D. R. Frolich and F. D. Parker.
Nest building behavior and development of the sunflower leafcutter bee: Eumegachile (Sayapis) pugnata (Say) (Hymenoptera: Megachilidae).
Psyche 90:193-210, 1983.

Full text (searchable PDF, 2400K)
Durable link: http://psyche.entclub.org/90/90-193.html

The following unprocessed text is extracted from the PDF file, and is likely to be both incomplete and full of errors. Please consult the PDF file for the complete article.

PSYCHE
Vol. 90 1983 No. 3
NEST BUILDING BEHAVIOR AND DEVELOPMENT
OF THE SUNFLOWER LEAFCUTTER BEE:
EUMEGA CHILE (SA YAPIS) PUGNATA (SAY)
(HYMENOPTERA: MEGA CHILIDA E)
BY D. R. FROLICHI AND F. D. PARKER
Bee Biology & Systematics Laboratory
Agricultural Research
Science & Education Administration
USDA
Utah State University, UMC 53
Logan, Utah 84322
Eumegachile (Sayapis) pugnata (Say), formerly Megachile (Say- apis)pugnata Say (Mitchell 198 l), is a large (13-1 8 mm) leafcutter bee that is widely distributed throughout the United States and southern Canada (Hurd 1979). Eumegachilepugnata nests in a wide variety of situations including man-made borings in wood and is easily trapped in the wild (Medler 1964, Krombein 1967, Parker & Frohlich in prep.).
Since E. pugnara is oligolectic to flowers of the Compositae (Tepedino & Frohlich 1982), attention has recently been directed toward developing the bee as a pollinator of commercial sunflower. Parker and Frohlich (1983) described its use in hybrid sunflower pollination; Tepedino and Frohlich (1982) discussed mortality fac- tors, pollen utilization and sex ratio; and Frohlich (1982) described various aspects of its ecology. The purpose of this study was to 'Current address: University of Idaho, SW Idaho Research and Extension Center, Parma, Idaho 83660.
Manuscript received by the editor March 29, 1983.



================================================================================

19831 Frolich & Parker - Eumegachile 195 Figure 1. Glass covered stick and glass tube with plastic insert used for nests, Figure 2,
Schematic drawing showing construction of a partition. Whole leaf pieces are added in sequence (starting with No. 1) and are sealed to the nest wall, each subsequent piece partially covering the previous piece. Figure 3,
Egg in late embryogenesis, attached to provision. Figure 4. Cocoon containing prepupal larva, showing incorporated fecal pellets, with a dissecting microscope fitted with fiber optics lighting (to reduce heat load). Larvae that died and examples of each instar were preserved in picroformalin.
RESULTS
Within-Nest Biology
Females began nesting in the greenhouse 4 June 1981, within 3 days after release. The following is a composite account, in temporal sequence, from selection and preparation of a new nest to nest closure. Each activity discussed was observed for several different females.
Nest Selection - Preparation,
Before beginning cell construc-
tion females investigated both types of potential nest substrates. Sticks and glass tubes that were not covered (darkened) in some way were either ignored or only casually inspected. Usually before pre-



================================================================================

19831 Frolich & Parker - Eumegachile 197 same position as the first thus further sealing the leaf pieces to the walls.
Once the second ring was in place the female continued to add to it by placing more masticated Oenothera on the inside of the ring and chewing and spreading it toward the center with the mandibles until a thin layer of moist leaf pulp covered the whole leaf pieces. Next, moist soil particles (not mud) were collected and placed at the base of the partition. These clods were cut into many tiny slivers which were taken singly or in groups and pressed into the pulpy partition with the mouthparts. These were then tamped in with the head as before. Oenothera and soil particles were retrieved alter- nately until the partition approached its ultimate size. As the partition increased in thickness the periods of tamping with the head grew longer. During the last half hour of partition construction tamping often lasted as long as 5 minutes and became combined with a grooming behavior. Before tamping the female groomed the posterior portion of the abdomen with her hind legs and collected a droplet of fluid that was passed to the middle legs and then the front legs. The fore tarsi with the secretion were then used to wipe down the face and antennae; especially the clypeal and mandibular areas that came in contact with the partition during tamping. Possibly the act of tamping or packing at this point not only shaped and defined the partition but incorporated a secretion as well.
After the last leaf pulp and soil were added the concave surface of the partition was further modified. The female laid on her back and groomed the posterior portion of the abdomen and again passed a droplet of liquid to the middle and fore-legs. This time the secretion was placed between the mandibles and chewed vigorously. The female then chewed and licked the outer surface of the partition. As this was finished, provisioning ensued. No threshold or rudiment of an apical partition was laid down prior to provisioning. Provisioning.
The female first backed into the cell with a load of pollen carried on the abdominal scopa. Deposition of the first pollen load began about 3 mm in front of the basal partition and was spread backwards with the feet in the kicking motion. The pollen was removed first by the hind legs rubbing together toward the middle of the sterna. Pollen remaining on the venter between the



