The influence of azadirachtin on the feeding behaviour of cereal aphids and slugs

The probing behaviour of Rhopalosiphum padi (L.) and Sitobion avenae (F.) and the feeding behaviour of several slug species, (Deroceras reticulatum (Müller), Arion distinctus Mabille, Agriolimax caruanae Pollonera, Maximus sp.) were assessed on seedlings of winter barley (Hordeum marinum) treated with different concentrations of azadirachtin. Settling behaviour of both aphid species was strongly biased towards the untreated seedlings or those treated with low concentrations of azadirachtin. Concentrations of <500 ppm were effective with topical application and probing activity was reduced for at least 4 days after application. Systemic activity of azadirachtin against cereal aphids was also demonstrated. Feeding behaviour of the slug species, as seen by the amount of leaf eaten compared to the controls, was not affected by the presence of azadirachtin at those concentrations which deterred aphids from feeding. The relevance of these results to crop protection is discussed.     

Tracking predator density dependence and subterranean predation by carabid larvae on slugs using monoclonal antibodies

1. Subterranean carabid larvae are more numerous than surface‐active adults, yet very little is known about their ecological significance, dietary preferences or ability to regulate populations of prey species, particularly pests. Part of the reason for this is that predator–prey interactions beneath the soil are almost impossible to observe. 2. Extensive field studies have shown that adult Pterostichus melanarius (Illiger) can affect the temporal and spatial dynamics of their slug prey. However, if larvae too are feeding on slugs, this could radically affect overall predator–prey dynamics. 3. We tested the hypotheses that P. melanarius larvae would kill and consume two slug species, Deroceras reticulatum Müller and Arion intermedius Normand, under laboratory and semi‐field conditions, and that there would be no significant difference in rates of predation on these slug species. 4. A new monoclonal antibody was developed that was capable of detecting the presence of slug proteins in the guts of P. melanarius larvae. 5. Pterostichus melanarius larvae killed both A. intermedius and D. reticulatum in the laboratory, feeding to a greater extent, and growing more rapidly, on the latter. The larvae were equally effective at reducing numbers of both slug species in a crop of wheat grown in semi‐field mini plots, but predation was affected by density‐dependent intra‐specific competition amongst the beetle larvae. 6. Future modelling of the dynamic interactions between carabids and slugs will need to take into account predation by larvae.     

Contrasting predation pressure of different ground beetles on slugs and their eggs

Slugs such as Deroceras reticulatum Müller (Pulmonata: Agriolimacidae) cause crop losses in temperate regions worldwide. Numerous species of ground beetles (Coleoptera: Carabidae) feed on slugs, but possible interactive effects are poorly known. Here, we compared predation pressure on slug eggs and slug immatures among Abax parallelepipedus Piller and Mitterpacher, Pterostichus niger Schaller, and Pterostichus melanarius Illiger. The latter was most effective against slug eggs but least effective against immature slugs compared to the other species, demonstrating some specificity of ground beetle predation on life stages. Slug egg predation of P. niger in combination with both other species was synergistic, with up to twice as many eggs consumed as for single species treatments. The effect of species combinations on immature slugs showed no differences from expectations based on single species treatments. Our results indicate that combinations of ground beetle species are favourable for the suppression of slugs in early life stages.     

Development of a Monoclonal Antibody for the Detection and Quantification of Predation on Slugs within the Arion hortensis agg. (Mollusca: Pulmonata)

The Arion hortensis agg. (Mollusca: Pulmonata) are major slug pests of agriculture and horticulture throughout much of the temperate World. A monoclonal antibody was created that could specifically identify and quantify the remains of these slugs within the carabid predator Pterostichus melanarius Illiger, a polyphagous species found in arable crops in Europe and North America. The antibody was shown to be specific for the two species of pest slug within this species aggregate, Arion distinctus Mabille and A. hortensis Férussac, and did not cross-react with any other invertebrates tested, including other slugs in the same genus. It proved to be highly sensitive in an enzyme-linked immunosorbent assay. The mean detection period for the remains of A. distinctus in predator foregut samples was 3.28 days at 16°C. However, A. distinctus remains could be identified in male carabids for 30% longer than in females, emphasizing the importance of separate analyses. The value of the antigen half-life as a measure of the detection period was questioned because analysis of covariance showed that the regression slopes for antigen decay were not significantly different between the two sexes, giving very similar half-lives (approx 18.5 h for females and 19 h for males). Calculated quantities of soluble slug proteins in predator foreguts declined more rapidly over time than concentrations, allowing separate assessment of the importance of these two variables on detection periods. It was concluded that a valuable new antibody had been created and characterized, which can be used for the analysis of predation in the field.     

