Grey Field Slug Deroceras Reticulatum Research Articles

Spatial Aggregations of the Grey Field Slug Deroceras reticulatum Are Unstable Under Abnormally High Soil Moisture Conditions.

Deroceras reticulatum in arable fields display spatio-temporally stable slug patches that have been well documented under typical soil moisture conditions. The effect of abnormally high soil moisture on slug patch stability, however, is unknown. In this study, stepped gradient choice tests comparing soil moisture levels of 50-125% soil capacity showed slug preferences for levels in a range near to 125%. Activity became erratic, however, when given a choice of high moisture levels (125-370%), potentially because slugs searched for preferred conditions. Slug spatial aggregation was investigated in 21 commercial fields in 2023/24, a season of extreme rainfall, and then compared to years exhibiting typical rainfall (2015-2018). Slug patches occurred in 27.2% of assessment visits to fields during 2023/24 compared to 96.4% in typical years, suggesting weather conditions leading to abnormally high soil moisture are significantly associated with the breakdown of slug spatial aggregation behaviour. Random forest models identified the weather predictors (precipitation, relative humidity, temperature) with the highest impact on slug distribution and relative abundance, with the assessment date and region also related to relative abundance. However, a complex of environmental parameters affects soil moisture content, and no statistically significant effects of individual weather predictors emerged. The results are discussed in relation to slug behaviour in the context of their impact on targeted slug treatments.

Stability of Patches of Higher Population Density within the Heterogenous Distribution of the Gray Field Slug Deroceras reticulatum in Arable Fields in the UK.

Simple SummaryThere is growing public and legislative pressure to reduce the use of pesticides in crop production. It is thought that the gray field slug is not uniformly distributed in arable fields, but that patches of higher slug densities occur, interspersed within areas of lower slug numbers. Targeting molluscicide applications only at these patches, leaving other areas untreated, would substantially reduce the amount of molluscicide used but relies on patches being a feature of slug populations in all susceptible crops, and always occurring in the same places during the periods slug control is needed. This study investigated these requirements in 22 commercial arable field crops from different regions of the UK, and in three different years. Despite a variable proportion of slug populations being found below the soil surface (where they could not be assessed) on different sampling dates, existence of higher density patches were confirmed in all fields, although it was noted that, when too few slugs were active on the soil surface, they could not be reliably detected. When they were detected, they occurred in the same locations in each field. The potential for using these patches in more sustainable slug control approaches is discussed.Exploitation of heterogenous distributions of Deroceras reticulatum, in arable fields by targeting molluscicide applications toward areas with higher slug densities, relies on these patches displaying sufficient spatio-temporal stability. Regular sampling of slug activity/distribution was undertaken using 1 ha rectangular grids of 100 refuge traps established in 22 commercial arable field crops. Activity varied significantly between the three years of the study, and the degree of aggregation (Taylor’s Power Law) was higher in fields with higher mean trap catches. Hot spot analysis detected statistically significant spatial clusters in all fields, and in 162 of the 167 individual assessment visits. The five assessment visits in which no clusters were detected coincided with low slug activity (≤0.07 per trap). Generalized Linear Models showed significant spatial stability of patches in 11 fields, with non-significant fields also characterized by low slug activity (≤1.2 per trap). Mantel’s permutation tests revealed a high degree of correlation between location of individual patches between sampling dates. It was concluded that patches of higher slug density were spatio-temporally stable, but detection using surface refuge traps (which rely on slug activity on the soil surface) was less reliable when adverse environmental conditions resulted in slugs retreating into the upper soil horizons.

