Slug Numbers Research Articles

Comparison of molluscicides based on metaldehyde, methiocarb or aluminium sulphate

In a field trial in November 1984, six proprietary molluscicides reduced slug damage to Chinese cabbage seedlings. None gave complete protection. Plant damage was less after treatment with a paste formulation of metaldehyde than after application of metaldehyde in loose bran, but no other significant differences between chemicals were observed. Effects of molluscicides on slug numbers and activity from 2 to 14 days after application, as determined by traps baited with loose bran, were more complex. Neither metaldehyde nor methiocarb pellets significantly decreased the numbers of Deroceras spp., Arion ater, A. hortensis agg. and Milex sowerbyi that were trapped. Numbers of D. reticulatum trapped in grass and M. sowerbyi in all traps were significantly greater on plots treated with metaldehyde than on untreated plots. Methiocarb pellets significantly reduced numbers of A. fasciatus agg., A. subfuscus and M. budapestensis. The times taken to apply different treatments in the field were noted. In the laboratory, some Deroceras reticulatum recovered from all molluscicide treatments used at recommended rates. Only methiocarb killed significant numbers in the laboratory. Even apparently healthy slugs consumed less food for c. 6 days after exposure to metaldehyde or methiocarb. The relevance of these observations to prevention of slug damage is discussed.

Slugs as a primary limitation to establishment of sod-seeded lucerne

The variable degree of success obtained with sod-seeded lucerne in the north-eastern United States had been attributed to slug and insect activity, although the evidence was circumstantial. Our aims were to examine the effects of a molluscicide (methiocarb) and an insecticide (carbofuran), and their interaction with level of vegetative cover on response of sod-seeded lucerne plants (establishment and damage) and slug numbers and to determine what relationship (if any) there was between slug numbers and plant response. Results are based on six field experiments seeded in mid-August and early September 1980 at Ithaca, NY. Removal of vegetation and application of pesticides reduced seedling losses and damage and generally reduced slug numbers, but response to the pesticides varied according to presence or absence of vegetative cover and whether the experimental site carried a ‘high’ or ‘low’ slug activity. As reflected by increased seedling numbers and reduced damage, the main response to molluscicide (and insecticide) occurred in the presence of cover at ‘low’ activity sites. However, at the site with a ‘high’ slug activity, slug numbers were reduced by the molluscicide only where cover had been removed. It was concluded that insects and slugs, particularly the latter, can seriously limit establishment of sod-seeded lucerne in the north-eastern United States.

Slug numbers, biomass and respiratory metabolism in a beech woodland - Wytham Woods, Oxford.

Four species of slug occurred on the site but a single species, Arion hortensis Férussac, dominated in terms of numbers, biomass and respiratory metabolism. This species was found to have two main generations per year, a finding which contrasts with the annual life-cycle described for arable situations in NE England. A majority of slugs was found in areas with deep leaf litter and ground vegetation. Mean annual population density was 34 m-2 while mean biomass equalled 266 mg d.wt.m-2. Respiratory metabolism was calculated to be in a range equivalent to 18.101-29.686 kJ m-2 yr-1. The most probable figure for annual food consumption was estimated at 3 to 4 g d.wt. m-2 yr-1 i.e. 1.28 to 1.70% of ground litter disappearance yr-1. The P/B ratio was 3.1 and net population production efficiency 36.4%.

Field Trials for the Control of Slugs on Winter Wheat

SUMMARYIn a series of field trials during 1968–1970, 4 per cent methiocarb or 3 per cent metaldehyde baits, applied to plots before drilling winter wheat, effectively reduced the numbers of slugs found by various methods of trapping after treatment. In the dry conditions prevailing at most of the sites, there were few consistent differences between methiocarb and metaldehyde. Little grain damage occurred on the control plots at any of the sites as weather conditions after drilling did not favour slug activity. Small increases in plant stand were obtained on the treated plots but differences between treatments were not significant.

