The 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.

The nematode Phasmarhabditis hermaphrodita is the only commercial biological control agent for terrestrial slugs. We investigated whether the predicted conditions of winter warming could have any effect on its performance. In the presence of nematodes, slug damage to lettuce plants and slug survival were significantly lower under the predicted conditions of winter warming than under normal winter conditions, while in the absence of nematodes, slug damage and survival were similar under the conditions of winter warming and under current winter conditions. The data suggest that P. hermaphrodita may perform better under the predicted conditions of winter warming.

Harpalus rufipes and Poecilus cupreus are two widespread polyphagous carabids which are known to destroy eggs of the pest slug Deroceras reticulatum in the laboratory. To examine the effect of temperature on the predation of the eggs of D. reticulatum by H. rufipes and P. cupreus, a laboratory experiment with different temperatures and a semi-field experiment including simulated warming were performed. In both experiments, H. rufipes killed more eggs than P. cupreus, and the predatory activity of the former increased significantly with increasing temperature. To our knowledge, this is the first study on predatory activity of polyphagous carabids on the eggs of a pest slug performed under a climate warming scenario. Results suggest that biological pest control performed by polyphagous carabids such as H. rufipes upon pest slugs may be enhanced under predicted climate warming conditions. K E Y W O R D S biological control, climate change, Deroceras reticulatum, Harpalus rufipes, Poecilus cupreus, slug eggs HE was supported by a scholarship from the Egyptian Higher Ministry of Education. AUTHOR CONTRIBUTION HE and JI conceived research, conducted the experiments, statistical analysis and wrote the manuscript. ORCID H. El-Danasoury http://orcid.org/0000-0001-6462-3440 J. Iglesias-Piñeiro

The pestiferous status of the terrestrial slug Deroceras reticulatum and the strong dependence of its biology and ecology on climatic factors have driven research on the potential responses of the slug to predicted scenarios of climate change. Here, we report two short-term experiments performed outdoors, under seminatural conditions, to assess the behavioural response of D. reticulatum to different climate manipulations in terms of herbivory, by measuring over 7 days the damage inflicted by slug populations to lettuce seedlings. The climate manipulations tested emulate predicted climatic conditions for northwest Spain, specifically winter warming and increased summer rainfall, in contrast respectively with normal winter conditions and summer without rain conditions. In a winter experiment, we compared a normal winter treatment with a winter warming treatment; with respect to the normal winter treatment, the winter warming treatment was characterised by higher temperature, lower relative humidity and the absence of rainfall. In a summer experiment, we compared a summer drought treatment with an increased summer rainfall treatment; with respect to the summer drought treatment, the increased summer rainfall treatment was characterised by the presence of rainfall, while the conditions of temperature and relative humidity were similar in both treatments. Neither winter warming nor increased summer rainfall did lead to a significant increase on the number of seedlings damaged by the slugs. However, with both treatments, we found a moderate increase on the amount of damage suffered by the seedlings. The results are discussed in the context of the potential responses of D. reticulatum to future climatic conditions.

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