Effects of Aldicarb and Its Sulfoxide and Sulfone on the Biology of Tylenchulus semipenetrans

In laboratory testing, egg hatch of Tylenchulus semipenetrans was stimulated at concentrations of 1 and 10 μg/ml aldicarb solution and inhibited at 50 and 100 μg/ml. Aldicarb was more inhibitory to egg hatch than the aldicarb sulfoxide and the aldicarb sulfone. Inhibition of hatch at the high concentration was associated with delays in the molting processes, lack of larval movement within the egg, and delays in embryonic development. Nematode motility was reduced at 10, 50, and 100 μg/ml of aldicarb and aldicarb sulfoxide solution, and at 50 and 100 μg/ml aldicarb sulfone. Male development was retarded at 10 μg/nrl and almost completely inhibited at 50 and 100 μg/ml of the three chemicals. In greenhouse tests, female development antl reproduction on roots of citrus seedlings were suppressed by aldicarb at rates of 2.6 μg/ml and completely inhibited at 10.6 μg/ml of soil solution during a 50-day experimental period. Under field conditions, there was little systemic movement of aldicarb into roots located outside treated areas. Aldicarb reduced the nematode larvae and the female adult population in the second year after the second treatment. There were no differences in egg hatch and sex ratio of citrus nematodes between treated and nontreated roots.     

Effects of Two Carbamates on Infective Juveniles of Stemernema carpocapsae All Strain and Steinernema feltiae Ume? Strain

Laboratory bioassays were conducted to determine the effects of two carbamates, carbofuran (an acetylcholinesterase inhibitor) and fenoxycarb (a juvenile hormone analog), on survival and infectivity of the infective juveniles (IJ) of Steinernema feltiae Umeå strain and Steinernema carpocapsae All strain. Both insecticides caused mortality of IJ in a dose-related fashion. The two nematode species were equally sensitive to fenoxycarb (LD₅₀ ca. 0.03mg/ml). Whereas IJ of S. feltiae were several orders of magnitude more sensitive to carbofuran (LD₅₀ ≤ 0.2 μg/ml) than to fenoxycarb, S. carpocapsae IJ displayed approximately the same degree of sensitivity to carbofuran (LD₅₀ 0.01-0.03 mg/ml) as they did toward fenoxycarb. Toxicity of the carbamates was the same at all exposure periods from 24 to 168 hours'' duration. Determinations of infective doses of nematodes required to cause 50% mortality of Galleria mellonella larvae showed that the infectivity of IJ that survived exposure to either of the two carbamates was not compromised by treatment.     

Effects of Environmental Factors and Cultural Practices on Parasitism of Alfalfa by Ditylenchus dipsaci

Cool humid weather enhanced development and reproduction of Ditylenchus dipsaci in alfalfa in laboratory and field studies in Utah. Relative humidity and nematode reproduction were positively correlated (P < 0.05), whereas air temperature and nematode reproduction were negatively correlated (P < 0.05). The greatest number of nematodes per gram of alfalfa tissue was found in nondormant Moapa alfalfa tissue at St. George during April, whereas the greatest numbers of nematodes were found in dormant Ranger alfalfa in June at West Jordan and Smithfield. There was 100% invasion of both resistant Lahontan and susceptible Ranger alfalfa plants at soil moisture levels of 61-94% field capacity. Fall burning of alfalfa to control weeds reduced, and spring burning increased, the incidence of invaded plants, nematodes per gram of plant tissue, and the mortality of susceptible Ranger (P < 0.01) and Moapa (P < 0.01) alfalfa plants over that of plants in nonburned control plots. Fall burning also reduced and spring burning increased the incidence of invaded plants (P < 0.05), but had no influence on nematodes per gram of plant tissue or the mortality of resistant Lahontan and Nevada Synthetic XX alfalfa over those of plants in control plots.     

Nonfumigant Nematicides for Control of Root-knot Nematode to Protect Carrot Root Growth in Organic Soils

Greenhouse tests were conducted to determine the effects of two kinds of Meloidogyne hapla inoculum on the growth and quality of carrot roots, and the protection afforded in each case by nonfumigant nematicides in organic soils. For all treatments the percentage of carrots damaged was greater with larvae alone as inoculum than with larvae and eggs, indicating that most of the damage occurs early during formation of the taproot. Fosthietan, aldicarb, and oxamyl at 4 and 6 kg ai/ha protected the roots during formation and gave a lasting control of root-knot nematode. There was some nematode damage to the roots with phenamiphos and carbofuran at 4 and 6 kg ai/ha. Isazophos, diflubenzuron, and fenvalerate gave little protection to carrot roots and did not control root-knot nematode effectively.     

