Pterotylenchus cecidogenus n. gen., n. sp., a New Stem-gall Nematode Parasitizing Desmodium ovalifolium in Colombia

Pterotylenchus cecidogenus n. gen., n. sp. from stem-galls of Desmodium ovalifolium Wall. in Colombia is described and illustrated. The new genus belongs to Anguinidae and is related to Orrina Brzeski, 1980 but is unique in having large vulval flaps. P. cecidogenus has females with body 0.59-0.8 mm long, stylet 9-11 μm long, no median oesophageal bulb, a crustaformeria of 32-36 cells, a short post-vulval uterine sac, and a conical pointed tail.     

Effects of Soil Compaction and Meloidogyne incognita on Cotton Root Architecture and Plant Growth

The effects of a soil hardpan and Meloidogyne incognita on cotton root architecture and plant growth were evaluated in microplots in 2010 and 2011. Soil was infested with M. incognita at four different levels with or without a hardpan. The presence of a hardpan resulted in increased plant height, number of main stem nodes, and root fresh weight for cotton seedlings both years. Meloidogyne incognita decreased height and number of nodes for seedlings in 2010. Nematode infestation increased seedling root length and enhanced root magnitude, altitude, and exterior path length in 2010. This was also the case for root length and magnitude in 2011 at lower infestation levels suggesting compensatory growth. A hardpan had no consistent effect on these root parameters but increased root volume in both years. A hardpan hastened crop maturity and increased the number of fruiting branches that were produced, while M. incognita infection delayed crop development and reduced plant height and number of bolls. Both M. incognita infection and a hardpan reduced taproot length and root dry weight below the hardpan in both years. Root topological indices under all the treatments ranged from 1.71 to 1.83 both years indicating that root branching followed a herringbone pattern. The techniques for characterizing root architecture that were used in this study provide a greater understanding of changes that result from disease and soil abiotic parameters affecting root function and crop productivity.     

Effect of Plant Age and Transplanting Damage on Sugar Beets infected by Heterodera schachtii

Sugar beet (Beta vulgaris L. cv. Monogerm C.S.F. 1971) seeds sown into Vineland fine sandy loam, infested with 15,500 H. schachtii juveniles/pot, showed little growth during an 11-week test in the greenhouse. Seedlings transplanted at 2, 4, and 6 weeks of age had 32, 30, and 31% less top weight and 71, 68, and 59% less root weight, respectively, compared to controls grown in nematode-free soil. Nematode reproduction in both direct-seeded and transplanted sugar beets was limited and related to root weight. Shoot/root ratios were increased by the nematodes in all nematode-infected beets compared to those grown in soil without nematodes. In contrast to seeding or transplanting sugar beets into nematode-infested Vineland fine sandy loam, an inoculation of Beverly fine sandy loam supporting 0 (seeds), 2-, 4-, and 6-week-old sugar beet seedlings with 7,400 juveniles/pot, followed by 11 weeks of growth in the growth-room, resulted in top weight losses of only 13, 3, 18, and 15% and losses in root weight of 44, 38, 36, and 38%, respectively. Nematode reproduction was high and all shoot/root ratios were increased by the nematode compared to the noninoculated controls. These experiments have shown that sugar beets sown into nematode-infested soil are damaged much more heavily by H. schachtii juveniles than seeds inoculated with the nematode immediately following sowing. Results indicate that an increase in tolerance of sugar beets to attack by H. schachtii does not occur beyond the first 2 weeks of growth and that transplanting damage lowers the tolerance of seedlings to nematode attack.     

The Nematode Heterotylenchus autumnalis and Face Fly Musca autumnalis: A Field Study in Northern California

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.     

Effects of Environments,Meloidogyne incognita Inoculum Levels,and Glycine max Genotype on Root-knot Nematode-Soybean Interactions in Field Microplots

Five soybean cultivars (Braxton, Gordon, Jeff, Bragg, and Wright) resistant to Meloidogyne incognita (Mi) and three susceptible cultivars (Coker 156, GaSoy 17, and Coker 237) were grown at two locations for four seasons in microplots with increasing initial soil population densities (Pi) of Mi. The resistant cultivars and Coker 156 yielded better than GaSoy 17 and Coker 237 at all Pi. Yield response was dependent on environmental conditions and at one location was stimulated on Braxton, Gordon, Jeff, and Bragg by low Pi. Although Mi reproduced well on all cultivars, the pattern of reproduction differed. Population densities of Mi leveled off after 90 days on GaSoy 17 and Coker 237 but were still increasing after 120 days on the resistant cultivars; population densities were lower on resistant than on the susceptible cultivars. The population density of Mi on Coker 156 after 120 days was intermediate between those on the other susceptible and on the resistant cultivars. Mi population densities followed the same pattern under varying environmental conditions.     