================================================================================

PSYCHE
Vol. 90 1983 No. 3
NEST BUILDING BEHAVIOR AND DEVELOPMENT
OF THE SUNFLOWER LEAFCUTTER BEE:
EUMEGACHILE (SAYA PIS) PUGNATA (SAY)
(H YMENOPTERA: MEGA CHILIDA E)
BY D. R. FROLICH~ AND F. D. PARKER
Bee Biology & Systematics Laboratory
Agricultural Research
Science & Education Administration
USDA
Utah State University, UMC 53
Logan, Utah 84322
Eumegachile (Sayapis) pugnata (Say), formerly Megachile (Say- apis)pugnata Say (Mitchell 1981), is a large (13-18 mm) leafcutter bee that is widely distributed throughout the United States and southern Canada (Hurd 1979). Eumegachilepugnata nests in a wide variety of situations including man-made borings in wood and is easily trapped in the wild (Medler 1964, Krombein 1967, Parker & Frohlich in prep.).
Since E. pugnata is oligolectic to flowers of the Compositae (Tepedino & Frohlich 1982), attention has recently been directed toward developing the bee as a pollinator of commercial sunflower. Parker and Frohlich (1983) described its use in hybrid sunflower pollination; Tepedino and Frohlich (1982) discussed mortality fac- tors, pollen utilization and sex ratio; and Frohlich (1982) described various aspects of its ecology. The purpose of this study was to 'Current address: University of Idaho, SW Idaho Research and Extension Center, Parma, Idaho 83660.
Manuscript received by the editor March 29. 1983.



================================================================================

194 Psyche [VOI. 90
elucidate the within-nest biology of E. pugnata, including develop- ment, nesting and provisioning behaviors, and nest architecture. Within-nest behaviors were observed from a wooden box (lXlX3m) located in a green house (6X6X5m). Nests of 2 types were fastened to cardboard sheets which were then mounted onto the observation box. 1. Elderberry sticks that had been drilled (9mm diameter) and planed lengthwise, were covered with a glass plate to expose the boring; and 2. Glass tubes with plastic inserts were taped to cigarette filters to facilitate handling (8mm diameter) (Fig. 1). The end of the glass tube that served as the nest entrance was dipped in black India ink and inserted into a cork ring to allow the bee secure footing (Torchio 1972). Nests were darkened with paper slip covers until cell construction began. Removal of slip covers after the onset of nesting did not appear to affect females, though no females nested in uncovered nests. A small swamp cooler mounted above the wooden box maintained temperatures below 40å¡ in order to avoid egg-larval mortality due to heat buildup. Commercial Helianthus annuus L. and 3 garden variety compos- ites (Cosmos, Bachelor's Button, Callendula) were provided as pollen and nectar sources in beds of approximately equal size. Because of its usefulness in similar studies of other megachilids (Parker & Tepedino 1982, Frohlich 1983) Oenothera hookeri T. & G. was used as nest partition material. A tape recorder, otoscope, and stopwatch facilitated within nest observations. As nests were completed, most were removed and replaced. Com- pleted nests were incubated at 30å¡ and used to study aspects of larval development and behavior. The glass plates on the elderberry sticks were removed prior to incubation and replaced with clear plastic food wrap. The plastic inserts of the glass tube nests were also removed and provisions containing eggs were cut away and placed separately in BEEM@ capsules, commonly used in electron microscopy. As each egg eclosed, the emergent instar was marked with a tiny spot of pink fluorescent Day-Glo@ powder applied with a watchmaker's forceps. Disappearance of spots indicated molting and new marks were made. Larvae were inspected several times a day and various behaviors associated with each instar were observed



