Author Manuscript This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/jen.12745 This article is protected by copyright. All rights reserved Fresh, frozen or fake: a comparison of predation rates measured by various types of sentinel prey Rebecca K. Nagya,b, Nancy A. Schellhornb† and Myron P. Zaluckia aSchool of Biological Sciences, The University of Queensland, St Lucia, Qld 4072, Australia bCSIRO, Brisbane, Qld 4001, Australia †RapidAim, Brisbane, Qld 4000, Australia Acknowledgements Thanks goes to UQAuthor Manuscript Gatton for allowing access to their property to conduct this research. Thanks also to Anna Marcora for her help procuring insects from Narrabri and Dr Lynda Perkins for her help with statistics. R.K.N.’s research is funded by the Australian This article is protected by copyright. All rights reserved Government Research Training Program (RTP), AW Howard Memorial Trust and Advance Queensland. Author Manuscript This article is protected by copyright. All rights reserved 1 2 MRS. REBECCA NAGY (Orcid ID : 0000-0002-5562-7957) 3 4 5 Article type : Advances in Methodology 6 7 Formatted: Left, Line spacing: Multiple 1.08 li 8 Corresponding author mail id: [email protected] Formatted: Font: 12 pt 9 Fresh, frozen or fake: a comparison 10 of predation rates measured by 11 various types of sentinel prey 12 13 Rebecca K. Nagya,b, Nancy A. Schellhornb and Myron P. Zaluckia 14 aSchool of Biological Sciences, The University of Queensland, Brisbane, Qld 4072, Australia 15 bCSIRO, Brisbane, Qld 4001, Australia 16 17 18 Abstract 19 Arthropod predators and parasitoids support the health and functioning of the world’s 20 ecosystems, most notably by supplying biological control services to agricultural landscapes. Author Manuscript This article is protected by copyright. All rights reserved 21 Quantifying the impact that these organisms have on their prey can be challenging, as direct 22 observation and measurement of arthropod predation is difficult. The use of sentinel prey is 23 one method to measure predator impact; however, despite widespread use, few studies 24 have compared predation on different prey types within a single experiment. This study 25 evaluated the predation rates on four sentinel prey items in grass and wheat fields in south- 26 east Queensland, Australia. Attack rates on live and dead Helicoverpa armigera eggs, and 27 dead H. armigera larvae and artificial plasticine larvae, were compared and the predators 28 that were attracted to each prey type were documented with the use of field cameras. There 29 was no significant difference in predation rates between sentinel eggs, while dead larvae 30 were significantly more attacked than artificial larvae. Prey were attacked by a diverse range 31 of predators, including ants, beetles, various nymph and juvenile insects and small 32 mammals. Different predators were active in grass and crop fields, with predator activity 33 peaking around dawn and dusk. The same trends were observed within and between the 34 two habitats studied, providing a measure of confidence in the sentinel prey method. A 35 range of different sentinel prey types could be suitable for use in most comparative studies; 36 however, each prey type has its own benefits and limitations, and these should be carefully 37 evaluated to determine which is most suitable to address the research questions. 38 39 40 Keywords 41 Predation; grassland; crop; Helicoverpa armigera; plasticine 42 43 44 Introduction Author Manuscript This article is protected by copyright. All rights reserved 45 Ecosystem services play a vital role in maintaining the health and functioning of the world’s 46 habitats. Predation is one of the most important ecosystem services, as it has the ability to 47 alter the structure and stability of entire ecosystems. Predation can influence all ecosystem 48 levels, from individual organisms (determining colour, body size, behaviour and life history), 49 to populations (size and stability) and whole communities (species abundance and diversity, 50 regulating herbivore abundance and reducing resource depletion effects) (Powell, Walton, & 51 Jervis, 1996; Sam, Remmel, & Molleman, 2015; Sih, Crowley, McPeek, Petranka, & 52 Strohmeier, 1985). Insects are arguably the largest and most diverse group on the planet, 53 and are also valuable predators, with one quarter of all insect species believed to be 54 predatory or parasitic in at least one life-history stage (Gullan & Cranston, 2014). Insect 55 predators are most well known for their role in agricultural biological control programs, with 56 the economic value of insect-mediated pest control estimated to be over $4.5 billion annually 57 in the US alone (Losey & Vaughan, 2006). 58 Almost every ecosystem in the world benefits from insect predation services; however, 59 measuring and quantifying predators’ impact on their prey is challenging, and the reliability of 60 such evaluations are often questionable (Furlong & Zalucki, 2010; Losey & Vaughan, 2006). 