CALCIUM CHLOROACETATE AS A SOIL DRESSING AGAINST BEET EELWORM: HETERODERA SCHACHTH SCHMIDT, WITH CERTAIN ADDITIONAL OBSERVATIONS

Calcium chloroacetate at 3 and 6 cwt./acre produced significant increases in the yields of sugar beet (both washed beet and total sugar) in a trial on fen soil of the 'skirt' type infested with beet eelworm, Heterodera schachtii Schmidt. However, the material had no effect on the eelworm content of the soil whether measured by cysts, viable cysts or eggs and larvae. An instance is recorded of a significant drop in the level of the beet eelworm infestation in the presence of sugar beet.     

Field trials with D-D mixture against potato-root eelworm

A D-D mixture has been tested against Heterodera rostochiensis at seven 2-acre sites on sands, silts and blackland soils. Apart from a pilot trial where soil was injected in spring, injections were carried out in the autumn, and potatoes were grown the following year. Factors investigated were rate of application (0, 200, 400 and 800 lb. D-D/acre), depth of injection (4 or 8 in.) and the effect of rolling after injection. At the most responsive of the sites (Wainfleet), increases in yield, kill, and the post-crop eelworm population were all roughly proportional to the rate of application. Under favourable circumstances a 50% increase in yield and something like a 50% reduction in eelworm population 4 weeks after injection can be expected from 800 lb./acre, but the reduction is more than made good during the growth of the subsequent crop; accelerated multiplication of eelworm on the treated plots leads to their having a larger population than the untreated controls at lifting time. Of the sites tested, the blackland soils gave a lower eelworm kill and a much lower yield increase from D-D than silts or sands. After autumn injection the nematocidal, and probably the phytocidal, effects of D-D persist in the soil for many weeks. The hypochlorite method of 'hatching' eelworm larvae for counting has proved unreliable.     

Effect of Meloidogyne incognita and Importance of the Inoculum on the Yield of Eggplant

The relationship between population densities of race 1 of Meloidogyne incognita and yield of eggplant was studied. Microplots were infested with finely chopped nematode-infected pepper roots to give population densities of 0, 0.062, 0.125, 0.25, 0.50, 1, 2, 4, 8, 16, 32, 64, and 128 eggs and juveniles/cm³ soil. Both plant growth and yield were suppressed by the nematode. A tolerance limit of 0.054 eggs and juveniles/cm³ soil and a minimum relative yield of 0.05 at four or more eggs and juveniles/cm³ soil were derived by fitting the data with the equation y = m + (1 - m)z^P⁻T. Maximum nematode reproduction rate was 12,300. Hatch of eggs from egg masses in water or from sodium hypochlorite dissolved egg masses was similar (41% and 39%), but egg viability was significantly greater from egg masses in water (58%) than from sodium hypochlorite dissolved egg masses (12%) after 4 weeks. Greater numbers of nematodes were collected from roots of tomatoes from soil infested with entire egg masses than from tomato roots from soil infested with egg masses dissolved by sodium hypochlorite.     

A comparison of wheat bulb fly (Delia coarctata) egg numbers in ridge and furrow soil samples from potato crops

In soil samples taken with a shovel from 97 potato maincrops in east Scotland during 1978 to 1981, wheat bulb fly (Delia coarctata) eggs were more numerous on ridges than in furrows. The ratio of the number of eggs on the ridge to the number of eggs in the furrow was higher in Lothian Region (3·25) than in Fife Region (1·59) but differed significantly (P < 0·05) from 1·0 in both Regions. To obtain maximum precision of the estimate of the total wheat bulb fly egg population in a potato field, more samples should be taken from the ridge than from the furrow, in approximate proportion to the egg numbers.     

Control of the potato-root eelworm, Heterodera rostochiensis Wollenweber, by allyl isothiocyanate, the mustard oil of Brassica nigra L

Previous work showed that, in the presence of root excretioci of certain crucifen, larvae of the potato-root eelworm do not emerge from the cysts when stimulated by potato-root excretions; a similar lack of response is also shown in the presence of dilute solutions of allyl isothiocyanate, the mustard oil of black mustard. The present paper describes a small-scale field trial in which this mustard oil is applied with peat to the drills at the time of planting. An increase in yield of about 100% resulted from a dressing of the oil equivalent to o.1 cwt/acre.     