Exotic Slugs Pose a Previously Unrecognized Threat to the Herbaceous Layer in a Midwestern Woodland

Developing effective restoration strategies requires first identifying the underlying factors limiting native plant recovery. The slug Deroceras reticulatum is an important herbivore in Europe, a global agricultural pest, and is introduced and abundant throughout eastern North America, but little information is available on the effect of this exotic herbivore on the forest herbaceous layer. Here, we test the palatability of 12 forest herbs to the introduced slug D. reticulatum and use field surveys to determine the degree to which slugs are damaging plants in the field. In laboratory feeding trials, slugs readily consumed most plants, but avoided the grass Elymus virginicus, the invasive forb Alliaria petiolata (garlic mustard), and thicker leaved plants. In the field, we documented significant slug damage, with close to 50% or more of plant leaves damaged by slugs on five of the six native species tested. Slug damage in the field was predicted by laboratory‐determined acceptability, but was significantly greater on short‐statured rosette species than on erect plants for a given acceptability value. Our results identify introduced slugs as an important, but overlooked obstacle to forest herb restoration and potential drivers of larger scale understory compositional change. The relaxed herbivore pressure on A. petiolata, relative to native competitors, suggests that invasive plant removal alone may not result in the recovery of native flora. Rather, restoration of unpalatable native species should accompany invasive plant control in slug invaded areas. Erect forbs, thick‐leaved plants, and graminoids should have the greatest success where introduced slugs are abundant.     

The role of different slug species in damage to oilseed rape bordering on sown wildflower strips

Damage caused by different slug species on above and below ground parts of young oilseed rape bordering on sown wildfower strips was studied. Slug densities and damage were recorded in the field and damage rates for each slug species were measured in the laboratory. Severe slug damage was observed in rape areas 1 m from the wildflower strips. Damage rates of slug species feeding above ground were distinctly higher than those feeding below ground. The estimated damage caused by above-ground feeding in all four study fields ranged between 72% and 89 % and was always distinctly higher than damage caused by below-ground feeding (11% to 28 %). The estimated damage caused by Arion lusitanicus above ground was between 54% and 69 %, followed by Deroceras reticulatum (3% to 26 %). Thus A. lusitanicus was responsible for the majority of damage in the rape crops studied.     

Abundance,species richness and feeding preferences of introduced molluscs in native grasslands of Victoria,Australia

Abstract Introduced molluscs have invaded endangered, remnant native grasslands of south‐eastern Australia, but few studies have investigated their distribution, abundance or potential impact. Molluscs were surveyed in grassland sites across an urban to rural transect west of Melbourne, Australia. It was confirmed that several introduced mollusc species have invaded these areas. Three snail and five slug species were identified, none of which was native to Australia. The most common species was the brown field slug (Deroceras panormitanum). Mollusc capture and species richness were positively related to the degree of urbanization in the surrounding landscape. There was also a negative relationship with fire frequency. Feeding trials revealed selective herbivory by the black‐keeled slug (Milax gagates) among native plants. Anecdotal evidence that variable glycine (Glycine tabacina) and button wrinklewort (Rutidosis leptorrhynchoides) are palatable to molluscs was supported. Mollusc herbivory may potentially lead to reduced fitness of palatable species, and changes in community composition and structure.     

Microsatellites for the slugs Deroceras reticulatum and Arion intermedius

Microsatellites were developed for two pest slug species: self‐fertilizing Arion intermedius and outcrossing Deroceras reticulatum. Six microsatellites from each species were tested on individuals collected from within and between arable fields. The 39 individuals analysed per species had 3–9 and 7–26 alleles per microsatellite for A. intermedius and D. reticulatum, respectively. Gene diversity, [1 ? Σp_i²] , ranged from 0.19 to 0.75 and 0.74 to 0.95, respectively.     

