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Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(2): 494-506, April-June 2021 (Published Apr. 01, 2021)
Diversity and foraging patterns of bees on flowers
of Cucurbita pepo (Cucurbitaceae) in Costa Rica
Jorge A. Lobo
1
*; Orcid: 0000-0002-8974-2355
Yanil Bravo Méndez
1
; Orcid: 0000-0003-2430-7536
1. Escuela de Biología, Universidad de Costa Rica, San José, Costa Rica; jorge.lobo@ucr.ac.cr (*Correspondence);
cryanil.bravo@ucr.ac.cr
Received 02-X-2020. Corrected 23-II-2021. Accepted 02-III-2021.
ABSTRACT
Introduction: The species and functional diversity of pollinators are important components for the reproduc-
tion of cultivated plants. More information is necessary about this diversity and its geographical variation in
crops such as Cucurbita pepo, an important crop in global agriculture. Objective: To describe the taxonomic
diversity, geographic variation and foraging patterns of the community of bees that visit C. pepo crops in Costa
Rica. Methods: Squash fields were visited at 11 locations within three geographic regions of the country,
where the groups of bees and their relative frequency were determined. Through video recordings, information
was obtained on their behavior at two locations. Results: A minimum of 27 species belonging to 19 genera
and 2 families of bees were found. Three species were dominant in 10 localities (Eucera limitaris, Apis mel-
lifera and Trigona corvina). Altitude reduces bee diversity due to the dominance of Bombus ephipiatus in high
regions. Two genera of halictids (Megalopta and Caenaugochlora) that are rarely reported in this crop were
frequently observed. Trigona bees dominated among the flowers later in the morning, lacerating nectary holes
to facilitate nectar collection. Conclusions: Squash fields in Costa Rica are visited by a highly diverse bee
community, which may ensure pollination via complementarity in the face of spatial or seasonal changes in
environmental conditions.
Key words: Cucurbita; bees; crop pollination; stingless bees; squash bees; squash.
Lobo, J.A. & Bravo Méndez, Y. (2021). Diversity and
foraging patterns of bees on flowers of Cucurbita pepo
(Cucurbitaceae) in Costa Rica. Revista de Biología
Tropical, 69(2), 494-506. DOI 10.15517/rbt.v69i2.44076
Temporal and spatial variation in the diver-
sity and composition of the pollinator commu-
nity of a plant species is a frequent conclusion
of pollination studies (Herrera, 1989; Waser,
Chittka, Price, Williams, & Ollerton, 1996;
Price, Waser, Irwin, Campbell, & Brody, 2005;
Winfree et al., 2018), although the amplitude
of this variation may be restricted to the taxo-
nomic groups favored by the floral syndrome
(Rosas-Guerrero et al., 2014). This variation is
an important condition for evaluating selection
pressures on floral traits (Santiago-Hernández
et al., 2019), as well as the diversity of pol-
linators required for the reproduction of a plant
species at a scale larger than a population or
locality (Winfree et al., 2018). The quantity and
diversity of pollinators plays an important role
in the productivity of crops worldwide, particu-
larly in small farms aimed at the production of
fruits and vegetables (Hoehn, Tschamtke, Tyli-
anakis, & Steffan-Dewenter, 2008; Garibaldi et
al., 2016; Reilly et al., 2020).
The cultivated species of the genus Cucur-
bita (Cucurbitaceae) (pumpkin or squash;
DOI 10.15517/rbt.v69i2.44076
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Revista de Biología Tropical, ISSN electrónico: 2215-2075, Vol. 69(2): 494-506, April-June 2021 (Published Apr. 01, 2021)
Spanish common names include calabaza,
ayote, zapallo, and pipian) comprise a group
of five species with a proposed center of ori-
gin in North America that have been devel-
oped through the domestication of a collection
of wild species (Hurd, Linsley, & Whitaker,
1971). The species of this genus are character-
ized by being monoecious, with large season-
ally produced yellow flowers in which both
the staminate and pistillate flowers produce
large amounts of nectar. Nectaries are found
in a chamber at the base of the stamens in
staminate flowers and in a lower ring at the
base of the pistil in pistillate flowers (Nepi &
Paccini, 1993; Nepi, Guarnieri, & Pacini, 2001;
Vidal, Jong, Wien, & Morse, 2006). Therefore,
Cucurbita species depend on pollinating agents
for their reproduction.
