Relationships of Initial Population Densities of Meloidogyne incognita and M. hapla to Yield of Tomato

Microplots 80 × 100 cm, infested with varying initial population densities (P_i) of Meloidogyne incognita or M. hapla, were planted to tomato at two locations. Experiments were conducted in a sandy loam soil at Fletcher, N. C. (mountains) where the mean temperature for May to September is ca 20.7 C, and in a loamy saml at Clayton, N. C. (coastal plain) where the mean temperature for May to Septemher is ca 24.8 C. In these experimentally infested plots, M. incognita and M. hapla caused maximunt yield losses of 20-30%, at lhe mountain site with Pi of 0-12,500 eggs and larvae/500 cm³ of soil. In the coaslal plain, M. incognita suppressed yields up to 85%, and M. hapla suppressed yields up to 50% in comparison with the noninfested control. A part of the high losses at this site apparently was due to M. incognita predisposing tomato to the early blight fungus. In a second experintent, in which a nematicide was used to obtain a range of P_is (with P_i as high as 25,000/50 cm³ of soil) at Fletcher, losses due to M. incognita were as great as 50%, but similar densities of M. hapla suppressed yields by only 10-25%. Approximate threshold densities for both species ranged from 500 to 1,000 larvae and eggs (higher for surviving larvae) for the mountain site, whereas nutnbers as low as 20 larvae/500 cm³ of soil of either species caused signiticant damage in the coastal plain. Chemical soil treatments proved useful in obtaining various initial population densities; however, problems were encountered in measuring effective inoculum after such treatments, especially in the heavier soil.     

Efficacy of Oxamyl Against Heterodera schachtii on Cabbage

The efficacy of oxamyl in controlling Heterodera schachtii on cabbage was determined by applying various contbinations of soil drenches at 6.7 kg (a.i.)/ha and foliar sprays at 0.04 kg (a.i.)/100 liters of water to cabbage seedlings. Pretransplant drenches provided some control of H. schachtii over a 13-week period. A single foliar spray of oxamyl 1 week before transplanting apparently prevented penetration of H. schachtii larvae; post-transplant sprays were relatively ineffective. A pretransplant or transplant drench combined with a foliar application 2 weeks after transplanting provided the most effective control. The effectiveness of drenches plus post-transplant sprays is probably due to the spray augmenting the action of the drench in inhibiting the development of larvae after penelration.     

Efficacy of Multiple Applications of Oxamyl and Phenamiphos for Controlof Pratylenchus penetrans in Birdsfoot Trefoil

Preplant soil applications of granular phenamiphos effectively reduced Pratytenchus penetrans in soil during the seeding year and 1 year after, and in the roots of birdsfoot trefoil 2 years after seeding. Forage yields were increased in the season following application of phenamiphos, but stands of plants/m² were not greater (P = 0.05) than those in the checks 1 and 2 years after treatment. Additional spring applications of phenamiphos 1 and 2 years after seeding further reduced numbers of nematodes in the soil but did not improve forage yields or plant stand over that of a single application. Broadcast preplant soil sprays of oxamyl followed by several foliar sprays at different rates and frequencies of application over a 3-year period restricted populations of P. penetrans in the soil and roots of birdsfoot trefoil but did not consistently result in increased forage yields. Stands of birdsfoot trefoil continued to decline each year even with oxamyl treatments.     

Enzymes of the tricarboxylic acid cycle in Obeliscoides cuniculi (Nematoda; Trichostrongylidae) during parasitic development

The specific activities of the enzymes of the tricarboxylic acid cycle; citrate synthase, aconitase, isocitrate dehydrogenase, succinate dehydrogenase, fumarase, and malate dehydrogenase, were determined in early fifth-stage, young and mature adult Obeliscoides cuniculi, the rabbit stomach worm. ∝-Ketoglutarate dehydrogenase activity could not be determined in any fraction. Fumarate reductase activity was found only in the mitochondrial fraction while all other enzymes, including an NADP-dependent malic enzyme were localized in the cytoplasm. Glutamate dehydrogenase, acid and alkaline phosphatase activities were also recorded. High levels of those enzymes acting in the “reversed” direction, i.e. MDH and fumarase relative to the enzymes of the “forward” direction, i.e. citrate synthase, aconitase and isocitrate dehydrogenase suggests that under anaerobic conditions a modified tricarboxylic acid cycle can operate. Some variations in specific activities were apparent as the worms matured but no qualitative differences were observed.     

