Gaseous Requirements for Postparasitic Development of Romanomermis culicivorax

The development of postparasitic stages of Romanomermis culicivorax was studied under various concentrations of oxygen and carhon dioxide. The nematode developed poorly if only nitrogen was supplied; only one-third molted and all died eventually. In the presence of 5% CO₂ - 95% N₂, development was normal; most nematodes molted and oviposited with respective mean developmental times of 32 and 50 d. Addition of 0.2% O₂ stimulated development; molting and oviposition commenced at days 18 and 41, respectively. There was an additional stimulation of development by increasing amounts of O₂ up to 1%, but concentrations greater than 1% produced no additional stimulation. Carbon dioxide was required for development after exsheathment under anaerobic conditions or O₂ concentrations less than 1%. Oxygen or CO₂ were not required for embryological development or egg hatch. It is suggested that post-parasitic stages function as facultative anaerobes,     

Carbon Dioxide and Temperature Gradielits in Baermann Funnel Extraction of Rotylenchulus reniformis

Vermiform Rotylenchulus reniformis were anesthetized in water by 10-40% CO₂ but were fully motile for 24 hours in water below 5% CO₂. When air containing 2.5% CO₂ was blown onto agar, nematodes accumulated at the point of highest CO₂ concentration. Nematodes also accumulated when chilling (0.2-1 C) of agar by the gas flow at the accumulation point was offset with heat from a fiber optic. In Baermann funnels containing R. reniformis in silt loam and sandy clay loam soils, CO₂ in funnel water increased during 24 hours from 0 to ca. 1%; more CO₂ accumulated below the soil layer than above. Bubbling air with 2.5% CO₂ into water below soil in covered funnels increased the CO₂ gradient and increased nematode extraction, whereas bubbling air without CO₂ below soil purged CO₂ from the water and decreased nematode extraction. Manipulation of CO₂ within funnels usually increased extraction by only 30% and never by more than 3-fold. Controlling temperature gradients consistently increased extraction by 2-30-fold.     

Respiration Rate of Steinernema feltiae Infective Juveniles at Several Constant Temperatures

Respiration was measured in dauer stages of the insect-parasitic nematode Steinernema feltiae (= Neoaplectana carpocapsae) at 7, 17, and 27 C. Respiration, Q₁₀, and nematode viability were temperature dependent. Mean O₂ consumption for 5 × 10⁵ nematodes the first 24 hours was 0.27 ml at 7 C, 0.83 ml at 17 C, and 2.68 ml at 27 C. The Q₁₀ was 3.10 for 7-17 C and 3.24 for 17-27 C. Some nematodes died during 2, 14, and 21 days at 27, 17, and 7 C, respectively. The respiratory quotient was below 1 at all temperatures tested. A standard asymptotic model is expressed as oxygen consumed = 2.77 * {1 - exponent[-time * exponent(-B + C * temperature)]}; where 2.77 is the maximum response at 27 C. This model estimates nematode O₂ consumption and viability at storage temperatures between 7 and 27 C. The nematodes died when the O₂ concentration reached 0.5 ml/5 × 10⁵ nematodes. This model may be used to predict O₂ requirements of S. feltiae infective juveniles when stored as a waterless concentrate.     

Pathogenicity of Meloidogyne hapla to Lettuce as Affected by Inoculum Level, Plant Age at Inoculation and Temperature

Pathogenicity of Meloidogyne hapla to lettuce was influenced by inoculum level, age of plant at inoculation and temperature. Top weight of ''Minetto'' lettuce was reduced 32% when 2-week-old lettuce plants were each inoculated with five egg masses. Higher inoculum levels did not further decrease top weight significantly. Inoculation at seeding reduced top growth more than inoculation of 1-, 2- or 3-week-old seedlings. M. hapla reduced growth more at the intermediate (21.1 C night and 26.7 C day), than at the low (15.5 C night and 21.1 C day) or high (26.7 C night and 32.2 C day), temperature regimes.     

