Not All Slugs Are the Same: Variation in Growth and Development of the Slug Deroceras reticulatum.

Mark Shirley,Gordon Port,Sally Howlett

doi:10.3390/insects11110742

Abstract

Models to forecast slug populations make assumptions about growth and mortality in response to environmental factors. To refine these models, the growth trajectories and survival of Deroceras reticulatum, a worldwide pest, hatching in spring and autumn were compared at three rearing temperatures (ambient, 12 °C and 15 °C). Deroceras reticulatum reared under identical conditions showed great variation in growth and strong bimodality in growth rates. At all rearing temperatures, growth was influenced by hatching season; in all cases, fast growers dominated in autumn and slow growers dominated in spring. Survival was influenced by hatching season: autumn-born slugs survived better at ambient temperatures, but spring-born slugs had better survival at 15 °C. Deroceras reticulatum may be partitioned into "slow growers" and "fast growers". Fast growers responded to warmer conditions, growing to large sizes. Slow growers, in contrast, gained weight at comparable rates to ambient reared slugs, regardless of the elevated constant temperatures. The peaks of slug activity in autumn and spring are possibly not distinct generations as some slugs may mature early/late and slip into the alternative cohort. Rather, the observed autumn and spring peaks in slug numbers may be a response of a mixed-age population to the favourable environmental conditions at that time.

Highlights

Underpinning effective slug control is the need to predict when and where particular increases in populations are likely to occur so that steps can be taken in advance to minimise the economic loss that would otherwise result [1]
It is well-established that temperature influences many aspects of the biology of terrestrial slugs, including growth rate [5,6,7]
For Deroceras reticulatum, most studies have shown that the relationship between growth rate and temperature is approximately hyperbolic; there is a positive association up to an optimum of 17–19 ◦ C after which higher temperatures have a detrimental effect on development [8,9,10,11]

Summary

Introduction

Underpinning effective slug control is the need to predict when and where particular increases in populations are likely to occur so that steps can be taken in advance to minimise the economic loss that would otherwise result [1]. There is a need, for studies to bridge these gaps in the knowledge of slug biology so that models can give more accurate predictions. The potential of a slug population to attain pest proportions is largely determined by its initial size and the speed with which it can complete its lifecycle whilst favourable conditions prevail. It is well-established that temperature influences many aspects of the biology of terrestrial slugs, including growth rate [5,6,7]. For Deroceras reticulatum, most studies have shown that the relationship between growth rate and temperature is approximately hyperbolic; there is a positive association up to an optimum of 17–19 ◦ C after which higher temperatures have a detrimental effect on development [8,9,10,11]

Methods

Results

Conclusion