Squash Bees Research Articles

Confirmed presence of the squash bee, Peponapis pruinosa (Say, 1837) in the state of Oregon and specimen-based observational records of Peponapis (Say, 1837) (Hymenoptera: Anthophila) in the Oregon State Arthropod Collection

A new Oregon record for Peponapis pruinosa (Say, 1837) is presented with notes on its occurrence and photographs. This record provides the first empirical evidence of the genus and species in the state of Oregon. A dataset of Peponapis (Say, 1837) specimens in the holdings of the Oregon State Arthropod Collection is included with a brief summary of its contents.

Preference of Peponapis pruinosa (Hymenoptera: Apoidea) for Tilled Soils Regardless of Soil Management System.

Concerns about global pollinator declines have placed a growing focus on understanding the impact of agriculture practices on valuable native pollinators in these systems. Cultivation practices such as tillage disturb agroecosystems and can have negative impacts on ground-nesting pollinators. The squash bee, Peponapis pruinosa (Say), is a ground-nesting specialist pollinator of Cucurbita (Cucurbitaceae) crops (i.e., pumpkins and squash) that often nests in agricultural fields and thus may be vulnerable to these practices. We investigated the impact of tillage on nesting behavior of P. pruinosa in plasticulture and strip-tilled squash systems. We used choice experiments to test nesting substrate preference and nesting success of caged P. pruinosa in two soil tillage systems: strip tillage and plasticulture. The strip tillage system comprised two tillage zones (strip-tilled row with no-till edges), and the plasticulture system comprised two tillage zones (plastic bed and conventional tillage edge). The results of our study indicate that P. pruinosa nesting density did not significantly differ between the strip tillage and plasticulture systems. Within each system, P. pruinosa preferred excavating nests in the most disturbed soil zones (strip-tilled row and conventionally tilled edge). In the strip tillage system, the strip-tilled row had significantly more nests than the no-till edge. Results of these studies suggest that soil tillage practices can influence P. pruinosa nesting choice and production practices should be considered when developing a pollinator protection plan.

Impact of Global Climate Change on Pollinator Diversity and Conservation: Current Issues and Future Challenges

Over 75% of the major world crops and 80% of all flowering plant species rely on animal pollinators. Of the hundred or so animal-pollinated crops which make up most of the world's food supply, 15% are pollinated by domestic bees, while at least 80% are pollinated by wild bee species and other wildlife. Most of the 25, 000 to 30, 000 species of bees are effective pollinators, and together with moths, flies, wasps, beetles and butterflies, make up the majority of pollinating species. Vertebrate pollinators include bats, non-flying mammals (several species of monkey, rodents, lemur and tree squirrels etc.) and birds (humming birds, sun birds, honey creepers and some parrot species). Current understanding of pollination process shows that, while an interesting specialized relationship exist between plants and their pollinators, healthy pollination services are best ensured by an abundant diversity of pollinators. Thus, pollinators are essential for diet diversity, biodiversity, and maintenance of natural resources. Pollinators which evolved over million of years, are eroding at a fast rate from the globe. During the past few years, many pollinators especially honey bees have been dying across the globe in unprecedented number and, no one has so far been able to prove beyond a reasonable doubt what the causes may have been. The economic implications of these deaths are immediate because honey bees are integral to the pollination of tens of millions of dollars of cash crops in the world. Despite much of the world's agriculture relying on pollination by honeybees, especially European honeybees, their number across the globe has also declined. Many other pollinators such as digger bees, sweat bees, alkali bees, squash bees, leafcutter bees, carpenter bees, mason bees, and shaggy fuzzy foot bees could also be on decline, but data providing unambiguous documentation of trends are simply not available. Threats to pollinators and the services they provide are perceived to be increasing around the world and are mainly man-made in origin. Climate change could be a major factor in weakening the bees and has affected the pollination of crops in many agricultural areas. An attempt has been made to know the causes behind the decline of pollinators, especially in relation to climate change, their conservation and management and impact of declining pollinator population on horticulture in the changed global scenario.