Desiccation and egg viability of the ragwort flea beetle,Longitarsus flavicornis (Coleoptera: Chrysomelidae)

A study was conducted to investigate the effect of desiccation on the survival of eggs of Longitarsus flavicornis. Eclosion of L. flavicornis eggs in laboratory trials decreased with increasing desiccation time between 0 days (93% hatching) and 42 days (no egg hatching) at 50±2% relative humidity and 23±2°C. Probit analysis indicated that 25, 50 and 99% mortality of L. flavicornis eggs occurred after 5.7, 9.3 and 50.4 days desiccation, respectively. Egg development varied between a minimum of 8 days at 7 days desiccation to a maximum of 15 days at 28 days desiccation. Hatching span did not differ between treatments with all eggs hatching within 12 days of each other. A relative humidity of 88–100% was measured under ragwort rosettes in non-drought field conditions. This would be expected to facilitate successful egg eclosion. However, the occurrence of summer drought could be detrimental to egg survival.     

Probability of Globodera rostochiensis Spread on Equipment and Potato Tubers

The probability of spreading cysts of Globodera rostochiensis on farming equipment and potato tubers was investigated in naturally infested field plots. The number of cysts recovered from soil that adhered to equipment differed significantly between different pieces of equipment. These differences were related to initial nematode density and, in most cases, to the volume of soil that adhered to the equipment. At an initial density of 0.04 egg/cm³ of soil, significantly more cysts were recovered from a potato digger than from a potato hiller, cultivator, or plow. At an initial density of 0.90 egg/cm³ of soil, significantly more cysts were recovered from the plow than from the other equipment. Although the population density was 22 times greater, only 10 times more cysts adhered 3 to equipment used in soil with a density of 0.90 egg/cm³ of soil than when used in soil infested at 0.04 egg/cm³. The number of potato tuber samples (4.5 kg) that contained cysts with viable eggs was positively correlated with the initial densities of G. rostochiensis in soil in which they were produced. The percentage of tuber samples with cysts containing viable eggs was 10-12% for tubers harvested from soil with densities less than 1 egg/cm³ and 30-76% for tubers harvested from soil with densities greater than 4 eggs/cm³ of soil.     

Studies on the relation between density of Longidorus elongatus and growth of sugar beet, with supplementary observations on Trichodorus spp

Longidorus elongatus attacks sugar beet on light sandy soils in the West Midlands. Severely damaged plants may die or recover, producing fanged roots. Up to 335 L. elongatus/200 g of soil were found around attacked seedling plants and were often visible to the unaided eye on the roots of freshly lifted plants. Five experiments were made and regressions computed of yield of beet, total numbers of plants and numbers of normal and fanged beet on L. elongatus numbers. Between 24% and 50% of roots per 100 L. elongatus/ 200 g were killed or became fanged. Corresponding figures for loss of plant were between 7.5% and 33%. Estimated loss of yield varied between 0.8 and 7.3 tons (2.0–18.3 t/ha)/acre/100 L. elongatus/200 g, the former where the potential yield was high and the latter where poor growing conditions hindered recovery. Large numbers of Trichodorus occurred in two trial sites and there is some evidence of competition between the two genera. Significant negative regressions for Trichodorus spp. were obtained in one trial suggesting a loss of 12% total and 17% normal roots per 100 Trichodorus spp./200 g.     