The Influence of Environmental Factors on the Respiration of Plant-Parasitic Nematodes

Respiration of selected nematode species was measured relative to CO₂ level, temperature, osmotic pressure, humidity, glucose utilization and high ionic concentrations of sodium and potassium.In general, respiration was stimulated most by the dominant environmental factors at levels near those expected in the nematode''s "natural" habitat. Soil-inhabiting nematodes utilized O₂, most rapidly with high (1-2%) CO₂ whereas a foliar nematode (Aphelenchoides ritzemabosi) did so with 0.03% CO₂, the concentration typically found in air. Temperature optima for respiration corresponded closely to those for other activities. Ditylenchus dipsaci and Pratylenchus penetrans adults and Anguina tritici and A. agrostis second-stage larvae respired within the range of osmotic pressures from 0 to 44.8 arm and respiration of their drought-resistant stages was stimulated by increasing osmotic pressure which accompanies the onset of drought. Rehydration of A. tritici and A. agrostis larvae with RH as low as 5% stimulated measurable respiration. Glucose utilization from liquid medium by A. tritici larvae or A. ritzembosi was not detectable. Supplemental Na⁺ stimulated respiration of Anguina tritici, K⁺ did not.     

Effect of Temperature on Growth, Development and Reproduction of Meloidogyne hapla in Lettuce

Temperature was an important factor in growth, development and reproduction of Meloidogyne hapla in lettuce. Growth, as measured by increase in diameter of females, was not appreciably different at the intermediate (21.1 C night and 26.7 C day) and high (26.7 C night and 32.2 C day) temperature regimes, but was considerably less at the low temperature regime (15.5 C night and 21.1 C day) than at the two higher temperature regimes. Second-stage female larvae developed into adults 14 days after inoculation at the high, 18 days at the intermediate and 34 days at the low temperature regime. Eggs were observed 20 days after inoculation at the high, 26 days at the intermediate and 54 days at the low temperature regime. Number of eggs and larvae after 6 weeks was greater at the high than at the intermediate temperature regime and no eggs or larvae occurred at the low temperature regime during the observed 6 weeks.     

Effects of Oxygen and Temperature on the Activity and. Survival of Nothanguina phyllobia

The effects of oxygen and temperature on the activity and survival of infective forth-stage juveniles of Nothanguina phyllobia Thorne were examined in aqueous suspension. Rate of movement was not affected by a wide range of O₂ concentration (0.8-8.6 ppm). Activity decreased below 0.8 ppm 0 2, and at 0.15 ppm O₂ nematodes became motionless. Activity increased as a linear function of temperature up to a thermal optimum of 24 C; beyond 24 C activity decreased. Survival was greatly prolonged at low temperature. At 23 C, 50% mortality occurred within 7 d, whereas at 4 C, 70% survived after 98 d.     

Interrelationship of Heterodera schachtii and Meloidogyne hapla on Tomato

Invasion of tomato (Lycopersicon esculentum L.) roots by combined and sequential inoculations of Meloidogyne hapla and a tomato population of Heterodera schachtii was affected more by soil temperature than by nematode competition. Maximum invasion of tomato roots, by M. hapla and H. schachtii occurred at 30 and 26 C, respectively. Female development and nematode reproduction (eggs per plant) of M. hapla was adversely affected by H. schachtii in combined inoculations of the two nematode species. Inhibition of M. hapla development and reproduction on tomato roots from combined nematode inoculations was more pronounced as soil temperature was increased over a range of 18-30 C and with prior inoculation of tomato with H. schachtii. M. hapla minimally affected H. schachtii female development, but there was significant reduction in the buildup of H. schachtii when M. hapla inoculation preceded that of H. schachtii by 20 days.     

