Insects attracted to Maple Sap: Observations from Prince Edward Island, Canada

Abstract The collection of maple sap for the production of maple syrup is a large commercial enterprise in Canada and the United States. In Canada, which produces 85% of the world’s supply, it has an annual value of over $168 million CAD. Over 38 million trees are tapped annually, 6.5% of which use traditional buckets for sap collection. These buckets attract significant numbers of insects. Despite this, there has been very little investigation of the scale of this phenomenon and the composition of insects that are attracted to this nutrient source. The present paper reports the results of a preliminary study conducted on Prince Edward Island, Canada. Twenty-eight species of Coleoptera, Lepidoptera, and Trichoptera were found in maple sap buckets, 19 of which are known to be attracted to saps and nectars. The physiological role of sap feeding is discussed with reference to moths of the tribe Xylenini, which are active throughout the winter, and are well documented as species that feed on sap flows. Additionally, 18 of the 28 species found in this study are newly recorded in Prince Edward Island.


Introduction
Th e collection of maple sap for the production of maple sugar has a long history in North America. Before the arrival of European settlers, native people in northeastern North America collected maple sap, pouring it into hollowed-out logs in which heated stones were placed to evaporate the water and concentrate the syrup. In the 1880's a signifi cant innovation was the introduction of the forerunner to the contemporary fl ue pan evaporator (Chapeske and Henderson 2007). Two species of trees, sugar maple (Acer saccharum Marsh.) and black maple (Acer nigrum Michx.) are employed in maple sugar production, although the former accounts for the majority of trees tapped (Chapeske and Henderson 2007).
In 2006 in Canada, 9,731 maple sugar producers had an average per-farm tap number of 3,913 indicating that approximately 38,077,400 trees were being tapped. Two collection methods are used: the traditional bucket system placed on trees, and plastic tube collection. In Ontario 78% of collection is with plastic tubing and 22% is by traditional buckets (Chapeske and Henderson 2007). In Québec 97.7% collection is with plastic tubing, and only 2.3% with traditional buckets (Johannie Coiteux, Federation of Quebec Maple Syrup Producers, pers. comm.). Employing these percentages indicates that in Canada some 1.5 million trees are tapped using traditional buckets.
Despite the long history of maple syrup production, which has evolved to become a signifi cant industry in Canada and the northeastern United States, and the very sizeable number of trees that are tapped over a considerable portion of the continent, there has been remarkably little attention paid to the insects that are attracted to maple sap during extraction and collection. Sap is largely contained with the plastic tubing collection method and except for local spots surrounding the borehole, there is little opportunity for insects to avail themselves of this resource. In traditional bucket collection the opportunity for attracting insects to sap is considerably greater. Maple sap typically consists of 97.5% water, 2.4% sugars (primarily sucrose with small amounts of glucose), and 0.1% minerals (primarily potassium and calcium, with smaller quantities of zinc and manganese, and trace amounts of other minerals). Th ere are also trace amounts of phenolic compounds, primary amines, peptides, amino acids, and other organic compounds. (Ball 2007).
Many species of moths attracted to sugar solutions on trees, indeed "sugaring" for moths is an important collection technique for many species of nocturnal Lepidoptera. In a poetic essay entitled "Sugaring for Moths" in Th e Moth Book, Holland (1903: 146-150), an important fi gure in the history of North American lepidopterology, outlined the technique in a lyrical style, now long vanished from entomological literature. Smith (1900) noted the propensity of many moths to be attracted to the sap of trees, particularly that of sugar maples. He highlighted Xylena spp., Eupsilia spp., Metalepsis salicarum (Walker), Orthosia hibisci (Guenee), and Xystopeplus rufago (Hübner) (all Noctuidae) as species particularly attracted to maple sap. Miller (1997) noted that adult moths of four families -Noctuidae, Sphingidae, Geometridae, and Tortricidaeare attracted to natural sap fl ows.
Th ere has been considerable interest in sap fl ows caused by Yellow-bellied Sapsuckers (Sphyrapicus varius Linnaeus) (Aves: Picidae) and the insects attracted to these. Studies such as Foster and Tate (1966) and Rissler et al. (1995) recorded a large diversity of insects in Lepidoptera, Hymenoptera, Diptera, Coleoptera, Hemiptera, Homoptera, Collembola, and Psocoptera frequenting sapsucker induced fl ows. Unfortunately, in many instances identifi cations were done only to the level of Family.
Th ere are few references in entomological literature of insects specifi cally associated with the collection of maple sap. Arnett (2000) noted that Hypogastrura nivicola (Fitch) (Collembola: Poduridae), the common and familiar "snow fl ea", is attracted to maple sap and can attain pest status in buckets during periods of harvest. Rings (1969Rings ( , 1973 drew attention to Lithophane antennata (Walker), Lithophane laticinerea Grote, and Lithophane unimoda (Lintner) (Lepidoptera: Noctuidae) as moths attracted to maple sap, which can become a nuisance by accumulating on the surface in collection buckets. Dearborne (1999) reported that adult Ellychnia corrusca (Linnaeus) (Coleoptera: Lampyridae) often become a pest by falling into maple sap buckets.

