Rory J. Mc Donnell

Key Aspects of the Biology of Snail-Killing Sciomyzidae Flies

The biology of snail-killing flies (Diptera: Sciomyzidae) has been studied intensively over the past half-century, especially over the past decade. Today, sciomyzids are biologically the best-known group of higher Diptera. The overarching research objectives are evaluation of sciomyzids as biocontrols of disease-carrying or agriculturally important snails and slugs and as a paradigm group for the study of the evolution of diverse feeding and associated behaviors in flies. We present reviews and analyses of some key features of particular scientific and societal interest, including behavioral and phenological groups; laboratory experimental studies on behavior and development; population biology, bioindicators, ecosystem service provision, and conservation; phylogenetics, molecular studies, and evolutionary biology; and biocontrol.

Description of Phasmarhabditis californica n. sp. and first report of P. papillosa (Nematoda: Rhabditidae) from invasive slugs in the USA

A new species of Phasmarhabditis and the known species P. papillosa were isolated from cadavers of invasive slugs in California. Phasmarhabditis papillosa is the type of the genus and has not previously been reported from the Americas. Both species are characterised based on morphology, morphometrics and molecular data. Molecular phylogenies were inferred from concatenated DNA sequence alignments of nearly complete SSU and the D2-D3 domains of the LSU rDNA. Phasmarhabditis californica n. sp. is characterised by a robust body, mature egg-laying specimens almost spindle-shaped when relaxed, 1.5 (1.3-1.8) mm long, tapering to a bluntly rounded anterior end with stoma about as long as lip region diam., six inner labial papillae and four outer cephalic papillae, pharynx with rounded to pyriform basal bulb, vulva located halfway along the body, hermaphroditic, didelphic, amphidelphic, and short, conoid tail constricted at one-third its length with prominent phasmids. Not a single male was found among five strains. Phasmarhabditis papillosa is gonochoristic and has a longer isthmus, pyriform basal bulb and longer, dome-shaped spicate female tail constricted halfway along its length. Sequence analysis revealed unambiguous autapomorphies for P. papillosa and P. californica n. sp. Phylogenetic analyses placed these two species in a monophyletic clade comprising Phasmarhabditis species and other gastropod-parasitic taxa. Morphology, genetic distance, reproductive strategy and nucleotide autapomorphies support the new taxon.

Trail-Following Behaviour in the Malacophagous Larvae of the Aquatic Sciomyzid Flies Sepedon spinipes spinipes and Dictya montana

The ability of neonate larvae of the aquatic sciomyzids, Sepedon spinipes spinipes (Scopoli) and Dictya montana Steyskal (Diptera), to follow snail mucus trails was assessed using filter paper Y-mazes. On finding a mucus trail, larval behaviour of both species switched from unstimulated to stimulated searching behaviour, the latter being characterised by an increase in larval velocity and the frequency of lateral head taps. When fresh mucus trails were used, all of the neonates displayed a positive response and followed the mucus trail into the experimental arm. In addition, for S. s. spinipes and D. montana 80.00% and 86.67% of larvae respectively exhibited a strong response and followed the trail to its end. The stimulatory substance (s), however, appears to become inactive with time and after 45 minutes none of the tested larvae reached the trail end. These results are discussed in relation to the ability of aquatic species to forage outside of water for prey and the implications for their use in the biological control of nuisance snails.

Molecular and Morphological Evidence for the Occurrence of Two New Species of Invasive Slugs in Kentucky, Arion intermedius Normand and Arion hortensis Férussac (Arionidae: Stylommatophora)

Abstract Arion intermedius Normand and Arion hortensis Férussac are invasive mollusks in North America, having been previously reported in thirteen and seven U.S. States, respectively. We report here the first records of both species in Kentucky. Because slug species within the genus Arion Férussac show high degrees of intra-specific variation, identifications were confirmed using both morphological and molecular (partial COI gene sequences) methods. These new records are of concern because invasive slugs are major pests in agriculture, horticulture and floriculture, causing considerable damage to wheat, alfalfa, corn, soybean and tobacco that are amongst the most economically important crops in Kentucky. This study also highlights the important need for additional gastropod surveys throughout the U.S.A.

Factors affecting wetland ground beetle (Carabidae) assemblages: how important are habitats, conservation designations and management?

