temperature survival strategy in steinernematid nematodes

1. Entomopathogenic nematodes penetrate and kill Galleria mellonella within 48 h at optimal temperatures.

2. Low temperature induces infection latency, preventing host death until optimal conditions resume.

3. Infected Galleria survived 25 days at 5°C. On transfer to 25°C, 100% and 12.5% of Steinernema carpocapsae and Steinernema riobravis infected larvae died within 72 h.

4. Infective juvenile penetration decreased with decreasing temperature; declining from 49.7 and 49.3 nematodes/host at 25°C to 6.3 and 0.25 nematodes/host at 5°C for S. carpocapsae and S. riobravis, respectively.

5. Latent infection occurs, albeit infrequently, due to low host penetration at low temperature.

Molecular and morphological characterization of heterorhabditid entomopathogenic nematodes from the tropical rainforest in Brazil

Despite massive losses of primary forest, the Amazonian rainforest remains an extremely rich source of biodiversity. In recent years, entomopathogenic nematodes (EPNs) have been isolated from soil in various parts of the world and used successfully as biological control agents against numerous insect pests. Therefore, a sampling in the rainforest of Monte Negro, Rond?nia, Brazil was conducted with the aim of discovering new strains and/or species of EPNs for future development as biological control agents. From 156 soil samples taken at nine collecting sites, 19 isolates were obtained, all of them belonging to the genus Heterorhabditis. Four strains were subjected to detailed morphological and molecular evaluation. Based on morphometrics and internal transcribed spacer (ITS) sequence data, the strains LPP1, LPP2 and LPP4 were identified as Heterorhabditis indica, whereas LPP7 was considered Heterorhabditis baujardi. Comparative analysis of the ITS1 sequence of H. indica and H. baujardi isolates showed a polymorphic site for the restriction enzyme Tth 111 that could be used to distinguish the two species. Consequently, strains LPP1, LPP2, LPP3, LPP4, and LPP9 were identified as H. indica, whereas LPP5, LPP7, LPP8 and LPP10 were identified as H. baujardi.     

Screening Spanish isolates of steinernematid nematodes for use as biological control agents through laboratory and greenhouse microcosm studies

Entomopathogenic nematodes (EPNs) are one of the best non-chemical alternatives for insect pest control, with native EPN strains that are adapted to local conditions considered to be ideal candidates for regional biological control programs. Virulence screening of 17 native Mediterranean EPN strains was performed to select the most promising strain for regional insect pest control. Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) Rioja strain produced 7%, 91% and 33% larval mortality for the insects Agriotes sordidus (Illiger) (Coleoptera: Elateridae), Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) and Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), respectively, and was selected as the most promising strain. The S. feltiae Rioja strain-S. littoralis combination was considered the most suitable to develop the Rioja strain as a biocontrol agent for soil applications. The effect of soil texture on the virulence of the Rioja strain against S. littoralis was determined through dose-response experiments. The estimated LC₉₀ to kill larvae in two days was 220, 753 and 4178 IJs/cm² for soils with a clay content of 5%, 14% and 24%, respectively, which indicates that heavy soils produced negative effects on the virulence of the Rioja strain. The nematode dose corresponding to the LC₉₀ for soils with a 5% and 14% clay content reduced insect damage to Capsicum annuum Linnaeus (Solanales: Solanaceae) plants under greenhouse microcosm conditions. The results of this research suggest that an accurate characterization of new EPN strains to select the most suitable combination of insect, nematode and soil texture might provide valuable data to obtain successful biological control under different ecological scenarios in future field applications.     

Laboratory infection of terrestrial isopods (Crustacea: Isopoda) with neoaplectanid and heterorhabditid nematodes (Rhabditida: Nematoda)

Under laboratory conditions, the nematodes Neoaplectana carpocapsae and Heterorhabditis heliothidis were able to infect and develop inside the hemocoel of terrestrial isopods belonging to the genus Porcellio. Armidillidium vulgare was also infected by N. carpocapsae, but this host was less susceptible than Porcellio. Results show that, under suitable ecological conditions, it would be feasible to utilize N. carpocapsae as a biological control agent of sowbugs (Porcellio spp.). This is the first report showing the ability of neoaplectanids and heterorhabditids to invade representatives of the Crustacea.     