Methods
On 4 April 2010 while at a maple sugar collection site in Woodville Mills, Prince Edward Island, (46°14'22"N; 62°31'04"W), insects in maple sap collection buckets (n=70) were surveyed. Th e forest stand (4.2 hectares) consists of primarily deciduous trees [sugar maple, red oak (Quercus rubra L.), yellow birch (Betula alleghaniensis Britt), linden (Tilia europea L), pin cherry (Prunus pensylvanica L.f.), and others) with occasional intermixed conifers [red spruce (Picea rubens Sarg,), white spruce (Picea glauca (Moench) Voss), balsam fi r (Abies balsamaea (L.) Mill)]. It is bounded along its lower margin by a small stream fl owing from a marsh and beaver pond, along its upper margin by an apple orchard, and along both sides by agricultural fi elds. Th e spacing of sap collection buckets varied within this area. In some instance as many as three buckets were place on a single tree; in other instances buckets were as much as 10 meters apart, depending on the size and spacing of the sugar maple trees.
All buckets had covers on them to prevent extraneous debris from falling into the maple sap. Th erefore insects present inside would almost certainly have had to actively enter the buckets, either from beneath the lids (where there was a gap at the front of the bucket) or in the small open area near the spigot. Th us, the suite of insects present would largely represent species actively attracted to maple sap, or seeking shelter in the buckets, as opposed to specimens that had accidentally fallen into the containers.
It was not possible to strictly quantify the results, since diff erent buckets had been hanging with uncollected sap for varying periods (1-4 days) due to the impending conclusion of the sap collection season. Nevertheless general categories of abundance [scarce, fewer than 10 specimens; abundant, 10-30 specimens; very abundant, more than 30 specimens] were assigned for each of the species found.

Results and discussion
Th e results of this investigation are shown in Table 1. Diptera were also present but were not collected. Twenty-eight species were recorded including 18 Coleoptera, eight Lepidoptera, and two Trichoptera. After reviewing the biology of each species, it was possible to categorize them as species associated with sap and nectar, or accidental visitors.
Due in large measure to the comparative dearth of entomological research on Prince Edward Island, it is possible to report that 18 of the 28 species found in this study are newly recorded in the province. In the case of some species of Coleoptera (i.e., Ellychnia corrusca, Cyphon variabilis, C. confusus, and Nudobius cephalus (Say)) these new records represent broadly distributed species that belong to groups that have not yet been surveyed on Prince Edward Island. However the Prince Edward Island Curculionidae were surveyed by Majka et al. (2007), the Nitidulidae were surveyed by Majka and Cline (2006a), and the Maritime Provinces Aleocharinae by Majka and Klimaszewski (2010) so the new records of Trypodendron retusum (LeConte), Xyloborinus alni (Niisima), Cryptarcha ampla Erichson and Silusa californica Bernhauer are additions to a fauna which has already received recent attention.
Similarly, although some research has been conducted on the Noctuidae of Prince Edward Island, the fauna remains poorly known and none of the species recorded herein have previously been recorded from the province (Troubridge and Lafontaine 2004).