Feeding deterrent effect of carvone, a compound from caraway seeds, on the slug Arion lusitanicus

The feeding deterrent effect of carvone on the slug Arion lusitanicus was investigated. Carvone, a natural compound from caraway seeds, was incorporated into mulch to reduce its inherent volatility. In a laboratory choice experiment, boxes were filled on one side with carvone‐treated mulch and on the other side with untreated mulch. At carvone concentrations ranging from 0.03–0.75 ml litre^?1 mulch, slugs ate significantly more lettuce on the untreated side. In a laboratory based no‐choice experiment, carvone concentrations of 0.25 and 0.75 ml litre^?1 mulch significantly reduced slug feeding in comparison with the untreated control. Moreover at the highest concentration of carvone (0.75 ml litre^?1 mulch) 50% mortality was recorded over a period of 5 days, indicating a clear molluscicidal effect. Due to its volatility carvone did not decrease plant defoliation by A. lusitanicus when applied directly onto lettuce. Subsequent field evaluation showed 0.75 ml litre^?1 mulch to partially reduce slug feeding damage. However, this effect was not sufficient to significantly increase lettuce yield. The incorporation of a higher carvone concentration into mulch is still to be tested to confirm whether carvone‐treated mulch can be recommended as an effective alternative approach to chemical slug control.     

Fumigant activity of essential oils and their components from Eucalyptus codonocarpa and E. dives against Tetranychus urticae (Acari: Tetranychidae) at three temperatures

Essential oils derived from eighteen species of the Myrtaceae family native to Australia, and major constituents of two oils selected from these oils were tested for their fumigant activity against adult females and eggs of Tetranychus urticae Koch (Acari: Tetranychidae) at 5, 15 and 25°C. Essential oils of Eucalyptus codonocarpa and Eucalyptus dives showed the highest fumigant activity against female adults at 10 μl/l at 15 and 25°C. Among major constituents of the two essential oils, piperitone was the most effective against female adults, followed by terpinene‐4‐ol at 10 μl/l at all three temperatures. The two essential oils and these two constituents lowered egg hatchability at 10 μl/l at 25°C. Our results suggest that piperitone should be further investigated as a potential fumigant against T. urticae.     

Fugitive species and priority during colonization in carrion-breeding Diptera communities

ABSTRACT.

• 1 Experiments were conducted to test for the presence of fugitive species and priority effects among the Diptera species that breed in dead slug carcasses (Limax maximus L.).
• 2 Slug carcasses exposed for only 1 day produced a community that was very similar to that bred from carcasses exposed until fully decomposed. This suggests that competitive ability and dispersal ability are positively correlated in this system.
• 3 The colonization of flies was manipulated by transferring larvae of the phorid, Megaselia scalaris Loew, to carcasses before and after they were exposed in the field. A‘priority effect’was demonstrated in that M.scalaris survived better and had a stronger impact on other species when it was the first species to colonize slug carcasses.

     

Predation on the slug Deroceras reticulatum by the carabid beetles Pterostichus madidus and Nebria brevicollis in the presence of alternative prey

1 Slugs are important pests in many agricultural crops and potential biological control agents are being studied as an alternative to molluscicides. Carabid beetles may be able to reduce slug populations, but their role as control agents may be influenced by the presence of alternative prey. 2 Attacks on the pest slug Deroceras reticulatum (Müller) by the carabid beetles Pterostichus madidus (Fabricius) and Nebria brevicollis (Fabricius) were investigated in the presence of alternative prey (earthworms and Calliphora fly larvae). Consumption of slug eggs and aphids was also investigated. 3 All five prey types were consumed to varying degrees during the experiments. Both beetle species showed a significant preference for Calliphora larvae over slugs. Pterostichus madidus showed a significant preference for earthworms over slugs. No preference was shown between earthworms or Calliphora larvae by P. madidus females or N. brevicollis. However, P. madidus males showed a significant preference for Calliphora larvae over worms. Pterostichus madidus showed no preference between slug eggs and aphids; N. brevicollis showed a significant preference for aphids over slug eggs. 4 The results from this study indicate that generalist beetles will often attack other prey in preferences to adult slugs. Slugs may not be preferred because of their mucus. Other prey items occur frequently in arable soils and generalist carabids may ignore slugs altogether and may only feed on them when slug density is high or other prey are unavailable.     