短舌熊蜂及红光熊蜂耐寒力的测定

以过冷却点和冰点为评价指标,对短舌熊蜂Bombus terrestris的幼虫,蛹,成年工蜂,成年雄蜂,处女蜂王,越冬后的蜂王及红光熊蜂Bombus ignitus的成年工蜂,成年雄蜂,处女蜂王的耐寒力进行检测。结果显示,短舌熊蜂幼虫期耐寒力最低,其次是蛹,工蜂和雄蜂,处女王较高。耐寒力最高的是越冬后的蜂王,其含水量也最低。将短舌熊蜂与红光熊蜂的成年工蜂,成年雄蜂和处女蜂王三型蜂分别进行对比,结果显示,红光熊蜂成年雄蜂与处女蜂王的耐寒力要比短舌熊蜂高。样本的湿重和含水量与过冷却点和冰点无显著相关性。     

Cold tolerance and critical temperature of the Japanese

Five male Japanese subjects, undressed, were investigated at rest and during ergometer work at 30°, 25°, 20°, 15° and 10°C and the results were compared with similar measurements on Caucasians. The metabolic rate and mean skin temperature were higher at temperatures below 20°C than in Caucasians, while the correlation curve of metabolic rate versus skin temperature was similar. The rectal temperature decreased with lowering of the air temperature in these subjects in contrast to the observations in Caucasians. The thermal conductance of the Japanese was higher at the control air temperature, but became lower or equal in cool air as compared with that of Caucasians. The lower critical temperature was around 24°C. The results indicate that Japanese men react to cold with a mixture of both metabolic and insulative adaptation which differs from the response of Caucasians. The difference may be due to the environment, living habits and bodily constitution.

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Zusammenfassung Fünf Japaner wurden unbekleidet in Ruhe und während Ergometerarbeit bei 30°, 25°, 20°, 15° und 10°C Raumtemperatur untersucht und die Ergebnisse mit ähnlichen Untersuchungen an Personen der weissen Rasse (Kaukasiern) verglichen. Stoffwechselrate und mittlere Hauttemperatur waren unterhalb 20°C bei den Japanern höher als bei den Kaukasiern, während die Korrelationskurve der Stoffwechselrate versus Hauttemperatur gleich waren. Die Rektaltemperatur fiel bei den Japanern mit Senkung der Lufttemperatur ab, umgekehrt zu den Beobachtungen an Kaukasiern. Die Wärmeleitung war bei den Japanern höher im Bereich der Temperaturen bis 25°C, dagegen in kühler Luft niedriger oder blieb auf dem gleichen Niveau beim Vergleich mit den Werten von Kaukasiern. Die untere kritische Temperatur war 24°C. Die Ergebnisse zeigen, dass Japaner auf Kälte mit metabolischer und insulativer Adaptation reagieren, anders als Kaukasier. Diese Unterschiede können Ausdruck der Lebensgewohnheiten, Umweltbedingungen und der Konstitution sein.

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Resume Cinq Japonais ont été examinés nus au repos et au travail à l'ergomètre par des températures ambiantes de 30°, 25°, 20°, 15° et 10°C. On a comparê les reléves ainsi effectués avec ceux provenant de personnes de race blanche (Caucasiens). Le métabolisme et la température cutanée moyenne furent, au dessus de 20°C, plus élevés chez les Japonais que chez les Caucasiens, alors que le rapport métabolisme-température cutanée restait identique. La température rectale a baissé chez les Japonais avec un refroidissement extérieur, contrairement à ce qui se passait chez les Caucasiens. La conductibilité thermique fut plus élevée chez les Japonais pour des températures supérieures à 25°C et diminua ou resta stationnaire dans de l'air plus frais — tous ces chiffres sont relatifs aux valeurs relevées sur les Caucasiens. La température critique inférieure se situe à 24°C. Ces résultats montrent que les Japonais réagissent autrement au froid que les Caucasiens, c'est à dire que leur adaptation métabolique et insulative est différente. Ces différences peuvent résulter de leur manière de vivre, des conditions ambiantes ou de leur constitution.