Impact of tillage on the crop pollinating, ground-nesting bee, Peponapis pruinosa in California

Wild bees, especially ground-nesting species, are important for crop pollination. However, the extent to which regular disturbance, such as tillage, impacts ground-nesting bees is poorly known. We conducted a two-year tillage experiment on the squash bee, Peponapis pruinosa (Say), to quantify how tillage impacted offspring survival, offspring sex ratio, and timing of emergence. We established P. pruinosa nests in twenty 3m by 3m cages and then randomly assigned a tillage treatment to half of those cages. The following summer we trapped emerging offspring. We used a Bayesian framework to analyse the data. Offspring emergence varied greatly, but there was modest evidence that tillage reduced offspring emergence in treatment cages. There was limited evidence that tillage reduced the proportion of male bees emerging into cages, suggesting that tillage did not impact sex ratio. There was strong evidence that tillage delayed emergence of surviving offspring. Tillage practices should be considered when managing fields for this ground nesting bee. However, even disturbed squash fields may contribute to this species’ persistence in agricultural landscapes.

Crop domestication facilitated rapid geographical expansion of a specialist pollinator, the squash bee Peponapis pruinosa.

Squash was first domesticated in Mexico and is now found throughout North America (NA) along with Peponapis pruinosa, a pollen specialist bee species of the squash genus Cucurbita The origin and spread of squash cultivation is well-studied archaeologically and phylogenetically; however, no study has documented how cultivation of this or any other crop has influenced species in mutualistic interactions. We used molecular markers to reconstruct the demographic range expansion and colonization routes of P. pruinosa from its native range into temperate NA. Populations east of the Rocky Mountains expanded from the wild host plant's range in Mexico and were established by a series of founder events. Eastern North America was most likely colonized from squash bee populations in the present-day continental Midwest USA and not from routes that followed the Gulf and Atlantic coasts from Mexico. Populations of P. pruinosa west of the Rockies spread north from the warm deserts much more recently, showing two genetically differentiated populations with no admixture: one in California and the other one in eastern Great Basin. These bees have repeatedly endured severe bottlenecks as they colonized NA, following human spread of their Cucurbita pollen hosts during the Holocene.

Use of video surveillance to measure the influences of habitat management and landscape composition on pollinator visitation and pollen deposition in pumpkin (Cucurbita pepo) agroecosystems.

Pumpkin (Cucurbita pepo) production relies on insect-mediated pollination, which is provided by managed and wild pollinators. The goals of this study were to measure the visitation frequency, longevity and temporal activity patterns of pumpkin pollinators and to determine if local habitat management and landscape composition affected this pollination service. We used video surveillance to monitor bee acitivty within male and female pumpkin flowers in 2011 and 2012 across a pollination window of 0600–1200 h. We also quantified the amount of pollen deposited in female flowers across this time period. In 2011, A. mellifera made significantly more floral visits than other bees, and in 2012 Bombus spp. was the dominant pumpkin pollinator. We found variation in visitation among male and female pumpkin flowers, with A. mellifera visiting female flowers more often and spending longer per visit within them than male flowers in both 2011 and 2012. The squash bee P. pruinosa visited male flowers more frequently in 2012, but individuals spent equal time in both flower sexes. We did not find variation in the timing of flower visitation among species across the observed pollination window. In both 2011 and 2012 we found that the majority of pollen deposition occurred within the first two hours (0600–0800 h) of observation; there was no difference between the pollen deposited during this two-hour period and full pollination window (0600–1200 h). Local additions of sweet alyssum floral strips or a field buffer strip of native wildflowers did not have an effect on the foraging activity of bees or pollen deposition. However, semi-natural and urban habitats in the surrounding landscape were positively correlated with the frequency of flower visitation by wild pollinators and the amount of pollen deposited within female flowers.

