The slug Geomalacus maculosus is a prominent member of the Lusitanian fauna. As its global distribution is restricted to western Ireland and northern

While carabid beetles have been shown to feed on a variety of crop pests, little is known about their species assemblages in US annual ryegrass crops, where invertebrate pests, particularly slugs, lepidopteran larvae and craneflies, incur major financial costs. This study assesses the biological control potential of carabid beetles for autumn- and winter-active pests in annual ryegrass grown for seed by: (a) investigating the spatial and temporal overlap of carabids with key pests; and (b) molecular gut content analysis using qPCR. Introduced Nebria brevicollis was the only common carabid that was active during pest emergence in autumn, with 18.6% and 8.3% of N. brevicollis collected between September and October testing positive for lepidopteran and cranefly DNA, respectively, but only 1.7% testing positive for slug DNA. While pest DNA was also detected in the guts of the other common carabid species—Agonum muelleri, Calosoma cancellatum and Poecilus laetulus—these were active only during spring and summer, when crop damage by pests is less critical. None of the four carabid species was affected by disk tilling and only N. brevicollis was significantly associated with a vegetated field margin. However, as its impact on native ecosystems is unknown, we do not recommend managing for this species.

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.