Montana's Huckleberry (Vaccinium globulare) Mystery: Pollinators, Pests, and Potential Threats
Importance of Huckleberries in Montana
Crops and livestock of primary economic importance in the State of Montana include wheat, barley, oats, corn, alfalfa, cattle, sheep, goats, pigs, and chickens (USDA 2014, MDA 2016). Specialty crops, such as honey and sweet cherries, add an additional component to Montana’s economy (USDA 2014). One of the most important of these specialty crops in Montana, which also holds a strong cultural association, is the huckleberry, Vaccinium globulare Rydberg (Jahrig et al. 1997).
In 1996, 59,000 pounds of huckleberries were processed by Montana facilities. Most of these berries (85%) were from northwestern Montana, while the rest came from northern Idaho (Jahrig et al. 1997). Jams, jellies and preserves accounted for 55% of that year's huckleberry product sales of $1.16 million (Jahrig et al. 1997). However, this is mostly likely a gross underestimate of the huckleberry’s economic value because it was based on only 14 of the state’s major huckleberry manufacturers (Jahrig et al. 1997) and by 2010, at least 30 Montana companies were known to be making hundreds of local huckleberry products (Skornogoski 2010).
Aside from the commercial pickers and huckleberry manufacturers, there are many individual entrepreneurs picking huckleberries for personal use or to sell to local businesses (Vasquez and Buttolph 2010, ACD personal observation 2014), especially in the Northwest portion of the state. One small cafe owner in Libby, MT estimated that she purchased hundreds of gallons of huckleberries in 2013, mostly from locals who spend their days out picking (ACD personal conversation 2014). Gallon bags of frozen huckleberries sold for $35-$45 each during the summer of 2014 (ACD personal observation 2014), but a bag can sell for as much as $70 at supermarkets in Bozeman (ACD personal observation 2016).
In addition to the berries’ economic value, V. globulare is known to be of ecological importance in Montana. In the northwest region of the state, it is one of the most important food sources for bears in late summer and fall (Mace and Jonkel 1986). Dietary analyses suggest that huckleberries make up 10% or more of grizzly bear diets in Glacier National Park (Martinka and Kendall 1986). In the Cabinet-Yaak region, in the far northwest corner of Montana, huckleberries appear to provide an even greater amount of food for bears, most likely due to the shrub’s wide distribution and ability to thrive in previously disturbed landscapes (Kasworm et al. 2013). Because low berry production is detrimental for bears attempting to store fat before hibernation, huckleberry productivity surveys have been a part of grizzly bear recovery efforts by the United States Fish and Wildlife Service (USFWS) since 1989, with between 11 and 21 huckleberry transects evaluated each year (Kasworm et al. 2013). High levels of black bear damage to cultivated crops, beehives, and livestock are correlated with low berry and mast crop productivity (Rogers 1976), further suggesting the value of wild berries to bear diets.
Huckleberry shrubs also play a role in forest succession and are a key understory species, contributing to a forest’s overall diversity and long-term productivity (Kerns et al. 2004). Vaccinium globulare is specifically listed as an important shrub component of a climax forest community in Montana. Research has shown that undisturbed forests contain the least productive huckleberry patches while the most plants were found on slopes that were disturbed by fire 10-50 years earlier (Martin 1979). Greatest fruit production is associated with these previously burned sites before the reestablishment of a coniferous tree overstory (Lesica 2012). Once the overstory is reestablished, shrubs do not die out, but tend to grow taller and flower less, thereby decreasing berry production.
