G. D. Alpert and P. O. Ritcher.
Notes on the Life Cycle and Myrmecophilous Adaptations of Cremastocheilus armatus (Coleoptera: Scarabaeidae).
Psyche 82(3-4):283-291, 1975.

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NOTES ON THE LIFE CYCLE AND
MYRMECOPHILOUS ADAPTATIONS OF
CREMASTOCHEILUS ARMATUS
(COLEOPTERA : SCARABAEIDAE)
Adult cetonine scarabs of the genus Crernastocheilus are known for their association with ant colonies (Wheeler, 1908). The genus consists of approximately 40 species and has been recorded only in North America north of the Isthmus of Tehuantepec (Howden, 1971 ). Twenty-three species have been collected with I I different genera of ants, yet their true relationship with the host ants remains unknown. Cazier and Statham (1962) and Cazier and Mortenson (1965) have summarized current knowledge of the genus based largely on their own studies of adult bionomics of several species from Arizona. The only information, however, on the development of the immature stages of this genus is a few scattered notes that the larvae of some species do occur in ant nests (Mann, 1911 ;
Wheeler, 19083; Windsor, 1964; and Ritcher, 1966). This is the first account of the life history and development of C. armatus Walker, a western species (Fig. I) occurring with different species of Formica ants from British Columbia to California and Nevada (Potts, 1945). The major host ant, F. obscuripes Forel. is one of the most common mound building ants in western North America. A very pugnacious and aggressive ant, obscuripes builds large mounds of soil and vegetation containing 50,000 or more individuals (King and Walters, 1950). How armatus su-vives from egg to adult w'thin these nests was the object of field and laboratory studies.
The following account is a synthesis of results obtained in western and central Oregon from
1957 to 1961 and eastern and western
Washington from 1970 to 1975. All four study areas were charac- lMuseum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138.
department of Entomology, Oregon State University, Corvallis, Oregon 97331.
Manuscript received by the editor December 29, 1975. Psit-fie 81:281-W t 1975). http:l/psycb cnlclub orBig1Ìö1-28 html



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Psyche
[September-December
Figure 1.
lections and
on field col-
terized by regions of high host ant density and the presence of a large population olf armatus adults and immatures. Nest material was sorted, beetles were counted, and observations made on interactions with ants. All nest material was replaced to minimize the adverse .
impact of the sampling technique. The sex of the adult was identified in the field and later verified under a dissecting microscope. The sex was determined by evident geometrical differences of the last ventrite and the pygidium.
Adults and larvae were kept in the laboratory for many months with and without host ants. Larvae were most successfully reared in containers filled with original ant nest material. Adults were kept in closed containers at below room temperatures during the winter and were fed ant larvae the following spring.



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19751 Albert and Pitcher - Cremastocheilus armatus 285 LIFE HISTORY
E.
During the month of May, females laid eggs scattered throughout the outer soil edges of the ant nest. Here rich deposits of vegetative debris had accumulated and ant activity was low. Under laboratory conditions 'females laid a total of 3 to 12 eggs each. The broadly oval white eggs (Fig. 2) hatched after two weeks. First larval instars were collected until the middle of June. Second instars were found from June until the middle of July, and third instars were collected from the middle of June to the middle of August. The pupal stage lasted two more weeks, indicating that under field con- ditions development from egg to adult occurred in less than 4 months. Most ant nests contained fewer than 30 larvae, although several nests contained well over 200. Second and third instars were gre- garious, feeding within the vegetative debris just below the soil surface. Late third instars were darkened posteriorly due to the large number of fecal pellets retained in the abdomen. When un- covered, the larvae were quickly seized and bitten by many ants. They escaped the ants by rapidly burrowing down through the nest material. Late third instars left the outer soil edges and moved inward towards the center of the thatch mound to pupate. This took place during the hotter days of July when the ants were not very active in the upper mound area.
In the dry twig area above the ants' brood chamber larvae con- structed elliptical earthen cases within which they pupated (Fig. 3). Easily damaged when newly formed, several of these pupal cases soon dried and hardened together into a protective clump. Adults eclosed during the late summer days and a few could be found on the surface of ant mounds at this time (Fig. 4). As colder weather approached, the beetles moved deeper within the nest, often ending up a meter or more below the soil surface. Here the adults overwintered surrounded by dormant ants (Fig. 5). Periodic collections of overwintering adults revealed that within a few minutes at room temperature the beetles became active, even if temperatures outside the nest were below loO C. Females often laid several eggs within a few days at room temperature but none of the eggs laid during the winter period hatched. The following spring the adults moved back up to the outer areas in the mound- Most of the adults were collected within 3 centimeters of the nest surface at this time. Flight was so rapid at temperatures above 24' C. that mark and recapture methods were unsuccessful in determining the flight range. During this same period adult beetles