Distribution of Nothanguina phyllobia and Its Potential as a Biological Control Agent for Silver-leaf Nightshade

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.     

斜纹夜蛾的生物学特性

通过室内饲养及田间调查,揭示了斜纹夜蛾生活史、各虫态发育历期及存活率;测定了各龄幼虫的取食量、成虫性比及产卯量;同时揭示了田间成虫种群消长动态。     

Phenology of recruitment and infection patterns of Ascocotyle pachycystis, a digenean parasite in the sheepshead minnow, Cyprinodon variegatus

In northwest Florida, Cyprinodon variegatus are parasitized by Ascocotyle pachycystis, a digenean parasite that forms metacercarial cysts in the lumen of the bulbus arteriosus. Field experiments revealed that fish accumulated parasites at an uneven rate within the highly seasonal trematode recruitment period. Older (= larger) fish had higher rates of parasite recruitment and higher parasite prevalences and densities (numbers of metacercariae per individual fish) than did younger (= smaller) fish. Nearly all adults were parasitized (prevalence range 70-100%), and parasite densities ranged from zero to 6800 per fish. Parasite distributions were clumped (= aggregated) in fish of all age classes but were less heterogeneous in early juveniles and adults than they were in late juveniles. Parasites affected the population dynamics of sheepshead minnows by causing reduced winter survivorship, as evidenced by an increase in the average size of fish and a decrease in the average infection intensity over the winter. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature Effects on Survival and Development of Heleidomermis magnapapula in the Laboratory

The mermithid Heleidomermis magnapapula Poinar and Mullens, a parasite of the biting midge Culicoides variipennis (Coquillett), was exposed to constant temperatures in the laboratory. Survival of the free-living stages and development times of eggs and the parasitic phase were inversely related to temperature. Average preparasite longevity was 70, 46, 42, and 22 hours at 15.6, 21.1, 26.7, and 32.2 C, respectively. Females survived significantly longer than males. Longevity in days (females/males) at different temperatures was 17.3/11.0 at 4.4 C, 9.0/8.2 at 15.6 C, 5.9/5,1 at 21.1 C, 5.2/4.7 at 26.7 C, and 4.4/3.6 at 32.2 C. Embryogenesis required 44 ± 2 degree days above a thermal minimum of 10.1 C, while parasitic development in host larvae required 214 ± 10 degree days above a thermal minimum of 8.9 C. Parasite responses to temperature were very closely related to temperature-dependent host development patterns.     

Biology of parasite populations: population dynamics of bothriocephalids (Cestoda-Pseudophyllidea) in teleostean fish

Relationships between sympatric populations of four species of Cestoda belonging to the genus Bothriocephalus ( B. barbarus. B. gregarius, B. funiculus and B. scorpii ) and populations of their respective hosts Scophthalmus rhombus, Pserra maxima, Ciliata mustela and Myoxocephalus scorpius were investigated. The parasites were overdispersed within their host populations. The mean intensities of B. burbarus were 1.59 ( s.d. =0.83) in the Mediterranean (Gulf of Lions) and 1.25 ( s.d. =0.53) in the Atlantic (coasts of Brittany). The mean intensities of B. gregarius were 62.3 ( s.d. =49.7) in the Mediterranean and 14.06 ( s.d. =18.48) in the Atlantic, compared to 1.78 ( s.d. =0.3) for B. funiculus and 21.6 ( s.d. =17.3) for B. scorpii .
The distribution of prevalence of B. gregarius corresponded to a lognormal distribution while those of B. barbatus and B. fwticulus corresponded to negative binomials. No differences in infection could be related to host sex. The parasitization of B. gregariusdepended on host size. In brill, infection by E. barbatus was independent of host size and remained stable after the fish reached 180mm in length. Parasitization of turbot by E. gregarius was lower in young fish (≤110–150 mm) and increased with the host size. Compared to the Atlantic populations of B. gregarius and B. barbatus, the Mediterranean populations were more frequently and intensively infected. The differences in the population dynamics of B. gregarius and B. barbarus would appear to depend on whether or not the life cycle involves a paratenic host.     