Population Development and Reproduction of Fungus- and Bacterium Feeding Nematodes in the Presence of Insect Growth Regulators

The insect growth regulators (IGRs), diflubenzuron and BAY SIR 8514, at 300 and 1,000 ppm a.i. in potato dextrose agar (PDA) inhibited the radial growth of the fungus Rhizoctonia solani host of Aphelenchus avenae. The IGRs had no effect on the growth of the bacterium Pseudomonas pseudoalcaligenes host of Acrobeloides nanus and Diplogaster iheritieri. At 59 ppm a.i., neither IGR inhibited the population development of A. nanus and D. iheritieri on P. pseudoalcaligenes; however, diflubenzuron stimulated the population development of D. iheritieri. At 300 ppm, both IGRs inhibited the population development of A. nanus and D. iheritieri; however, BAY SIR 8514 was more effective than diflubenzuron except on A. nanus L₄''s. At 300 ppm, only BAY SIR 8514 affected the population development of A. avenae, except the L₄''s. At 1,000 ppm, both IGRs inhibited development, except diflubenzuron for L₂ and L₃''s. Again, BAY SIR 8514 was more effective than diflubenzuron. With single females of A. nanus and D. iheritieri, both IGRs at 300 ppm reduced egg laying, inhibited embryonation, and slowed larval development.     

Effect of Aldicarb,Ethoprop, and Carbofuran on Control of Coffee Root-knot Nematode,Meloidogyne exigua

Egg hatch of Meloidogyne exigua was significantly inhibited in 14 days pretreatment with aldicarb, ethoprop, or carbofnran at concentrations higher than 0.1 μg/ml; these eggs were found to delay hatch in 19 days posttreatment in ethoprop. Aldicarb and carbofuran solutions at concentrations greater than 0.1 μg/ml significantly decreased the motility and the life span of the second-stage juveniles; aldicarb was more toxic than carbofuran to the nematode. In a field test, aldicarb (Temik 10G), ethoprop (Mocap 10G), and carbofuran (Furadan 5G and Furadan Liquid 350F) significantly decreased M. exigua populations.     

Effects of Oxamyl on the Citrus Nematode,Tylenchulus semipenetrans,and on Infection of Sweet Orange

Foliar sprays of 4 μg/ml oxamyl on sweet orange trees in a greenhouse slightly depressed the number of Tylenchulus semipenetrans larvae obtained from roots and soil, but similar treatments were not effective in two orchards. Soil drench treatments decreased the number of citrus nematode larvae obtained from roots or soil of citrus plants grown itt a greenhouse and in orchards. Exposure to 5-10 μg/ml of oxamyl in water was lethal to only a few second-stage larvae treated 10 days, and many second-stage larvae in 2.0 μg/ml oxamyl recovered motility when transferred to fresh water. Aqueous solutions of 50 and 100 μg/ml of oxamyl were toxic to citrus nematode larvae. Additional observations indicate that oxamyl interfered with hatch of citrus nematode larvae and was nematistatic and/or protected sweet orange roots from infection. Oxamyl degraded at different rates in two soils. The number of citrus nematode larvae that infected and developed on sweet orange roots was increased by an undetermined product of the degradation of oxamyl in soil, water, and possibly within plants. This product apparently was translocated in roots.     

Interaction of Vesicular-arbuscular Mycorrhizal Fungi and Phosphorus with Meloidogyne incognita on Tomato