================================================================================

19831 Frolich & Parker - Eumegachile 195 Figure I,
Glass covered stick and glass tube with plastic insert used for nests. Figure 2.
Schematic drawing showing construction of a partition. Whole leaf pieces are added in sequence (starting with No. I ) and are sealed to the nest wail, each subsequent piece partially covering the previous piece. Figure 3.
Egg in late embryogenesis, attached to provision. Figure 4. Cocoon containing prepupal larva, showing incorporated fecal pellets. with a dissecting microscope fitted with fiber optics lighting (to reduce heat Ioad). Larvae that died and examples of each instar were preserved in picroformatin.
RESULTS
Within-Nest Biology
Females began nesting in the greenhouse 4 June 1981, within 3 days after release. The following is a composite account, in temporal sequence, from selection and preparation of a new nest to nest closure. Each activity discussed was observed for several different females.
Nest Selection - Preparation.
Before beeinning cell construc-
tion females investigated both types of potential nest substrates. Sticks and glass tubes that were not covered (darkened) in some way were either ignored or only casually inspected. Usually before pre-



================================================================================

196 Psyche [VOI. 90
paring her nest a female would sit quietly at the back of the stick or just inside the entrance for a few minutes to an hour. Once a choice was made, extraneous pith particles were picked up with the man- dibles and jettisoned outside of the nest during flight. Females did not make the nest walls completely smooth but cut away gross irregularities with the mandibles and removed large pith particles. As many as 24 pith removal trips were observed before nest initia- tion. During this period of preparation females were especially sen- sitive to any activity around the nest site. On several occasions females abandoned nests when an observer approached the nest entrance. In general nesting E, pugnata were very wary of intruders. Partition Building.
Basal and apical partitions of each cell were constructed similarly and were composed of the same materials so construction details of each will be considered together. After preparing her nest site for cell construction the female left the nest to retrieve a strip of 0. hookeri leaf. The bee landed on the plant, straddling the leaf, and quickly cut, while walking backwards, a thin strip Vi to % as long as her body, and returned to the nest. After entering the nest with the unmodified leaf in her mandibles the female masticated it into a shiny ball which was pressed into the back wall, or along the floor where the cell was to be initiated. From the leaf material a thin ring of moist chewed leaf was formed around the inner circumference of the tunnel. Three to 6 trips were usually required to complete the ring. The female then left and returned with a large oval-shaped leaf piece that was carried beneath the body by all 6 legs and the mandibles.
The mandible and front legs were used to spread and position the leaf piece along a portion of the chewed ring thus closing a portion of the circle (Fig. 2). The outer edge of the unmodified leaf confluent with the ring was chewed into the ring and the 2 were sealed. The female also used her head in an extremely fast jackhammer-like motion to tamp the ring and leaf pieces together. The clypeus and proximal outer surfaces of the mandibles appeared to be the point of impact. Subsequent leaf pieces were brought in and fastened to the ring in the same manner until the base of the cell was covered (Fig. 2). Three or 4 oval-shaped leaf pieces were required to form the base of the partition. After the leaf pieces were positioned more masticated Oenothera strips were used to form a second ring in the



================================================================================

19831 Frolich & Parker - Eumegachile 197 same position as the first thus further sealing the leaf pieces to the walls.
Once the second ring was in place the female continued to add to it by placing more masticated Oenothera on the inside of the ring and chewing and spreading it toward the center with the mandibles until a thin layer of moist leaf pulp covered the whole leaf pieces. Next, moist soil particles (not mud) were collected and placed at the base of the partition. These clods were cut into many tiny slivers which were taken singly or in groups and pressed into the pulpy partition with the mouthparts. These were then tamped in with the head as before. Oenothera and soil particles were retrieved alter- nately until the partition approached its ultimate size. As the partition increased in thickness the periods of tamping with the head grew longer. During the last half hour of partition construction tamping often lasted as long as 5 minutes and became combined with a grooming behavior. Before tamping the female groomed the posterior portion of the abdomen with her hind legs and collected a droplet of fluid that was passed to the middle legs and then the front legs. The fore tarsi with the secretion were then used to wipe down the face and antennae; especially the clypeal and mandibular areas that came in contact with the partition during tamping. Possibly the act of tamping or packing at this point not only shaped and defined the partition but incorporated a secretion as well.
After the last leaf pulp and soil were added the concave surface of the partition was further modified. The female laid on her back and groomed the posterior portion of the abdomen and again passed a droplet of liquid to the middle and fore-legs. This time the secretion was placed between the mandibles and chewed vigorously. The female then chewed and licked the outer surface of the partition. As this was finished, provisioning ensued. No threshold or rudiment of an apical partition was laid down prior to provisioning. Provisioning.
The female first backed into the cell with a load of pollen carried on the abdominal scopa. Deposition of the first pollen load began about 3 mm in front of the basal partition and was spread backwards with the feet in the kicking motion. The pollen was removed first by the hind legs rubbing together toward the middle of the sterna. Pollen remaining on the venter between the