Effects of Temperature and Root Leachates on Embryogenic Development and Hatching of Meloidogyne chitwoodi and M. hapla

At 20 C the duration of the embryogenic development of Meloiclogyne chitwoodi and M. hapla was about 20 days. At 10 C the embryogenic development was 82-84 days for M. chitwoodi and 95-97 days for M. hapla. The effect of distilled water and root leachates of potato cv. Russet Burbank, tomato cv. Columbian, and wheat cv. Hyslop on the hatching of eggs of the two root-knot nematode species was investigated at 4, 7, 10, 15, 20, and 25 C (± 1 C). Cumulative egg taatch was no greater in root leachates titan in distilled water, but temperature did significantly affect egg hatch (P = 0.05). Less than 1% of the eggs of both nematode species hatched at 4 C. The percent cumulative hatch at 10 C was significantly less (P = 0.05) than at higher temperatures for both nematodes and significantly more (P = 0.05) M. chitwoodi eggs hatched than did M. hapla eggs. At 15 G the percent cumulative hatch of both species was significantly lower (P = 0.05) than that at 20 and 25 C. The percent cumulative egg hatch of two species did not differ at 25 C, but was higher (P = 0.05) at 25 C than at 20 C. At 7 C the emergence of M. chitwoodi juveniles was about seven times (P = 0.01) greater than that of M. hapla in distilled water.     

The Effect of Single and Combined Heat and CO2 Stimuli at Different Ambient Temperatures on the Behavior of Two Plant-Parasitic Nematodes

Pratylenchus penetrans and Ditylenchus dipsaci were reared at 15-16 C, and their behavior towards single and combined heat and CO₂ stimuli was studied at ambient temperatures of 8.6 and 27.3 C. At the lower temperature, attractivity of the heat source was prevalent in both species, but CO₂ was also attractive. At the higher ambient temperature (27.3 C), the reaction to CO₂ was more positive and more rapid than to heat. In fact, at this temperature only D. dipsaci was attracted to the heat source, whereas P. penetrans did not react positively. The combined stimulation of heat and CO₂ caused D. dipsaci to aggregate more strongly than did a single stimulus; this applied to both ambient temperatures. For P. penetrans exposed to the low temperature (8.6 C), the combined stimuli were about as attractive as was the better of the single stimuli; i.e., heat. At the high temperature (27.3 C), the combined stimulation was less effective than the better of the single stimuli; i.e., CO₂. At this ambient temperature, the thermonegative reaction seems to dominate over the CO₂-positive one. The reaction of D. dipsaci was generally stronger in all experimental variants than that of P. penetrans. Insofar as temperature gradients play a role in locating host plant roots, their efficacy would seem to be restricted to a favorable temperature range. Within this range, combined heat and CO₂ stimuli might improve attractivity.     

Populations of Pratylenchus penetrans Relative to Decomposing Nitrogenous Soil Amendments

Populations of Pratylenchus penetrans decreased in soil following addition of 70 and 700 ppm N in the form of nitrate, nitrite, organic nitrogen, or ammonium compounds. Nitrate was less effective than other nitrogen carriers. Population reduction is principally attributed to ammonification during decomposition. This hypothesis is supported by chromatographic analyses of soil atmospheres, survival of nematodes in pure CO₂ and N₂, inverse relationship of CO₂, content in amended soils to nematode populations, and direct relationship of NH₃-N content of amended soils to nematode populations.     

Pratylenchus penetrans (Cobb) Populations as Influenced by Microorganisms and Soil Amendments

Numbers of Pratylenchus penetrans in sterilized soil decreased significantly 2 weeks after the addition of 1% w/w (700 ppm N) nonsterile soybean meal (SBM), or sterilized SBM in combination with selected microorganisms. Sterilized SBM had no effect on nematode populations in steamed soil. Bacteria and fungi in the presence of SBM were more effective than the actinomycetes tested, causing up to 96-100% reduction in nematode populations. Simpler nitrogenous compounds included KNO₂, Ca(NO₃)₂, NH₄NO₃, (NH₄)₂CO₃, urea, and peptone, decreased nematode populations with variable effectiveness when added to steamed soil at 700 ppm N; KNO₂ was the most nematicidal.     

