insects Review A Review of Sampling and Monitoring Methods for Beneficial Arthropods in Agroecosystems Kenneth W. McCravy Department of Biological Sciences, Western Illinois University, 1 University Circle, Macomb, IL 61455, USA; [email protected]; Tel.: +1-309-298-2160 Received: 12 September 2018; Accepted: 19 November 2018; Published: 23 November 2018 Abstract: Beneficial arthropods provide many important ecosystem services. In agroecosystems, pollination and control of crop pests provide benefits worth billions of dollars annually. Effective sampling and monitoring of these beneficial arthropods is essential for ensuring their short- and long-term viability and effectiveness. There are numerous methods available for sampling beneficial arthropods in a variety of habitats, and these methods can vary in efficiency and effectiveness. In this paper I review active and passive sampling methods for non-Apis bees and arthropod natural enemies of agricultural pests, including methods for sampling flying insects, arthropods on vegetation and in soil and litter environments, and estimation of predation and parasitism rates. Sample sizes, lethal sampling, and the potential usefulness of bycatch are also discussed. Keywords: sampling methodology; bee monitoring; beneficial arthropods; natural enemy monitoring; vane traps; Malaise traps; bowl traps; pitfall traps; insect netting; epigeic arthropod sampling 1. Introduction To sustainably use the Earth’s resources for our benefit, it is essential that we understand the ecology of human-altered systems and the organisms that inhabit them. Agroecosystems include agricultural activities plus living and nonliving components that interact with these activities in a variety of ways. Beneficial arthropods, such as pollinators of crops and natural enemies of arthropod pests and weeds, play important roles in the economic and ecological success of agroecosystems. These arthropod-mediated ecosystem services (AMES) increase agroecosystem productivity and sustainability by enhancing crop yields and reducing reliance on pesticides. The annual combined value of pollination services by non-Apis bees and pest control provided by insect predators and parasitoids has been estimated at $7.5 billion annually in the USA [1]. Land use practices can have adverse effects on these beneficial arthropods. Intensive agriculture can negatively affect bee diversity and pollination, and there is evidence of causal connections between decline of pollinators and decline of plants to which they are functionally linked [2]. Such adverse effects can be mitigated if undisturbed pollinator habitat is available [3,4]. Likewise, agroecosystems are often unfavorable environments for arthropod natural enemies of agricultural pests, but efforts such as habitat enhancement to conserve these natural enemies can provide important control of these pests [5]. For bees and natural enemies of insect pests, the ability to effectively assess and monitor their abundance and diversity, and potential effects of land use practices on them, is of vital importance. A variety of sampling methods is available, but these methods can be biased and vary widely in performance [6–11]. Some may provide absolute estimates of abundance (density, or numbers per unit area), but most provide relative estimates that are related to the sampling method being used (e.g., numbers per trap per day, numbers per hour of aerial netting, etc.). In this paper I present a brief overview of these beneficial arthropods and their importance, and some general concerns in regard to sampling and monitoring of these organisms. I then review the major sampling and monitoring Insects 2018, 9, 170; doi:10.3390/insects9040170 www.mdpi.com/journal/insects InsectsInsects2018 2018, 9,, 9 170, x FOR PEER REVIEW 22 of of 27 26 importance, and some general concerns in regard to sampling and monitoring of these organisms. I methodsthen review employed the major to assess sampling these and organisms, monitoring and me thethods advantages employed and to limitations assess these of theseorganisms, methods. and Itthe is hopedadvantages that this and paper limitations will provide of these entomologists methods. and It cropis hoped protection that specialiststhis paper with will aprovide useful overviewentomologists of sampling and crop methods protection available specialists and with will encouragea useful overview awareness of sampling and further methods research available and conservationand will encourage of these awareness important and arthropods. further research and conservation of these important arthropods. 2.2. Non- NonApis-ApisBees Bees TheThe total total value value of of pollination pollination servicesservices worldwideworldwide hashas beenbeen estimatedestimated atat $217$217 billionbillion [12[12].]. 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High diversity of bees can of bees enhance can enhancepollinator pollinator functional functional complimentarity complimentarity and ensure and ensure pollination pollination function function [17–19]. [17– 19Pollination]. Pollination can cancontribute contribute to the to the nutritional nutritional value, value, shelf shelf life, life, and and quality quality of offood food crops crops as aswell well [20,21]. [20,21 ]. SomeSome studies studies have have documented documented declines declines of non-of non-ApisApisbees bees in specific in specific geographic geographic locations locations [22– 24[22–], but24], large-scale, but large-scale, long-term, long-term, and statistically and statistically robust monitoring robust monitoring programs thatprograms yield datathat onyield population data on changespopulation are badly changes needed. are badly To document needed. 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SomeSome economicallyeconomically importantimportant non-non-ApisApis bees: ( (aa)) Blue Blue orchard orchard bee, bee, OsmiaOsmia lignaria lignaria Say,Say, a acommon common orchard orchard pollinator; pollinator; (b ()b southeastern) southeastern blueberry blueberry bee, bee, HabropodaHabropoda laboriosa laboriosa (Fabricius),(Fabricius), an early an earlyspring spring pollinator pollinator of rabbit-eye of rabbit-eye blueberry, blueberry, VacciniumVaccinium virgatum virgatum Aiton;Aiton; (c) ( cPeponapis) Peponapis pruinosa pruinosa Say,Say, a apollinator pollinator of of CucurbitaCucurbita spp.;spp.; and and (d (d) )the the orchid orchid bee bee EulaemaEulaema mocsaryi mocsaryi Friese,Friese, a pollinator a pollinator of Brazil of Brazil nut, nut,BertholletiaBertholletia excelsa excelsa Humb.Humb. & Bonpl. & Bonpl. Attributions: Attributions: (a) Robert (a) Robert Engelhardt Engelhardt [27]; ( [b27) ];Jerry (b) JerryA. Payne, A. Payne, USDA USDAAgricultural Agricultural Research Research Service Service [28]; ( [c28) Jim]; (c Cane,) Jim Cane, USDA USDA Agricultural Agricultural Research Research Service Service [29]; and [29]; (d and) M. (dC.) M. Cavalcante, C. Cavalcante, F. F. Oliveira, F. F. Oliveira, M. M. M. Maués, M. Mau andés, B. and M. B. Freitas M. Freitas [30]. [30]. Insects 2018, 9, 170 3 of 27 2.1. Bee Trapping Methods The three most commonly used