The nematode Nothanguina phyllobia Thorne was found within large foliar galls on the perennial weed Solanum elaeagnifolium Cav. in west Texas. A two-year survey of a 6400 sq-km area in west Texas showed extensive distribution of the nematode. No hosts other than S. elaeagnifolium were observed. Densities of juvenile nematodes in the soil were high. N. phyllobia spread rapidly after small numbers of infective juveniles were applied in a foliar spray to an S. elaeagnifolium population. The host plant declined in vigor and frequently died. Artificial inoculation of an S. elaeagnifolium population with large numbers of the nematodes by broadcasting infected plant tissue resulted in high infection incidence.
leaf gall nematode; biological weed control
Meloidogyne grahami n. sp. is described and illustrated from specimens on tobacco (Nicotiana tabacum) originally from Florence, South Carolina. Considered for several years to be only a race of M. ineognita, this new species readily attacks NC-95 tobacco, a variety with resistance to the M. incognita group that is common in the major U.S. tobacco-producing areas. M. grahami n. sp. is related most closely to the three subspecies of the M. incognita group but differs from all of them, especially in its distinctive perineal pattern and larger larvae (av. 421 μm, vs. 385 μm or less). Also, the dorsal esophageal gland orifice of females of M. grahami n. sp. is further from the base of the styler (5 μm) than in M. i. incognita and M. i. acrita. Comments are given on the distribution of this new species.
taxonomy; morphology; new Meloidogyne species; resistance-breaking; Nicotiana tabacum
Egg masses of Meloidogyne incognita and M. hapla were placed in soil at 10, 12, 16, and 20 C. At regular intervals, eggs from samples of egg masses were released from the gelatinous matrices and their developmental stages recorded. The number of days necessary to complete each stage from gastrulation to hatch is given for each temperature. The minimal temperature threshold for the development of eggs was computed by linear regression to be 8.26 C for M. incognita and 6.74 C for M. hapla.
threshold temperatures; root-knot nematode; development rate
C. elegans responds directionally to a DC current. The response may be to the anode or cathode, depending on the current, potential difference, and ion concentration of KC1, Tracks of the responding nematodes show that electrotaxes are genuine orientation phenomena. The directional movement is not due to the passive movement of nematodes or to the influence of currents on the muscular physiology; electrotaxes are mediated sensorily. Details of the response are described.
behaviour; galvanotaxes; electric current; electric potential
The infectivity of Pratylenchus penetrans on alfalfa seedlings cv. Du Pulls was studied. The dense root-hair zone was the preferred zone of penetration by females, males, and third-stage larvae. A lesion initially appeared as a water-soaked area at the root surface, becoming yellow and elliptical as the nematode entered the cortex, with dark-brown cells later appearing in the centre as the nematode fed. At 20 C, females penetrated roots earlier, faster, and in greater numbers than either males or third-stage larvae. Females penetrated roots at temperatures from 5 to 35 C, with maximum penetration between 10 and 30 C, while males and third-stage larvae penetrated roots only between 10 and 30 C with maximum penetration a t 20 C. Penetration of roots by females, males, and third-stage larvae increased after storage of 5 C for 35 days, but decreased after storage of 140 days or more. Combinations of the three life stages in pairs neither enhanced nor inhibited penetration of roots by individual life stages; males were not attracted to females. Increasing inoculum density up to 20 nematodes/seedling did not affect penetration.
root-lesion nematode; penetration; lesion; Medicago sativum
Helerolylenchus aulumnalis was found in six northern California counties surveyed, and the incitlence of nematode infection of face flies ranged from 4.7 to 43.8%. Intensive studies at a cattle ranch in Yuba County showed that population densities of the host and nematode infections were highest in flies from cow pats receiving full sun. Average host population density was 105.7 puparia per pat, and nematode infection averaged 38.6%. Pats in partial sun averaged 13.5 puparia and 13,1% nematode infection. No face fly was recovered from shaded pats. When data from pats first exposed during day or night were compared, no significant differences in host population density or nematode infection rates were apparent. Uninfected and superinfected flies were more frequent than predicted by a Poisson distribution.