Floral visitors of Cucurbita include several
species of the subgenera Eucera (Peponapis)
and Eucera (Xenoglossa), which are native to
America and have evolved specialization in
collecting pollen exclusively from Cucurbita
sp. (Hurd et al., 1971). These bees have been
identified as the most effective pollinators
of wild and cultivated species of Cucurbita,
and their current distribution range has been
attributed to the expansion of the crop (Hurd et
al., 1971). However, across the American con-
tinent, these crops are visited by highly diverse
bee species, whose composition depends on
the species of Cucurbita, geographic region
and season of the year (Ashworth & Galetto,
2001; Meléndez-Ramírez, Magaña-Rueda,
Parra-Tabla, Ayala, & Navarro, 2002; Shuler,
Roulston, & Farris, 2005; Krug, Alves-dos-
Santos, & Cane, 2010; Serra & Campos, 2010;
Vidal, Jong, Wien, & Morse, 2010; Zambra-
no, Gonzales, Hinojosa-Diaz, & Engel, 2013;
Enríquez, Ayala, Gonzales, & Nuñez-Farfán,
2015; Phillips & Gardiner, 2015, Delgado-
Carrillo et al., 2018; Pfister, Eckerter, Schirmel,
Cresswell, & Entling, 2017). A review of bee
inventories of C. pepo, C. moschata and C.
maxima flowers (Digital Appendix) shows that
nonnative Apis mellifera (nonnative), Eucera
and several species of Bombini, Meliponini
and Halictidae are the most common groups of
bees visiting Cucurbita crops on this continent.
Some studies have analyzed the geograph-
ic diversity of the abundance and composition
of Cucurbita crop-associated bees showing
that factors such as changes in forest cover, the
type of management, the area of cultivation,
and altitude influence the spatial variation of
these bee communities (Meléndez-Ramírez et
al., 2002; Shuler et al., 2005; Krug et al., 2010;
Serra & Campos, 2010; Vidal et al., 2010;
Zambrano et al., 2013; Enríquez et al., 2015;
Phillips & Gardiner, 2015). Spatial changes in
the composition of species that pollinate a crop
require the conservation of pollinator diversity
at local and regional spatial scales to maintain
the ecosystem services provided by local bees
at different locations (Winfree et al., 2018),
particularly when the pollination services of
managed honeybees may be endangered by the
decline in their populations (Carreck & New-
man, 2010). These conservation efforts repre-
sent a challenge for our societies because of the
serious threat of decline of bees due to different
causes of human origin (Potts et al., 2010).
In Central America, there have been few
studies of the bees associated with Cucurbita
crops. In Costa Rica, Wille (1985) found 5
species of the genus Eucera in crops from the
Central Valley and Guanacaste, but no informa-
tion was reported for the other bees associated
with these crops. In Guatemala, Enríquez et al.
(2015) reported 27 species of bees, belonging
to Apidae and Halictidae, visiting these crops
in highlands regions. These authors conclude
that there is high variation between locations
in the composition of species but that a frac-
tion of dominant species may generally ensure
the pollination of the crop. Both countries are
characterized by great altitudinal and climatic
heterogeneity within a relatively small terri-
tory, presenting ideal conditions for studying
geographic variation in the pollination of crops
such as squash.
This study was aimed at increasing our
knowledge about the community of visiting
bees of Cucurbita pepo crops in the Central
American region through an inventory of bees
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in different squash fields in three regions of
Costa Rica. The main objective is to determine
the taxonomic diversity and composition of
bee species visiting Cucurbita pepo crops in
different localities in Costa Rica, and their geo-
graphic and temporal pattern variation within
the study area. These observations would allow
us to determine whether the Eucerini species
observed by Wille (1985) in Costa Rica can
still be found 35 years later. In addition, this
study recorded some aspects of intrafloral
behavior of dominant species that may be
related to pollinator potential. These observa-
tions would let us to understand better the
importance of bee diversity as a pollinator of
this crop in Neotropical regions.
