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Citation: Akram, W.; Sajjad, A.;
Ghramh, H.A.; Ali, M.; Khan, K.A.
Nesting Biology and Ecology of a
Resin Bee, Megachile cephalotes
(Megachilidae: Hymenoptera).
Insects 2022,13, 1058. https://
doi.org/10.3390/insects13111058
Academic Editor: Brian R. Johnson
Received: 6 October 2022
Accepted: 9 November 2022
Published: 16 November 2022
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4.0/).
insects
Article
Nesting Biology and Ecology of a Resin Bee,
Megachile cephalotes (Megachilidae: Hymenoptera)
Waseem Akram 1, Asif Sajjad 1,* , Hamed A. Ghramh 2,3,4, Mudssar Ali 5and Khalid Ali Khan 2,3,6,*
1
Department of Entomology, Faculty of Agriculture and Environment, The Islamia University of Bahawalpur,
Bahawalpur 63100, Punjab, Pakistan
2Research Center for Advanced Materials Science (RCAMS), King Khalid University, P.O. Box 9004,
Abha 61413, Saudi Arabia
3
Unit of Bee Research and Honey Production, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia
4Biology Department Faculty of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia
5Institute of Plant Protection, Muhammad Nawaz Shareef University of Agriculture,
Multan 60000, Punjab, Pakistan
6Applied College, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia
*Correspondence: asifbinsajjad@gmail.com (A.S.); khalidtalpur@hotmail.com (K.A.K.)
Simple Summary:
Megachile cephalotes is a solitary bee that is widely distributed in Sindh and Punjab,
Pakistan. It has been reported as an effective pollinator of Grewia asiatica and some other crops.
Bees are declining around the world, threatening the productivity of field crops, vegetables, and
fruits. Among the Megachilini tribe, the only European leaf-cutting bees, Megachile rotundata has
been artificially reared and conserved on a commercial scale in different parts of the world. Some
recent studies have shown a high pollination potential of M. cephalotes owing to its gregarious nesting
and foraging behavior. In the present study, the nesting biology and ecology of M. cephalotes were
reported for the first time in this region. The bees remained active during the spring and summer
seasons, and females preferred to construct their nests in bamboo sticks and wooden blocks. They
used plant resin for the construction of brood cells and placed several types of pollen grains in these
cells. The males took fewer days to become adults than the females. The present study will help in
the commercial-scale artificial nesting and conservation of M. cephalotes.
Abstract:
We report the nesting biology and ecology of Megachile cephalotes Smith, 1853 for the first
time in Pakistan. Wooden and bamboo trap nests were deployed at three different locations in
Bahawalpur district, Pakistan, from January 2020 to May 2021. A total of 242 nests of M. cephalotes
were occupied in all three locations with the maximum abundance in the Cholistan Institute of Desert
Studies. Megachile cephalotes remained active from March to September (the spring and summer
seasons). In a nest, females made 7–8 brood cells each having a length of 1.2–2.3 cm. Plant resin
was used to construct cells and mud or animal dung to plug the nest entrance. A vestibular cell was
also made between the outermost brood cell and the nest entrance that ranged from 1.4 to
2.5 cm
in length. No intercalary cells were observed in the nests. The males took 65.3 days to become
adults, while the females took 74.78 days. The sex ratio was significantly biased toward females in all
three locations. Grewia asiatica was the predominant pollen grain species found in the brood cells.
Megachile cephalotes were observed collecting resin from Acacia nilotica,Prosopis juliflora, and Moringa
oleifera. Three cleptoparasites of this species were also recorded: Euaspis carbonaria,
Coelioxys sp.
,
and
Anthrax sp.
This study set up a background to encourage new studies on artificial nesting and
provides tools for proper biodiversity management and conservation.
Keywords: nesting; biology; ecology; Megachile cephalotes; resin bee
Insects 2022,13, 1058. https://doi.org/10.3390/insects13111058 https://www.mdpi.com/journal/insects
Insects 2022,13, 1058 2 of 14
1. Introduction
Managed bees are considered the most efficient pollinators throughout the world, but
wild bees have also received considerable attention for the last few decades due to their high
pollination efficiency and because they provide equivalent services to those of managed
bees [
1
,
2
]. Sometimes wild bees also enhance the pollination services provided by managed
bees through their behaviors [
3
,
4
]. Among 20,000 species of bees, the majority of the
species are wild [
5
]. The population of bees is declining throughout the world, ultimately
threatening the productivity of major crops, vegetables, and fruits [
6
,
7
]. Several factors
have been attributed to bee decline, e.g., habitat degradation, climate change, intensive use
of pesticides, predators, and parasites [
8
–
10
]. The availability of suitable foraging resources
and nesting habitats helps minimize the decline [11–14].