Dictyocaulus viviparus: The role of pepsin in the exsheathment of infective larvae

Following the report of Silverman and Podger (1964) that pepsin formed an association with larval receptor sites on D. viviparus and that exsheathment had an absolute requirement for pepsin, the role of pepsin was studied in greater detail. A range of enzyme incubation, pepsin labeling, histochemical and electron microscopical techniques were used. Pepsin did cause exsheathment of D. viviparus but, it was not an absolute requirement. Exsheathment occurred in a range of proteolytic enzymes each at its optimum pH. Findings suggest that the area of weakness around the anterior end of the larvae is digested by external protease and that, in vivo, exsheathment is caused by the gut enzymes of the host.     

Stimuli for cuticle formation and ecdysis in vitro of the infective larva of Anisakis sp. (Nematoda: Ascaridoidea)

Third-stage larvae of the genus Anisakis from the fish Leionura atun (Trichiuroidei: Perciformes) form a new cuticle and moult in vitro in about 72 h. If the culture medium is Krebs-Ringer under 5% carbon dioxide in air at 37°C, relatively few moult and survival is poor. But more moult and survival is enhanced if worms are incubated in tissue culture medium 199, even if the gas phase is air, although they moult more quickly if it contains 5% carbon dioxide. In both Krebs-Ringer and 199 the benefits of high concentrations of carbon dioxide only accrue if the gas is present during the first 40 h of incubation. Worms do not feed in these media until they have moulted.     

Some Ultrastructural Changes Induced in Resistant and Susceptible Soybean Roots Following Infection by Rotylenchulus reniformis

A developmental electron microscopic study of the parasitism of Rolylenchulus reniforrnis in resistant ''Peking'' and susceptible ''Lee'' soybeans was made during a 21-day period under controlled conditions. Within 2 days of inoculation, the nematode had penetrated the cortical cells to the endodermis where it inserted its stylet, secreted and initiated syncytial formation and cell hypertrophy. Syncytia primarily involved pericycle tissues and, to a lesser extent, xylem parenchyma and endodermis. When identifiable, the cell into which the nematode stylet was inserted to initiate syncytial development was endodermal. Susceptible tissues exhibited two basic phases of development during this infection period: (i) an initial phase represented by partial cell wail lysis and separation; and (ii) an anabolic phase, characterized by organelle proliferation and development accompanied by secondary wall deposits, which provided nutrition for sessile female development. The resistant or hypersensitive reaction (HR) lacked the anabolic phase found in the susceptible reaction, and was characterized by an extension and usually accelerated type of Iysis found in the first phase of the syncytial development. The HR was usually very evident 4 days after inoculation, and could be identified by an almost complete lysis of the cell walls and cytoplasm. The possibility that the initial cell of the developing syncytium or "prosyncyte" may influence a susceptible or resistant reaction is discussed. Successive stages of cell wall dissolution and the deposition of secondary cell walls are described.     

Freezing and Storing Ditylenchus dipsaci in Liquid Nitrogen

After 18 months of storage at -150 C, some larvae of Ditylenchus dipsaci, which had been treated in a 7.5% solution of dimethyl sulphoxide and cooled to -25 C before storage, were still viable on thawing. Some survivors penetrated and developed normally in stems of alfalfa seedlings. Tests showed that active larvae could be frozen directly, thus eliminating the need to use the quiescent stage of this nematode previously thought necessary for successful storage at cryogenic temperatures. The method described is suitable for long-term storage of D. dipsaci and may, with slight modifications, be used to preserve other plant-parasitic nematodes.     

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.     

Rhabditis pellio Schneider (Nematoda) from the Earthworm,Aporrectodea trapezoides Duges (Annelida)

Studies were conducted on the behak, ior of the nematode, Rhabditis pellio, in the earthworm, Aporrectodea trapezoides, from southern California. Juvenile and adult nematodes were found in the bladders and tubules of the metanephridia of the host. Similar nematodes that entered the coelom were encapsulated and incorporated into multiple capsules ("brown bodies"). It was demonstrated that this host response is an effective defense reaction since dead and dying nematodes, as well as living forms, were found in the capsules.