MATERIALS AND METHODS
Study locations: During the years 2016-
2019, collections were carried out in Costa
Rica in different squash fields in the Central
Valley (7 locations), in Guanacaste Province
(2 locations) and in the Western sector of the
Talamanca mountain range (2 locations). The
landscape characteristics, climate and altitude
of each location are presented in Table 1. Local
climatic conditions were obtained from region-
al climatic analysis of the Costa Rican National
Meteorological Institute (CRRH, 2008). In
these locations cultivation of Cucurbita pepo is
done without irrigation, which limits the growth
and flowering of the crop to the rainy season
(May-November). C. moschata, another squash
TABLE 1
Sampling sites of Cucurbita pepo bees in Costa Rica, with biophysical and landscape characteristics of each location
Region Locality
Geographic
Coordinates
Altitude
(m.a.s.l)
Annual
Precipitation (mm) /
Rainy days
Dimension of
the squash field
*
Landscape
features
Central
Valley
Piedades 9
o
56’10” N
84
o
13’26” W
818 1 947/145 Large Semiurban/
gallery forest
Cerro Colón 9
o
54’42” N
84
o
13’03” W
1 120 - Large Pastures/
Forest fragments
Acosta 9
o
46’ 8” N
84
o
12’22” W
760 2 370/149 Medium Pastures/
Forest fragments
Sta Cecilia 10° 2’ 5” N
84° 2’17” W
1 520 2 531/152 Small Pastures/
Forest fragments
Pacayas 9
o
54’24” N
83
o
47’42” W
1 760 2 245/193 Small Pastures/
Crops
Cervantes 9
o
53’13” N
83
o
47’42” W
1 250 2 000/193 Large Crops
Juan Viñas 9
o
53’37” N
83
o
44’28” W
1 200 1 675/163 Small Pastures/Crops
Guanacaste Cuajiniquil 10
o
56’08” N
85
o
41’13” W
15 1 517/89 Medium Pastures
Sta Cruz 10
o
10’13” N
85
o
32’15” W
675 2 116/89 Small Crops/
Forest fragments
Talamanca La Cangreja 9
o
47’45” N
83
o
57’20” W
1 830 1 751/182 Small Crops/Pastures/
Fragments forests
La Cima 9
o
39’34” N
83
o
54’54” W
2 146 2 632/192 Large Crops/Pastures/
Primary forests
* - Small (< 20), medium (20-200), large (> 200 open flowers at the time of collection).
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species cultivated in Costa Rica, is grown
under the same time schedule of C. pepo in
Costa Rica. Flowering peak commonly occurs
between May to August, period when sampling
of bees was done. The maximum distance
between two locations, except Cuajiniquil,
Guanacaste, was 50 km. Cuajiniquil is located
approximately 190 km from the Central Valley.
The minimum distance was 5 km. Most of the
localities were grouped in the Central Valley
and Cordillera de Talamanca, relatively close
to one another, but with important contrasting
values of altitude and precipitation (Table 1).
Most of the sampling sites were in agricultural
regions with high forest fragmentation, where
forest patches subsist as gallery forests of dif-
ferent sizes, with the exception of La Cima de
Dota and Santa Cruz, where agricultural farms
close to protected areas with mature or second-
ary forests were visited. Another important
variable was the number of open flowers at
the time of sampling, with localities ranging
from small family crops (< 20 open flowers
at the time of collection) to farm crops with
more than 200 open flowers. The diversity and
abundance of bees attracted to these sites may
be influenced by the size of the floral display.
Wild Cucurbita species or others domesticated
Cucurbita crops were not observed near the
visited farms.
Bee collection and counting: At each
site, a collection of bees was obtained from
5:00-9:00 am. Bees were trapped in male and
female flowers, although most of the samples
were collected in male flowers because of
their higher frequency. The squash field was
explored for periods of 15 min, during which
all the bees observed in flowers were col-
lected except for Apis mellifera, Trigona and
Bombus species. These species were common
and easy to identify in the field; thus, only the
number of individuals in the flowers during
each census was registered. The maximum
number of individuals counted in a census was
used as an estimate of the local abundance of
these species. All collections were performed
on sunny days. As the composition of spe-
cies can change with the time of the day, 6
collections were performed, distributed among
early (4:45-5:00 am; 5:15-5:30 am), middle
(5:45-6:00 am; 6:15-6:30 am) and late hours
(6:45-7:00 am; 7:30-8:45 am). The last time
interval was a somewhat longer than the others
because we observed that species composition
remained stable after 7:00 a.m. (see below). It
was observed that bee activity declines drasti-
cally after 9:00 a.m. At that time, most of the
flowers were dominated by Trigona bees with
few visits by other species, or there were no
visits at all. Some localities (Piedades, Cerro
Colón, La Cima de Dota and Sta Cruz) were
visited once more approximately 1 week later.