The family Megachilidae, including more than 4000 species, occurs throughout the
world [
15
,
16
]. Within Megachilidae, Megachile Latreille, 1802 is the most diverse genus,
comprised of 32 subgenera and 431 species only in the neotropical region, along with
several unidentified species [
16
–
20
]. Numerous species of Megachile are efficient pol-
linators [
21
–
27
] and only M. rotundata could be artificially reared and conserved on a
commercial
basis [28,29]
. In Pakistan, 18 species of the genus Megachile are known [
15
], yet
no information is available on the nesting biology and ecology of megachilid bees.
Megachile species are solitary and highly adaptive and build their nests in pre-existing
cavities, e.g., wooden logs, hollow stems of bamboo and roses, burrows in the soil, cracks
and crevices, and slits in rocks or manmade structures [
16
,
30
–
33
]. For the construction
of their brood cells, female Megachile spp. use a variety of materials, e.g., leaf pieces,
flower petals, mud, pebbles, and a combination of resin and salivary
material [16,30,34–40]
.
A recent study reported the use of plastics from wrappings, flags, and bags [
41
]. This
behavior applies to some species, but it is not a general behavior of all Megachile species.
Poor knowledge about nesting biology is the main barrier to utilizing the diverse megachilid
bees as a management tool for pollination services.
Each nest consists of a linear series of brood cells with pollen provisions (nectar and
pollen mixture) packed by the female [
42
]. The female lays eggs on pollen provisions and
finally closes the cell with pieces of leaves [
43
]. Once the first cell is fully completed, the
females repeat this process several times from the closed to the open end of the nesting
cavity. When the nest is filled with cells, they close the nest from the outside with masticated
leaves or mud to protect their offspring [
42
]. Depending on their resources, Megachile bees
can be oligolectic [
44
] or polylectic [
16
,
45
]. Most research has been conducted on the nesting
biology of leafcutter bees [46–53], while resin bees are poorly understood [42,54–57].
By using bee hotels or trap nests, the nesting biology and ecology of bees are studied for
various purposes, i.e., the study of nest architecture [
50
,
58
,
59
], natural
history [60–63]
, evo-
lution [16], crop pollinators [64], population monitoring and community structure [13,65],
bioindication and recording changes in habitat type [
66
–
68
] and as a tool in conserva-
tion [
59
,
69
] and quantitative ecology [
70
–
72
]. The latter includes the quantification of
multiple trophic interactions between bees, wasps, their food objects, and natural ene-
mies [73].
Megachile (Callomegachile)cephalotes is a solitary bee that is widely distributed in Sindh
and Punjab, Pakistan [
15
]. From Pakistan, it has been reported as an effective pollinator of
Grewia asiatica [25,26]. The genus Grewia has 140 to 150 species, of which only G. asiatica is
of commercial importance as a fruit crop in subtropical and tropical regions [
74
,
75
]. Little
is known about the nesting biology and ecology of this bee [
54
]. The aim of this study was
to provide information about the nesting biology (nest architecture and pollen types used)
and ecology (seasonality and plant species providing pollen and nectar) of M. cephalotes for
the first time in Pakistan. This nesting behavior differs from that observed in other parts of
its range and can provide the basis for comparative studies.
Insects 2022,13, 1058 3 of 14
2. Material and Method
2.1. Study Site
The study was conducted from January 2020 to May 2021 at three different sites in
Bahawalpur district: Cholistan Institute of Desert Studies (CIDS; 29.3784
N, 71.7696
E),
the Agricultural Research Farm (ARF; 29.3714N, 71.7652E), and the Fisheries Complex
(FC; 29.3863
N, 71.6300
E). CIDS is comprised of a highly diverse landscape of over
40 hectares
, including desert, orchards, unmanaged land, lawns, horticultural landscaping,
and some agricultural land. A diverse array of floral resources remains available year-
round. Natural or artificial nesting resources, i.e., cracks or holes in mud walls, hollow
tree branches, and bamboo or reed sheds are also abundant. The ARF is 65 hectares and is
comprised of agricultural and horticultural crops. Cotton and maize are the major crops,
and the need-based application of insecticides is a usual practice. The FC is 27 hectares and
is comprised of G. asiatica fields, citrus orchards, and some other horticultural flowering
plants. Natural and artificial nesting resources are also abundant for bees, i.e., cracks or
holes in brick walls, empty fish ponds, and hollow tree trunks or branches.
The climate of the district is arid with mild winters and hot summers. There are four
seasons in this zone: spring (March to May), summer (June to September), autumn (October
to November), and winter (December to February) [
76
]. The mean daily minimum and
maximum temperatures are 28
C and 42
C in the summer and 6
C and 22
C in the
winter, respectively. The average annual rainfall in Bahawalpur is 169.8 mm [77].