Development of the False Root-knot Nematode,Nacobbus aberrans, on Sugarbeet

The duration of the embryogenic development of Nacobbus aberrans (= N. batatiformis) took 9-10 days at 25 C and 51 days at 15 C. The J₁ molted in the egg; hence the Je emerged from the egg. The effect of distilled water attd root leachates of kochia and sugarbeet was investigated at 5, 10, 15, 20, and 25 C. Root leachates did not significantly affect the percent of cumulative hatch of eggs, but temperature did significantly affect emergence of juveniles (p = 0.05). Less than 1, 5, and 20% of eggs hatched at 5, 10, and 15 C, respectively. The percent of cumulative hatch at 20 C was four times greater than at 15 C, while the highest percentage of juveniles emerged at 25 C. The duration of postembryogenic development from J₂ inoculation until the appearance of mature females with egg masses took 38 days, and the life cycle from egg to egg was completed in 48 days at 25 C. All immature stages, young females and males were migratory endoparasites. Young females were able to leave the root swellings, where they developed from juvenile stages, and re-enter the root, where they formed a true gall and became sedentary. Thirty days after inoculation with J₂ nematodes, specimens were detected in root tissues at 10, 15, 20, 25, and 30 C, hut not at 5 C. Five days after inoculation at 23 C ( ± 2 C), juveniles had penetrated the roots and caused slight swellings of the tip and axis of sugarbeet feeder roots. Large cavities extended from the cortical parenchyma to the periphery of the stelar area, and 50 % of the central cylinder was destroyed 25 days after inoculation at 23 C. No syncytia formation were detected in the sugarbeet root swellings infected with juveniles. Syncytia were associated only with adult females; hyperplasia, abnormal proliferation of lateral roots, and asymmetry of root structure were additional anatomical changes induced by adult females. Only very smooth annules but no cuticular ornamentations were noted by SEM on the perineal area of adult females.     

Decomposition of Plant Debris by the Nematophagous Fungus ARF

In the study of the biological control of plant-parasitic nematodes, knowledge of the saprophytic ability of a nematophagous fungus is necessary to understand its establishment and survival in the soil. The objectives of this study were (i) to determine if the nematophagous fungus ARF (Arkansas Fungus) shows differential use of plant residues; and (ii) to determine if ARF still existed in the soil of a field in which ARF was found originally and in which the population level of Heterodera glycines had remained very low, despite 15 years of continuous, susceptible soybean. Laboratory studies of the decomposition of wheat straw or soybean root by ARF were conducted in two separate experiments, using a CO₂ collection apparatus, where CO₂-free air was passed through sterilized cotton to remove the microorganisms in the air and then was passed over the samples, and evolved CO₂ was trapped by KOH. Milligrams of C as CO₂ was used to calculate the percentage decomposition of the plant debris by ARF. Data indicated ARF decomposed 11.7% of total organic carbon of the wheat straw and 20.1% of the soybean roots in 6 weeks. In the field soil study, 21 soil samples were taken randomly from the field. Only 3 months after the infestation of the soil with H. glycines, the percentage of parasitized eggs of H. glycines reached 64 ± 19%, and ARF was isolated from most parasitized eggs of H. glycines. Research results indicated ARF could use plant residues to survive.     

Repulsion of Meloidogyne incognita by Alginate Pellets Containing Hyphae of Monacrosporium cionopagum,M. ellipsosporum,or Hirsutella rhossiliensis