The influence of two vesicular-arbuscular mycorrhizal fungi and phosphorus (P) nutrition on penetration, development, and reproduction by Meloidogyne incognita on Walter tomato was studied in the greenhouse. Inoculation with either Gigaspora margarita or Glomus mosseae 2 wk prior to nematode inoculation did not alter infection by M. incognita compared with nonmycorrhizal plants, regardless of soil P level (either 3 μg [low P] or 30 μg [high P] available P/g soil). At a given soil P level, nematode penetration and reproduction did not differ in mycorrhizal and nonmycorrhizal plants. However, plants grown in high P soil had greater root weights, increased nematode penetration and egg production per plant, and decreased colonization by mycorrhizal fungi, compared with plants grown in low P soil. The number of eggs per female nematode on mycorrhizal and nonmycorrhizal plants was not influenced by P treatment. Tomato plants with split root systems grown in double-compartment containers which had either low P soil in both sides or high P in one side and low P in the other, were inoculated at transplanting with G. margarita and 2 wk later one-half of the split root system of each plant was inoculated with M. incognita larvae. Although the mycoorhizal fungus increased the inorganic P content of the root to a level comparable to that in plants grown in high P soil, nematode penetration and reproduction were not altered. In a third series of experiments, the rate of nematode development was not influenced by either the presence of G. margarita or high soil P, compared with control plants grown in low P soil. These data indicate that supplemental P (30 μ/g soil) alters root-knot nematode infection of tomato more than G. mosseae and G. margarita.     

In-Vitro and In-Vivo Effects of Aldicarb on Survival and Development of Heterodera schachtii

Aqueous solutions of 5-500 μg/ml aldicarb inhibited hatching of Heterodera schachtii. Addition of hatching agents, zinc chloride, or sugarbeet root diffusate, to the aldicarb solutions did not decrease the inhibition of hatching. When cysts were removed from the aldicarb solufions and then treated for 4 wk in sugarbeet root diffusate, larvae hatched and emerged. Treatments of newly hatched larvae of H. schachtii with 5-100 μg/ml aldicarb depressed later development of larvae on sugarbeet (Beta vulgaris). Similar treatments with aldicarb sulfoxide had less effect on larval development, and aldicarb sulfone had no effect. Numbers of treated larvae that survived and developed were inversely proportional to concentration (0.1-5.0 μg/ml) and duration (0-14 days) of aldicarb treatments. Development of H. schachtii on sugarbeet grown in aldicarb-treated soil was inversely proportional to the concentration of aldicarb in the tested range of 0.75 - 3.0 μg aldicarb/g of soil. Transfer of nematode-infected plants to soil with aldicarb retarded nematode development, whereas transfer of plants first grownin treated soil to nematode-infested soil only slightly suppressed nematode development. Development of H. schachtii was inhibited in slices of storage roots of table beet (B. vulgaris), sugarbeet and turnip, (Brassica rapa), that had grown in soil treated with aldicarb.     

Distributed Egg Production Functions for Meloidogyne arenaria in Grape Varieties and Consideration of the Mechanistic Relationship between Plant and Parasite

Nematode egg production rates, as mediated by environmental conditions and host status, are important determinants of population development. Rates of egg production by Meloidogyne arenaria varied from 0.48 to 1.0 egg per female per DD₁₀ (degree days above 10 C) in different grape varieties. The length of the egg production period ranged from 550 to 855 DD₁₀ where measurable, and was generally longer in those varieties where the production rate was slow. We hypothesize that if a successful infection site is established, a constant number of eggs is produced if favorable environmental conditions prevail. Mechanistic coupling structures between plant growth and nematode population models are formulated. The nematode population influences metabolite supply through its effect on physiological efficiency and also acts as a metabolic sink; the degree of plant physiological stress influences nematode population development by affecting the sex ratio and egg production rates.     

Toxicity of several insecticide formulations against adult German cockroaches (Dictyoptera: Blattellidae)

Toxicity of bendiocarb, chlorpyrifos, cyfluthrin, cypermethrin, fenvalerate, hydramethylnon, malathion, propetamphos, propoxur, and pyrethrins against the adult German cockroaches, Blattella germanica (L.), was investigated. At LD50, cyfluthrin was the most toxic insecticide to adult males (0.53 microgram/g), adult females (1.2 micrograms/g), and gravid females (0.85 microgram/g). Malathion was the least toxic insecticide to adult males (464.83 micrograms/g), adult females (335.83 micrograms/g), and gravid females (275.90 micrograms/g). Males and gravid females were generally more sensitive than nongravid females to the insecticides that we tested. In tests with malathion, however, males were more tolerant. The order of toxicity of the insecticide classes varied among the stages of adult German cockroaches. The order of toxicity for males and nongravid females was pyrethroids greater than pyrethrins = organophosphates (except malathion) greater than carbamates = amidinohydrazone. The order of toxicity for gravid females was pyrethroids greater than pyrethrins = organophosphates (except malathion) greater than carbamates greater than amidinohydrazone. These differences in toxicity suggest that sex differences should be considered when determining insecticide toxicity for German cockroaches.     