Mulch Effects on Floral Resources and Fruit Production of Squash, and on Pollination and Nesting by Squash Bees

Zucchini squash (Cucurbita pepo) has a high pollination demand, and the native, ground-nesting squash bee (Peponapis pruinosa) provides the majority of the crop’s pollination requirement in some environments. Squash bees nest directly in crop fields, and nests can be disturbed by tillage and other management operations. Mulches that use municipal waste materials may provide a weed control strategy for squash plantings that is more benign to squash bees than cultivation. Field and greenhouse studies were conducted in 2011 and 2012 to compare the effects of nontillage weed control methods including polyethylene black plastic, woodchips, shredded newspaper, a combination of shredded newspaper plus grass clippings (NP + grass), and bare soil (control) on soil characteristics, squash pollination and fruit production, and squash bee nesting. Woodchips, shredded newspaper, and NP + grass mulch decreased soil temperature, while soils beneath newspaper mulch retained more moisture. Unmarketable, misshapen fruit occurred more frequently in plastic than in the other mulch treatments. No measurable differences in floral resource production or crop pollination were found among treatments, suggesting that misshapen fruit resulted from high soil temperatures in black plastic plots rather than poor pollinator attraction. Squash bee nests were located within bare soil, newspaper, and NP + grass plots, indicating that these mulches did not prevent nesting. NP + grass mulch had a positive effect on plant growth and fruit production, possibly from an addition of plant-available nitrogen or the presence of preferable nesting ground. Shredded newspaper when combined with grass clippings performed as an effective mulch material that improved crop performance with no apparent negative impacts on squash bee nesting or on squash floral resources and pollination.

From April to August—Wild Bees Pollinating Crops Through the Growing Season in Virginia, Usa

Few baseline data exist regarding the role of wild, primarily native, non-Apis bees in pollinating crops through the growing season in the mid-Atlantic United States. Apis mellifera L., honey bees, generally are assumed to provide the majority of crop pollination, with the value of pollination provided by non-Apis bees estimated at between one-half and one-sixth the value of honey bees, though many non-Apis bees are known to be more effective in pollinating some crops. In this study, the first documenting wild bees visiting crop flowers through the growing season, non-Apis bees accounted for the majority of crop visitation for several economically important entomophilous crops in Virginia, such as apple, blueberry, caneberry, and cucurbit) and likely provided most of the pollination. Wild bees made up between 68% (in caneberries) and 83% (in cucurbits) of bees visiting crop flowers. Between 43 and 59 non-Apis bee species visited flowers of each crop (105 species overall). Species turnover was very high between sites, ranging from only 13% shared species in pairwise comparisons for blueberries to 30% shared species for caneberries. Native bee taxa most abundant on crops were Andrena F., mining bees, Bombus Latreille, bumble bees, and Osmia Panzer, mason bees, on apples and blueberries; Losioglossum Curtis, sweat bees, on caneberries; and Peponapis pruinosa Say, squash bees, and Bombus on cucurbits. Overall, this study highlights the substantial role of native bees in agricultural pollination in this region.

Two new species of the bee genus Peponapis, with a key to the North and Central American species (Hymenoptera: Apidae: Eucerini)

Two new species of squash bees, Peponapis pacifica Ayala and Griswold sp. n. and P. parkeri Griswold and Ayala sp. n., are described and illustrated. Peponapis pacifica is oligolectic on flowers of Schizocarpum longisepalum (Cucurbitaceae) endemic to Mexico, where it is found in the tropical dry forest along the Pacific Coast, between Sonora and Chiapas and in the Balsas River basin; and P. parkeri is known only from the Pacific slope of Costa Rica. A key for the North and Central American species of Peponapis is provided.

Buttercup Squash Provides a Marketable Alternative to Blue Hubbard as a Trap Crop for Control of Striped Cucumber Beetles (Coleoptera: Chrysomelidae)

Winter squash is a vital agricultural commodity worldwide. In the Northeastern United States, the primary insect pest is the striped cucumber beetle, Acalymma vittatum F. Using a Blue Hubbard squash (Cucurbita maxima Duchesne) perimeter trap crop system can reduce insecticide use by >90% in butternut squash (C. moschata Poir), the primary winter squash grown in this region. Despite the savings in insecticide costs, growers may be reluctant to give up field space for a perimeter crop of Blue Hubbard squash, which comprises only 5% of the winter squash market in New England as compared with 19% for buttercup squash. Finding a more marketable trap crop would lower the barrier for adoption of this system. We tested eight varieties of three species of cucurbits for attractiveness to beetles relative to Blue Hubbard and butternut squash, and chose buttercup squash as the most promising replacement. We compared the effect of a buttercup border, Blue Hubbard border, or control (no border) on beetle numbers, herbivory, insecticide use, pollination, and pollen limitation in the main crop. We found that buttercup squash performed equally well as Blue Hubbard as a trap crop, with 97% reduction in total insecticide use compared with control fields. Honey bees (Apis mellifera L.) and squash bees (Peponapis pruinosa Say) were the predominant pollinators, and border treatments did not affect visitation. Hand pollination did not increase reproduction or yield, indicating that natural pollination was sufficient for full yield. This study confirms the effectiveness of perimeter trap crop systems and offers growers a more marketable trap crop for managing cucumber beetle damage.