2.2. Nesting Material
At each site, one wooden frame with dimensions of 152 cm (length)
⇥
92 cm
(width)
⇥
30 cm (depth) was installed on 3 January 2020. Each wooden frame consisted of
seven partitions, and each partition was filled with certain nesting material. The nesting
materials included wooden logs, mud blocks, wooden blocks, cardboard tubes, bamboo
sticks, dry reeds, and plastic straws. Two wooden plates (18 cm long) with longitudinal
groves were stacked on each other so that they made complete holes [
53
]. Five such plates
were stacked and tied with adhesive tape to form a wooden block. Only bamboo sticks
and wooden blocks were considered for further study, as the females of Megachile cephalotes
constructed their nests in bamboo sticks and wooden blocks. One thousand bamboo sticks
and one hundred wooden blocks were placed in each wooden frame.
2.3. Nest Sampling
Trap nests were checked weekly for occupied nests. The occupied nests were removed
and replaced with new ones. The collected nests were marked with the nest collection
date, and the open end was covered with nylon mesh bags to check the adult emergence.
All the collected nests were placed in cages, and the emergence of adult M. cephalotes
was observed. The date of emergence of male and female individuals was recorded. The
time period between nest collection and the emergence of individuals was considered the
developmental period. The sex ratio of M. cephalotes was also noted.
2.4. Nesting Biology and Ecology
Five completely occupied wooden blocks were shifted to the laboratory and dissected
to study the nest structure. The following parameters were evaluated: total nest length,
nest diameter, brood cell length, vestibular cell length, total number of brood cells/nest,
and nest closure material. The digital Vernier caliper was used to measure the length
and diameter of the nests. For comparison, four occupied nests in bamboo sticks were
X-ray-photographed with an X-ray machine (Figure 1).
Insects 2022,13, 1058 4 of 14
Insects 2022, 13, x FOR PEER REVIEW 4 of 15
Figure 1. X-ray photographs showing four nests of Megachile cephalotes. Nest entrance is at the left.
The floral host plants were recorded by directly observing M. cephalotes foraging at
the study sites. The weekly random walks were made between 9:00 am to 5:00 pm to rec-
ord the plant species foraged by M. cephalotes. The resin collection was also directly ob-
served in the field by focusing on resin-producing plants. To identify and measure the
pollen grains of the brood cells, reference glass slides were made first by removing pollen
grains from the available blooming plants during the spring and summer seasons when
M. cephalotes were active. These vouchers aided in the identification of pollen provisions
in brood cells. Pollen provisions were sampled from 15 different brood cells, acetolized,
and mounted on glass slides [78,79]. Using the reference slides, pollen grains collected
from the brood cells were identified. From each sample, 1000 pollen grains were identified
and counted under a 60× stereomicroscope.
2.5. Statistical Analysis
A t-test was applied to compare male and female M. cephalotes in terms of the mean
number of days to become adults. The Chi-square goodness of fit test was applied to de-
termine the effect of location on the sex ratio of M. cephalotes.
3. Results
A total of 242 nests (bamboo sticks = 184, wooden blocks = 58) of M. cephalotes were
collected from January 2020 to December 2020 at three locations: CIDS, ARF, and FC. The
maximum number of nests was collected from CIDS, followed by the FC and ARF (Figure
2).
Vestibular cells
Figure 1. X-ray photographs showing four nests of Megachile cephalotes. Nest entrance is at the left.
The floral host plants were recorded by directly observing M. cephalotes foraging at the
study sites. The weekly random walks were made between 9:00 am to 5:00 pm to record
the plant species foraged by M. cephalotes. The resin collection was also directly observed in
the field by focusing on resin-producing plants. To identify and measure the pollen grains
of the brood cells, reference glass slides were made first by removing pollen grains from
the available blooming plants during the spring and summer seasons when M. cephalotes
were active. These vouchers aided in the identification of pollen provisions in brood cells.
Pollen provisions were sampled from 15 different brood cells, acetolized, and mounted on
glass slides [
78
,
79
]. Using the reference slides, pollen grains collected from the brood cells
were identified. From each sample, 1000 pollen grains were identified and counted under a
60⇥stereomicroscope.
2.5. Statistical Analysis
At-test was applied to compare male and female M. cephalotes in terms of the mean
number of days to become adults. The Chi-square goodness of fit test was applied to
determine the effect of location on the sex ratio of M. cephalotes.
3. Results
A total of 242 nests (bamboo sticks = 184, wooden blocks = 58) of M. cephalotes were
collected from January 2020 to December 2020 at three locations: CIDS, ARF, and FC.
The maximum number of nests was collected from CIDS, followed by the FC and ARF
(Figure 2).