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.     

A Bioassay to Estimate Root Penetration by Nematodes

An in vitro bioassay with a 96-well microtiter plate was used to study the effect of lectins on burrowing nematode penetration of citrus roots. In each well, one 4-mm root segment, excised from the zone of elongation of rough lemon roots, was buried in 0.88 g dry sand. Addition of a Radopholus citrophilus suspension containing ca. 300 nematodes in 50 μ1 test solution completely moistened the sand in each well. The technique assured uniform treatment concentration throughout the medium. Within 16-24 hours, burrowing nematodes penetrated citrus root pieces, primarily through the cut ends. The lectins (100 μg/ml) Concanavalin A (Con A), soybean agglutinin (SBA), wheat germ agglutinin (WGA), and Lotus tetragonolobus agglutinin (LOT) stimulated an increase in penetration of citrus root segments by Radopholus citrophilus. Concentrations as low as 12.5 μg/ml Con A, LOT, and WGA stimulated burrowing nematode penetration of citrus roots. Heat denaturation of the lectins reversed their effect on penetration; however, incubation of nematodes in lectin (25 μg/ml) with 25 mM competitive sugars did not. The reason for enhanced penetration associated with lectins is unclear.     

Influence of Volcanic Ash on Infectivity and Reproduction of Two Species of Meloidogyne

Mount St. Helens volcanic ash was incorporated into a loamy sand greenhouse soil mix to produce concentrations of 0, 0.5, 1.0, 2.0, 4.0, 8.0, 25, 50 and 100% ash. Chemical and physical properties of the various mixtures were determined. Three experiments were conducted in a greenhouse to determine if volcanic ash had any influence on root-knot nematode survival and infectivity. Tomato, Lycoperscion esculentum, seedlings cv. Columbia, susceptible to Meloidogyne hapla and M. chitwoodi were planted into pots of the soil-ash concentrations and infested with one of the two nematode species. Tomato seedlings were harvested 30, 50 and 60 days later and the roots examined for nematode infection and reproduction. Ash incorporation had no deliterious effect on root-knot nematodes in any of the experiments reported here. Nematode infection and reproduction on tomato were not affected at any ash concentration.     

Factors Affecting the Biology and Pathogenicity of Heterodera schachtii on Sugarbeet

A direct relationship exists between soil temperature and Heterodera schachtii development. The average developmental period of two nematode populations from Lewiston, Utah, and Rupert, Idaho, from J2 to J3, J4, adult, and the next generation J2 at soil temperatures of 18-28 C were 100, 140,225, and 399 degree-days (base 8 C), respectively. There was a positive relationship (P < 0.05) between nematode Pi, nematode generations, and sugarbeet yields. The greatest sugarbeet growth inhibition (87%) occurred when sugarbeets were exposed to a Pi of 12 eggs/cm³ soil for five generations (1,995 degree-days), compared with a 47% inhibition when plants were exposed to the same Pi for two generations. There was a negative correlation (P < 0.05) between the Pi, Pf, and sugarbeet yield for each population threshold. The smaller the Pi, the greater the sugarbeet yields and the greater the Pf. Root yields were 80 and 29 t /ha and Pf were 8.4 and 3.6 eggs/cm³ soil when sugarbeet seeds were planted at Pi of 0.4 and 7.9 eggs/cm³. respectively, at a soil temperature of 8 C. The number of years rotation with a nonhost crop required to reduce the nematode population density below a damage threshold level of 2 eggs/cm³ depends on the Pi. A Pi of 33.8 eggs/cm³ soil required a 5-year crop rotation, whereas a Pi of 8.4 eggs/cm³ soil required a 2-year crop rotation.     

Growth of Potato and Control of Pratylenchus penetrans with Oxamyl-treated Seed Pieces in Greenhouse Studies

Oxamyl was applied to both uncut and cut potato tubers in aqueous solutions of 1,000 to 32,000 μg/ml. Emergence in greenhouse pots was delayed for a day or more after soaking cut tuber pieces in 32,000 μg/ml. After 10 weeks plant growth was greater, relative to the control, when Pratylenchus penetrans-infested soil was planted with cut tubers soaked for 20 minutes in 32,000 μg/ml. Soaking for 40 minutes did not increase nematode control nor affect plant growth. Oxamyl applied to tubers at 1,000 μg/ml reduced the numbers of P. penetrans in the soil by 20% and in the roots by 35%; at 32,000 μg/ml, the numbers of P. penetrans in the soil were reduced by 73-86% and in the roots by 86-97%. The numbers of P. penetrans did not increase in the roots of plants developed from cut tubers soaked in 32,000 μg/ml over a period of 10 weeks, but numbers of lesion nematodes had begun to increase in the soil.     

