Invasive slug pests and their parasites—temperature responses and potential implications of climate change

Abstract

It is generally accepted that climate change is likely to disrupt host-parasite relationships, but little consideration has been given to how this may affect agricultural pests. Here, we study the potential influence of climate change on the pest slug Deroceras reticulatum and its nematode parasite Phasmarhabditis hermaphrodita. The European slug D. reticulatum is a major pest of agriculture and has become invasive in many countries throughout the world, including the Americas, Asia and Australasia. P. hermaphrodita strongly inhibits feeding and causes mortality in host slugs. The parasite is widely distributed in the slugs' native range but is very rare in some countries where the slug is invasive, for example the USA. The influence of temperature on D. reticulatum has been studied previously but the temperature response of P. hermaphrodita is unknown. The current study showed that while host and parasite have similar optimum growth temperatures, the parasite is much less tolerant of temperatures above optimum than the host. As a result, when parasites were present, slug feeding increased significantly above the slug's optimum of 14 up to 24°C as the inhibitory effect of the parasites lessened. Conversely, in the absence of parasites, slug feeding significantly decreased over the same temperature range. This finding suggests that given adequate moisture, rising temperatures may increase slug problems in D. reticulatum's European home range, but possibly reduce problems in invasive territories such as the USA. The relationship between high temperatures and poor parasite performance is supported by studying prevalence of Phasmarhabditis spp. in the UK where a significant negative relationship exists between the mean summer high temperature and parasite prevalence.

Performance of the slug parasitic nematode <i>Phasmarhabditis hermaphrodita</i> under predicted conditions of winter warming

“…10) Our results also support previous findings by Wilson et al 9) about the optimum population growth temperature range of P. hermaphrodita, which is between 12 and 18°C, since in the WW plots, the mean daily minimum and maximum temperatures were 11.3°C and 16.2°C, respectively, within a range of extreme values of 10.1 and 18.5°C. In the NW plots, the mean daily minimum temperature was 6°C, with an extreme value of 2.2°C, and it has been shown that the reproduction of P. hermaphrodita decreases significantly below 10°C.…”

“…In the NW plots, the mean daily minimum temperature was 6°C, with an extreme value of 2.2°C, and it has been shown that the reproduction of P. hermaphrodita decreases significantly below 10°C. 9) Thus, while in the WW plots, there were good conditions for the multiplication of P. hermaphrodita, in the NW plots, the population growth of nematodes should have been much more limited.…”

“…Forecasting the responses of particular organisms to future climatic conditions is difficult because climate change will also affect all natural enemies 9) and the quality and/or quantity of available food. 20) In the agricultural context, climate change is also expected to affect the varieties and species of crops grown, as well as the timing of agricultural practices, 21) among other factors that might affect any particular organism and its relationships with natural enemies.…”

“…10) Thus, predicted climate changes in terms of increased temperatures are likely to have important effects on both D. reticulatum and its nematode parasite P. hermaphrodita as well as on their relationship. 9) Although the thermal ecology of P. hermaphrodita is poorly understood, Wilson et al 9) recently demonstrated that the nematode is much less tolerant of increasing temperatures than the host slug D. reticulatum, in the range of 14 to 24°C. However, high levels of abundance and damage caused by D. reticulatum have been reported over the autumn and winter with lower temperatures, and crops such as winter wheat and winter rape are among the most susceptible to slug damage.…”

“…Slugs consume a high amount of water through mucus production for locomotion, lose water when breathing, and are very sensitive to drying conditions. 8) P. hermaphrodita is intolerant to moderately high temperatures 9) and very sensitive to desiccation and exposure to ultraviolet light when applied to the soil surface. 10) Thus, predicted climate changes in terms of increased temperatures are likely to have important effects on both D. reticulatum and its nematode parasite P. hermaphrodita as well as on their relationship.…”