The Squash Bee Xenoglossa kansensis Cockerell (Hymenoptera: Apidae) Found in Organic Farms in Northern Florida

In surveys of bees in organic farms and natural preserves in Alachua County, Florida, numerous Xenoglossa {Eo xenoglossa) kansensis Cockerell were caught in 2006 and 2007. This is the first record of this species in Florida, whereas presence of the similar X. (Eoxenoglossa) strenua (Cresson) has been documented previously (Mitchell, 1962; Hurd and Linsley, 1964). Genus Xenoglossa includes the large squash and gourd bees that collect pollen exclusively from Cucurbita flowers and are known to be highly effective pollinators (Hurd and Linsley, 1964, 1967; Hurd et al., 1971). Substantial amounts of squash are grown in Florida, and this newly detected bee species may contribute significantly to the production of this valuable crop.

Transgenic virus resistance in cultivated squash affects pollinator behaviour

Summary 1. Two ecological risks associated with the use of transgenic crops are transgene movement into wild populations and effects on non‐target organisms, such as pollinators. Despite the importance of pollinators, and their contribution to the global food supply, little is known about how they are affected by transgenic crops. Pollinator preferences affect plant mating patterns; thus understanding the effects of transgenic crops on pollinators will aid in understanding transgene movement. 2. Honey bee and squash bee visit number and duration were recorded on conventional and transgenic virus‐resistant squash Cucurbita pepo planted in a randomized block design. Floral characters were measured to explain differences in pollinator behaviour. The effect of Zucchini Yellow Mosaic Virus infection on pollinator behaviour was also examined. 3. Honey bees visited female conventional flowers more than female transgenic flowers. Conventional flowers were generally larger with more nectar than transgenic flowers, although floral traits did not account for differences in pollinator visitation. 4. Squash bees visited male transgenic flowers more than male conventional flowers; squash bees also spent more time in female transgenic flowers than in female conventional flowers. Transgenic flowers were significantly larger with greater amounts of sweeter nectar and they were present in greater number. Floral traits accounted for some of the variation in pollinator visitation. 5. Squash bee visit number and duration did not differ between virus‐infected and healthy plants, but this may be because pollinator behaviour was observed early in the virus infection. 6. Synthesis and applications. Pollinator behaviour controls patterns of plant mating thus non‐target effects of transgenic resistance, such as those observed here, may influence transgene movement into wild populations. These results suggest that transgenic crops should not be planted within the native range of wild relatives because pleiotropic effects may affect crop‐wild hybridization and transgene introgression into wild populations.

Differentiation and Range Expansion of North American Squash Bee, Peponapis Pruinosa (Apidae: Apiformes) Populations Assessed by Geometric Wing Morphometry

Abstract We studied the differentiation of North American squash bee (Apidae: Apiformes) populations by using geometric wing morphometry to evaluate hypotheses for the origin and possible expansion route of bees after the dispersal of their Cucurbita floral hosts. Two hypotheses consider the possible impact of early human cultures on the distribution of this mutualistic species complex: 1) the geographic range of the bees naturally expanded after the hypsithermal range expansion of the wild buffalo gourd, Cucurbita foetidissima Kunth; or 2) the bees shifted to mesophytic gourds of the C. pepo group at the Mexican Gulf coast and tracked the cultivation and/or trade by early human hunter-gatherer societies in the context of fishing technology along stream valleys to northeastern America. We morphometrically measured 228 specimens of Peponapis pruinosa (Say) collected at 15 sites between Mississippi and Ontario, Canada. Twenty-three landmarks were taken from the right forewings. The resulting measurements were analyzed by multivariate statistics. Our results support the first hypothesis of a western origin of North American squash bee populations and a mainly natural range expansion during the hypsithermal range expansion of the buffalo gourd.