Neoaplectana glaseri: essential amino acids

Required for a nematode's reproduction in a chemically defined medium are the nine mammalian essential amino acids (sensu strictu). Needed in addition to lysine, tryptophane, histidine, phenylalanine, leucine, isoleucine, threonine, methionine, and valine is arginine which is marginally essential for mammals. Tyrosine, nonessential for mammals, is not absolutely required by the nematode but is beneficial in terms of onset time and quantity of reproduction. Aspartic acid, nonessential for the nematode and mammals, is toxic for adult nematodes at and above 4.8 mg/ml medium. The nematode, Neoaplectana glaseri, is parasitic in insect grubs but the strain used has been cultivated in species isolation on kidney slices continuously since (1944).     

Evaluation of the Protective and Therapeutic Properties of DBCP for Control of Root-Knot Nematode on Tomato

Twelve soil drenches over a period of 30 days with DBCP concentrations of 40 μg/ml did not completely prevent infection of tomato plants by root-knot nematode juveniles. Repeated DBCP drenches of 40 μg/ml halted gall development during the drenches, but 10 days after drenching was discontinued galls were apparent. DBCP drenches at 200 μg/ml prevented tomato root development, and 40 μg/ml slowed it. Ten μg/ml increased the height of root-knot-infected plants, but not their top weights. Treated plants were lanky. Protective drenches of 2.5 to 40 μg/ml of DBCP decreased nematode populations and increased fruitfulness. DBCP as a therapeutant reduced the incidence of galling on new roots and halted increases in gall size on previously infected roots but did not improve fruitfulness or plant size significantly.     

In Vitro Hatch and Survival of Heterodera glycines as Affected by Alachlor and Phenamiphos

Heterodera glycines (race 1) eggs were exposed to aqueous solutions o f selected concentrations o f the herbicide alachlor and the organophosphate nematicide phenamiphos alone and in herbicide-nematicide combinations. Phenamiphos (0.5 μg/ml) + alachlor (0.063, 0.125, or 1.0 μg/ ml) treatments increased the incidence o f juvenile hatch over that of untreated controls at 18 days. At 18 and 25 days, phenamiphos (0.5 μg/ml) treatments contained more juveniles than did phenamiphos at 1.0 μg/ml. Phenamiphos (1.0 μg/ml) alone and in combination with alachlor (1.0 μg/ ml) suppressed hatch for 21 days and juvenile survival for more than 21 days. Alachlor treatments enhanced juvenile survival compared to the untreated control at 14 and 21 days. Technical alachlor gave results similar to those of the formulated product.     

Sensitivity of Meloidogyne incognita and Rotylenchulus reniformis to Fluopyram

Fluopyram is a succinate dehydrogenase inhibitor (SDHI) fungicide that is being evaluated as a seed treatment and in-furrow spray at planting on row crops for management of fungal diseases and its effect on plant-parasitic nematodes. Currently, there are no data on nematode toxicity, nematode recovery, or effects on nematode infection for Meloidogyne incognita or Rotylenchulus reniformis after exposure to low concentrations of fluopyram. Nematode toxicity and recovery experiments were conducted in aqueous solutions of fluopyram, while root infection assays were conducted on tomato. Nematode paralysis was observed after 2 hr of exposure at 1.0 µg/ml fluopyram for both nematode species. Using an assay of nematode motility, 2-hr EC₅₀ values of 5.18 and 12.99 µg/ml fluopyram were calculated for M. incognita and R. reniformis, respectively. Nematode recovery in motility was greater than 50% for M. incognita and R. reniformis 24 hr after nematodes were rinsed and removed from a 1-hr treatment of 5.18 and 12.99 µg/ml fluopyram, respectively. Nematode infection of tomato roots was reduced and inversely proportional to 1-hr treatments with water solutions of fluopyram at low concentrations, which ranged from 1.3 to 5.2 µg/ml for M. incognita and 3.3 to 13.0 µg/ml for R. reniformis. Though fluopyram is nematistatic, low concentrations of the fungicide were effective at reducing the ability of both nematode species to infect tomato roots.