     

Salt tolerance and survival thresholds for two species of Antarctic soil nematodes

We evaluated the response of the Antarctic soil nematodes Scottnema lindsayae and Plectus antarcticus to various salts (NaCl, MgSO₄, KNO₃ and NaCl + MgSO₄) and salt concentrations in prepared salt solutions ranging from 0.1 to 3 M, and in saturation paste extracts of soils collected from multiple locations where nematode abundance varied from zero to numerous, and where electrical conductivity ranged from 108 to >12,000 μS/cm. Nematode salt tolerance was salt specific; both nematode species survived in low-experimental concentrations of NaCl and MgSO₄, and neither species survived in KNO₃ solutions of any concentration. There was no survival of nematodes in the saturation paste extracts of highly saline soils (4,100 μS/cm), while survival was over 80–97% in less saline soils (1,945 μS/cm). A 1:1 dilution of these highly saline saturation paste extracts increased S. lindsayae survival to 80%, while survival of P. antarcticus was not observed until dilutions of greater than 200%. The results complement previous studies demonstrating niche partitioning of S. lindsayae and P. antarcticus across salinity gradients and strengthen interpretations of the physiological mechanisms underlying previously reported spatial correlation between soil salinity and nematodes abundance in the Antarctic Dry Valleys.     

Storage temperature influences desiccation and ultra violet radiation tolerance of entomopathogenic nematodes

1. The effect of cold (5 °C) and warm (35 °C) storage on desiccation tolerance of cold-adapted Steinernema feltiae, intermediate S. carpocapsae and warm-adapted S. riobrave was evaluated at 5 and 35 °C.     

Cold tolerance of micro-arthropods from Alaskan taiga

Abstract. Mean supercooling points for a variety of soil and litter arthropods including mites, springtails, a heteropteran and immature spiders from a central Alaskan taiga site ranged from -6.3 to -28.5°C during autumn. Variation in supercooling ability of five species of cryptostigmatid mites occurred throughout the year with increased cold tolerance in autumn and early winter concomitant with the temperature pattern of the habitat. No correlation between the level of supercooling and water content of the mites was evident. Changes in the frequency distribution of individual supercooling points occurred in autumn, winter, spring and summer samples which were species specific. All arthropods tested were susceptible to freezing, and the mites utilize supercooling to avoid freezing.     

Cold tolerance of New Zealand alpine insects

New Zealand has extensive alpine and subalpine habitats where, together with some lowland sites, insects are exposed to subzero temperatures. Studies of cold tolerance in New Zealand insects have centred on an alpine weta (Hemideina maori), which is the world's largest freezing tolerant insect, and an alpine cockroach (Celatoblatta quinquemaculata). Both of these insects are moderately freezing tolerant and have ice nucleating agents in their haemolymph and guts. There is some evidence for the survival of intracellular ice formation in the isolated gut tissue of C. quinquemaculata. Trehalose is a suggested cryoprotectant in both H. maori and C. quinquemaculata whilst proline also provides this role in H. maori. Cells and tissues of both insects maintain viability and physiological function during freezing to moderately low temperatures but viability declines at lower temperatures, the most vulnerable tissue presumably setting the limit to the survival of the animal. Antifreeze proteins are found in the gut tissue of C. quinquemaculata and may protect this tissue when freezing occurs in the gut. Several other New Zealand insects are also moderately freezing tolerant and the apparent dominance of this cold tolerance strategy in the New Zealand fauna may reflect the relatively mild climate but unpredictable exposure to subzero temperatures that is typical of many Southern Hemisphere environments.     

Cold tolerance and dehydration in Enchytraeidae from Svalbard

When cooled in contact with moisture, eight species of arctic Enchytraeidae from Svalbard were killed by freezing within minutes or hours at −3 and −5 °C; an exception was Enchytraeus kincaidi which survived for up to 2 days. When the temperature approached 0 °C the enchytraeids apparently tried to escape from the moist soil. The supercooling capacity of the enchytraeids was relatively low, with mean supercooling points of −5 to −8 °C. In contrast, specimens of several species were extracted from soil cores that had been frozen in their intact state at −15 °C for up to 71 days. Compared to freezing in a moist environment, higher survival rates were obtained during cooling at freezing temperatures in dry soil. Survival was recorded in species kept at −3 °C for up to 35 days, and in some species kept at −6 °C for up to 17 days. Slow warming greatly increased survival rates at −6 °C . The results strongly suggest that arctic enchytraeids avoid freezing by dehydration at subzero temperatures. In agreement with this, weight losses of up to ca. 42% of fresh weight were recorded in Mesenchytraeus spp. and of up to 55% in Enchytraeus kincaidi at water vapour pressures above ice at −3 to −6 °C. All specimens survived dehydration under these conditions. Accepted: 12 December 1997