61 Direct observation and measurement of insect predation is very difficult, due to the small 62 size of arthropods, their speed, cryptic habitats, infrequency of their attacks, frequent night 63 activity and the fact predation often leaves no evidence (Low, Sam, McArthur, Posa, & 64 Hochuli, 2014; Powell et al., 1996). As a result, predator presence, absence and density are 65 often measured and impact is inferred – a two-fold increase in predator density is presumed 66 to result in a two-fold increase in predation. This is rarely the case, however, and not a good 67 measure of likely predator effectiveness (Howe, Lövei, & Nachman, 2009; Macfadyen, 68 Davies, & Zalucki, 2015). Informed decisions regarding pest control and Integrated Pest 69 Management (IPM) cannot be made without some “more realisticdirect” evidence of the 70 impact of natural enemy activity (Macfadyen et al., 2015; Zalucki, Furlong, Schellhorn, 71 Macfadyen, & Davies, 2015). Author Manuscript This article is protected by copyright. All rights reserved 72 Evidence in the form of direct estimation of predator impact is required for practical decision- 73 making, and several methods have been developed to achieve this, including direct field 74 observation, use of sentinel prey, exclusion cage studies, use of in-field cameras and video 75 recording and gut content identification (Hughes et al., 1973; Macfadyen et al., 2015; Powell 76 et al., 1996; Sunderland, 1987). The use of sentinel prey involves monitoring the 77 disappearance of, or damage to, prey items provided by the researchers, and is one of the 78 easiest and most commonly used methods to obtain a direct, quantitative measure of 79 predation pressure under field conditions (Howe et al., 2009; Powell et al., 1996). There is 80 considerable flexibility in using sentinel prey: previous studies have used prey from a range 81 of insect orders (most commonly Lepidoptera, Coleoptera and Hemiptera), at every life stage 82 (egg, larvae, nymph, adult and pupae), either live or dead (Lövei & Ferrante, 2017). Another 83 potential ‘prey’ item gaining popularity in recent years is artificial sentinel prey – dummies, 84 created most often from plasticine, and used in place of insect ‘real’ prey (Howe et al., 2009; 85 Lövei & Ferrante, 2017). While certain characteristics of artificial prey may influence attack 86 rate, either positively or negatively, the use of dummy prey has certain advantages that may 87 still make it a suitable option for comparative studies. Artificial prey does not move or 88 behave as true prey might and lacks any potential chemical cues; however, it is cheap and 89 fast to produce, does not require mass rearing and predators can often be identified by 90 marks left in the plasticine (Lövei & Ferrante, 2017). 91 Considering the vast range of potential sentinel prey available, it is surprising that very few 92 studies have compared and evaluated several different sentinel prey types in a single study 93 (Ferrante, Barone, & Lövei, 2017; Peisley, Saunders, & Luck, 2016; Sam et al., 2015). All 94 prey have benefits and limitations, and will be better suited for certain studies over others. 95 Understanding how potential prey options perform in relation to each other is important to 96 ensure the most suitable prey are utilised to address the research questions. 97 This study evaluates the predation rates of four commonly used sentinel prey types. 98 Predation of live and dead Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) eggs, Author Manuscript This article is protected by copyright. All rights reserved 99 and dead H. armigera larvae and artificial plasticine larvae, were compared, and field 100 cameras were used to observe the predators that were attracted to each prey type. This 101 study was conducted in grass and wheat fields to determine whether the observed trends 102 were consistent across different habitat types. 103 104 105 Materials and Methods 106 Study region 107 This study was undertaken at the University of Queensland’s Gatton Campus (27.5521°S, 108 151.3356°E) in the Lockyer Valley, located 80 km west of Brisbane in south-east 109 Queensland, Australia. The region has a humid subtropical climate with hot, humid 110 summers (mean maximum 30-32°C), mild to cool winters (mean maximum 20-23°C) and 111 annual rainfall averaging 750-800 mm. It is a mixed farming region, with fertile soils and 112 intensively cultivated, dominated by vegetable crops, while also supporting fodder crop 113 production, mostly grains and lucerne, and beef and dairy cattle farming. 114 One grass and one crop site were selected, 2.5 km apart. The crop was winter wheat (mid 115 grain-fill, approx. BBCH 85; Lancashire et al., 1991), and was surrounded by other wheat 116 fields and small cattle holding yards (Figure 1a).