================================================================================

198 Psyche [VOI. 90
fore and mid-legs was scraped off initially by the mid-legs and then the fore-legs. Both pairs of legs then transferred the pollen to the hind legs where it was deposited by rubbing the legs together in a "hand washing motion." Pollen removal by the legs was aided by a complementary telescoping motion of the abdomen and elevation of sternal hairs. As the legs brushed pollen from the side, toward mid- sternum and backwards, the abdomen contracted so that the tarsi came in contact with the entire surface of the abdomen. The abdo- men then elongated and the contraction-brushing motion began again.
The first load of nectar was brought in on the second provisioning trip. The female entered head first and picked up the pollen left on the first trip with her mouthparts, mixing nectar and pollen into a moist paste that she spread over the concavity in the basal partition. She then went to the nest entrance, turned around outside on the nest face, backed in, and kicked any pollen remaining from the first deposition toward the partition. Before pollen deposition this time the female arched her body into a 'U' shape, with head and abdomen as its highest points. Front legs and hind legs were placed approxi- mately halfway up opposite walls of the nest, while mid-legs rested on the floor. The abdomen was arched and was backed into the cavity of the basal partition. Pollen removal then proceeded as before and the load fell into the concavity or onto the floor in front of the partition. On subsequent trips the female entered head first, swinging her head back and forth as she approached the provision, picking up stray pollen with her mouthparts. The dry pollen from the previous trip was then chewed and mixed with nectar to form a paste which she molded into a loaf with her mandibles. Pollen was then deposited atop the growing provision and the sequence was repeated.
Prior to nectar regurgitation, the bee usually cleaned her face and antennae, removing pollen with her front legs and passing it to her hind legs, where it was deposited along the sides of the abdomen. She also stopped just in front of the entrance and preened again before embarking on the next foraging trip. Once the pollen loaf was approximately Vz its ultimate size the female used the abdomen tip to plunge a shallow hole in the loaf after each pollen deposition. This hole was then filled with nectar on



================================================================================

19831 Frolich & Parker - Eumegachile 199 the next trip and masticated. Dry pollen was deposited on it and a new hole was formed with the abdomen tip. This behavior con- tinued until the provision was about % its ultimate size whereupon the female tended to sprinkle pollen evenly over the entire surface. Nectar was also deposited more uniformly and the whole surface was chewed after each trip, incorporating pollen and nectar. On the last few pollen trips the bee used her face to flatten the vertical surface of the pollen loaf, using a motion similar to the tamping during partition construction.
Oviposition and Cell Closure. Once the cell was provisioned the female collected an unmodified Oenothera strip. She masticated it into a moist ball and wiped down the floor in front of the provision, picking up loose pollen. As when making the basal partition she used the leaf pulp to form a ring around the inner circumference of the tunnel close to the edge of the pollen loaf. Two or 3 leaf gather- ing trips sufficed; the ring was the initiation of the apical partition. The leaf pulp ring completed, the female made 3 or 4 more forag- ing bouts each time returning with only nectar. On returning from the first bout the bee plunged her mouthparts deeply into one side of the face of the provision and continued to do so in an extremely fast up and down fashion for several seconds. With the mandibles mov- ing in a cutting fashion much of the provision was pushed to the side opposite the female. After the next trip the other side of the pollen loaf was worked in a similar fashion until the front half of the entire provision had been thoroughly kneaded. At the end of the final foraging bout the female regurgitated a large quantity of nectar onto the middle of the provision face and plunged her mandibles in an around its center until a small wet hillock was formed. The front half of the provision was thoroughly wetted with nectar and appeared much darker in color than the back half. This completed, the female turned around at the entrance, backed in and oviposited. As she backed into the cell, she inserted her ovipositor into the upper half of the hillock, appearing to anchor to the provision. A series of pumping motions forced the egg onto the hillock where it appeared to sink into the nectar. When the egg was about halfway extruded from the female the pumping motions ceased and she pulled away, leaving the anterior portion of the egg free and at about a 45O angle (Fig. 3). During oviposition the female remained