No new species were observed in samples
obtained in these visits. It was also observed
that abundance estimates of each species were
approximately repeated on the second survey.
It was concluded that the sampling effort was
enough to obtain good estimates of bee taxo-
nomic diversity and species composition in the
studied localities for the specific flowering
period. To homogenize between localities, the
abundance data obtained in the first sampling
were selected in the localities visited twice. All
bees were identified to the species level except
Agapostemon and Augochlora. Identification
was performed using available taxonomic keys
and the collection of the Zoology Museum of
the Escuela de Biología, Universidad de Costa
Rica, where voucher specimens were depos-
ited. Eucera (Peponapis) specimens were sent
to the Bee Biology and Systematics Laboratory
(Utah) to help with identification.
In some localities, Piedades and Cerro
Colón, there are two squash crops per year, one
in the middle (August-September) and another
at the end of the rainy season (November-
December). To determine if composition of the
floral visitors changes between crop seasons,
sampling was performed during each crop
season in Piedades, one in August 2019 and
another in November of the same year, follow-
ing the same collection intensity protocols and
observation times.
Intrafloral behavioral observations: To
determine whether the different floral visitors
made contact with the reproductive parts of
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the flowers and to obtain observations of the
foraging behavior of each group of bees inside
the flowers, continuous video recordings were
performed in flowers from 5:00 am until 7:30
am at two localities (Piedades and La Cima
de Dota). Sony HDRCX700 Handycam video
cameras (San Diego, CA, USA) were used.
The recordings ended at 7:30 am because after
this time no significant changes were detected
in the activity pattern of the bees, except for
their near disappearance from the flowers after
10:00 a.m. when many flowers showed signs
of wilting. Six male and five female flowers
were chosen for filming in La Cima de Dota in
August 2016, and the same number of flowers
were chosen in the town of Piedades in August
2019. This comparison allowed us to visualize
the differences in behavior between localities
with different floral visitors (see below). A total
of 6 h of video recordings were obtained in
each location, which were manually analyzed
to check the foraging schedule and the behavior
of different bees in each location. Special atten-
tion was paid to the pollen load (large = body
densely covered by pollen, intermediate = pres-
ence of scattered pollen, more visible in corbi-
clae/escopae; small = pollen scattered with few
or no grains) and the visit duration. A sample
of 2-3 individuals of bee species observed at
flowers were collected and their pollen loads
visualized in a microscopy to check if it were
Cucurbita pollen.
Statistical analysis: Mean values and con-
fidence intervals of species richness (number
of species) for each locality and altitudinal
level were obtained by bootstrapping with
300 replicates (Hsieh, Ma, & Chao, 2016). We
grouped locations in three altitude categories:
low (< 1 000 m.a.s.l. 5 localities), intermedi-
ate (1 000-1 800 m.a.s.l. 5 localities) and high
(> 1 800 m.s.a.l. 2 localities). A generalized
linear model with a Poisson distribution was
used to test the effect of altitude on species
richness using altitude as a categorical variable.
To test differences in the composition (abun-
dance of each species) of the bee community
at different altitudes a Multivariate Analysis of
Variance with permutations (PERMANOVA)
was performed using the Bray-Curtis distance,
as implemented in the vegan package (Oksanen
et al., 2019).
RESULTS
Diversity and geographic variation: The
species collected and their order of dominance
(frequency rank order, 1= most frequent, 8=
least frequent) at each locality are shown in
Fig. 1. Some localities had very low visita-
tion rates (Juan Viñas and Santa Cecilia),
which is reflected in the low number of bees
collected from those locations. In total, indi-
viduals belonging to 19 genera and 2 families
(Halictidae and Apidae) of bees were obtained.
From the samples identified to the species
level, a total of 22 species were obtained,
while 5 groups of bees were only identified to
the genus level, for a minimum total number
of 27 species. The number of species could
increase by 2-3 if genera such as Augochlora
(very diverse) or Agapostemon were identified
to the species level. The presence of 2 species
of the genus Megalopta as well as one species
of Caenaugochlora (C. costaricensis) at high
levels of dominance, was noted at 5 and 4 loca-
tions, respectively.