The first occupied nest was seen on 26 March 2020. The males of M. cephalotes emerged
earlier than the females. The emergence started in the last week of April with a sharp
increase until July and then a gradual decline until September. We did not observe any
emergence from October 2020 to February 2021. These five months represented the hiberna-
tion period of M. cephalotes. The emergence of these hibernated populations started again
in the first week of March 2021. This showed that M. cephalotes remained active from March
to September, comprising the spring and summer seasons (Figures 3and 4).
Insects 2022,13, 1058 5 of 14
Insects 2022, 13, x FOR PEER REVIEW 5 of 15
Figure 2. Number of occupied nests of Megachile cephalotes at three different sites from January to
December 2020.
The first occupied nest was seen on 26 March 2020. The males of M. cephalotes
emerged earlier than the females. The emergence started in the last week of April with a
sharp increase until July and then a gradual decline until September. We did not observe
any emergence from October 2020 to February 2021. These five months represented the
hibernation period of M. cephalotes. The emergence of these hibernated populations
started again in the first week of March 2021. This showed that M. cephalotes remained
active from March to September, comprising the spring and summer seasons (Figures 3
and 4).
Figure 3. Emergence of male and female Megachile cephalotes from January 2020 to May
2021.
137 (57%)
28 (11%)
77 (32%)
CIDS ARF FC
0
50
100
150
200
250
300
350
Jan-20
Feb-20
Mar-20
Apr-20
May-20
Jun-20
Jul-20
Aug-20
Sep-20
Oct-20
Nov-20
Dec-20
Jan-21
Feb-21
Mar-21
Apr-21
May-21
No. of adults emerged
Male Female
Figure 2.
Number of occupied nests of Megachile cephalotes at three different sites from January to
December 2020.
Insects 2022, 13, x FOR PEER REVIEW 5 of 15
Figure 2. Number of occupied nests of Megachile cephalotes at three different sites from January to
December 2020.
The first occupied nest was seen on 26 March 2020. The males of M. cephalotes
emerged earlier than the females. The emergence started in the last week of April with a
sharp increase until July and then a gradual decline until September. We did not observe
any emergence from October 2020 to February 2021. These five months represented the
hibernation period of M. cephalotes. The emergence of these hibernated populations
started again in the first week of March 2021. This showed that M. cephalotes remained
active from March to September, comprising the spring and summer seasons (Figures 3
and 4).
Figure 3. Emergence of male and female Megachile cephalotes from January 2020 to May
2021.
137 (57%)
28 (11%)
77 (32%)
CIDS ARF FC
0
50
100
150
200
250
300
350
Jan-20
Feb-20
Mar-20
Apr-20
May-20
Jun-20
Jul-20
Aug-20
Sep-20
Oct-20
Nov-20
Dec-20
Jan-21
Feb-21
Mar-21
Apr-21
May-21
No. of adults emerged
Male Female
Figure 3. Emergence of male and female Megachile cephalotes from January 2020 to May 2021.
Insects 2022, 13, x FOR PEER REVIEW 6 of 15
Figure 4. Total emergence of male and female Megachile cephalotes in spring and summer seasons
from January 2020 to May 2021.
For the study of nest architecture, five completely occupied wooden block nests were
collected in May 2020. These nests were similar in length and diameter. The number of
cells ranged from 7 to 8 with minimum and maximum cell lengths of 1.2 and 2.3 cm, re-
spectively (Table 1). In each nest, all the cells were constructed in a linear series and
aligned horizontally. The construction of the first cell started at the base of the nest (Figure
5). Before constructing the first cell, female M. cephalotes collected resin and deposited it
at the base of the nest, making a thick layer. The brood cells were slightly rounded at the
base and elongated. The female made several trips to collect pollen and nectar to provision
the brood cells in the form of pollen lobes at the cell base. After provisioning the first cell,
the female laid a single egg on the provision mass. After oviposition, the female made
more trips to collect resin, which was used for cell closure. They made seven to eight such
cells in a single nest. They also left a space (a vestibular cell) ranging from 1.4 to 2.5 cm
long between the outermost brood cell and the nest entrance (Figure 1). The nests were
then plugged with mud or animal dung at the entrance (Figure 5).
Table 1. Nest measurements of Megachile cephalotes-occupied nests.
Nest 1 Nest 2 Nest 3 Nest 4 Nest 5
Nest length (cm) 16 15 15.5 16 16
Nest diameter (mm) 7 7 7 7 7
Nest closure Mud Mud Animal
dung
Animal
dung Mud
Number of cells 8 8 7 8 7
Vestibular cell length (cm) 1.5 2 2 1.4 2.5
Cell length (cm)
1st 1.7 1.8 1.65 2.1 1.8
2nd 1.2 1.6 1.7 1.5 1.65
3rd 1.9 1.5 1.7 1.7 1.3
4th 1.9 1.8 1.5 1.5 1.5
5th 1.7 2 2.3 1.6 1.6
6th 1.3 1.3 1.5 1.4 1.4
7th 1.25 1.2 1.3 1.6 1.4
8th 1.6 1.2 - 1.6 -
121
305 295
717
0
100
200
300
400
500
600
700
800
Male Female Male Female
Spring Summer
Ind ividuals
Figure 4.