Effects of dual infections of Puccinia hordei and Erysiphe graminis on barley, cv. Zephyr

Seed tubers of the varieties King Edward, Majestic and Pentland Crown selected as ‘clean’ (lesion-free), moderately, or severely affected by gangrene lesions were planted in field experiments. Infection delayed plant emergence, increased the number of stems/plant, sometimes caused gaps in crops and was associated with increased blackleg. On average severely affected seed yielded 20% less than ‘clean’ seed. Seed infection also increased the proportion of tubers in smaller size grades so that crops from severely infected King Edward seed averaged 1·4 ton/acre (3·5 t/ha) less small ware and 2·5 ton/acre (6·3 t/ha) less large ware than ‘clean’ seed. With Majestic, small ware was increased (0·7 ton/acre (1·8 t/ha)) and large ware decreased (4·4 ton/acre(11·0 t/ha)); Pentland Crown was similarly affected (small ware increased 0·8 ton/acre (2·0 t/ha); large ware decreased 3·9 ton/acre (9·8 t/ha)). In eight of twelve experiments unselected diseased stocks yielded significantly less than ‘clean’ tubers. Other experiments compared seed stocks with different proportions of gangrene-infected seed tubers. Yields decreased as the proportion of diseased seed tubers increased, but differences were significant only when more than 60% were affected. Surprisingly, yields from ‘clean’ tubers also decreased as the proportion of diseased tubers increased in the stocks from which they were selected. Gangrene on progeny tubers after storage was not always related to the amount of gangrene visible on the seed. It was increased by riddling or wounding and decreased by dipping tubers in organo-mercury fungicide before or soon after wounding.     

Assessment of the losses caused to potatoes by the potato cyst nematodes, Globodera rostochiensis and G. pallida

Nine field trials were carried out from 1967 to 1973 on sandy loam soils in Staffordshire and Worcestershire to study the relationship between potato yield and numbers of potato cyst nematodes (Globodera spp.). Three (probably five) of these trial sites appeared to be infested with G. rostochiensis only, whereas both species occurred on the remaining four sites which grew the resistant variety, Maris Piper. Although mixtures of the two species occurred on some plots they tended to have different distributions within each trial site. The results from this work have been analysed, together with those from earlier work in the Eastern Counties on peat and silt soils, over two population density ranges, 0–40 eggs/g (5 sites) and 0–160 eggs/g (16 sites). There is no evidence of any difference in the regression of yield on eggs/g amongst the five sites in the lower range (b =–0.90 + 0.11) nor amongst 15 of the 16 sites in the higher range (b = -0–40 ± 0–02). Analysis of 10 sites with sufficient data in the 40–160 eggs/g range gave b = -0.24 ± 0.06. Thus the regression lines are essentially parallel for each of the two ranges, covering several potato varieties, soil textures and different potential yields and suggest that the varieties used are equally tolerant. The losses are 6.25 t/ha/20 eggs/g for the 0.40 eggs/g range, 1.67 t/ha/20 eggs/g for the 40–160 eggs/g range, and 2.75 t/ha/20 eggs/g as a mean for the whole range. A maximum loss of 22 t/ha is indicated. Peat soils are less dense than mineral soils but there was no need for adjustment in nematode counts. Losses caused by potato cyst nematodes are better expressed as actual yield losses rather than as percentage decreases.     

Primary infection with mouse-derived cysticercoids of Hymenolepis nana prepared from baby or adult mice and secondary infections with eggs or cysticercoids

Oral infection with mouse-derived cysticercoids (cysts) of Hymenolepis nana on day 0 did not make the 5 ± 1 week old mouse host immune to egg challenge by day 7 of the prepatent period, although the number of cyst-derived tapeworms was 1000 times greater than that of egg-derived tapeworms sufficient to make the host immune by day 7. Neither cysts recovered from immunologically competent 5 ± 1 week old donor mice, which should have become immune within 2 days of egg inoculation, nor those from incompetent 5–7 day-old baby mice given eggs when 0–2 days old made the host immune. The time course of differentiation of cysts in baby mice was not different from that in 5 ± 1 week-old mice. Mice infected twice with cysts on days 0 and 4 did not become immune either. Rapid protective immunity against egg challenge was acquired by inoculation exclusively with eggs but not with cysts. Apparently cysts differ from oncospheres in their immunogenicity. The importance of cysts for analysing the mouse—H. nana system from the immunological point of view is discussed.     