The Distribution and Abundance of Slugs on an Arable plot in Northumberland

The variations in numbers of slugs on an arable plot at Close House, Northumberland (Grid Reference NZ 127658), were studied during a series of samples between January 1963 and March 1965. The plot, 15 x 25 yd (14 x 23 m), was on a loam soil in a market garden of about 2ac (0 8 ha). The dominant species on the plot were Agriolimax reticulatus (Muller), Arion hortensis Ferussac and Milax budapestensis (Hazay). Their life cycles in this area are as follows (Hunter 1966b): Agriolimax reticulatus has two generations per year, a spring generation hatching about May and an autumn generation hatching about September. Individuals hatching in autumn take longer (7 months) to complete their life cycle than those hatching in spring (5 months). Arion hortensis usually has an annual cycle, hatching about July and maturing and laying eggs at about a year old. A few, however, hatch later and are not ready to lay eggs until after their second winter, thus taking almost 2 years to complete their cycle. Milax budapestensis has usually a biennial cycle. The eggs hatch between May and August and individuals grow in weight during the following 18 months (except for a pause in growth during the winter) to mature during their second autumn. A few hatch as early as April and have grown enough during their first year to mature during their first winter.

Slug activity in relation to weather

SUMMARYMultiple regression analysis was carried out on the effect of certain meteorological factors on the numbers of slugs attracted by metaldehyde and bran biscuits at Cardiff in the autumn months. By far the greatest reduction in the variance in numbers of slugs attracted each morning was achieved by taking out the effects of two factors: (1) the length of time the biscuits had been exposed, and (2) the average night air temperature. The percentage relative humidity considered alone had little effect on the variance. Regression coefficients, at each site, for factors (I) and (2) on slug numbers appeared to be in close agreement and it is suggested that these figures would serve as a measure of slug activity. Arion hortensis behaved differently from the other species studied, its day‐to‐day variation in numbers not being tied so closely to the meteorological factors examined.Methods of assessing slug numbers in the field usually rely on the animals' activity. Barnes & Weil (1944) made direct counts on the slugs observable in half‐hourly periods, and Thomas (1944) based estimates of the number attracted to metaldehyde and bran biscuits overnight; Duthoit (1961) used baits of wheat seed in making weekly estimates. Measures of activity, however, may be less directly related to the actual population present than to day‐to‐day climatological variations. The aim of the work described below was to find if it was possible to arrive at more reproducible population estimates by using standard slug biscuits, and allowing for the effect of some of the meteorological variables.

Chromosome numbers of slugs.

CHROMOSOME numbers are becoming increasingly part of the taxonomic descriptions of animal and plant species.

Eradication of Slugs and Snails

SLUGS and snails are some of the most widespread pests on farms and in gardens, but owing to their nocturnal habits and their capacity for excreting slime which enables them to get rid of irritating substances, they are very difficult to control. Their natural enemies, for example, various birds, toads, moles, and predaceous ground beetles, are insufficient to keep their numbers in check, and special means of control are often necessary. Though no means of absolute eradication of these pests is as yet known, the Ministry of Agriculture has published an Advisory Leaflet (No. 115), in which various check measures are described. In gardens, large numbers of slugs may be caught by means of traps consisting of cut potatoes, orange skins, cabbage leaves, tiles, boards, or sacking placed on the soil, for the animals will collect under them for shelter during the day. Hand collecting at dusk is also recommended. For larger areas, the use of certain chemicals with a corrosive or toxic action is advised. Quicklime or salt are destructive if they come in contact with the upper part of the ‘slugs bodies, and applications made at night (or two or three times during the same night, if possible) should prove useful. Barriers of repellent material such as soot, washing soda, ‘dry ‘Bordeaux? etc., are often successful, and recent trials have shown that 1 part creosote mixed with 100 parts of precipitated chalk placed around each plant at the rate of ¼ oz. per plant is worth further trial.