Coleoptera: species associated with sap and nectar
Two species were hyper-abundant (more than 100 individuals each) in the sap buckets: E. corrusca and C. variabilis. Rooney and Lewis (2000) reported that adult E. corrusca feed actively on fl oral nectarines of Norway maple (Acer platanoides L.) and are attracted to natural sap fl ows on A. saccharum. As previously noted, Dearborne (1999) remarked on how this species was attracted to maple sap, often becoming a pest in sap buckets.  Klausnitzer (2009) described C. variabilis as a eurotypic species found in moderately acid Sphagnum moorlands, near eutrophic waters, beside muddy ditches, and along the banks of ponds. Th e species has not been generally associated with sap fl ows or the collection of maple sap in the literature, although Wolcott and Montgomery (1933) did note a specimen on a tamarack trunk, "feeding at small spot of exuding sap." Th e collection site is approximately 0.25 km from a small beaver pond and associated marsh that provide a suitable site for C. variabilis, however, the large number of specimens attracted to maple sap (and smaller numbers of the related Cyphon confusus Brown) is unexpected, apparently refl ecting an aspect of the biology of these marsh beetles not hitherto noted in the literature.
Trypodendron retusum, Xyloterinus politus (Say), and Xyloborinus alni are all ambrosia beetles (Curculionidae: Scolytinae) wherein adults excavate galleries beneath bark of unhealthy or dying trees. Th ese galleries are inoculated with symbiotic fungi carried in mycangial pits on the heads of the beetle. Adults and larvae feed on the resulting growth of fungal hyphae. Bark beetles are known to be attracted to tree volatiles such as terpenes and oleoresins, so it may be that these species are attracted to the maples via these chemicals signals, and in seeking their source, the beetles secondarily fall into the maple sap. Trypodendron retusum is associated with poplars (Populus grandidentata Michx. and Populus tremuloides Michx.) and is newly recorded on Prince Edward Island (Wood 1982;Majka et al. 2007). Xyloterinus politus is associated with a wide variety of primarily deciduous hosts (occasionally coniferous ones) including species of Acer, Alnus, Betula, Carya, Castanea, Fagus, Fraxinus, Quercus, Picea, Pinus, Tsuga, and Ulmus (Wood 1982). Xyloborinus alni is an adventive Oriental species recently found in North America (Haack 2006). Th e species was originally detected in 1995 in British Columbia, and 1996 in Washington State, and later reported in several eastern states in the USA (Haack 2006). Th is is the fi rst report of this species from Prince Edward Island. In North America the only reported hosts are Alnus spp. (Haack 2006).
Cryptarcha ampla, Glischrochilus fasciatus (Olivier), Glischrochilus quadrisignatus (Say), Glischrochilus sanguinolentus (Olivier), and Glischrochilus siepmanni Brown are all sap beetles (Nitidulidae: Cryptarchinae) well known to be attracted to a variety of saps and liquids. Vogt (1950) recorded C. ampla, G. fasciatus, and G. quadrisignatus from sap fl ows on maples. Parsons (1943) also noted that C. ampla occurs on sap fl ows on maple. Williams et al. (1992) collected large numbers of all fi ve of these species from a variety of baits including fermenting bread dough, a fermenting brown sugar solution, and decaying cantaloupes and bananas. Majka and Cline (2006a) noted that in the Maritime Provinces G. sanguinolentus was primarily found associated with coniferous trees (Pinus and Picea spp.) but was also occasionally found on sap fl ows on trembling aspen (Populus tremuloides) and red oak (Quercus rubra L.).
Although Anthrenus larvae such as Anthrenus castanae Melsheimer, like other dermestids, feed on dried animal and plants products, adults mate in the fi eld and feed on nectar and pollen (Bousquet 1990). Consequently, like other nectarivourous species, the single specimen collected may have been attracted to sugars found in maple sap.

Coleoptera: accidental species
Dromius piceus Dejean is a nocturnal, arboreal predaceous ground beetle found in deciduous, coniferous and mixed forests (Larochelle and Larivière 2003). One specimen was found, and is likely an accidental collection. Similarly Nudobius cephalus (Say) is a nocturnal, predaceous rove beetle found under the bark of trees feeding on various insects found in such habitats (Smetana 1982). Th e species is primarily associated with coniferous trees, but is occasionally found on deciduous trees (Acer, Betula, Populus spp.) (Smetana 1982). Th e single individual found may also have been an accidental collection in the course of nocturnal foraging activities. Anatis mali (Say) is a large lady beetle, frequently associated with conifer trees and an important predator of the balsam twig aphid (Mindarus abietinus Koch) (Bethiaume et al. 2004), and its presence in maple sap is probably accidental. Like other corylophids, adults of Orthoperus suturalis LeConte feed on fungal spores and are found in decompositional environments. Majka and Cline (2006b) reported it from Sphagnum bogs and red spruce (Picea rubens Sarg.) forests. Th erefore its presence in maple sap is probably accidental. Th e histerid Euspilotus assimilis (Paykull) is commonly found on carrion (Bousquet and Laplante 2006). Its presence in maple sap is also probably accidental. Silusa californica is a widely distributed boreal rove beetle found in forest litter, wet moss, on dung and fungi in coniferous, deciduous, and mixed forests (Klimaszewski et al. 2003). Its presence in maple sap is also probably accidental.

