Behavioural Studies ofHarpalus rufipesDe Geer: an Important Weed Seed Predator in Northeastern US Agroecosystems

Sara Harrison,Eric R Gallandt

doi:10.1155/2012/846546

Abstract

Harpalus rufipes, a member of the Carabidae, is the most common granivorous invertebrate in Maine agroecosystems. While previous research demonstrated a positive correlation between H. rufipes activity-density and weed seed predation, little is known about the behaviour of this seed predator. We conducted mesocosm experiments to examine seed burial, soil surface conditions, and seed mass effects while tracking H. rufipes movement using a video camera, capture card, and EthoVision software. H. rufipes showed a preference (<svg style="vertical-align:-0.30096pt;width:63.962502px;" id="M1" height="11.0625" version="1.1" viewBox="0 0 63.962502 11.0625" width="63.962502" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,11.0625)"> <g transform="translate(72,-63.15)"> <text transform="matrix(1,0,0,-1,-71.95,63.5)"> <tspan style="font-size: 12.50px; " x="0" y="0">𝑃</tspan> <tspan style="font-size: 12.50px; " x="10.890113" y="0"><</tspan> <tspan style="font-size: 12.50px; " x="22.930502" y="0">0</tspan> <tspan style="font-size: 12.50px; " x="29.182001" y="0">.</tspan> <tspan style="font-size: 12.50px; " x="32.307751" y="0">0</tspan> <tspan style="font-size: 12.50px; " x="38.559254" y="0">0</tspan> <tspan style="font-size: 12.50px; " x="44.810753" y="0">1</tspan> </text> </g> </g> </svg>), for seeds on the soil surface compared to those half or fully buried. Species with larger seeds were preferred, but Amaranthus retroflexus, which had the smallest seeds, had the highest feeding efficiency (i.e., seeds eaten per distance travelled). Undisturbed soil resulted in highest predation rates, presumably because seeds were easier to detect relative to disturbed soil. Video-tracking measurements of duration within areas of particular seeds, and efficiency of seed predation, indicate that H. rufipes behaviour is prey dependent.

Highlights

Seed predation is increasingly viewed as a critical component of multitactic, “Many Little Hammers,” weed management strategies [1,2,3,4], even an ecosystem service that can be considered at a national scale [5]
That is, seeds consumed per hour, and feeding efficiency, defined as amount of seed eaten per unit time per distance travelled, decreased with increasing seed burial (Figure 1)
H. rufipes spent considerable time travelling the perimeter of the arena (Figure 2(a)), but when in the central area, more time was spent in yellow foxtail and wild mustard Zones (Figure 2(b)), meaning that the beetle entered these feeding zones more regularly or remained there to a greater extent after entering, compared to the redroot pigweed or empty feeding zones

Summary

Introduction

Seed predation is increasingly viewed as a critical component of multitactic, “Many Little Hammers,” weed management strategies [1,2,3,4], even an ecosystem service that can be considered at a national scale [5]. Our work in organically managed vegetable-cover cropping systems indicated that invertebrates were responsible for the majority of predation estimated using feeding assays: 73% averaged over two field studies [6]. Pitfall trapping in these experiments indicated that the predominant invertebrate seed predator was Harpalus rufipes Degeer, a member of the Carabidae, a well-studied taxa with wide geographic distribution and notable services to agroecosystems [7]. The first reports came from Topsfield, Maine in 1966 [8]. The beetle is abundant throughout Canada, including New Foundland, Quebec, Nova Scotia, and New Brunswick and, in the USA, from Maine through to Connecticut [9]

Methods

Results

Discussion

Conclusion