C. H. Hicks.
Parasites and Habits of Dianthiedium pudicum Cresson.
Psyche 34:193-198, 1927.

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PSYCHE
VOL, XXXIV. DECEMBER 1927 No. 6
PARASITES AND HABITS OF DIANTHIDIUM PUDICUM CRESSON
CHARLES H. HICKS,
University of Colorado.
The habits of Dianthidium pudicum Cresson1 have not previously been known, as far as it can be learned from a review of the literature. The following account is based on studies of the species, at or near Boulder, Colorado. D. pudicum builds cells of pebbles and resin, placing them in depressions or attaching them to the sides of rocks, in fields and open places. Nests of this bee were first taken in the fall of 1925. Many have since been found at all seasons and, during the summer of 1926, observations were made on the constructing and provisioning of a nest.
Cells have been taken from the stones, brought to the labo- ratory where they were kept at room temperature, and the insects reared. In this way a number of bees and several par- asites have been obtained.
From a nest secured April 11, 1926 at East Boulder, a male and female parasitic wasp, Eusapyga proxima Cressonz, emerged on May 12, 1926; a female wasp May 14; a male D. pudicum May 18; and a male wasp on May 21.
Specimens of E. proxima
have emerged from some other nests of D. pudicum and always from the cocoon of the latter insect. This fact shows that the parasite lives on the tissues of the young bee larva or pupa and does not early crowd it out, using its food, as do certain bees living in the cells of other bees (e. g. Stelis sexmaculata on Al- cidamea producta)3.
kindly determined by Professor T. D. A. Cockerell. This wasp has been determined by Mr. S. A. Rohwer. 3Reported by Graenicher, 1905.




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194 Psyche [December
Nests of D. pudicum, although not very rare, are rather difficult to find, because of the fact that they often closely re- semble in color the rock to which they are attached. Again, they may fill in a depression, giving the rock a smooth outline and therefore easily overlooked. Many fields, in which these bees nest, are nearly covered with rocks and the task of finding ,
the ones used is great. However, a bee sometimes selects a very light or white rock and builds upon it a nest consisting of dark pebbles.
When the weather is dry, the pebbles and resin become very hard and the nest is difficult to remove. Rain or very moist weather softens the material and may aid in making it easier for the mature insect to emerge.
The number of cells to a nest have varied from 2 to 8. A cocoon, which appeared to be of average size, measured 9 mm. in length from the tip of the n~ammillary projection to the base of the cocoon.
The width at the center was a little over 4 mm. The base is slightly curved; the apex flat except for a short, blunt man~millary point.
This point was much lighter than the
dark, yellowish brown cocoon.
Observations were made on the habits of a bee of this species found nesting on a rock at Owens' Lake, late in the afternoon of August 24, 1926. When located one cell had already been constructed, with t'he orifice down. This opening was clear cut, or sharply and very neatly outlined. At 6 p. m. the female was resting within, where she spent the night, with the posterior part of her body towards the outside. Some data were obtained on following days, part of which are given below. August 25. By 11 a. m. the orifice of the first cell was closed and a second had been started. The bee was now carrying resin and pebbles to the nest. Later, when she was walking over it slowly, as though inspecting it, a male came and mated with her on the finished cell. The period of copulation was of about 30 seconds duration.
August 27. The bee was observed flying about in the morning, probably gathering honey.
August 31. To-day, the fourth cell has been made. The place and order of occurrence had been noted on previous days.



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19271 Parasites and Habits of Dianthidium pudicum Cresson 195 Three of the four cells were finished.
The second was to the
right of the first; the third to the left of the first; and the fourth above and over the first, being attached to the rock above and partially covering the finished cell. At 9:46 a. m. the bee re- turned pollen laden, from a collecting trip. She entered the cell head first, and stayed within 20 seconds. She then came out, backed in to deposit the pollen and remained 35 seconds. Later in the day, when she was collecting resin, it was observed t>hat she averaged 7 minutes in securing a load. She carried the lump of light colored resin in her mandibles and deposited it in the anterior part of the unfinished cell.
September 2. At 3 p. in. a fifth cell had been made. The sky being overcast, the bee was inside resting. The cell was above the second and parallel to the fourth. The opening was down, as has been found true of all others observed in the process of construction. Later in the afternoon, the bee was seen to be smoothing the inside of the cell with her mandibles. September 4. To-day, a sixth cell was partly finished and the bee was seen for the last time and no further work was done. The nest was taken home September 26.
Considerable time was spent in observing the bee construct- ing the cells. The resin, which had been placed in the anterior part of the cell after each collecting trip, was used as needed. The bee would take some of the resin and place it on the edge of the cell, often between two pebbles. Then she would fly to the ground and select a pebble, sometimes from very near and again as far as six feet away. The pebble was carried in her mandi- bles to the nest, where the legs and thorax were used to fit it, into place. It is worthy of note that the bee endeavoured to '
place the pebble where she had previously put the resin. If the pebble did not hold, as was sometimes the case, she would get some more resin and place it usually on the same spot. The pebble dropped was never immediately utilized again, but a new one selected. However, since she often gathered those near, she sometimes later used the ones previously tried.



