Comparison of orchid bee (Hymenoptera: Apidae) species composition collected with four chemical attractants.
Roubik & Hanson (2004) list nearly 50 chemicals that have been used as orchid bee attractants, and they also give species-specific lists of effective attractants in their orchid bee species accounts. However, while there is good qualitative knowledge of the species-specific effectiveness of many orchid bee attractants, there have been few studies that have quantitatively compared the species composition of orchid bees attracted by these chemicals.
Mesoamerica is one of the world's biodiversity hotspots (Mittermeier et al. 1999). Cusuco National Park, in northwest Honduras, has been designated a Key Biodiversity Area, but is threatened by human population growth and associated land cover changes (Green et al. 2012). The park contains a diverse assemblage of at least 24 species of orchid bees (McCravy et al. 2016). As part of an ongoing assessment of orchid bee diversity within the park, we did a study comparing the species composition of orchid bees attracted to 4 commonly used chemical attractants.
Materials and Methods
The study was done from 15 Jun to 30 Jul 2013 at Cusuco National Park (15.5333[degrees]N, 88.2500[degrees]W), about 30 km west of San Pedro Sula in the state of Cortes. Cusuco National Park has an area of about 23,400 ha and ranges in elevation from just above sea level to 2425 m. It is primarily cloud forest; habitat types include disturbed and undisturbed mature broadleaf forest, secondary broadleaf forest, disturbed pinebroadleaf forest, mature pine forest, open disturbed grassland, open disturbed logged areas, and open coffee plantations.
Orchid bees were collected with insect nets at bait stations that consisted of a cotton ball containing a chemical attractant suspended approximately 1.7 m above the ground by a string. Five bait stations, approximately 5 m apart, were established during each collection period. For each collection period, 1 of 4 chemical attractants was used. Attractants were purchased from Sigma Aldrich, Inc. (St. Louis, MO, USA) and included benzyl acetate (product # W213500; > 99% purity), eucalyptol (# W246506; > 99% purity), eugenol (# W246700; > 98% purity), and methyl salicylate (# W274518; > 98% purity). Product numbers and purity values were obtained from http://www.sigmaaldrich. com/united-states.html (accessed 4 Mar 2017). For each collection period, 1 of the 4 attractants was applied to all 5 bait stations. Each cotton ball received 30 drops initially; re-application with 20 additional drops was done every 30 min. Each collection period was from 9 AM to 11 AM. Sampling was done at 6 sites within the park (Table 1). Each site was sampled on 8 different dates, with each chemical being used twice at each site. Chemicals were randomly assigned to the first 4 collection dates at each site, then again to the last 4 collection dates. For each chemical, the 2 samples per site were pooled for analyses. Collected orchid bees were identified based on reference specimens and Roubik & Hanson (2004).
Because orchid bee species vary in their altitudinal distributions (Roubik & Hanson 2004), we compared species composition of each pair of sampling sites using the Morisita-Horn index of similarity (Morisita 1959; Horn 1966). We then used regression analysis to measure the potential association between Morisita-Horn values and altitudinal differences. Estimates version 9.1 (Colwell 2013) was used to calculate Morisita-Horn values, and regression analysis was done in Sigma Plot 13.0.
The Chao1 richness estimator (Chao et al. 2009) was used to estimate asymptotic orchid bee species richness overall and for each attractant. This analysis estimates the minimum species richness present, based on the relative numbers of singletons (1 individual of a species collected) and doubletons (2 individuals of a species collected). The Chao calculator (Ecological Archives E090-073-S1, Chao et al. 2009) was used to calculate Chaol estimates, as well as probabilities that an additional individual sampled would represent a previously undetected species ([q.sub.0], or the proportion of singletons in the sample, [f.sub.1]; / n). For each Chaol estimate, the proportion of singletons was less than 50% (i.e., [f.sub.1] / n < 0.5), as recommended by Anne Chao (cited in Colwell 2013).
Mean numbers of orchid bees collected were compared among attractants by 1-way ANOVA; pairwise multiple comparisons were done with the Holm-Sidak method. Data were square root transformed to satisfy the assumption of equal variances. Orchid bee species composition was compared among attractants by the multi-response permutation procedure (MRPP). The MRPP A value is a measure of the extent to which species composition of different groups diverge. A values <0.1 are common, and values >0.3 are relatively high (McCune & Grace 2002). To further examine differences in attractants, paired MRPP analyses were done. Holm's step-down procedure (Holm 1979) was used to control experiment-wise error rate for MRPP paired comparisons. In this procedure, the nth smallest P value is compared with 0.05 / (number of comparisons + 1 - n). Indicator species analysis (Dufrene & Legendre 1997), or ISA, was used to identify particular orchid bee species that were strongly associated with a particular attractant. ISA produces indicator values, ranging from 0 to 100, with the latter representing perfect association of that species with a particular attractant, ie., consistently associated with that attractant among different trials, and never associated with any other attractant. ANOVA was done in SigmaPlot, Version 13.0. MRPP and ISA were done by PC-Ord, Version 4.25.