Abundant species were observed in most
localities (Fig. 1): 2 species of Meliponini
tribe: Trigona corvina and Partamona oriza-
baensis, honey bees (Apis mellifera) and a
species of bee specialized on this crop, Eucera
(Peponapis) limitaris. A. mellifera workers
observed in the crops are probably originated
from feral colonies, as no commercial beekeep-
ing was observed near the studied crops. Other
species were frequent only in some locations:
i) Bombus ephipiatus was the most frequent
floral visitor in La Cima de Dota, the highest-
altitude location but was rare or absent in
other locations; ii) in Cuajiniquil (Guanacaste)
and Acosta, Eucera (Peponapis) crassiden-
tata was frequent. Among the two subgenera
of bees specialized on Cucurbita, four spe-
cies of Eucera (Peponapis) (E. limitaris, E.
crassidentata, E. utahensis and E. apiculata)
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Fig. 1. Bee species in squash crops (Cucurbita pepo) at 11 locations in Costa Rica. The level of shading in each box indicates the order of dominance of each species at each
locality, where black indicates the most frequent species (dominance 1). Species with very similar frequencies share the same shading. Level 8 represents rare species (frequently
1-2 individuals observed/collected).
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were collected, the last of which was only col-
lected in one locality (Cerro Colón) as a rare
species (Fig. 1).
Large differences in species richness were
found between localities (Fig. 2). The localities
with the highest species richness (species rich-
ness 10.5-15.2), were Piedades (Aug), Acosta
and Cuajiniquil, which were found at altitudes
less than 1 000 m. a. s. l. in medium-large
crops and in drier climatic regimes. Small
crops (La Cangreja, Juan Viñas, Sta Cecilia,
and Pacayas) showed lower species diversity
(species richness 1-4), although low diversity
was also found in a large crop in highland
regions (La Cima de Dota) (species richness 4).
Crops located at low altitude levels presented
higher species richness compared to medium
(Z = -3.897, P <0.001) and high altitudes (Z
= -2.174, P < 0.05) PERMANOVA analysis
showed that bee species composition changed
significantly between altitude levels (F = 2.03,
R
2
=0.31, d.f.= 2, 9, P < 0.01).
At Piedades, the two sequential collec-
tions corresponding to the two annual crops
separated by 3 months (August and November)
showed changes in the abundance and order of
dominance of the species (Fig. 1). In Novem-
ber, a frequent species (Apis mellifera) and sev-
eral rare species (Agapostemon sp., M. genalis,
and E. utahensis) observed in August disap-
peared, reducing the number of species from 10
to 4 as well as the abundance of bees collected
in flowers (150 to 45). In November, T. corvina
frequency was 95 % of the samples, while in
August this figure was approximately 60 %.
Behavior of common species: Table 2
summarizes the main observations of 5 of the
most common floral visitors of C. pepo in the
visited localities. All of these species touched
the reproductive parts of male and female flow-
ers. The largest and hairiest species (Eucera
and Bombus) and those that visit male flowers
earlier (Megalopta) were the ones that most
frequently carry large pollen loads classified as
“large”. A temporal sequence of foraging was
observed, in which the crepuscular Megalopta
sp. begins at 4:30 am (observed before the
initiation of the recordings), followed by the
arrival of Apis mellifera, Eucera and Bombus,
Fig. 2. Species richness of bee populations visiting C. pepo crops in each locality studied. Localities are grouped by altitude
level (low 0-1 000 m.a.s.l., medium 1 000-1 800, high > 1 800). Mean values and confidence intervals were obtained by
bootstrapping.
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among which the last genus was only observed
in highland areas. Different species of Trigona
or Partamona, especially Trigona corvina,
arrive somewhat later but quickly invade the
area around the nectaries of almost all flowers.
Megalopta and Trigona bees tend to spend long
times collecting nectar (Table 2). Trigona bees
exhibit two interesting foraging behaviors: i)
they enlarge the nectar chamber pores with
their jaws (Fig. 3) seeking nectar, ii) they tend
to repel other bees from flowers, because of
their abundance and activity, and on rare occa-
sions, by direct attacks. Eucera (Peponapis),
Bombus and A. mellifera are characterized by
short visits (16-27 s) and quick flights to flow-
ers (Table 2).
Fig. 3. Nectary pores in male C. pepo flowers. A. normal, B. enlarged by T. corvina bites.