Pollinator and Herbivore Attraction to Cucurbita Floral Volatiles

Mutualists and antagonists may place conflicting selection pressures on plant traits. For example, the evolution of floral traits is typically studied in the context of attracting pollinators, but traits may incur fitness costs if they are also attractive to antagonists. Striped cucumber beetles (Acalymma vittatum) feed on cucurbits and are attracted to several volatiles emitted by Cucurbita blossoms. However, the effect of these volatiles on pollinator attraction is unknown. Our goal was to determine whether pollinators were attracted to the same or different floral volatiles as herbivorous cucumber beetles. We tested three volatiles previously found to attract cucumber beetles in a factorial design to determine attraction of squash bees (Peponapis pruinosa), the specialist pollinators of cucurbita species, as well as the specialist herbivore A. vittatum. We found that 1,2,4-trimethoxybenzene was attractive to both the pollinator and the herbivore, indole was attractive only to the herbivore, and (E)-cinnamaldehyde was attractive only to the pollinator. There were no interactions among volatiles on attraction of squash bees or cucumber beetles. Our results suggest that reduced indole emission could benefit plants by reducing herbivore attraction without loss of pollination, and that 1,2,4-trimethoxybenzene might be under conflicting selection pressure from mutualists and antagonists. By examining the attraction of both mutualists and antagonists to Cucurbita floral volatiles, we have demonstrated the potential for some compounds to influence only one type of interaction, while others may affect both interactions and possibly result in tradeoffs. These results shed light on the potential evolution of fragrance in native Cucurbita, and may have consequences for yield in agricultural settings.

Effects of Honey Bee Pollination on Pumpkin Fruit and Seed Yield

The objective of this study was to measure honey bee (Apis mellifera L.) impact on seed set, fruit set, and yield of jack-o-lantern (Cucurbita pepo L.), large-sized (C. maxima Duch.), and processing pumpkins (C. moschata Duch. ex Poir.) under field conditions. There were sufficient natural pollinators [including bumblebees (Bombus spp.), carpenter bees (Xylocopa spp.), honey bees, and squash bees (Peponapis pruinosa Say)] provided under field conditions to induce fruit set of jack-o-lantern pumpkins as fruit number obtained per hectare was not affected by the addition of a honey bee colony. However, the addition of honey bees did increase fruit number per hectare of the C. moschata and C. maxima cultivars evaluated. Honey bee pollination resulted in larger-sized fruit, increasing individual fruit size of all but small-sized pumpkins (<0.5 kg). Individual pumpkin fruit weights of the Cucurbita pepo, C. moschata, and C. maxima cultivars evaluated increased by about, 26%, 70%, and 78%, respectively, when honey bee colonies were included. Natural pollination was insufficient to stimulate maximum fruit size development and seed number and seed weight per fruit. Although pumpkin fruit set will occur with natural pollinators, the addition of honey bee colonies will ensure the presence of pollinators to maximize fruit size. Since pumpkins are generally sold on a weight basis, growers may generate greater revenues with the addition of honey bee colonies in pumpkin fields.

Farming Practices Influence Wild Pollinator Populations on Squash and Pumpkin

Recent declines in managed honey bee, Apis mellifera L., colonies have increased interest in the current and potential contribution of wild bee populations to the pollination of agricultural crops. Because wild bees often live in agricultural fields, their population density and contribution to crop pollination may be influenced by farming practices, especially those used to reduce the populations of other insects. We took a census of pollinators of squash and pumpkin at 25 farms in Virginia, West Virginia, and Maryland to see whether pollinator abundance was related to farming practices. The main pollinators were Peponapis pruinosa Say; honey bees, and bumble bees (Bombus spp.). The squash bee was the most abundant pollinator on squash and pumpkin, occurring at 23 of 25 farms in population densities that were commonly several times higher than that of other pollinators. Squash bee density was related to tillage practices: no-tillage farms hosted three times as great a density of squash bees as tilled farms. Pollinator density was not related to pesticide use. Honey bee density on squash and pumpkin was not related to the presence of managed honey bee colonies on farms. Farms with colonies did not have more honey bees per flower than farms that did not keep honey bees, probably reflecting the lack of affinity of honey bees for these crops. Future research should examine the economic impacts of managing farms in ways that promote pollinators, particularly pollinators of crops that are not well served by managed honey bee colonies.