Finally, there is a strong cultural association to the huckleberries in Montana. Over the last two decades, Montana huckleberry products have gained recognition worldwide (Jahrig et al. 1997). But their cultural importance goes deeper than products for tourists. Before the arrival of white settlers in the 1800s, Northwest tribes relied on huckleberries as a major food source and entire villages would relocate to prime picking sites for as long as the berries were ripe (Richards and Alexander 2006). Ceremonial first fruits celebrations were a part of berry-picking traditions, along with feasts and periodic prescribed burns (Richards and Alexander 2006). Use of wild huckleberries by white settlers in Montana coincided with technological advances of the canning industry and by the mid-1920s commercial berry picking operations in Montana were well established, providing important jobs during the 1930s when the state’s mining and timber industries collapsed (Richards and Alexander 2006). The industry declined during and after World War II, and this downward trend persisted until the 1980s when it experienced a revival, primarily as a cultural symbol of state pride (Richards and Alexander 2006). The cultural importance of the huckleberry industry in Montana has continued into the 21st century.
Taxonomy of Montana’s Huckleberry
The huckleberry plants known from across the western U.S. are members of the heath family Ericaceae (Order: Ericales), which contains approximately 35 genera of herbs, shrubs, and trees (USDA-NRCS 2015). Within the family Ericaceae, western huckleberries, along with cranberries, grouse whortleberries and blueberries, are in the genus Vaccinium, which contains 43 species in North America (USDA-NRCS 2015). These species are not closely related to the eastern huckleberry, which is in the genus Gaylussacia, or the garden huckleberry, which is in the genus Solanum (USDA-NRCS 2015).
Of the seven species of Vaccinium known to occur in Montana, V. globulare is the most common and widespread, with records in all of the western, mountainous counties. Vaccinium membranaceum Douglas ex Torr. superficially resembles V. globulare, and some sources consider the two species synonymous (Vander Kloet 1988, Consortium of Pacific Northwest Herbaria 2013). In the Pacific Northwest, V. membranaceum is more widespread, occurring from coastal British Columbia south to California and less commonly east into Alberta, Idaho, Montana, and Wyoming. It is sporadic in the Montana portion of its range (Vander Kloet 1988, Lesica 2012). Vaccinium globulare is more commonly found further inland and is most abundant where British Columbia, Alberta, Idaho, and Montana converge (Lloyd 1996, Lesica 2012). For this project, we considered the two species to be separate and focused on V. globulare, the huckleberry plant most commonly encountered in Montana (Lesica 2012, M. Lavin personal communication 2015).
The “Globe Huckleberry” or “Blue Huckleberry,” V. globulare, is known for large, sweet berries (Lesica 2012). It is a spreading shrub with grayish bark that grows up to one and a half meters tall (Lloyd 1996). Like all other Vaccinium, V. globulare is rhizomatous, with rhizomes being the primary method of reproduction. These plants depend on mycorrhizae to help pull nutrients out of the acidic, often nutrient-poor soils in which they grow (Vander Kloet 1988). Flowers are urn-shaped, mature before the leaves (Lesica 2012), and individual flowers can produce a relatively large amount of nectar, visible to the naked eye as drop of liquid filling the inside of the flower (ACD personal observation 2014). Each berry contains many seeds and the seeds are animal dispersed (Lesica 2012).
Due to their economic and ecological importance, several studies have been conducted on huckleberries of the Pacific Northwest, primarily focused on understanding succession or as part of grizzly bear recovery efforts. In these studies, berry production has been linked to fire (Lesica 2012), climate (Holden et al. 2012), snow cover (Stark and Baker 1992), rainfall, soil pH, elevation, slope, and aspect (Martin 1979). Despite this accumulation of knowledge, V. globulare cannot be successfully cultivated and all harvest depends on wild plants (Gough 1998, Barney 1999). Additionally, one key aspect of V. globulare biology that has yet to be investigated is the impact of insects.
Insect/plant associations can include pollinators, herbivores, frugivores, and the predators and parasitoids associated with them. These associates may be polyphagous generalists or monophagous specialists. Published host plant data have documented numerous arthropod species associated with the genus Vaccinium, but no insect species have been specifically recorded to be associated with V. globulare. Only one species, the fruit-infesting tenthredinid Pristiphora macnabi (Ross) has a recorded association with V. membranaceum (Wong 1968). These host plant records are summarized in Appendix A and include insects in the orders Hymenoptera, Lepidoptera, Diptera, Hemiptera, and Coleoptera as well as two species of mites (Arachnida Subclass Acari).