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196 Psyche [December
In placing a pebble in a crevice or on a resin extension, the pebble was turned and rearranged, by means of the legs and abdomen, much as a mason fits a stone into place. The pebble remaining, the bee placed resin on its free edges and another was brought. Sometimes when a pebble did not fit into place, the bee tried it all about the edge of the cell in an attempt to get it to hold. After a few trips to the cell under construction, the bee was seen to carry a pebble and place or fit it onto the general surface of the outside of the other cells, mainly in the depressions be- tween them. This helped to break the outlines of the individual cells and make the surface more even, as well as make the walls thicker and the protection greater. Another nest of this bee, also found at Owens' Lake during this period, showed consider- able thickness of resin and pebbles placed after the cells had been made. Old nests, from which bees have emerged, often show little or no trace of individual cells, probably due to the heat making the resin soft and allowing the material gradually to settle.
The contents of the cells, of the nest observed, were examined on September 26, with the following facts noted. A cocoon was found each in cells 1 and 3; but larvae in 4 and 5. Number 2 contained much pollen and a small dead larva. The lower end of the first cell had been closed with a layer of pebbles and resin about one millimeter thick The upper end of the inner space of the cell was filled with a cocoon, surrounded with pellets of excre- ment; the lower part contained a space partly filled with ex- crement. The cocoon possessed a very distinct mammillary projection which extended downward. The head of the larva has always been towards this point.
The length of a typical cell has been found to be 15 mm. At the end opposite the location of the orifice the mass of pollen, filling the cell for a distance of 5 mm., is stored. The remaining 10 mm. of space is at first empty; later, when the larva has developed, part of the space is filled with the cocoon and part with excrement.
On October 3, the larva of cell number 4 had a fully formed cocoon which had been started October 1. The mammillary point first consisted of a round hole, with a white outer surface



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19271 Parasites and Habits of Dianthidium pudicum Cresson 197
of silk. The larva of number 5 started a cocoon on October 6. It was at first very thin and white and early had a mammillery point apparently closed. The following day the cocoon was more compact and darker. A few days later it had quite its normal color.
On January 31, 1926 a nest, agreeing in all points of con- struction with nests of D. pudicum, was found attached to a rock along the railroad of East Boulder. Four female and one male Monodontomerus montivagus Ashmead emerged from a typical Dianthidium cocoon on February 20. A single hole was chewed through the side of the cocoon, all emerging through this open- ing.
The male was observed to mate with two females. When
he first alighted on the female, she vibrated her antennae very rapidly, after which she remained nearly motionless. The male, well forward on the female, continued a rather periodic raising and lowering of his antennae, moving first the one and then the other. Frequently he would raise his wings, vibrate them rapidly for a second, then lower them until the performance was re- peated again in about 20 seconds. After 3 minutes the male moved back and copulation was effected, lasting but a second. , From another cocoon a wasp, Odynerus (Stenodynerus) n. sp.4 which appears to be parasitic on D. pudicum, emerged on March 5. No other insects emerged and on May 5 the remaining two cocoons were opened. Each contained a wasp, nearly mature, . but dead. These wasps were not easily determined but appeared to be young of E. proxima. The nest had been used a number of times as was evidenced by the fact that used cocoons were found, one within another, to the number of seven. While no bees were reared from the nest,, the cocoons, type of nest, etc., were so typically those of D. pudicum that it has seemed safe to consider it as such.
A nest, also agreeing with the nests of D. pudicum taken here, was found in the summer of 1926 by Mrs. Hicks at Uva, some 6 miles north of Wheatland, Wyoming. One of the cocoons of this nest contained dead, but nearly mature parasites, M. montivagus.
4Kindly determined by Mr. S. A. Rohwer. More evidence should be ob- tained before definitely ascribing this wasp a parasite of D. @.&cum.



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198 Psyche [~ecem ber
Bibliography.
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Fabre, J. Henri, Bramble-bees and others. Engl. trans. New
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Friese, H., Die europaischen Bienen (Apidse). 297-307. Berlin und Leipzig. 1923.
Grcenicher, S., "Some Observations on the Life History and Habits of Parasitic Bees."
Bull. Wisconsin Nat. Hist.
SOC., 3: 153-167. 1 pi. 1905.
Hicks, Charles H., "Nesting Habits and Parasites of Certain Bees of Boulder County, Colorado. Univ. Colo. Studies, 15: 217-252. 1926.
Hungerford, H. B., and Williams, F. X., '(Biological Notes on some Kansas Hymenoptera." Ent. News, 23: 241-260. PIS. XIV-XV. 1912.
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10 figs. 1902.




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