Crop/Weed gene flow:Cucurbita argyrosperma Huber andC. fraterna L. H. Bailey (Cucurbitaceae)

A mixed population of Cucurbita at Vado El Mow in northern Tamaulipas, Mexico showed an anomalous pattern of fruit bitterness. Some domesticated plants (C. argyrosperma andC. moschata) expressed cucurbitacin bitterness whereas some sympatric free-living plants produced non-bitter fruits. This reversal of typical cucurbitacin expression suggested gene flow between crop and weed at the site. Isozyme analysis provided little insight as to taxa involved in gene exchange, although progeny from a single free-living plant carried IDH allozymes that are associated with Mexican landraces ofC. pepo. Synthetic hybridization revealed that fertile F, hybrids are produced from crosses involvingC. fraterna as the pistillate parent andC. argyrosperma as the staminate parent. Interspecific crop/weed hybrids can produce viable progeny upon self-pollination or backcrossingto either parent, andF2 families display normal allozyme segregation. Hybrid fertility, as indicated by pollen stainability, increases in progeny produced by backcrossingfrom theC. argyrosperma parent. Interspecific hybridfertility represents a potential for crop/weed gene flow that would be realized under natural conditions if pollen flow occurs betweenC. fraterna andC. argyrosperma in the fields of Tamaulipas. Oligolectic “squash bees” (Teponapis), efficientCucurbita pollen vectors, are present at the site. Thus, it is likely that natural interspecific crop/weed hybridization has occurred at Vado El Moro and this might at least partially explain the anomalous distribution of fruit bitterness among extant populations at the site.

Insect pollinators and sustainable agriculture

AbstractUnderestimation of the pivotal role played by managed and native insect pollinators is a key constraint to the sustainability of contemporary agricultural practices. The economic value of such insects to pollination, seed set, and fruit formation greatly outweighs that suggested by more conventional indices, such as the value of honey and wax produced by honeybees. Although the European honeybee has been widely regarded as the single most important pollinating species, the increasing spread of trachael and Varroa mites and Africanized bees threatens the distribution and magnitude of traditional honeybeekeeping enterprises in North America. A number of other bee and insect pollinators, such as orchard bees, bumblebees, and squash bees, which are not affected by either the mites or the Africanized bees, are considered as likely candidates for management and use in commercial agriculture. An additional role can be played by native or wild pollinators, provided that attention is given to curtailing of population losses caused by both inadvertent insecticide poisoning and habitat destruction. To ensure a reliable source of pollinators, both managed and native, a more comprehensive strategy for management of crop pollination is needed. Elements of this strategy include an increased understanding of the biology and ecology of pollinating insects, as well as providing appropriate nesting habitat, and ensuring the availability of alternative sources of “forage” to sustain populations when the target crops are not in bloom. Examples are discussed to illustrate how private initiatives and changes to public policy can enhance pollinator habitat, and ultimately, agricultural productivity.

Experimental Introduction of Squash Bees (Peponapis) to Improve Yields of Squashes, Gourds and Pumpkins

In 1968 the authors of this article discussed in Bee World “The feasibility of introducing squash bees (Peponapis and Xenoglossa) into the Old World”. The significance of the suggested introduction is the efficiency of squash bees as pollinators of cucurbit crops. The present article brings the story up to date, describing experimental transport of pre-nesting females within California, and from California to Hawaii.

The Feasibility of Introducing Squash Bees (Peponapis and Xenoglossa) Into the Old World

The introduction of honeybees from the Old World to the New has been of the utmost significance, for the pollination of agricultural crops as well as for honey and wax production. And in New Zealand, red clover seed crops failed until bumble bees were introduced from England. The New World, as well as the Old, is rich in native wild bees, and the present article discusses the question of introducing to the Old World from the New certain species of “squash bees”, so called because they are especially adapted for pollinating squashes and other species of Cucurbita (gourds, pumpkins and vegetable marrows).