Infected and uninfected female flies of all ages captured on white sticky traps appeared to feed with similar frequency upon a creatny substance which was probably acquired from cattle, However, older infected females fed less on blood and more upon dung than older uninfected females. Percent nematode infection and host population densities were highest in spring and early summer, declined to a midsummer low, and then increased slightly. Both dung-reared flies and captured females showed similar trends in abundance anti infection rates. Regression analysis indicated that H. autumnalis may not be regulating face fly population density.
Biological control; host-parasite relationships; insect-nematode relationships; population dynamics
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.
A mturation-rate relationship for Meloidogyne incognita on Lycopersicon esculentum 'Rutgers' was derived and used to estimate harvest dates for maximmn egg hatch from laboratory cultures at ambient temperatures. Daily maturation increments were totaled (nematode maturation total, NMT) and correlated with hatch from isolated white, yellow, and amber egg masses. Hatch per mass fluctuated periodically from ca. 1.0 NMT, when egg masses were first visible, to 2.5 NMT by which time plants showed stress. Maximum yields from white and yellow masses occurred, with a shorter than expected periodicity, at 1.5-1.8 and 2.1-2.2 NMT. White masses decreased from 90% of the total masses at 1.0 NMT to 5% at 2.5 NMT, as the proportion of yellow and amber masses increased concomitantly. Harvested masses per gram of root varied from 97 to 276; hatch per gram of root, 11,000 to 86,000.
Root-knot nematode; Lycopersicon esculentum; maturation
Determinatitm and use of economic thresholds is considered essential in nematode pest management programs. The economic efficiency of control measures is lnaximized when the difference hetween the crop valne and the cost of pest control is greatest. Since the cost of reducing the nematnde pnpnlation varies with the magnitutle of the reduction attempted, an economic (optimizing) threshold can be determined graphically or mathematically if the nature of the relationships between degree of control and cost, and nematode densities and crop value are known. Economic thresholds then vary according to the nematode control practices used, environmental influences on the nematode damage fnnction, and expected crop yields and values. A prerequisite of the approach is reliability of nematode population assessment techniques.
Pest management; population dynamics; control costs; damage functions; sampling; optimizing thresholds
Proteins and various isozymes were investigated by direct analysis of single specimens in order to check molecular genetic variability, which is not rare in Meloidogyne species in spite of parthenogenetic reproduction. Variability was found in esterases, ocglycerophosphate, malate dehydrogenases, and some other proteins. Other loci appear monomorphic in the genus (for example, catalase), Distinct pools of genes are in a relative accordance with the common described species. Characteristic electrophoretograms are given for M. arenaria, M. javanica, M. incognita, M. hapla, and M. naasi, and it appears that nonspecific esterases are a useful tool supplementing morphology for specific characterization. Because the biochemical evidence is less subjective than the morphological, we believe it is more reliable.
genetic; electrophoresis; proteins; enzymes; Nematoda
Neoaplectaua carpocapsae developed and reproduced in armyworm hosts infected with a granulosis virus (GV). Macerated tissues of dauer juveniles from GV-infecled hosts had sufficient GV to infect 1st and 2nd instar armyworms. Electron-microscope examination of dauer juveniles and adult female nematodes confirmed the presence of GV in the lumen of the intestine. No GV was observed in other tissues of the nematode.