Oxygen and the hatch of eggs and migration of larvae of Meloidogyne javanica

The percentage hatch of eggs of Meloidogyne javanica increased asymptotically as the oxygen concentration increased from 0·2 to 21%. Hatch was unaffected by suction pressures of less than pF 3·4 at any oxygen concentration but was decreased by higher suctions. Both the development of embryos and the migration of larvae approached a maximum at an oxygen concentration of about 15%. Hatching was not limited by the rate oxygen diffused through the gelatinous matrix of the egg sac nor was the concentration of oxygen at the surface of an egg sac significantly lower than that within an individual egg. The maximum rate of metabolism appeared to need an oxygen concentration within the egg greater than 10%.     

Wheat bulb fly, Leptohylemyia coarctata Fall., and its effect on the growth and yield of wheat

In two experiments done in successive years to compare the growth and yield of Cappelle wheat either protected from or exposed to attacks by larvae of wheat bulb fly, the plots were previously fallowed, but egg laying was prevented on half of each plot by using Polythene soil covers. In the first season wheat was sown at the end of October, November and December and in the second season in late October and in early January, when there were two sowings, one with and one without a spring application of herbicide. The infestation rate was 1·1-1·7 million eggs per acre, typical of a moderate attack. Larvae had little effect on the yield of October-sown wheat as the plants had two shoots each when first attacked and few were killed. On plots sown late, yield was decreased by up to 22%, as plants had only a single shoot when attacked and many were killed. The main effect of wheat bulb fly was to reduce the number of ear-bearing shoots by killing plants and restricting the production of new shoots. Surviving plants partially compensated by producing more ear-bearing shoots with heavier ears and slightly heavier seeds than normal. Killed plants were not distributed uniformly but were often in patches several feet across. Wheat on the attacked plots ripened more slowly and unevenly than on the unattacked plots. Weather affects the growth of the plants and activity of the larvae and thus partly determines percentage shoot survival.     

Endosymbionts: factors on egg pattern formation

Elimination of the intracellular symbionts of Euscelis plebejus either by X-ray irradiation of the posterior pole of the freshly laid egg or by interruption of egg infection by application of tetracycline or lysozyme to female leafhoppers leads to the production of embryos without abdomens, ‘head-embryos’.Homogenates of symbiont-free eggs and symbiont-containing eggs in the state of invagination have a pH of 7·5±0·2 and 7·0±0·2 and an osmotic pressure (pO) of 8·3±0·2 and 7·8±0·2, respectively. The presence of symbionts leads to a decrease of both the pH and pO.These data indicate that the correct formation of the posterior gradient, necessary for normal abdomen development, is dependent on the presence of endosymbionts at the posterior pole. It is possible that the symbionts change the pH and pO of the posterior gradient. These results are consistent with a hypothetical model of early differentiation of the Euscelis egg.     

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.     

The relationship between numbers of Heterodera schachtii and sugar beet yields on a mineral soil, 1978-81

In a 4-yr field experiment on a mineral soil infested with beet cyst nematode (Heterodera schachtii) the relationship between root yield of sugar beet (y) and initial population of H. schachtii (P_i) fitted the equation: y=y min +(y max - y min) Z^Pi-T y min = 7·7 t/ha, y max = 39·4 t/ha, 2 = 0·99938 and T= 0 eggs/100 g soil. From this information and that obtained during a recent survey of 2766 beet fields, the total national root yield loss caused by H. schachtii was estimated as approximately 10 000 t/annum on mineral soils and (assuming a similar yield loss relationship on all soil types) 30 000 t/annum on organic soils. No consistent differences in efficiency of extracting cysts were found between the Fenwick Can and the flotation column. A bioassay technique was as effective as cyst extraction techniques in identifying infested soils.     