TABLE 2
Behavioral patterns of the most common bee visitors of C. pepo in Costa Rica obtained from video recordings
in two locations. See Methods for the classification of the pollen load and duration of visits
Bee taxa
Pollen
load
Time of foraging
Median of duration of
visit in seconds (s)
(interquartile range)
Observations
First individuals
observed
Last individuals
observed
Eucera (Peponapis) sp.
Large 5:00 a.m. rare after
7 a.m.
18 (5-62) Fast flights between
flowers.
Megalopta sp.
Large 4:30 a.m. 6 a.m. 225 (51-518) First floral visitor, starts
foraging at the beginning
of anthesis of male
flowers.
Bombus sp
Large 5:00 a.m. 10 a.m. 16 (7-30) Fast flights between
flowers.
Trigona corvina
Small 5:30 a.m. 12 m. 73 (39-106) Group recruitment.
Predominate at flowers
from 6-7 a.m. Aggressive.
Enlargement of the pores
of the floral nectary.
Apis mellifera
Medium-
Small
5:00 a.m. 12 m. 27 (9-45) Non-aggressive behavior.
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DISCUSSION
Bee diversity within and between localities
The data obtained in this study agree with
other studies carried out in various locations
in the Neotropics (Digital Appendix), showing
how different species of Cucurbita are visited
by a diverse spectrum of bee species, where
the species specialized for the collection of
pollen from cucurbits are not always the most
frequent (Canto-Aguilar & Parra-Tabla, 2000;
Meléndez-Ramírez et al., 2002; Zambrano et
al., 2013; Enríquez et al., 2015; Delgado-
Carrillo et al., 2018). The groups collected in
Costa Rica have been observed in these studies,
such as Trigona, Bombus, Augochlora, Cera-
tina, Eucera (Peponapis), and Africanized bees
(Apis mellifera), along with other rarer groups.
These inventories have shown a group of domi-
nant and widely distributed species in this crop,
accompanied by a series of rare species with
more restricted distributions.
Variations between localities in the degree
of alteration of the natural habitat and the
intensity of agricultural practices have been
mentioned as factors that explain changes
in the composition of bees species related to
squash fields (Krug et al., 2010; Enríquez et
al., 2015). However, Meléndez-Ramírez et al.
(2002) found a high diversity of bees that visit
cucurbit crops in locations with high degrada-
tion of their natural flora. To study the factors
that determine changes in the composition
of bee species that visit squash in Costa Rica
would require a more extensive and systematic
sampling of localities under variable condi-
tions of habitat alteration. However, certain
general trends can be reported. In our study,
an important effect of altitude was detected in
the composition and species richness of squash
fields. A large crop at more than 2 000 m eleva-
tion (La Cima de Dota) showed a strong reduc-
tion in species richness, while localities at low
elevations showed a greater number of species.
Hoiss, Krauss, Potts, Roberts and Steffan-
Dewenter (2012) have shown how altitude acts
as an environmental filter on diversity in bee
communities. In Costa Rica, pollination of C.
pepo at high elevations seems to be ensured by
the abundance of B. ephippiatus. Different spe-
cies of Bombus have been reported as among
the main pollinators of Cucurbita in temperate
regions (Shuler et al., 2005, Petersen, Rein-
ers, & Nault, 2013). The effect of changes in
altitude can be seen when bees visiting squash
plantations are compared between two locations
that are very close spatially (Cerro Colón and
Piedades, 5 km) but differ by 200 m in altitude.
These localities show strong differences in the
composition of bee species, particularly, the
presence of Eucera (Peponapis) apiculata at
only the highest locality. Changes in the char-
acteristics of the life zones are also important,
as evidenced by the exclusive presence of the
Eucera (Peponapis) crassidentata species in
dry forest (Cuajiniquil), an observation previ-
ously reported by Wille (1985). Another factor
that seems relevant is the size of the crop since
in small crops the species richness is lower.
However, in these small crops the presence of
Eucera (Peponapis) limitaris is constant. This
species seems to be ensuring the pollination
of small crops of C. pepo, even in deforested
regions and under strong agricultural pressure
(such as Pacayas and Juan Viñas).