Total emergence of male and female Megachile cephalotes in spring and summer seasons
from January 2020 to May 2021.
Insects 2022,13, 1058 6 of 14
For the study of nest architecture, five completely occupied wooden block nests were
collected in May 2020. These nests were similar in length and diameter. The number
of cells ranged from 7 to 8 with minimum and maximum cell lengths of 1.2 and 2.3 cm,
respectively (Table 1). In each nest, all the cells were constructed in a linear series and
aligned horizontally. The construction of the first cell started at the base of the nest (Figure 5).
Before constructing the first cell, female M. cephalotes collected resin and deposited it at the
base of the nest, making a thick layer. The brood cells were slightly rounded at the base
and elongated. The female made several trips to collect pollen and nectar to provision the
brood cells in the form of pollen lobes at the cell base. After provisioning the first cell, the
female laid a single egg on the provision mass. After oviposition, the female made more
trips to collect resin, which was used for cell closure. They made seven to eight such cells
in a single nest. They also left a space (a vestibular cell) ranging from 1.4 to 2.5 cm long
between the outermost brood cell and the nest entrance (Figure 1). The nests were then
plugged with mud or animal dung at the entrance (Figure 5).
Table 1. Nest measurements of Megachile cephalotes-occupied nests.
Nest 1 Nest 2 Nest 3 Nest 4 Nest 5
Nest length (cm) 16 15 15.5 16 16
Nest diameter (mm) 77777
Nest closure Mud Mud Animal
dung Animal
dung Mud
Number of cells 88787
Vestibular cell length (cm) 1.5 2 2 1.4 2.5
Cell length (cm)
1st 1.7 1.8 1.65 2.1 1.8
2nd 1.2 1.6 1.7 1.5 1.65
3rd 1.9 1.5 1.7 1.7 1.3
4th 1.9 1.8 1.5 1.5 1.5
5th 1.7 2 2.3 1.6 1.6
6th 1.3 1.3 1.5 1.4 1.4
7th 1.25 1.2 1.3 1.6 1.4
8th 1.6 1.2 - 1.6 -
Insects 2022, 13, x FOR PEER REVIEW 7 of 15
Figure 5. Samples of wooden plates consisted of Megachile cephalotes larval, pre-pupal, and pupal
stages.
There was a statistically significant difference in the development period of male and
female M. cephalotes. The males became adults earlier than the females, i.e., after 65.30 and
74.78 days, respectively (Table 2). There was no impact of the three locations on the sex
ratio of M. cephalotes. The sex ratio of M. cephalotes was significantly biased toward females
at all three locations (Table 3).
Table 2. Mean development days required for male and female Megachile cephalotes.
Sex Means ± SE t-Critical t-Critical df p-Value
Male 65.30 ± 3.67 1.9803 2.0936 118 0.0384
Female 74.78 ± 2.69
Table 3. Sex ratio of Megachile cephalotes that emerged from nests in CIDS, ERF, and FC.
Locations M:F Sex Ratio Chi-Square p-Value
CIDS 254:568 1:2.0 119.946 <0.0001
ERF 44:121 1:2.8 35.933 <0.0001
FC 118:333 1:2.8 102.494 <0.0001
Grewia asiatica was the predominant pollen grain species found in the brood cells of
M. cephalotes, followed by Alhagi graecorum and Parkinsonia aculeata. Among all plant spe-
cies, the minimum number of pollen grains was found for Rosa indica (Table 4).
1st Cell
2nd Cell
3rd Cell 4th Cell
5th Cell 6th Cell 7th Cell
8th Cell
Figure 5.
Samples of wooden plates consisted of Megachile cephalotes larval, pre-pupal, and
pupal stages.
Insects 2022,13, 1058 7 of 14
There was a statistically significant difference in the development period of male and
female M. cephalotes. The males became adults earlier than the females, i.e., after 65.30 and
74.78 days, respectively (Table 2). There was no impact of the three locations on the sex
ratio of M. cephalotes. The sex ratio of M. cephalotes was significantly biased toward females
at all three locations (Table 3).
Table 2. Mean development days required for male and female Megachile cephalotes.
Sex Means ±SE t-Critical t-Critical df p-Value
Male 65.30 ±3.67 1.9803 2.0936 118 0.0384
Female 74.78 ±2.69
Table 3. Sex ratio of Megachile cephalotes that emerged from nests in CIDS, ERF, and FC.