The responses of second-stage juveniles (J2) of Meloidogyne incognita race 3 to calcium alginate pellets containing hyphae of the nematophagous fungi Monacrosporiura cionopagum, M. ellipsosporum, and Hirsutella rhossiliensis were examined using cylinders (38-mm-diam., 40 or 72 mm long) of sand (94% <250-μm particle size). Sand was wetted with a synthetic soil solution (10% moisture, 0.06 bar water potential). A layer of 10 or 20 pellets was placed 4 or 20 mm from one end of the cylinder. After 3, 5, or 13 days, J2 were put on both ends, on one end, or in the center; J2 were extracted from 8-ram-thick sections 1 or 2 days later. All three fungal pellets were repellent; pellets without fungi were not. Aqueous extracts of all pellets and of sand in which fungal pellets had been incubated were repellent, but acetone extracts redissolved in water were not. Injection of CO₂ (20 μl/minute) into the pellet layer attracted J2 and increased fungal-induced mortality. In vials containing four randomly positioned pellets and 17 cm³ of sand or loamy sand, the three fungi suppressed the invasion of cabbage roots by M. javanica J2. Counts of healthy and parasitized nematodes observed in roots or extracted from soil indicated that, in the vial assay, the failure of J2 to penetrate roots resulted primarily from parasitism rather than repulsion. Data were similar whether fungal inoculum consisted of pelletized hyphae or fungal-colonized Steinernema glaseri. Thus, the results indicate that nematode attractants and repellents can have major or negligible effects on the biological control efficacy of pelletized nematophagous fungi. Factors that might influence the importance of substances released by the pellets include the strength, geometry, and duration of gradients; pellet degradation by soil microflora; the nematode species involved; and attractants released by roots.     

Food Consumption of the Free-Living Aquatic Nematode Pelodera chitwoodi

A Cartesian diver respirometer was used to measure O₂ uptake and respiratory quotients at 25 C. Respiratory quotients were about 0.70 in starved nematodes, and 0.80 in third-stage and adult nematodes that had fed on bacteria. The energy output as measured by O₂ uptake was inversely related to the concentration of bacteria in the medium, indicating reduction in feeding effort. Feeding bacteria to third-stage nematodes in divers quickly resulted in peak respiration rates averaging 6.4 nl O₂/μg wet weight nematode per hour (QO₂) or six times the endogenous rate. In about 4 hr, the rates fell and then stabilized at a QO₂ of 2.5. Adult males fed bacteria in divers had a peak QO₂ of 2.8 or twice the starved rate. Adult females fed bacteria had a peak QO₂ of 3.7. Starving adult males and third-stage larvae were estimated to lose 2.4% and 1.4%, respectively, of their body weight per day in the form of fat based on the caloric equivalent o f oxygen used and a respiratory quotient of 0.70. The caloric content of the bacteria fed to nematodes in divers was determined. It was then calculated that both third-stage larvae and adult males ingested bacteria equivalent to 4.4 × 10⁻⁵ cal/μg wet weight nematode tissue per hour when feeding. Of the bacterial calories ingested, the larvae used 27% and adults 21% for respiration. It was estimated that males ingested 3.1 × 10⁶ bacteria and females 10 × 10⁶ bacteria during an 8-day life span.     

Optimal Release Rates for Attracting Meloidogyne incognita,Rotylenchulus reniformis,and Other Nematodes to Carbon Dioxide in Sand

Movement of vermiform stages of Meloidogyne incognita, Rotylenchulus reniformis, Ditylenchus phyllobius, Steinernema glaseri, and Caenorhabditis elegans in response to carbon dioxide was studied in 40- and 72-mm-long cylinders of moist sand inside 38-mm-d acrylic tubes. Meloidogyne incognita, R. reniformis, and S. glaseri were attracted to CO₂ when placed on a linear gradient of 0.2%/cm at a mean CO₂ concentration of 1.2%. When CO₂ was delivered into the sand through a syringe needle at flow rates between 2 and 130 μl/minute, the optimal flow rate for attracting M. incognita and R. reniformis was 15 μl/minute, and maximal attraction of the two species from a distance of 52 mm was achieved after 29 and 40 hours, respectively. After 24 hours, a total CO₂ volume of 20 cm³ was sufficient to induce 96% of all M. incognita introduced to move into the half of the cylinder into which CO₂ was delivered and more than 75 % to accumulate in the 9 cm³ of sand volume nearest the source. Results indicate it may be possible to use a chemical or biological source of CO₂ to attract nematodes to nematicide granules or biocontrol agents.     