A total of 649 orchid bees representing 17 species and 3 genera were collected (Table 2). Euglossa imperialis Cockerell and Eulaema marcii Nemesio were the most abundant species collected, with 411 and 111 individuals, respectively. There was no significant relationship between Morisita-Horn index values and altitudinal differences between sampling sites (F = 0.011; df = 1, 13; P = 0.918), indicating that altitudinal differences among the sites did not affect orchid bee species composition in this study. There was a significant overall difference in the numbers of orchid bees collected with the different attractants (F = 11.702; df = 3, 20; P < 0.001), with pairwise comparisons showing that eucalyptol collected significantly greater numbers than each of the other 3 attractants (P < 0.05; Table 2). Eucalyptol also collected the greatest species richness (15 species), with the other attractants ranging from 5 to 7. The Chaol estimate of overall species richness was 17.40, and 15.29 for eucalyptol. Each of the other 3 attractants had an estimated species richness of 7.0 (Table 2).
Four orchid bee species were significantly associated with a particular attractant, based on ISA (Table 2). Three of these, E. imperialis, Euglossa obtusa Dressler, and Eufriesea mexicana (Mocsary), were associated with eucalyptol, and 1, E. marcii, with benzyl acetate. Large proportions of 2 other Eulaema species, Eulaema luteola Moure and Eulaema meriana (Olivier), were collected in equal numbers with benzyl acetate and methyl salicylate. Euglossa dilemma Bembe & Eltz, on the other hand, was similar in abundance in eucalyptol and eugenol collections. Of 154 total Eulaema collected, 118 (76.6%) were collected with benzyl acetate, whereas 400 of 489 (81.8%) Euglossa were collected with eucalyptol. All 6 Eufriesea individuals were collected with eucalyptol.
The MRPP revealed significant overall differences in orchid bee species composition collected with the 4 attractants (A = 0.30, P < 0.001). Each of the 6 MRPP pairwise comparisons showed a significant difference in species composition between attractants (Table 3). Effect sizes (A values) varied substantially; they were relatively high for eucalyptol/benzyl acetate and eucalyptol/eugenol comparisons, and low for all comparisons involving methyl salicylate.
Chao1 analyses suggested that the 4 attractants collected most of the species richness present, within the limits of the methodology used. Use of additional attractants in this study would have very likely yielded additional species. Incorporation of traps could also yield different species. Nemesio & Vasconcelos (2014) found that passive sampling with baited traps collected significantly different orchid bee species composition compared with active netting at bait stations, although all species collected by traps were also collected by active netting. However, they advise against relying on baited traps as the sole or main basis of orchid bee faunistic studies because of trap bias.
Overall, eucalyptol was the most effective attractant both in terms of numbers of individuals and species richness collected in our study, with E. imperialis being collected in greatest quantity (Table 2). But even rare species of Euglossa and Eufriesea were collected, with the exception of Euglossa obrima Hinojosa-Diaz, Melo & Engel. However, Eulaema were poorly represented in eucalyptol collections. Methyl salicylate and especially benzyl acetate were relatively effective in attracting Eulaema species, and the large eucalyptol vs. benzyl acetate A value (Table 3) suggests that these 2 attractants are highly complementary. But it should be noted that, of the paired attractant combinations, only eucalyptol and eugenol collected all 17 species, demonstrating that even an attractant that collects relatively few individuals can still be useful in species richness inventories.