Locations M:F Sex Ratio Chi-Square p-Value
CIDS 254:568 1:2.0 119.946 <0.0001
ERF 44:121 1:2.8 35.933 <0.0001
FC 118:333 1:2.8 102.494 <0.0001
Grewia asiatica was the predominant pollen grain species found in the brood cells
of
M. cephalotes
, followed by Alhagi graecorum and Parkinsonia aculeata. Among all plant
species, the minimum number of pollen grains was found for Rosa indica (Table 4).
Table 4. Percentage of pollen types used by Megachile cephalotes.
No. of Brood
Cells
Alhagi
graecorum
Grewia
asiatica
Parkinsonia
aculeata
Rosa
indica Prosopis
juliflora
Cajanus
cajan
1 31.22 63.75 1.94 - 3.09 -
2 - 98.67 - - 1.33 -
3 65.54 21.87 - - - 12.59
4 - 19.44 79.05 - 1.51 -
5 - - 98.91 0.45 0.64 -
6 12.76 82.11 5.13 - - -
7 72.12 8.47 11.65 1.17 - 6.59
8 0.67 99.33 - - - -
9 12.68 86.91 0.35 0.06 - -
10 92.39 6.81 - 0.8 - -
11 36.19 62.91 0.75 - - 0.15
12 15.97 84.03 - - - -
13 84.91 - - - 7.33 7.76
14 - 97.05 - 0.25 - 2.7
15 10.11 - 89.73 - - 0.16
The floral host plants of M. cephalotes are presented in Table 5. Females of M. cephalotes
visited six plant species. The maximum visits were recorded on G. asiatica, followed by
A. graecorum,P. aculeata, and Cajanus cajan (Table 5). Resin-producing plants visited by
M. cephalotes are presented in Table 6.
Table 5. Floral host plants visited by Megachile cephalotes.
Plants Family Habit Flower Type
and Color Floral Reward Abundance of
M. cephalotes
Percent
Proportion
Alhagi graecorum Fabaceae H, p Z, pi N, P 21 22.58
Grewia asiatica Malvaceae S, d A, y N, P 47 50.54
Parkinsonia aculeata Fabaceae T, p A, y N, P 12 12.9
Rosa indica Rosaceae d A, w N 1 1.08
Prosopis juliflora Fabaceae S, e, p A, y N, P 3 3.23
Cajanus cajan Fabaceae S, p Z, y N, P 9 9.68
Column 3: H = herb, S = shrub, T = tree, p = perennial, d = deciduous e = evergreen; Column 4: Z = zygomorphic,
A = actinomorphic, pi = pink, y = yellow, w = white; Column 5: N = nectar, P = pollen.
Insects 2022,13, 1058 8 of 14
Table 6. Resin-producing plants visited by Megachile cephalotes.
Plants Family Habit
Acacia nilotica Fabaceae T, E
Prosopis juliflora Fabaceae S, P
Moringa oleifera Moringaceae T, P, D
Column 3: T = tree, S = shrub, E = evergreen, P = perennial, D = deciduous.
Parasitoids
Adult parasitoids of three species emerged from 242 nests of M. cephalotes. Two
belonged to the order Hymenoptera, i.e., Euaspis carbonaria (Megachilidae) (Figure 6a) and
Coelioxys sp. (Megachilidae) (Figure 6b), and one belonged to Diptera, i.e., Anthrax sp.
(Bombyliidae) (Figure 6c).
Insects 2022, 13, x FOR PEER REVIEW 9 of 15
Figure 6. Parasitoids of Megachile cephalotes (a) Euaspis carbonaria, (b) Coelioxys sp., and (c) Anthrax
sp.
4. Discussion
We reported the nesting biology and ecology of Megachile cephalotes for the first time
in Pakistan. In the present study, the maximum number of nests was collected from CIDS,
followed by the FC and ARF. CIDS consists of a natural semi-desert landscape with abun-
dant nesting cavities (cracks or holes in mud walls, hollow tree branches, and bamboo or
reed sheds) and floral resources. The FC is mostly covered with G. asiatica fields that pro-
vide adequate nectar and pollen for bees. High species richness and an abundance of flow-
ers usually favor the species richness and abundance of bees [80,81]. Apparently, there are
factors other than floral availability that can limit wild bees. Empirical evidence shows
that nesting resources affect the abundance of bees. There is a need to study how the avail-
ability of natural nesting resources affects solitary bee populations [82
–
84] since this re-
source is also essential for bee existence.