Immunocytochemical Localisation of Glycosaminoglycan-Like Activity in the Mucus and Associated Tissues of Terrestrial Slug Species (Gastropoda: Pulmonata)

Indirect immunofluorescence assays were conducted on cryotome sections of four terrestrial slug species from three distinct phylogenetic groups, Arion ater (L.), Arion hortensis (Férussac), Tandonia (Milax) budapestensis (Hazay), and Deroceras reticulatum (Müller) using monoclonal antibodies for two glycosaminoglycans (GAGs), heparan sulphate, and chondroitin sulphate. Specific staining for a heparan sulphate-like component was demonstrated in the foot and tail regions of each species and was particularly intense in A. ater and A. hortensis, notably in the epidermis and associated mucus-like material, and in mucus-like material from the pedal gland region of the latter species. Subsequent studies with A. ater confirmed the presence of heparan-sulphate–like activity in the caudal gland duct region. No evidence of specific staining for chondroitin sulphate-like activity was found in any of the slug species. This work suggests that a specific GAG, or a group of closely related GAGs, is a common component of mucus in a range of slug species and of different types of mucus, including trail (pedal) mucus and the more viscous mucus produced by the caudal gland.     

A method to study slug predation on seedlings in the field

Dandelion is a common Asteraceae species that populates disturbed sites and gaps within swards where it becomes an important competitor of grasses. The natural control against dandelion includes seedling predation, with slugs, particularly Arion lusitanicus, being the most important in the Czech Republic. However, the study of slug seedling consumption is difficult because naturally established seedlings are not always available. Therefore, we developed a method of exposing laboratory‐grown seedlings as bait for slug predation. Dandelion seeds were sown in plastic cups containing a bottom layer of moist substrate. The emerged seedlings were thinned to 20 and displayed in an open area. During 2008–2010, the seedling baits were placed at 15 sites at 1 month intervals throughout the dandelion vegetative season, in parallel with plasticine baits that monitored slug feeding activity. For each 1 month interval, seedling survival was observed for a period of 8 days, and the estimated time to death was calculated; the percentage of surviving seedlings was then recorded. This method of seedling presentation demonstrated that local and temporal variation in seedling survival is correlated with slug feeding activity. The advantage of this technique is that the seedlings in baits may be presented at any place and time, as required by the experimental design; however, we found that the estimated time to seedling death was shorter for the exposed baits than for the naturally established seedlings. The method is suitable for the study of plant species other than dandelion, and also for aims other than the study of spatiotemporal trends in seedling consumption by slugs.     

The rhabditid nematode Phasmarhabditis hermaphrodita as a potential biological control agent for slugs

A nematode, Phasmarhabditis hermaphrodita, known to be associated with slugs but not previously thought to be parasitic, was shown to be a parasite capable of killing the pest slug Deroceras reticulatum. The parasite infects slugs in the area beneath the mantle surrounding the shell, causing a disease with characteristic symptoms, particularly swelling of the mantle. Infection leads to death of the slug, usually between seven and 21 days afterwards. The nematode then spreads and multiplies in the cadaver. In an experiment where individual D. reticulatum were exposed to different numbers of P. hermaphrodita, a significant positive relationship was found between nematode dose and slug mortality. In two experiments on host range, the nematode was found to infect and kill all pest slug species tested: Deroceras caruanae, Arion distinctus, Arion silvaticus, Arion intermedius, Arion ater, Tandonia sowerbyi and T. budapestensis, in addition to D. reticulatum.     

Size-specific susceptibility of the pest slugs Deroceras reticulatum and Arion lusitanicus to the nematode biocontrol agent Phasmarhabditis hermaphrodita

The nematode Phasmarhabditis hermaphrodita is a commercially available biocontrol agent against slugs. This product is especially interesting for use in organic farming, where products containing metaldehyde or carbamates cannot be used for controlling pest slugs. We investigated the potential of P. hermaphrodita for the control of the pest slugs Deroceras reticulatum and Arion lusitanicus. These two species are the most harmful slug pests in Switzerland. At different times of the year, we collected slug specimens of different weight and assessed their susceptibility to P. hermaphrodita in the laboratory. Batches of five slugs were subjected to five different doses of nematodes plus an untreated control and replicated three times. During six weeks, feeding and survival of the slugs were recorded. D. reticulatum was strongly affected by increasing nematode doses, irrespective of the slugs' body weight. In small specimens of A. lusitanicus, feeding and survival were strongly affected by the nematodes, while larger specimens remained almost unaffected. Because A. lusitanicus has an asynchronous development in Switzerland, it seems difficult to control the entire population with a single nematode application. To what extent nematodes will be used in practice for slug control depends on their effectivity against the pest slugs of major importance, on the longevity of the molluscicidal effect and on the price of nematodes.     

