A review of the sentinel prey method as a way of quantifying invertebrate predation under field conditions

Abstract

Sentinel prey can provide a direct, quantitative measure of predation under field conditions. Live sentinel prey provides more realistic data but rarely allows the partitioning of the total predation pressure; artificial prey is less natural but traces left by different predators are identifiable, making it suitable for comparative studies. We reviewed the available evidence of the use of both types of invertebrate sentinel prey. Fifty-seven papers used real prey, usually measuring predation on a focal (often pest) species, with studies overwhelmingly from North America. The median predation was 25.8% d . Artificial sentinel prey (45 papers) were used in both temperate and tropical areas, placed more above ground than at ground level. The most commonly used artificial prey imitated a caterpillar. Up to 14 predator groups were identified, registering a median of 8.8% d predation; half the studies reported only bird predation. Predation on real prey was higher than on artificial ones, but invertebrate predation was not higher than vertebrate predation. Invertertebrate but not vertebrate predation was negatively related to prey size. Predation near the Equator was not higher than at higher latitudes, nor in cultivated than noncultivated habitats. The use of sentinel prey is not yet standardised in terms of prey size, arrangement, exposure period or data reporting. Due to the simplicity and ease of use of the method, such standardisation may increase the usefulness of comparative studies, contributing to the understanding of the importance and level of predation in various habitats worldwide.

Predators do not spill over from forest fragments to maize fields in a landscape mosaic in central Argentina

“…Overall, we registered high predation pressure on the artificial caterpillars: nearly half of them were attacked within 24 hr in chaco serrano forest fragments. This is among the higher values recorded so far worldwide (Lövei & Ferrante, ). There are few data from cultivated fields (but see Howe, Nachman, & Lövei, ; Barbaro et al., ), and no published studies from maize fields from anywhere, making direct comparisons impossible.…”

Manipulating field margins to increase predation intensity in fields of winter wheat (Triticum aestivum)

“…These data do not support our third hypothesis. Predation on artificial caterpillars may reflect the activity of only a part of the natural enemy community, as not all will attack such potential prey (the size of the sentinel prey may discourage small predators (Lövei and Ferrante ), and parasitoids rarely attack such artificial prey (Howe et al. )).…”

“…As both may be important in pest regulation, agro‐environments should be managed as a mosaic of different habitats, which may include flower margins and grassy strips, to provide abiotic and biotic resources to the whole natural enemy community. To date, predation rates in agroecosystems have been measured using artificial caterpillars only in tropical areas (Lövei and Ferrante ). Our results confirm the applicability of the method in European agroecosystems.…”

Elevational contrast in predation and parasitism risk to caterpillars in a tropical rainforest

“…Live (sentinel) insects, mostly represented by lepidopteran eggs or larvae, have been used mainly in temperate and subtropical regions, primarily for studies of interactions between pests and their enemies in agricultural habitats (Lemessa et al, ; Macfadyen et al, ; Begg et al, ; Lovei & Ferrante, ). To our knowledge, the only previous study conducted in a tropical rainforest exposed caterpillar of an endemic crambid at three different islands of the Hawaiian archipelago, and found a 14% per day predation rate and a 5% parasitism rate (Kaufman & Wright, ).…”