LABORATORY ERRORS ASSOCIATED WITH THE ESTIMATION OF THE POPULATION DENSITY OF HETERODERA SPECIES IN SOIL

As unexpectedly large sampling errors were obtained in preliminary population studies on Heterodera , an examination was made of the laboratory errors associated with sampling for H. göttingiana and H. schachtii. Soil samples were taken from microplots and appeared to be satisfactory, being without the usual heterogeneity found in sampling from fields. There was little evidence of errors introduced by the technique used for estimating the number of eggs and larvae in a subsample. These errors, when they occurred, were always small, and this standard technique was deemed satisfactory. The logarithmic transformation was suitable for statistical analysis of both cyst and egg counts.
Apart from the residual variation, there were two other important sources of variation when sampling for eggs. There was a large variation between sub-samples, caused by differences in the number of cysts and in the number of eggs per cyst. There was also in some instances a difference between observers counting the same eggs of up to 20%. Where a comparative measure of density is sufficient, this bias is probably unimportant, and to increase accuracy of estimates of eelworm density, most laboratory work should be devoted to the separation of cysts from the soil sample.     

Temporal variability in egg production rates of Acartia tonsa Dana in Long Island Sound

The relationship between week-by-week variations in the in situ egg production rates of Acartia tonsa Dana and changes in chlorophyll concentration in several size fractions was investigated by incubating adult females in natural sea water for 24-h periods. Our results indicate that the egg production of A. tonsa in Long Island Sound was better related to the 10 μm chlorophyll size fraction than to the total chlorophyll concentration. The < 10 μm size fraction comprised the greatest percentage of the chlorophyll during July and August when the water column was stratified. Egg production rates were lowest (8.7 eggs · female⁻¹ · day⁻¹) in early August when less than 0.5 μg chlorophyll 1 ⁻¹ was observed in the 10 μm chlorophyll a size fraction. Following destratification in late August, the “fall” diatom bloom occurred and egg production rates increased to the maximum observed rate of 56.6 eggs · female⁻¹ · day⁻¹. At this time, the concentration of the 10μm chlorophyll size fraction was 5.5 μg 1⁻¹. Maximum egg production rates were observed at chlorophyll concentrations as low as 0.8 μg 1⁻¹ in the 10 μm size fraction.     

THE EMERGENCE OF LARVAE FROM FREE EGGS OF THE POTATO-ROOT EELWORM HETERODERA ROSTOCHIENSIS (WOLL.)

A technique for conducting hatching experiments on eggs freed from cysts is described. The form of the hatching response was found to be similar to that of eggs contained within cysts, but the response of the free eggs to the hatching stimulus was slightly more rapid. Investigations into factors affecting free egg hatching showed that it was necessary to presoak cysts before extracting the eggs from them for hatching. Eggs taken from dry cysts or from cysts that had been opened or cracked before presoaking did not respond to diffusate. When free eggs and whole cysts were exposed to the same graded series of dilutions of diffusate, the L.A. values (i.e. log concentrations of hatching factor) derived from plotting the hatching curves were in very close agreement.     

Reproduction of Lumbricillus rivalis (Levinsen) in laboratory cultures and in decaying seaweed

The cocoon production of 144 Lumbricillus rivalis cultured in pairs at 10 ± 1 °C was high over the first 2 weeks of breeding activity and then declined, chiefly because of high mortality. Cocoon deposition lasted for between 1 and 16 weeks, eight pairs of worms producing cocoons for 9 weeks and one pair for 16 weeks. During the total period of cocoon deposition over 9000 eggs (mean 17·4 per cocoon) were deposited. Two decaying wrack bed populations of L. rivalis showed a low level of cocoon and egg production in autumn, rising to an annual maximum in late winter/early spring. In these populations the mean egg content varied seasonally from 17·1 to 47·8 eggs per cocoon. When cocoons in the laboratory were transferred from the site of deposition to incubation dishes 31% hatched, but those left in the substrate showed a 92% hatch. In the naturally occurring populations 19% of the cocoons detached from seaweed fronds hatched, but 62% of those left in situ. Eggs and worm embryos developed to relatively late stages in most cocoons, whatever the rate of hatching; development often continued for up to 2 months after deposition without hatching. Over 50% of the fertile eggs in cocoons from decaying wrack hatched and developed to 5 mm worms.