In a study of orchid bees at a lowland site in Costa Rica, Janzen et al. (1982) used the same attractants that we used, plus a fifth attractant, methyl cinnamate. They also found eucalyptol (referred to by the alternate term "cineole" in their study) to be most effective in terms of orchid bee abundance and species richness collected among the 4 attractants (excluding methyl cinnamate). However, in that study, orchid bee abundance was more evenly distributed among the 4 attractants, with eucalyptol accounting for 38.7% (670 of 1731) of total captures vs. 63.0% in our study. Eugenol, on the other hand, collected 33.6% of total captures in the Janzen et al. (1982) study, vs. only 4.0% in our study, and benzyl acetate accounted for only 4.4% of captures in the Costa Rica study, vs. 19.0% in our study. These differences could be due to a variety of factors. There is evidence that the effectiveness of chemical attractants varies both geographically and temporally (Nemesio 2012), even within a species. This may be due to a variety of climatological or biotic factors. Perhaps eugenol volatilizes and disperses more readily in warmer lowland conditions than in the higher elevation cloud forest environment of our study. Of the 4 attractants we used, eugenol has the highest boiling point of 254 [degrees]C, vs. 212 [degrees]C, 176 to 177 [degrees]C, and 222 [degrees]C for benzyl acetate, eucalyptol, and methyl salicylate, respectively (http://www.sigmaaldrich.com/united-states.html; accessed 4 Mar 2017). Interestingly, there was an inverse relationship between attractant effectiveness and attractant boiling point in our study, suggesting that, in addition to inherent "attraction," volatility may play an important role in the effectiveness of orchid bee attractants. For comparison purposes, we used the chemicals in their "out of the bottle" state, but mixing with a volatile carrier such as ethyl alcohol might increase the effectiveness of some chemicals, such as eugenol. Factors such as volatility, climatic conditions, amount of attractant used, time of day that sampling is done, and many others may greatly affect results. Nemesio (2012) provides a thorough review of methodological concerns associated with factors such as these that could affect orchid bee sampling.
Of the 32 species of orchid bees Janzen et al. (1982) collected, only 10 overlapped with our study. In general, among the species in common to both studies, species-attractant relationships were similar. In the Janzen et al. (1982) study, eucalyptol and methyl salicylate accounted for almost all (68.3% and 31.4%, respectively) of E. imperialis captures, as was the case in our study (87.1% and 11.9%, respectively). Likewise, benzyl acetate and methyl salicylate accounted for the great majority of E. meriana collected in their study (90.4%) as well as ours (87.5%). All E. mexicana collected in both studies were attracted by eucalyptol, whereas E. mixta was collected primarily with methyl salicylate in both our study (80%) and the Janzen et al. (1982) study (100%). In our study, Euglossa heterosticta Moure was captured in equal numbers with eucalyptol and methyl salicylate, whereas in Janzen et al. (1982) all 4 individuals of this species were collected with eucalyptol.
Orchid bees are vital components of Neotropical forest ecosystems. Orchid bee conservation requires increased knowledge of their diversity and ecology, and much of this knowledge base depends on rigorous sampling methodology using chemical attractants. There are numerous chemicals available for use as orchid bee attractants, and these attractants vary widely in their overall and species-specific effectiveness. While there is substantial qualitative knowledge of orchid bee species attraction to specific chemicals, more detailed comparative information is needed on chemical attractants and the species assemblages they attract.
We thank David Roubik (Smithsonian Tropical Research Institute) for helpful advice on orchid bee biology and for our reference collection that was used in the identification of the orchid bees collected in this study. We also thank Sarah Wilcer (Western Illinois University) for help with orchid bee pinning and labeling. Finally, we thank Operation Wallacea for invaluable financial and logistical support, and the Western Illinois University Office of Sponsored Projects and Research Foundation for generous funding for this study.
Ackerman JD. 1983. Diversity and seasonality of male euglossine bees (Hymenoptera: Apidae) in Central Panama. Ecology 64: 274-283
Ackerman JD, Roubik DW. 2012. Can extinction risk help explain plant-pollinator specificity among euglossine bee pollinated plants? Oikos 121: 1821-1827.
Briggs HM, Perfecto I, Brosi BJ. 2013. The role of the agricultural matrix: coffee management and euglossine bee (Hymenoptera: Apidae: Euglossini) communities in southern Mexico. Environmental Entomology 42: 1210-1217.
Chao A, Colwell RK, Lin C-W, Gotelli NJ. 2009. Sufficient sampling for asymptotic minimum species richness estimators. Ecology 90: 1125-1133.
Colwell RK. 2013. Estimates: Statistical estimation of species richness and shared species from samples, Version 9, http://purl.oclc.org/estimates (last accessed 4 Mar 2017).
Dodson CH, Dressier RL, Hills HG, Adams RM, Williams NH. 1969. Biologically active compounds in orchid fragrances. Science 164: 1243-1249.
Dressler RL. 1982. Biology of the orchid bees (Euglossini). Annual Review of Ecology and Systematics 13: 373-394.
Dufrene M, Legendre P. 1997. Species assemblages and indicator species: the need for a flexible asymmetrical approach. Ecological Monographs 67: 345-366.
Green S, Slater K, Burdekin O, Long P. 2012. Cusuco National Park, Honduras: 2012 Status Report. Operation Wallacea, Lincolnshire, United Kingdom.