Host Suitability of Twelve Leguminosae Species to Populations of Meloidogyne hapla and M. chitwoodi

Legumes of the genera Astragalus (milkvetch), Coronilla (crownvetch), Lathyrus (pea vine), Lotus (birdsfoot trefoil), Medicago (alfalfa), Melilotus (clover), Trifolium (clover), and Vicia (common vetch) were inoculated with a population of Melaidogyne chitwoodi from Utah or with one of three M. hapla populations from California, Utah, and Wyoming.Thirty-nine percent to 86% of alfalfa (M. scutellata) and 10% to 55% of red clover (T. pratense) plants survived inoculation with the nematode populations at a greenhouse temperature of 24 ± 3°C. All plants of the other legume species survived all nematode populations, except 4% of the white clover (T. repens) plants inoculated with the California M. hapla population. Entries were usually more susceptible to the M. hapla populations than to M. chitwoodi. Galling of host roots differed between nematode populations and species. Root-galling indices (1 = none, 6 = severely galled) ranged from 1 on pea vine inoculated with the California population of M. hapla to 6 on yellow sweet clover inoculated with the Wyoming population of M. hapla. The nematode reproductive factor (Rf = final nematode population/initial nematode population) ranged from 0 for all nematode populations on pea vine to 35 for the Wyoming population of M. hapla on alfalfa (M. sativa).     

In Vitro Embryo Explant Cultures of Peanut to Evaluate Resistance to Ditylenchus destructor

Population densities of D. destructor on embryo explants of 22 peanut genotypes grown in vitro were compared with those in roots and seeds of the same genotypes grown in the greenhouse. During the first 8 weeks after inoculation, the optimum incubation period was 6 weeks for maximum reproduction of Ditylenchus destructor on embryo explants of peanut (Arachis hypogaea L. cv. Sellie) inoculated with 250 nematodes at 25 C. Nematode numbers increased 17-fold. Deletion of MnSO₄ H₂O and a higher KH₂PO₄ concentration in the medium resulted in higher nematode reproduction. Resistance or susceptibility to D. destructor was observed in seeds of several genotypes but was not matched by differences in host suitability in roots. The results indicate that the factor for resistance or susceptibility to D. destructor is synthesized in the seeds of peanut but is not translocated to the roots. Use of embryo explant cultures of peanut as a rapid method to evaluate resistance to D. destructor did not work under the conditions described.     

Long-Term Conditioning to Elevated pCO2 and Warming Influences the Fatty and Amino Acid Composition of the Diatom Cylindrotheca fusiformis

The unabated rise in anthropogenic CO₂ emissions is predicted to strongly influence the ocean’s environment, increasing the mean sea-surface temperature by 4°C and causing a pH decline of 0.3 units by the year 2100. These changes are likely to affect the nutritional value of marine food sources since temperature and CO₂ can influence the fatty (FA) and amino acid (AA) composition of marine primary producers. Here, essential amino (EA) and polyunsaturated fatty (PUFA) acids are of particular importance due to their nutritional value to higher trophic levels. In order to determine the interactive effects of CO₂ and temperature on the nutritional quality of a primary producer, we analyzed the relative PUFA and EA composition of the diatom Cylindrotheca fusiformis cultured under a factorial matrix of 2 temperatures (14 and 19°C) and 3 partial pressures of CO₂ (180, 380, 750 μatm) for >250 generations. Our results show a decay of ~3% and ~6% in PUFA and EA content in algae kept at a pCO₂ of 750 μatm (high) compared to the 380 μatm (intermediate) CO₂ treatments at 14°C. Cultures kept at 19°C displayed a ~3% lower PUFA content under high compared to intermediate pCO₂, while EA did not show differences between treatments. Algae grown at a pCO₂ of 180 μatm (low) had a lower PUFA and AA content in relation to those at intermediate and high CO₂ levels at 14°C, but there were no differences in EA at 19°C for any CO₂ treatment. This study is the first to report adverse effects of warming and acidification on the EA of a primary producer, and corroborates previous observations of negative effects of these stressors on PUFA. Considering that only ~20% of essential biomolecules such as PUFA (and possibly EA) are incorporated into new biomass at the next trophic level, the potential impacts of adverse effects of ocean warming and acidification at the base of the food web may be amplified towards higher trophic levels, which rely on them as source of essential biomolecules.