Changes in the composition of pollinators
in collections spaced 3 months apart during the
rainy season were observed in Piedades. The
dominance of social bees of the genus Trigona
increased in the second sampling. This varia-
tion shows the importance of diversity in the
pollination of this crop, where meliponine bees
could be ensuring production during times of
population decline of other species. The impor-
tance of pollinator complementarity during
different seasons of a crop has been studied
by Delgado-Carrillo et al. (2018) for Cucur-
bita moschata and by Genung et al. (2017)
for other crops.
Bee species rarely reported
in Cucurbita crops
This is the first study to show the use
of Cucurbita pepo as a resource by bees of
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the genus Megalopta, bees with the ability to
forage during twilight (Wcislo et al., 2004).
Megalopta were found at high frequencies
in several locations in our study. Some spe-
cies of this genus show social polymorphism
(Wcislo et al., 2004). In this study, two species
of Megalopta that show facultative eusociality
were found, and it was observed that Cucurbita
nectar is used by macro- and microcephalic
individuals of both species, which reveals that
it is a resource used by potential workers and
queens. Another genus not reported previously
in C. pepo flowers is Caenaugochlora, a rare
bee distributed between Mexico and Northern
South America (Michener, McGinley, & Dan-
forth, 1994). Of the various bee inventories
in squash plantations in the Neotropics, only
Meléndez-Ramírez et al. (2002) have reported
the collection of 1 individual of this genus in
the Yucatán. However, in this study, it was
observed in flowers of C. pepo at different
locations; it was among the 3 or 4 most fre-
quent species and practiced early foraging on
male flowers. Both Megalopta and Caenau-
gochlora belong to Halictidae, a family with
various species reported in crops of different
Cucurbita species, but where this family was
represented by other genera, such as Augochlo-
ra, Lasioglossum, Augochloropsis and Agap-
ostemon (Canto-Aguilar & Parra-Tabla, 2000;
Meléndez-Ramírez et al., 2002; Zambrano et
al., 2013; Enríquez et al., 2015; Delgado-Car-
rillo et al., 2018). These groups were relatively
rare or absent in our collections. In a study
of the social behavior of Halictidae in Costa
Rica, Michener and Kerfoot (1967) observed
the presence of Caenaugochlora costaricen-
sis (formerly known as Pseudoaugochlorop-
sis costaricensis) exclusively in Cucurbita
flowers. Megalopta bees excavate their nests
in dead wood, most frequently in fallen tree
branches in the understory (Wcislo et al.,
2004). C. costaricensis is a ground-nesting
species whose nests have been found in slope
banks in roadsides sites (Michener & Kerfoot,
1967). Therefore, these species have different
nesting sites. Their presence in squash cultures
is favored by small forest fragments, isolated
trees and secondary growth nearby farms in the
localities where these bee species were found.
Comparison with earlier Costa Rican
Eucerini bees surveys
The same species of the subgenus Pepo-
napis reported in this study were observed by
Wille in 1985 (Wille, 1985). This stability may
be due to the continuous presence of Cucurbita
crops in the Central Valley and Guanacaste
since 1985 as well as the relative capacity
of these species to adapt to rural landscapes,
especially small crops, where ground nesting
areas are available (Phillips & Gardiner, 2015;
Delgado-Carrillo et al., 2017). However, in
Guanacaste no individuals of Eucera (Xeno-
glossa) gaabi, a species reported by Wille
(1985), were observed. More collections in
Guanacaste are necessary to confirm the pos-
sible loss of this species. It is interesting to note
that recent inventories of bees in Cucurbita
plantations in Mexico have not reported the
presence of Xenoglossa subgenus (Meléndez-
Ramírez et al., 2002, Delgado-Carrillo et al.,
2018, Digital Appendix), even though Hurd
and Linsley (1966) showed that Mexico was
part of the natural distribution of these species.
Behavioral observations
The various floral visitors observed in this
study display differences in foraging strate-
gies. Eucera (Peponapis) and Bombus prac-
tice a type of foraging characterized by rapid
exploration and extraction of nectar from each
flower, allowing them to visit many flowers
per unit of time (pers. obs.). This strategy,
combined with an early foraging schedule,
dense hair and relatively large size, makes
these bees very efficient potential pollinators of
different species of Cucurbita (Canto-Aguilar
& Parra-Tabla, 2000; Serra & Campos, 2010;
Delgado-Carrillo et al., 2018). Megalopta and
Caenaugochlora, although not large or hairy
bees, visit flowers very early, taking advantage
of the onset of nectar flow in male flowers,
which also makes them potential pollinators. A
very different pattern was observed in Trigona,
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particularly in T. corvina. These bees monopo-
lize the flowers shortly after the start of for-
aging, practicing a slower and more detailed
exploration of flower resources, including the
slight laceration of the pores leading to the
nectar chamber. The congregation of T. corvina
bees near the nectar chamber sometimes repels
other larger bees from 7-8 a.m., such as Apis
mellifera and Eucera (Peponapis). These char-
acteristics of Trigona foraging on Cucurbita
flowers were also noted by Serra and Campos
(2010) in Brazil.