We investigated factors affecting wetland carabid diversity and assemblage dynamics as part of the first national survey in the Republic of Ireland. Species richness was significantly different among habitat types and was significantly higher on designated as opposed to undesignated land. However, red‐data‐book species richness was significantly higher on undesignated land, highlighting the importance of land outside the conservation network. This was largely due to the prominence of Carabus clatratus L. outside designated areas and often on high‐disturbance land. Management for species of conservation interest outside of designated areas, and in concert with existing agri‐environment, schemes is apparent. Shannons entropy was significantly greater on grazed as compared to ungrazed land, further highlighting the importance of management in maintaining high diversity carabid assemblages, which should be included in future conservation plans for ground dwelling invertebrates. Models of diversity partitioning for a number of variables (location, habitat type, perceived habitat quality, designation status and grazing) indicated a significantly lower α (within sites) diversity than would be expected by chance, but significantly higher β diversities, indicating that diversity was significantly structured among rather than within groups of these variables. A multi‐response permutation procedure, however, indicated that carabid assemblage composition was significantly, but weakly, structured in terms of domestic grazing, location and both broad and narrow habitat classifications. This indicates a difference in the significance of the effects of variables on beta‐diversity as assessed through partitioning using a dimensionless value and assessments based on the pairwise dissimilarity matrix.

EU-protected slug Geomalacus maculosus and sympatric Lehmannia marginata in conifer plantations: what does mark-recapture method reveal about population densities?

Geomalacus maculosus Allman, 1843 is an EU-protected slug species which is only found in the west of Ireland and northern Iberia. There is little knowledge of its population sizes throughout its range and no long-term studies have been conducted to calculate estimates. Localized populations of G. maculosus and the sympatric slug Lehmannia marginata (Müller, 1774) were monitored over one year using the mark-recapture approach at five different sites within a commercial conifer plantation in Ireland. Slugs were marked using visible-implant elastomers injected into the foot. Up to 23.9 /m2 (G. maculosus) and 5.6 /m2 (L. marginata) specimens were observed during the first survey in August; however, these densities varied greatly in different areas of the plantation and throughout the year. Population-size estimates were also calculated using the Jolly-Seber method. Temperature was significantly correlated with capture success, with fewer captures during the colder months. This is the first long-term study that uses visible-implant elastomers as markers for slugs and we evaluate their use, provide guidelines for trapping intensity, discuss limitations of the mark-recapture method and advise on the optimal survey time and conditions.

Tetanocera elata (Diptera: Sciomyzidae) Larvae Feed on Protected Slug Species Geomalacus maculosus (Gastropoda: Arionidae): First Record of Predation

The Family Sciomyzidae (Diptera) is one of the best studied groups of malacophagous insects containing some of the most important enemies of slugs. Larvae of the fly Tetanocera elata are known obligate feeders on slugs both as parasitoids and predators. We tested whether predatory larvae of T. elata can feed on the protected slug species Geomalacus maculosus, for which there appear to be no published records of natural enemies. Using an infra-red video camera, we recorded the behaviour of third instar T. elata in the presence of: 1) a single specimen of G. maculosus and 2) one specimen each of G. maculosus and Deroceras reticulatum, a known slug prey of T. elata. We describe the behaviour of the larvae where they killed and consumed G. maculosus and D. reticulatum in experiments 1 and 2 respectively. Since T. elata has been suggested as a potential biocontrol agent of pestiferous slugs, the possibility of predation on the protected species G. maculosus is discussed from this perspective.

First Report of the Invasive Slug Boettgerilla pallens Simroth, 1912 (Boettgerillidae) in the United States

Abstract: Boettgerilla pallens Simroth, 1912 is reported for the first time in the United States. Identification was based on combined morphological and molecular data (mitochondrial cytochrome c oxidase I and 16S rRNA sequences) of a specimen collected in a retail garden center in northern California. We provide some background information on the biology and ecology of the slug and discuss the pest status of the species.

Nematode associates and susceptibility of a protected slug (Geomalacus maculosus) to four biocontrol nematodes

ABSTRACT The impact of selected entomopathogenic nematodes and Phasmarhabditis hermaphrodita on the European-Union-protected slug Geomalacus maculosus and the sympatric Lehmannia marginata was investigated. There was no significant difference in mortality between slugs treated with nematodes and their controls. The presence of P. hermaphrodita in two G. maculosus cadavers may be the result of necromenic behaviour. This study constitutes the first record of P. californica in Europe.

The feeding behaviour of Rumina decollata (Subulinidae: Gastropoda) raises questions about its efficacy as a biological control agent for Cornu aspersum (Helicidae: Gastropoda)

ABSTRACT The facultative predatory snail Rumina decollata (L.) has been used as a biological control agent for Cornu aspersum (Müller) in Californian citrus orchards for almost half a century despite there being little laboratory and field evidence of its efficacy. We have demonstrated that R. decollata can only successfully kill C. aspersum that are <13 mm (shell diameter) and if given a choice between a known food plant (carrot roots) and C. aspersum within this vulnerable size range, the majority of R. decollata (∼93%) chose carrots. Adult R. decollata will feed on C. aspersum eggs and mean total consumption per individual was ∼3 eggs over a 7-day period. These experimental results support previous anecdotal suggestions that R. decollata may not be an effective snail predator.