Analysing the impact of trap shape and movement behaviour of ground‐dwelling arthropods on trap efficiency

Danish A Ahmed,Sergei V Petrovskii

doi:10.1111/2041-210x.13207

Abstract

Abstract The most reliable estimates of the population abundance of ground‐dwelling arthropods are obtained almost entirely through trap counts. Trap shape can be easily controlled by the researcher, commonly the same trap design is employed in all sites within a given study. Few researchers really try to compare abundances (numbers of collected individuals) between studies because these are heavily influenced by environmental conditions, e.g. temperature, habitat structure and food sources available, directly affecting insect movement activity. We propose that useful insights can be obtained from a theoretical‐based approach. We focus on the interplay between trap shape (circle, square, slot), the underlying movement behaviour and the subsequent effect on captures. We simulate trap counts within these different geometries whilst considering movement processes with clear distinct properties, such as Brownian motion (BM), the correlated random walk (CRW) and the Lévy walk (LW). (a) We find that slot shaped traps are far less efficient than circular or square traps assuming same perimeter length, with differences which can exceed more than two‐fold. Such impacts of trap geometry are only realized if insect mobility is sufficiently large, which is known to significantly vary depending on type of habitat. (b) If the movement pattern incorporates localized forward persistence then trap counts accumulate at a much slower rate, and this rate decreases further with higher persistency. (c) If the movement behaviour is of Lévy type, then fastest catch rates are recorded in the case of circular trap, and the slowest for the slot trap, indicating that trap counts can strongly depend on trap shape. Lévy walks exacerbate the impact of geometry while CRW make these differences more inconsequential. In this study we reveal trap efficiencies and how movement type can alter capture rates. Such information contributes towards improved trap count interpretations, as required in ecological studies which make use of trapping systems.

Highlights

Trapping of insects is central to many ecological studies, in ecosystem services ecology (Work et al, 2002)
Simulation models have been used to optimize the spatial distribution and other features of traps in agricultural fields, especially trap cropping (Holden et al, 2012), but the geometry of these structures have very rarely been assessed on trapping efficiency, for e.g. Hannunen (2005) only consider slot shaped crop patches. We investigate this issue in more depth, with interest in the precise rank order of trap shapes in terms of efficiency and the corresponding trap count patterns that emerge
We focused on trapping efficiency of different trap shapes, and how capture rates are affected by movement behaviour, and to what extent

Summary

Introduction

Trapping of insects is central to many ecological studies, in ecosystem services ecology (Work et al, 2002). Most common sampled species include; ground beetles (Coleoptera: Carabidae), rove beetles (Coleoptera: Staphylinidae), wandering spiders (Aranae: Lycosidae and Clubionidae), and ants (Hymenoptera: Formicidae) (Woodcock, 2005) The advantages of such a sampling technique is that pitfall traps are simple to install, easy to transport and cost-effective, studies are easy to replicate and enable large data collection useful for statistical analyses (Greenslade, 1964). Pitfall traps are used for general survey of insect diversity, detection of new invasions of insect pests for delimitation of area of infestation, and for monitoring population levels of established pests Such information aids the decision making process for the initiation of control measures or to measure effectiveness of a pest management program (Pimentel, 2009). Another example which is different from pitfall trapping, but as relevant, and suggested to have great potential is the installation of trap crops, which are plant stands that are grown to attract pests to reduce pest density in the main crop (Hannunen, 2005)

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Conclusion