Distribution of Tylenchulus semipenetrans in a Texas Grapefruit Orchard

Distribution of the citrus nematode (Tylenchulus semipenetrans) was studied over 18 months in a 6-year-old orchard of grapefruit (Citrus paradisi cv. Ruby Red) on sour orange (C. aurantium) rootstock. The 1.8-ha orchard was under chemical weed control, no tillage, and flood irrigation. Highest numbers of nematodes were found in the top 15 cm of the soil profile. The nematode population peaked in April and declined to lowest levels in August and September. Numbers of nematodes were negatively correlated (r = -0.95) with soil temperatures above 29 C. Soil populations of nematodes were not correlated with soil moisture. The distribution of the nematode in the field was highly skewed and was described by a negative binomial. In this 1.8-ha block, five soil samples of 12 cores each would provide an estimate within 20% of the true nematode population mean with 95% confidence.     

Influence of Alfalfa Plant Growth on the Multiplication Rates and Ceiling Population Density of Meloidogyne hapla

The rates of reproduction and multiplication of Meloidogyne hapla decreased as a result of self-regulatory, density-dependent processes with time and nematode population increase in the soil and roots of Medicago sativa cv. Cuf 101. Juvenile, egg, and mature female population densities increased at a maximum rate until damage to the host resulted in alfalfa yield reductions. Temporal differences in multiplication and reproduction rates of M. hapla were observed to be a function of initial population density (Pi), host damage, and root biomass, indicating increased levels of competition for a constant but limited number of feeding sites. Over time, a log linear relationship emerged between multiplication rate of M. hapla and Pi. Slopes of -0.90953 for combined eggs and juveniles and -0.71349 for mature females indicated a gradual approach to ceiling densities. Reproductive rates decreased exponentially from an initial maximal value of 200 to a relatively constant rate of 53 eggs per female.     

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.     

Morphological and Histochemical Changes Occurring during the Life-span of Root-tip Galls on Lolium perenne Induced by Longidorus elongatus

The RNA and protein content of perennial ryegrass root-tip galls induced by Longidorus elongatus were measured from transverse sections and the morphology described. Galls progressed through five distinct stages and were viable for only 10-12 days at 18 C, after which they collapsed and became necrotic. In the initial stage hypertrophy occurred and cells contained enlarged nuclei and nucleoli, a greater proportion of cytoplasm, and increased concentrations of protein. This was followed by hyperplasia; cells divided to give two or four daughter cells, accompanied by a proportionate reduction in volumes of cytoplasm, nuclei, and nucleoli and reduced concentrations of RNA and protein. The third stage was secondary hypertrophy with enlarged, amoeboid nuclei and nucleoli and a significant increase in concentration of RNA and protein. In the final two stages, as feeding by L. elongatus progressively removed cell contents, most cells were devoid of inclusions and galls collapsed and were invaded by soil bacteria. This ordered development and exploitation of galls suggests that L. elongatus may have two phases in its feeding.     

Influence of Meloidogyne incognita on Resistant and Susceptible Sweet Potato Cultivars

Effects of several population densities ofMeloidogyne incognita on the sweet potato cultivars Centennial (susceptible) and Jasper (moderately resistant) were studied. Field plots were infested with initial levels (Pi) of 0, 10, 100, 1,000, 5,000, and 10,000 eggs and juveniles/500 cm³ soil in 1980 and 0, 100, 1,000, 2,000, 3,000, 4,000, and 5,000 in 1981. M. incognita population development trends were similar on both cultivars; however, at high Pi, more eggs and juveniles were recovered from Centennial than from Jasper. The highest Pi did not result in the highest mid-season (Pm) counts. Pi was negatively correlated with the number of marketable roots and root weight but positively correlated with total cracked roots, percentage of cracked roots, and cracking severity. Jasper tolerated higher Pi with greater yields and better root quality than Centennial. Cracking of fleshy roots occurred with both cultivars at low Pi.     

Comparative genetic diversity of parasites and their hosts: population structure of an urban cockroach and its haplo-diploid parasite (oxyuroid nematode)

Few studies have investigated the genetic structure of both host and parasite populations at a level of populations and at a level of individuals. We investigated the genetic structure of the urban cockroach Blattella germanica and its oxyuroid parasite Blatticola blattae. Random amplified polymorphic DNA (RAPD) markers were used to quantify genetic diversity between and within four populations (from two cities in France) of the host and its parasite. Diversity based on phenotypic frequencies was calculated for each RAPD marker using Shannon-Wiener's index. We used multivariate analyses to test the significance of genetic differentiation between host and parasite populations. Analysis of molecular variance was also used. Both methods gave similar results. Diversity between pairs of individuals was estimated by Nei & Li's index. Genetic diversity was higher within host or parasite populations (80% and 82%, respectively, of explained diversity) than between host or parasite populations (20% and 18%, respectively, explained diversity). The genetic distances between pairs of parasite populations (or individuals) were not correlated with the genetic distances between the corresponding pairs of host populations (or individuals).