In summary, crops of C. pepo in Costa
Rica are visited by diverse bees, among which
some species may be the main pollinators and
others play a secondary role. The importance
level of each species in the pollination may
be determined by the abundance of each spe-
cies, their foraging schedule and efficiency in
pollen transfer (Herrera 1987; Herrera 1989).
This diversity allows the crop to be productive
throughout different geographic and seasonal
environments (Delgado-Carrillo et al., 2018;
Hoehn et al., 2008). It could be suggested that
the pollination of this crop is maintained in dif-
ferent geographical regions and different times
of the year thanks to the spatial and temporal
complementarity of pollination services by dif-
ferent species of bees. More information on the
pollinating role of Trigona bees would allow a
better understanding of the regulatory factors
related to the productivity of this crop. The
preservation of nesting sites and diverse floral
resources (represented by other crops or wild
plant species) are crucial factors to maintain
the diverse bee community associated with
cultivated Cucurbita, which is very important
in the diet and regional culture of the Americas.
Ethical statement: authors declare that
they all agree with this publication and made
significant contributions; that there is no con-
flict of interest of any kind; and that we fol-
lowed all pertinent ethical and legal procedures
and requirements. All financial sources are fully
and clearly stated in the acknowledgements
section. A signed document has been filed in
the journal archives.
ACKNOWLEDGMENTS
We thank deeply to the farmers and their
families who gave us guidance and allowed
us to collect bees in their gardens. We would
like to especially thank Heiner Morales who
provided us with his garden in Piedades to
enable more detailed analysis of the behavior
of bees. J. García, M. Chavarría and F. Pacheco
collaborated with the authors in contacting crop
owners. G. Jones provided facilities for field
work in Sta. Cruz. T. Griswold and C. Ritner
collaborated in the identification of bees.
RESUMEN
Diversidad y patrones de búsqueda de alimento
de las abejas en flores de Cucurbita pepo
(Cucurbitaceae) en Costa Rica
Introducción. Dada la importancia del componente
diversidad para la polinización de plantas cultivadas, es
necesario obtener más información de esta diversidad y su
variación geográfica en cultivos como Cucurbita pepo, uno
de los cultivos más importantes de la agricultura centroa-
mericana. Objetivo: Describir la diversidad y la variación
geográfica de la comunidad de abejas que visitan este
cultivo en Costa Rica, y algunos aspectos de sus patrones
de búsqueda de alimento. Métodos: Se visitaron cultivos
de C. pepo en 11 localidades dentro de tres regiones geo-
gráficas de Costa Rica, donde se determinó los grupos de
abejas y su frecuencia relativa. Por medio de grabaciones
de video se registró el comportamiento de cada grupo en
dos localidades. Resultados: Fueron encontradas un míni-
mo de 27 especies pertenecientes a 19 géneros y 2 familias
de abejas. Tres especies son dominantes en 10 localidades
(Eucera limitaris, Apis mellifera y Trigona corvina). La
altitud reduce la diversidad de abejas debido a la dominan-
cia de Bombus ephipiatus en regiones altas. Se observaron
dos géneros de halíctidos (Megalopta y Caenaugochlora)
no previamente reportados en este cultivo. Abejas Trigona
dominan las flores en horarios más tardíos de la mañana,
donde algunas veces muerden los orificios de los nectarios
para facilitar la recolecta de néctar. Conclusiones: La
diversidad de abejas que visitan C. pepo en Costa Rica
parece asegurar su polinización ante cambios espaciales o
estacionales en condiciones ambientales.
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Palabras clave: Cucurbita; abejas; polinización de culti-
vos; abejas sin aguijón; abejas de las calabazas, abejas sin
aguijón; calabazas; ayote.
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