================================================================================

Psyche
[Vol. 90
fairly rigid with the exception of the abdominal pumping motion and a slight rocking of the body. The head was cocked downward somewhat and the antennae wiggled slightly. The whole process lasted about 60 seconds.
Immediately after oviposition the female left the nest and returned with leaf material. Most often this was a large oval-shaped piece that was sealed to the leaf pulp ring. An occasional female returned with Oenothera strips and added to the ring but most often the entrance to the cell was immediately closed by adding the oval- shaped pieces. Once the cell was closed, the apical partition was constructed in the same manner as the basal partition. In almost all nests at least 1 partition, not associated with a provisioned cell, was constructed in the front of the nest to form a vestibular and an intercalary cell. This partition was constructed in the same manner as partitions defining provisioned cells, i.e., soil, leaf pulp, and whole leaf pieces were incorporated. The nest plug made to close the entrance was also constructed of the same mate- rial as partitions but was considerably thicker. The behaviors involved in plug construction were identical to those involved in partition formation. In addition to size, the closing plug differed from partitions in that it was often a series of partitions interspersed with soil and leaf pulp placed one atop the other. The outside sur- face of the plug was also different in that it contained much more soil than partition surfaces. Often what appeared to be pure soil was found on the outside surface of the plug, although leaf pulp was still used as the binding matrix.
Usually E. pugnata built 1 cell a day, but occasionally some females began provisioning a second cell. In the greenhouse E. pug- nata provisioned cells in the morning when pollen was available and built partitions and plugs in the afternoon and early evening hours. Cell provisioning took 3.5 hours on the average. The number of pollen-nectar trips per cell varied from 36-44. Nectar and pollen deposition took roughly the same amount of time; nectar deposition = 38.7 sec. (standard deviation, sd = 12.3), pollen deposition = 32.4 sec. (sd = 6.6). Foraging trips ranged from 2 min. 28 sec. to 9 min. 22 sec. and averaged 4 min. 59 sec. (sd = 1 min. 38 sec.). Plug and partition construction took approximately the same amount of time as provisioning so that a nest with 1 cell, 1 intercalary partition and



================================================================================

Frolich & Parker - Eumegachile
a plug took about 7 hours to complete. Approximately 15 Oeno- thera, 15 soil, and 3-4 large oval leaf collecting trips were required per partition. Plug construction required roughly twice those num- bers. Collection of oval leaf pieces took longer than collection of Oenothera strips (Z = 1 min. 23 sec., sd = 49 sec. vs F = 40 sec., sd = 9.4 sec.) and soil collecting trips were shortest of all (E = 22.5 sec., sd = 7.7 sec.).
In most cases females constructed nests in hollow sticks. How- ever, when undrilled sticks, with shallow (5 mm) starter holes drilled in the side, were placed in the greenhouse for use by another bee 2 E. pugnata widened the cavities and nested therein. Development
Egg Hatching. The egg, which was attached to the provision by its posterior VA, was opaque when deposited but gradually became translucent as it developed. It measured 1-1 '/2 mm wide anteriorly and posteriorly, 3-4 mm in length, and was straight (Fig. 3). Embryogenesis took an average of 5.1 days at 30å C (Table 1) and some structures became grossly visible through the chorion approxi- mately 1 day before eclosion.
Eclosion usually took from 10 to 12 hours and became evident with the appearance of a clear fluid-filled area in the region of the poste- rior attachment. At this time the dorsal vessel, spiracles and major tracheal branches were visible. As the fluid increased in the poste- rior pole the embryo exhibited undulating waves that passed from anterior to posterior and perhaps aided in concentrating the fluid in the posterior region. Thus, the chorion was stretched very tightly over the head of the enclosed embryo. After fluid disappeared from the posterior pole the embryo appeared to remain quiescent for a short time. Fluid then began to collect at the anterior pole of the egg, accompanied by undulating waves moving in the opposite direction (posterior to anterior). As the chorion became tightly stretched over the posterior embryo a longitudinal-lateral split in the chorion became visible at the level of the spiracles. This rupture divided the chorion into upper and lower halves. As the pressure and peristaltic waves receded the lower half of the chorion slipped from the larva and came to lay directly between it and the pollen