The results of the present study showed that M. cephalotes remained active from
March to September, comprising the spring and summer seasons. The data over several
years suggest that solitary bees exhibit marked spatiotemporal fluctuations in their abun-
dance and diversity [16]. The species of the Megachilini tribe are reported to have two
generations a year in northwestern India, and emergence occurs from late February or
early March until May and again at the start of August until November [85]. Kunjwal et
al. [86] reported that in India, M. cephalotes is multivoltine by nature and remains active
from March to December. Moreover, they recorded the peak activity of Megachile spp. two
times throughout the year: from March to May and from October to November. Rauf et
al. [14] also found that M. cephalotes remained active from March to November in Punjab,
Pakistan. Kumari and Kumar [85] reported gregarious nesting and foraging behavior in
M. cephalotes that could be helpful for pollination. Depending on the locality and re-
sources, Megachile bees remain active during the hottest months of the year [16]. Several
seasonal and regional factors might affect the voltinism in Megachile bees. For example,
M. rotundata is univoltine in its native range in Eurasia but bi- or multivoltine in North
America, where it was accidentally introduced in the late 1940s [87–90]. Hence, there is a
need to study these factors thoroughly in order to determine their effects on voltinism.
In the present study, female M. cephalotes construct their nests in bamboo sticks and
wooden blocks with lengths and diameters of 15–16 cm and 7 mm, respectively. This spe-
cies preferred to construct its nests in bamboo sticks with diameters ranging from 8 to 10
mm [14] and lengths from 8.2 to 18 cm [54]. In our study, females of M. cephalotes con-
structed 7 to 8 brood cells with minimum and maximum cell lengths of 1.2 and 2.3 cm,
respectively. Previously, the nesting biology of this species had been described in India
[54]. They reported that females construct 7 to 12 brood cells in castor sticks with mini-
mum and maximum cell lengths of 1.0 and 1.8 cm, respectively. The number of brood cells
constructed can vary depending on the sex ratio, nest length, and age of the female provi-
sioner. Cavity nesters typically provision multiple nests. As a female ages and approaches
a
b
c
Figure 6.
Parasitoids of Megachile cephalotes (
a
)Euaspis carbonaria,(
b
)Coelioxys sp., and (
c
)Anthrax sp.
4. Discussion
We reported the nesting biology and ecology of Megachile cephalotes for the first time
in Pakistan. In the present study, the maximum number of nests was collected from
CIDS, followed by the FC and ARF. CIDS consists of a natural semi-desert landscape with
abundant nesting cavities (cracks or holes in mud walls, hollow tree branches, and bamboo
or reed sheds) and floral resources. The FC is mostly covered with G. asiatica fields that
provide adequate nectar and pollen for bees. High species richness and an abundance
of flowers usually favor the species richness and abundance of bees [
80
,
81
]. Apparently,
there are factors other than floral availability that can limit wild bees. Empirical evidence
shows that nesting resources affect the abundance of bees. There is a need to study how
the availability of natural nesting resources affects solitary bee populations [
82
–
84
] since
this resource is also essential for bee existence.
The results of the present study showed that M. cephalotes remained active from March
to September, comprising the spring and summer seasons. The data over several years
suggest that solitary bees exhibit marked spatiotemporal fluctuations in their abundance
and diversity [
16
]. The species of the Megachilini tribe are reported to have two generations
a year in northwestern India, and emergence occurs from late February or early March until
May and again at the start of August until November [
85
]. Kunjwal et al. [
86
] reported that
in India, M. cephalotes is multivoltine by nature and remains active from March to December.
Moreover, they recorded the peak activity of Megachile spp. two times throughout the
year: from March to May and from October to November. Rauf et al. [
14
] also found that
M. cephalotes remained active from March to November in Punjab, Pakistan. Kumari and
Kumar [
85
] reported gregarious nesting and foraging behavior in M. cephalotes that could
be helpful for pollination. Depending on the locality and resources, Megachile bees remain
active during the hottest months of the year [
16
]. Several seasonal and regional factors
might affect the voltinism in Megachile bees. For example, M. rotundata is univoltine in its
Insects 2022,13, 1058 9 of 14
native range in Eurasia but bi- or multivoltine in North America, where it was accidentally
introduced in the late 1940s [
87
–
90
]. Hence, there is a need to study these factors thoroughly
in order to determine their effects on voltinism.
In the present study, female M. cephalotes construct their nests in bamboo sticks and
wooden blocks with lengths and diameters of 15–16 cm and 7 mm, respectively. This
species preferred to construct its nests in bamboo sticks with diameters ranging from
8 to 10 mm
[
14
] and lengths from 8.2 to 18 cm [
54
]. In our study, females of M. cephalotes
constructed 7 to 8 brood cells with minimum and maximum cell lengths of 1.2 and 2.3 cm,
respectively. Previously, the nesting biology of this species had been described in India [
54
].