DD-136 nematode; nematode-insect virus interaction; insect virus; Baculovirus
The infectivity of Neoaplectana carpocapsae and Heterorhabditis heliothidis to Apanteles militaris, a gregarious parasite of the armyworm, was deterntined at 100. 1,000, 5,000, and 10,000 nematodes per petri dish. For both nematode species, the percentage of infected A. militaris within a cocoon cluster decreased as inoculum levels decreased. At the highest inoculum level, N. carpocapsae infected an average of 32% of the parasite pupae within a cocoon cluster, whereas H. heliothidis infected an average of 22%. Covariance analysis indicated, however, that N. carpocapsae had significantly greater infectivity than did H. heliothidis. Some of the dauer juveniles of N. carpocapsae on the body of the armyworm contacted the emerging parasites and eventually became enveloped within the silken cocoons. Dauer juveniles produced by N. carpocapsae in parasite pupae could not penetrate and escape from silken cocoons even when the cocoons were placed in a moist environment.
nematode-insect parasite interaction
Resistant and susceptible cultivars of tomato, lima beans, cotton, and alfalfa were tested with 10 populations of Meloidogyne incognita from different California locations. Nine of the populations differed in aggressiveness on the nine cultivars tested. Two populations were especially aggressive toward resistant tomato cultivars.
resistant cultivars; tomato; lima bean; cotton; alfalfa; root-knot nematodes
Metyrapone, an inhibitor of steroid synthesis, affected the survival and rate of development of Heterodera glycines. Metyrapone in aqueous tartaric acid solvent influenced sex ratios. The effect on sex ratios was mediated through the host, whereas the effect on survival was apparently effected directly. Tartaric acid increased larval penetration of soybean roots.
sex ratio; cyst nematodes; soybean
The effect of morphological variants of females of Pratylenchus penetrans, P. neglectus, and P. crenatus on the growth of three vegetables was studied. Variants were characterized by having either a smooth or crenate tail terminus. Pea was inoculated with variants of P. penetrans, one female per seedling, and grown at light intensities ranging from 1,350 to 21,600 lux in a series of five experiments. Only crenate-tailed females of P. penetrans suppressed the growth of pea and only when pea was grown at 3,900 lux. Radish was inoculated with morphological variants of P. penetrans, P. neglectus, and P. crenatus, four females per seedling, and grown at 3,900 lux in two experiments. Again, truly creuate-tailed females of P. penetrans inhibited growth. The two variants of P. penetrans had a similar infectivity, greater than that of the other two species of Pratylenchus. Only crenate-tailed P. penetrans reproduced on radish. Onion was inoculated with variants of P. penetrans and P. crenatus, four females per seedling, and grown at 14 C at 12,900 lux. Again, only crenate-tailed P. penetrans inhibited growth. The variants of P. penetrans had a similar infectivity, greater than that of P. crenatus. Neither species reproduced on onion at low temperatures.
Pea; radish; onion; light intensity
High initial population densities of Heterodera schachtii larvae (36 and 108/gm of soil) greatly retarded the seedling emergence of sugar beet 'Monogerm CSF 1971' in Vineland fine sandy loam. In comparison with controls, initial population densities (Pi's) of 1.7, 3.0, 6.2, and 14.4 larvae/gm of soil respectively reduced the weight of storage roots by 38, 56, 64, and 92%. Weights of tops also decreased with increases in Pi; weights of tap and small feeder roots tended to be higher at all Pi's except the highest. Sucrose percentage was not affected by any initial nematode density. The populations were lower at midseason than at seeding, and at harvest had increased greatly, with respective populations of 339, 402, 222, and 140 larvae/gm of soil. At harvest, cysts/gm of soil and cysts/gm of root were respectively 4.4 and 72, 6.1 and 99, 6.1 and 191, and 5.8 and 140. The maximum rate of multiplication was 150-200. and maximum density was 400 larvae/gm of soil. The high pathogenicity and multiplication rate of the nematode was attributed to optimum temperature conditions and soil type.
sugar beet nematode; Beta vulgaris; crop losses
Thecavermiculatus gracililancea n. gen., n . sp. is described from the roots of Festuca myuros L. ("rattail fescue") a range grass in Monterey County, California. Thecavermiculatus females have a slight terminal prominence on which are located the vulva and anus, while its closest relatives, Atalodera and Sherodera, have a large terminal prominence. Furthermore, in T. gracililancea the hatched second-stage juveniles are retained in the female body while Atalodera and Sherodera females retain embryonated eggs.