Lepidoptera: species associated with sap and nectar
Xylena cineritia (Grote), Lithophane innominata (J.B. Smith), Lithophane petulca Grote, Lithophane pexata Grote, Eupsilia vinulenta (Grote), and Eupsilia tristigmata (Grote) (Noctuiodae: Cuculliinae: Xylenini) were well represented in the maple sap buckets. Th ey are all members of genera well known to be attracted to maple sap (Rings 1969(Rings , 1973Smith 1900). Th e physiology and behaviour of moths in these genera (specifically L. innominata, E. tristigmata, and E. vinulenta), all of which are active during the winter months whenever ambient temperatures rise above 0°C, was thoroughly investigated by Heinrich (1987). He found that they are active at low temperatures because they maintain thoracic temperatures 10°C higher than other moths. Th is is accomplished through a combination of behavioural adaptations (shivering to warm the thorax, which can commence at temperatures of -2°C, much lower than in other Lepidoptera) and anatomical features (a thick pile on the head and thorax, a series of abdominal air sacks that act as insulators, and an aortic confi guration that acts as a thoracic heat exchanger). Th e moths obtain the energy for these physiological processes and activities by utilizing sugar saps. Heinrich (1987) observed that, given the opportunity, these moths will bloat themselves by consuming saps, increasing their body weight by up to 94.5%. Heinrich (1987) used sugar solutions containing approximately 10 times as much sugar as found in maple sap, and calculated that a meal of this kind contained energy reserves that would last a single moth 31 days. Presumably, a meal of maple sap, containing 10% of the concentration employed by Heinrich (1987), would yield a moth approximately 3 days of energy reserves. Th us, the presence of a diversity of species and substantial numbers of moths in the genera Eupsilia, Lithophane, and Xylena in maple sap buckets is not unexpected.
In addition to the noctuids discussed above, one tortricid, Acleris chalybeana (C.H. Fernald), was abundant in maple sap buckets. Th is is a widespread species whose hosts include apple, beech, birch, maple, and oak (Covell 1984). Tortricids are one of the four families of moths noted by Miller (1997) and Foster and Tate (1966) that are attracted to natural sap fl ows. Acleris chalybeana is known to defoliate sugar maple under certain circumstances (Horsley et al. 2002;Hallett et al. 2006). A specifi c attraction of this species to maple sap, and what role it may play in the physiology of the moth, have not been documented.

Lepidoptera: accidental species
Th e one noctuid collected which is not a member of this suite of moths, was a single specimen of Crocigrapha normani (Grote), a species whose hosts include apple, cherry, oak, and other deciduous trees (Covell 1984). It would appear that its presence in the maple sap buckets was accidental.

Trichoptera
Almost all adult Trichoptera are liquid feeders, consuming sap and fl oral nectar (Malicky 2004). Single individuals of two species of caddisfl ies, Glyphopsyche irrorata (Fabricius) and Limnephilus ornatus Banks, were found in the maple sap buckets. Glyphopsyche irrorata is a caddisfl y which over-winters as an adult and, like moths of the genera Eupsilia, Lithophane, and Xylena, is regularly active in the winter months at temperatures near 0°C (Berté and Prichard 1983;South 1983).

Conclusion
In summary, 28 species of Coleoptera, Lepidoptera, and Trichoptera were recovered from maple sap buckets at one site in Prince Edward Island. Nineteen of these are known to be attracted to sap and nectar. Two species, Cyphon variabilis and C. confusus, have not been documented as exhibiting an association with such substances, but the hyper abundance of the former species in collection vessels appears to indicate that an association does exist and refl ects a hitherto undocumented feature of the biology of these species of marsh beetles. Th e remaining seven species (all represented by single individuals) are mostly found in deciduous forest stands, and their presence in maple sap containers would appear to be accidental.
Given that some 1.5 million are tapped in Canada employing traditional buckets, the number of insects collected annually through such activities must be considerable. Th is phenomenon may have both ecological repercussions, in terms of the impact of removing a sizeable number of adults from the population early in the reproductive season, as well as an economic impact in terms of the removal of drowned insects in the maple sap before processing. Th is preliminary study suggests further research on this phenomenon is needed to document not only a more complete taxon list, but also to aid the maple syrup industry in controlling unwanted insect contaminants through methods utilizing the biology of the species.