They reported that females construct 7 to 12 brood cells in castor sticks with minimum and
maximum cell lengths of 1.0 and 1.8 cm, respectively. The number of brood cells constructed
can vary depending on the sex ratio, nest length, and age of the female provisioner. Cavity
nesters typically provision multiple nests. As a female ages and approaches mortality,
cavity nesters tend to build fewer cells per nest since if she dies before completing the nest
closure, the cells will be unprotected.
In the current study, the vestibular cell was recorded in each nest with lengths ranging
from 1.4 to 2.5 cm. Many studies have reported that the majority of Megachile species made
a vestibular cell in each nest [
50
,
53
,
57
,
91
,
92
]. In the present study, female M. cephalotes
constructed their brood cells exclusively using plant resin. Contrarily, Gupta et al. [
54
]
found that this bee solely used mud for its nest construction. Species of the subgenus
Callomegachile mostly collect plant resin but sometimes also collect mud for their nest
construction, hence the name resin bees [
93
]. Plant resin is a versatile material that can
easily be shaped when fresh and structurally rigid when hardened, and it can be used as a
nest substrate or to bind loose structural or camouflaging materials for the construction of
brood cells. Resin is also waterproof, which permits moisture regulation in the nest, and
some resins display potent anti-microbial properties [94–99].
The sex ratio of M. cephalotes was significantly biased toward females at all three
locations. Our results are in agreement with those of Torretta et al. [
91
], who found that
the sex ratio in M. gomphrenoides was female-biased. Contrarily, few studies have found
that the sex ratio of Megachile spp. is male-biased [
51
,
100
]. Nest length, availability of floral
resources, and flight distance from the nest to floral resources are the major factors that
affect the sex ratio of bees. In short nesting cavities, the sex ratio shifted toward the sex
whose brood cells were closest to the nest opening [
101
]. Gruber et al. [
102
] found that
lengths shorter than 15 cm favored male production, which acted as a shield for females
from parasites [
103
]. A female-biased sex ratio is the outcome of rich floral resources,
whereas a male-biased sex ratio is the outcome of low floral resources [104]. Peterson and
Roitberg [
105
] found that more sons were produced with an increase in the flight distance
between the nest and floral resources. Furthermore, females provide fewer resources, which
also results in fewer offspring.
Grewia asiatica was the predominant pollen grain species found in the brood cells of
M. cephalotes, followed by Alhagi graecorum and Parkinsonia aculeata.Megachile cephalotes
exhibited a wider range of plant interactions [
106
]. The yellow flowers of G. asiatica are
zygomorphic with a good “side on” advertisement [
107
]. Bees tend to forage on food
resources near their nest site. Bees exhibit floral constancy as a strategy that targets rewards
and balances energy expenditure, i.e., they tend to feed on the most dominant species
in the landscape [
108
]. Megachilid bees prefer zygomorphic and yellow-colored flowers,
i.e., flowers with high UV reflection and pigmentation patterns and with a “side on”
advertisement [109–112].
In the present study, adult parasitoids of three species, Euaspis carbonaria,
Coelioxys sp.
,
and Anthrax sp. emerged from the nests of M. cephalotes. Similarly, Rauf et al. [
14
]
found that the nests of M. cephalotes were parasitized by E. carbonaria and Anthrax sp.
All three species have already been reported as cleptoparasites of Megachile spp. in different
regions [113–118].
Insects 2022,13, 1058 10 of 14
5. Conclusions
In the present study, we reported the nesting biology and ecology of M. cephalotes for
the first time in the arid zone of Punjab, Pakistan. Megachile cephalotes pursued their nesting
activity in the spring and summer seasons (March to September) and hibernated in the
autumn and winter seasons (October to February). Bamboo sticks and wooden blocks were
the preferred nesting materials of M. cephalotes. Females constructed 7 to 8 brood cells in a
single nest with a male-to-female brood ratio of 1:2.8. Males developed into adults earlier
than females. Grewia asiatica was the major host plant for adults and broods. Future studies
should investigate the effects of ecological and regional conditions on the voltinism of this
bee and develop commercial rearing methods for crop pollination.
Author Contributions:
W.A., A.S. and H.A.G. conceived the research. A.S. and H.A.G. designed the
experiments. W.A., M.A. and K.A.K. collected and prepared the materials. W.A. and A.S. conducted
experiments and collected data. A.S. supervised the experiments. A.S., H.A.G., M.A. and K.A.K.
analyzed the data. W.A., A.S., M.A. and K.A.K. wrote the manuscript. All authors have read and
agreed to the published version of the manuscript.
Funding:
The authors extend their appreciation to the Deanship of Scientific Research at King Khalid
University, Saudi Arabia, for funding this work through the Large Groups Project under grant
number RGP.2/28/43.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Available on demand.
Conflicts of Interest:
The authors declare that they have no conflict of interest that could have
appeared to influence the work reported in this paper.
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