Huckleberries, like many other fruit crops, are most likely insect-pollinated and, due to the structure of Vaccinium flowers (De Luca and Vallejo-Marin 2013), buzz pollination may be required. However, no specific pollinators associated with either V. globulare or V. membranaceum have been reported. Martin (1979) reports that fruit is set by insect pollination, but no species are reported. The loss of native bee populations in the Pacific Northwest following the eruption of Mt. St. Helens was implicated in a drastically unproductive year for V. membranaceum (Hunn and Norton 1984), but details of that native bee community were not reported. Stark and Baker (1992) suggest that pollination is achieved by bees and possibly by ants, but, again, no specific species were documented. Vaccinium membranaceum was one of nine plants in a study on the factors limiting alpine seed production in British Columbia (Straka and Starzomski 2015). Potential pollinators recorded from this study included Lepidoptera, Diptera, and Hymenoptera (Tenthredinidae, Halictidae, Andrenidae), but these specimens were collected in pan traps, not in association with any particular plant.
Flowers of many species of plants require what is referred to as “buzz pollination.” Buzz pollination is a description of the manner in which some bees collect pollen (i.e., by rapidly vibrating their bodies using their wing muscles to loosen pollen from anthers, effectively sonicating the flower). Bumble bees (Bombus spp.) are known to be buzz pollinators (De Luca and Vallejo-Marin 2013). In other regions of North America, small, native bees in the genera Andrena and Halictus have also been observed buzz pollinating Vaccinium flowers (Javorek et al. 2002). Bombus species, Andrena species, and Apis mellifera L. have been documented visiting the flowers of other species of Vaccinium across North America (Vander Kloet 1988) and A. mellifera has been used commercially in blueberry fields to supplement native bee populations (Kloet 1988). Montana’s overall bee fauna has not been fully documented, and species inventories are just starting to be developed. Thus, we don’t even know which bees inhabit most of the forests where V. globulare is found. In the midst of concern over declining bee populations (Chaplin-Kramer et al. 2014, Goulson et al. 2015) it is even more important to learn which pollinators are present in Montana’s forests, in addition to which are associated with V. globulare, because a lack of suitable pollinators could have both economic and ecological impacts on Montana’s huckleberry industry.
Pollinators are not the only insects that affect plants. There are many insects, both native and introduced, that are considered pests of economically important crops. Martin (1979) reported observations of partial defoliation of V. globulare in Montana. This partial defoliation was attributed to either disease or insects and was connected to lower overall productivity, smaller berries, and fewer seeds per berry (Martin 1979). Stark and Baker (1992) also reported damage to V. globulare fruits and implicated leafcutting bees (Megachilidae), though this group of bees is known for damage to foliage of plants, not to fruits. The spotted-wing drosophila (SWD), Drosophila suzukii (Matsumura), is an invasive fruit fly from Southeast Asia that attacks healthy, ripening fruit (Lee et al. 2011). This fly has been known to cause serious damage to fruit crops including cherries, raspberries, strawberries, and plums (Lee et al. 2011). It was detected in Montana for the first time in 2011 (O’Neill et al. 2011). If SWD finds its way to Montana’s huckleberries, there could be significant economic and ecological damage. Similarly, the German yellowjacket (Vespula germanica (Fabricius)) is an invasive wasp in North America known to be a scavenger of both sweets and meat (Bechinski et al. 2009). It has been in the northwestern U.S. since the 1970s and in Idaho since the 1980s (Bechinski et al. 2009). It has also been documented in Montana (Montana Entomology Collection, MTEC). If a non-native scavenger like V. germanica spreads into V. globulare habitat, it could negatively affect production by robbing nectar from flowers or causing damage to fruits.
Due to the importance of insects as both pollinators and pests, the purpose of this project was to provide the first documentation of insects associated with V. globulare in Montana. Results from this work can be used to inform future research, conservation, and management efforts.