Holm S. 1979. A simple sequentially selective multiple test procedure. Scandinavian Journal of Statistics 6: 65-70.
Horn HS. 1966. Measurement of "overlap" in comparative ecological studies. American Naturalist 100: 419-424.
Janzen DH, De Vries PJ, Higgins ML, Kimsey LS. 1982. Seasonal and site variation in Costa Rican euglossine bees at chemical baits in lowland deciduous and evergreen forests. Ecology 63: 66-74.
McCravy KW, Van Dyke J, Creedy T, Roubik DW. 2016. Orchid bees (Hymenoptera: Apidae: Euglossini) of Cusuco National Park, State of Cortes, Honduras. Florida Entomologist 99: 765-768.
McCune B, Grace JB. 2002. Analysis of Ecological Communities. MjM Software Design, Gleneden Beach, Oregon, USA.
Mittermeier RA, Myers N, Mittermeier CG [eds.]. 1999. Hotspots: Earth's Biologically Richest and Most Endangered Terrestrial Ecoregions. CEMEX/Conservation International, Mexico City, Mexico.
Morisita M. 1959. Measuring of interspecific association and similarity between communities. Memoirs of the Faculty of Science, Kyushu University, Series E (Biology) 3: 65-80.
Nemesio A. 2012. Methodological concerns and challenges in ecological studies with orchid bees (Hymenoptera: Apidae: Euglossina). Bioscience Journal 28: 118-134.
Nemesio A, Vasconcelos HL. 2014. Effectiveness of two sampling protocols to survey orchid bees (Hymenoptera: Apidae) in the Neotropics. Journal of Insect Conservation 18: 197-202.
Roubik DW, Hanson PE. 2004. Orchid Bees of Tropical America: Biology and Field Guide. INBio, Santo Domingo de Heredia, Costa Rica.
Zimmermann Y, Ramirez SR, Eltz T. 2009. Chemical niche differentiation among sympatric species of orchid bees. Ecology 90: 2994-3008.
Kenneth W. McCravy (1,2,*), Joseph Van Dyke (2,3), Thomas J. Creedy (2,4,5,6), and Katie Williams (2)
(1) Department of Biological Sciences, Western Illinois University, 1 University Circle, Macomb, Illinois 61455, USA; E-mail: KW-McCravy@wiu.edu (K. W. M.)
(2) Operation Wallacea, Hope House, Old Bolingbroke, Spilsby, Lincolnshire, PE23 4EX, UK; E-mail: firstname.lastname@example.org (K. W.)
(3) Department of Biology, West Virginia University, Morgantown, West Virginia 26505, USA; E-mail: email@example.com (J. V D.)
(4) Hope Entomological Collections, Oxford University Museum of Natural History, Parks Road, Oxford, OX1 3PW, UK; E-mail: firstname.lastname@example.org (T. J. C.)
(5) Department of Life Sciences, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
(6) Natural History Museum, Cromwell Road, London, SW7 5BD, UK
(*) Corresponding author; E-mail: KW-McCravy@wiu.edu (K. W. M.)
Table 1. Locations and altitudes of orchid bee sampling sites within Cusuco National Latitude Longitude Altitude (m) 15.5114[degrees]N 88.1855[degrees]W 999 15.4964[degrees]N 88.1899[degrees]W 1202 15.5005[degrees]N 88.2144[degrees]W 1631 15.5021[degrees]N 88.2046[degrees]W 1403 15.4944[degrees]N 88.2139[degrees]W 1600 15.4971[degrees]N 88.2211[degrees]W 1685 Table 2. Numbers of orchid bees collected (with mean [+ or -] SE) using 4 chemical attractants (BA = benzyl acetate, EUC = eucalyptol, EUG = eugenol, MS = methyl salicylate) at Cusuco National Park, Honduras, in Jun to Jul 2013, with observed and estimated species richness values, [q.sub.0] values, and results of indicator species analysis (ISA). Species BA EUC Euglossa imperialis Cockerell 3(0) 358(87) Eulaema marcii Nemesio 98(88) 0(0) Euglossa dilemma Bembe & Eltz 1(1) 11(24) Eulaema luteola Moure 13(32) 1(1) Euglossa obtusa Dressler 1(1) 13 (81) Eulaema meriana (Olivier) 7(29) 2(4) Euglossa mixta Friese 0(0) 2(3) Euglossa heterosticta Moure 0(0) 4(25) Euglossa tridentata