Predation by the carabid beetle Harpalus rufipes on the pest slug Deroceras reticulatum in the laboratory

AbstractThe Harpalini species Harpalus rufipes, as many other generalist carabids, consume a wide variety of prey and it is known to feed on pest slugs such as the grey field slug Deroceras reticulatum, but quantitative data about the predatory activity of H. rufipes on slugs are very scarce. In laboratory experiments, we assessed the capability of male H. rufipes to kill eggs and different‐sized slugs of the pest species D. reticulatum in either the absence or the presence of alternative live prey (dipteran larvae and aphids). We also investigated the preference of H. rufipes for eggs and hatchlings of D. reticulatum in a choice experiment. H. rufipes killed considerable amounts of eggs and small juveniles (≤5.0 mg) of D. reticulatum, both in no‐choice and in choice situations. Medium‐sized juvenile slugs (10–20 mg) were seldom killed only in no‐choice situations, and no large juveniles (50–60 mg) were killed. Dipteran larvae and aphids were killed also in no‐choice and in choice situations. The type of alternative prey presented with slug eggs affected the survival of the eggs to H. rufipes predation. The presence of dipteran larvae as alternative prey did not affect the survival of juvenile slugs. When eggs and small juvenile slugs were offered together, the survivals of both items were similar. The obtained results under laboratory conditions suggest that the generalist predator H. rufipes might realise an important contribution to the control of pest slugs.

Recombinant conotoxin, TxVIA, produced in yeast has insecticidal activity

Conotoxins are a diverse collection of more than 50,000 peptides produced by predatory marine snails of the genus Conus in order to immobilize their prey. Many conotoxins modulate the activity of ion channels, and show high specificity to their targets; as a result, some have valuable pharmaceutical applications. However, obtaining active peptide is difficult and to date has only been achieved though natural collection, chemical synthesis, or the use of prokaryotic expression systems, which often have the disadvantage of requiring subsequent steps to correctly fold the peptide. This paper reports the production of a conotoxin, TxVIA from Conus textile, as a biologically active recombinant protein, using the yeast Pichia pastoris as expression host. The presence of the pro-peptide was found to be necessary for the expression of biologically active conotoxin. We also show that TxVIA is not, as previously reported, mollusc-specific, but also shows insecticidal activity when injected into lepidopteran (cabbage moth) and dipteran (house fly) larvae. In contrast, recombinant TxVIA was not found to be molluscicidal to the grey field slug Deroceras reticulatum.

The efficacy of various bait products against the grey field slug <i>Deroceras reticulatum</i>

The grey field slug Deroceras reticulatum is one of the most dominant slug pests in temperate climates In mild moist conditions populations can rapidly reach economically damaging levels Largescale control relies heavily on the use of molluscicide baits The active ingredients in molluscicides are often in themselves repellent to slugs and must be formulated with other more palatable substances to ensure sufficient ingestion A study was undertaken to compare the efficacy of four bait products at various time intervals after application to bare soil Slug morbidity following bait application 48 h prior to exposure was significantly higher for methiocarb products while metaldehyde products experienced reduced efficacy after the same time period

Impacts of Food Diversity on some Reproductive Attributes in the Gray Field Slug <i>Deroceras reticulatum</i> (Müller)

Using a food choice design consisting of a single, double and multiple diets, impacts of three common vegetables viz. cabbage (CAB), lettuce (LET) and potato (POT) on some important reproductive attributes of the gray field slug Deroceras reticulatum (Müller) have been assessed. Although adult body weight was not affected by the diets, brood size was maximum in a double diet (CAB+POT), but multiple diets (CAB+LET+POT) did not enhance egg productivity. Both LET and POT had induced significantly greater number of eggs per day in comparison with CAB. Multiple diets resulted in significantly heavier eggs than the eggs from single or double diet regimes. Eggs laid on LET had the lowest and that on CAB+LET+POT had the highest developmental time but the hatch rate across the diet regimes did not differ significantly. Hatchlings from the single diet treatment were heavier than the double diet regime, but those between single vs. multiple or double vs. multiple diets did not vary statistically. The heaviest hatchlings were from LET and the lightest ones were from the CAB+LET treatments. The present results would help researchers in selecting a convenient culture medium for rearing experimental slugs in the laboratory. In addition, the data suggest that polyculture of vegetables might reduce slug damage, especially by reducing the brood size, egg production and hatchling size of D. reticulatum in the fields. Key words: Deroceras, field slug, food diversity, reproductive attributes, alternative food source  doi: 10.3329/jbs.v15i0.2198 J. bio-sci. 15: 15-21, 2007