Regeneration of Salix arbuscula and Salix lapponum within a Large Mammal Exclosure: The Impacts of Microsite and Herbivory

Over‐grazing or browsing by large herbivores may result in the loss of individual plant species or entire plant communities. Restoration schemes often involve exclusion of large mammals, but the resulting changes in vegetation may alter other important ecological processes such as regeneration, via changes in microsite availability for seed germination or increases in populations of seedling predators. Working within a large fenced area from which large mammals were excluded, we experimentally tested the effects of microsite, small herbivores, and their interactions on post‐dispersal seed and early seedling mortality of one nationally scarce (Salix arbuscula) and one nationally rare (S. lapponum) species of montane willow. Seeds were sown in three different microsites: natural vegetation, mown vegetation (mimicking grazed sward), and bare ground. Small exclosures and slug pellets were used to examine the effects of small mammal and slug predation, respectively. Survival of seedlings was monitored during the summer following planting. The presence of bare ground, rather than the absence of herbivores, was of over‐riding importance for early seedling survival and establishment. Protecting seedlings from small mammals made no difference to the levels of survival; however, protecting seedlings from slugs (Arion spp.) resulted in approximately 45% of seedlings surviving until the end of the summer compared to only 30% when seedlings were available to slugs. Although excluding large herbivores may increase seed production of existing individuals, the impacts of changes to plant communities on processes such as regeneration need to be considered if restoration projects are to be fully successful.     

Spatial sampling to detect slug abundance in an arable field

Overuse of molluscicides by farmers in arable systems can lead to environmental and product contamination. Here we assess a simple and inexpensive surface trapping method for monitoring populations of slugs (Deroceras reticulatum and Arion intermedius). This method was biased against small slugs, and against A. intermedius, when compared to direct soil sampling. Regression was used to model the relationship between the results of surface trapping and soil sampling methods. Spatial Analysis by Distance IndicEs (SADIE) algorithms were used to describe the spatial relationships between the two sets of samples. Using both traditional statistical methods and spatial statistics, the spatial information collected from surface traps was sufficient to identify patches and gaps in slug numbers and possibly to allow the spot application of slug control, and thus provide land managers who experience slug damage with a way of reducing molluscicides use, whilst maintaining slug control. Further improvements and applications of the model are discussed.     

Solar ultraviolet-B radiation can affect slug feeding preference for some plant species native to a fen ecosystem in Tierra del Fuego,Argentina

The objectives of this study were to test potential effects of solar ultraviolet-B (UV-B) radiation on (i) foliage nutritional quality and foliage decomposition rates of six plant species of this fen ecosystem (Nothofagus antarctica, Carex curta, C. decidua and C. magellanica; Acaena magellanica and Gunnera magellanica) and (ii) feeding preferences for these plant species of the slug Deroceras reticulatum prevalent in this ecosystem. In a mixed-diet selection slugs were offered leaves of the six species that had been grown for three years in experimental field plots under either near-ambient or reduced solar ultraviolet-B (UV-B) radiation. The chosen characteristics of leaf quality (nitrogen concentration, carbon:nitrogen ratio, specific leaf area) and leaf decomposition rates of the six species varied significantly among species but were not affected by the UV-B treatments. However, there were UV-B treatment effects on slug feeding preference for two plant species. For the tree species, Nothofagus, slugs had consumed only one-third as much foliage grown under near-ambient UV-B radiation as of foliage grown under reduced UV-B by the end of the feeding experiment. In contrast, leaves of the sedge C. decidua that had been grown under near-ambient UV-B were consumed twice as much as leaves grown under reduced UV-B radiation. Consumption of foliage for the other four species was similar for the two UV-B treatments. Additionally, diet selection of the slugs was also significantly affected by prior UV-B conditions under which foliage had been grown. Nothofagus leaves were consumed proportionately less and C. decidua proportionately more if the foliage had been grown under near-ambient UV-B radiation. This revised version was published online in August 2006 with corrections to the Cover Date.