Moure 0(0) 4(17) Eufriesea mexicana (Mocsary) 0(0) 3(50) Eufriesea rugosa (Friese) 0(0) 2(33) Euglossa cybelia Moure 0(0) 2(17) Euglossa hansoni Moure 0(0) 2(17) Euglossa purpurea Friese 0(0) 2(33) Euglossa variabilis Friese 0(0) 2(17) Eufriesea schmidtiana (Friese) 0(0) 1(17) Euglossa obrima Hinojosa-Diaz, 0(0) 0(0) Melo & Engel Total 123 409 Mean number per site [+ or -] 20.5 [+ or -] 5.4a 68.2 [+ or -] 16.7b SE (b) Observed species richness 6 15 Estimated species richness 7.00 15.29 Probability of an additional 0.0163 0.0049 individual being a previously undetected species ([q.sub.0]) Species EUG MS Euglossa imperialis Cockerell 1(0) 49 (10) Eulaema marcii Nemesio 8(2) 5(2) Euglossa dilemma Bembe & Eltz 14(38) 5(8) Eulaema luteola Moure 0(0) 13(40) Euglossa obtusa Dressler 2(2) 0(0) Eulaema meriana (Olivier) 0(0) 7(29) Euglossa mixta Friese 0(0) 8(40) Euglossa heterosticta Moure 0(0) 4(17) Euglossa tridentata Moure 0(0) 0(0) Eufriesea mexicana (Mocsary) 0(0) 0(0) Eufriesea rugosa (Friese) 0(0) 0(0) Euglossa cybelia Moure 0(0) 0(0) Euglossa hansoni Moure 0(0) 0(0) Euglossa purpurea Friese 0(0) 0(0) Euglossa variabilis Friese 0(0) 0(0) Eufriesea schmidtiana (Friese) 0(0) 0(0) Euglossa obrima Hinojosa-Diaz, 1(17) 0(0) Melo & Engel Total 26 91 Mean number per site [+ or -] 4.3 [+ or -] 1.9a 15.2 [+ or -] 4.7a SE (b) Observed species richness 5 7 Estimated species richness 7.00 7.00 Probability of an additional 0.0769 0.0000 individual being a previously undetected species ([q.sub.0]) ISAP Species Total value (a) Euglossa imperialis Cockerell 411 0.001 Eulaema marcii Nemesio 111 0.001 Euglossa dilemma Bembe & Eltz 31 0.141 Eulaema luteola Moure 27 0.074 Euglossa obtusa Dressler 16 0.001 Eulaema meriana (Olivier) 16 0.292 Euglossa mixta Friese 10 0.101 Euglossa heterosticta Moure 8 0.278 Euglossa tridentata Moure 4 1.000 Eufriesea mexicana (Mocsary) 3 0.040 Eufriesea rugosa (Friese) 2 0.217 Euglossa cybelia Moure 2 1.000 Euglossa hansoni Moure 2 1.000 Euglossa purpurea Friese 2 0.231 Euglossa variabilis Friese 2 1.000 Eufriesea schmidtiana (Friese) 1 1.000 Euglossa obrima Hinojosa-Diaz, 1 1.000 Melo & Engel Total 649 Mean number per site [+ or -] 108.2 [+ or -]20.0 SE (b) Observed species richness 17 Estimated species richness 17.40 Probability of an additional 0.0031 individual being a previously undetected species ([q.sub.0]) Numbers in parentheses are indicator values, with statistically significant indicator values in bold. (a) P values represent the proportion of 1000 randomized trials with an indicator value equal to or exceeding the observed indicator value. (b) Mean numbers of orchid bees collected followed by the same letter are not significantly different (ANOVA, Holm-Sidak multiple pairwise comparison method, P > 0.05). Table 3. Multi-response permutation procedure A values (with associated P values in parentheses) for paired comparisons of orchid bee species composition collected using 4 chemical attractants (BA = benzyl acetate, EUC = eucalyptol, EUG = eugenol, MS = methyl salicylate) at Cusuco National Park, Honduras, in Jun -Jul 2013. All paired comparison A values were significant after adjustment for multiple comparisons using Holm's step-down procedure. Comparison A value (P value) BA vs. EUC 0.35 (<0.001) BA vs. EUG 0.21 (0.002) BA vs. MS 0.19 (0.002) EUC vs. EUG 0.27 (0.001) EUC vs. MS 0.18 (0.002) EUG vs. MS 0.17 (0.005) Overall 0.30 (<0.001)
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|Author:||McCravy, Kenneth W.; Dyke, Joseph Van; Creedy, Thomas J.; Williams, Katie|
|Date:||Sep 1, 2017|
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