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Figures 2-4.
Developmental stages of Cremastorhe-ilus armuiu% (2) Egj (3) Late third larval instar insirie earthen case. (,+.), Adult. (Scale: fi, 2 ~2rnm; figs. 3 and 4= 4rnm).
1 ,




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19751 Albert and Ritcher - CreinastocheiZus armatus 287 readily fed on ant larvae and pupae. As many as 85 pairs (male and female) of adult C. armatus were collected in the outer nest galleries. Although they were not in copula, the females later laid fertile eggs. No mating was ever observed in the nest or in the laboratory. Data from museum collections indicate a peak of flight activity during April and May, the time during which mating may occur. Gravid females normally laid their eggs below the surface at the periphery of the nest.
Host records fox armatus are probably incomplete (Table I ) . F. obscur'ipes is the most common host but dispersal flights may introduce these beetles into a wide variety of ant nests. In western Oregon adults were collected from Formica fusca mounds, although immature stages were never found there.
Larvae have been collected
and reared from rich garden soil in western Oregon (Ritcher, 1966) indicating that under certain circumstances the immature stages may not have an obligatory relationship with ants. Table 1. Host records for Cremastocheilus armatus Host Locality Collector Life-Stage Reference Formica
ebscuripes
Formica
fmca
Formica
subpolita
camponoticeps
Formica
integra
tahoensis
Formica
integroides
su bnitens
E. Wash.
W. Wash.
W. Oregon
British
Columbia
E. Oregon
British
Columbia
Mann adult/larvae
Alpert idult/larvae
Pitches: adult
Howden adult
Ritcher adult/larvae
Ayre adult
Mann (1911)
New Record
New Record
Cazier (1962
Ritcher (1966)
Cazier (1962)
To examine escape behavior, larvae were removed from the ant nests and placed in a series of containers with one to several ants. The normal feeding position of the larva is a C-shaped curve with the head and anal area closing off the ventral region from attack. The



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288 Psyche [September-December
ants readily attempted to bite the larvae but were unable to grasp a larva firmly with their mandibles from a dorsal approach because the dorsal surface was too convex. If however an ant came into contact with the head or ventral region there was a very rapid strike response from the larva. The larva struck at the ant with its mandibles as it coiled more tightly into the C-shape. A dark fluid was released from between the larval mandibles at the time of the strike. As the larva wriggled to escape, several wet fecal pellets were expelled which had a deterrent effect on aggressive ants. There was also a strong, unpleasant odor associated with the mandibular and anal secretions.
The above reaction was repeated until the mandibles made con- tact with and crushed the body of the ant. When this happened the ant immediately released its grasp of the larva and within a few seconds it collapsed. Movement was usually limited to tremors of the appendages until death occurred. Occasionally a beetle larva was fatally injured by attack from too many ants. The mandibular strike was most effective when a minor worker ant was attacked by a third instar larva.
When first attacked, the beetle assumed a characteristic death feigning posture with all its legs out and slightly up at the sides. In the laboratory this position was seldom held for less than 5 minutes and showed little habituation. The ants grasped the beetles by their legs and pronotal projections and dragged them randomly about, eventually releasing their hold. Host ants regularly attacked beetles on the mound surface but as the beetles burrowed down into the thatch, most of the ants were removed. Beetles were able to penetrate the mound surface in less than one minute. In addition the beetle's heavily sclerotized integument, retractible an- tennae, and concealed mouth parts also represent adaptations for survival in ant nests.
If the beetle was violently disturbed or turned over by the ants, a droplet of viscous fluid was released from the anal opening. This fluid had an offensive odor and was effective in repelling the ants. When an ant came into physical contact with this fluid, it became agitated and spent considerable time grooming. Defensive
secretions have been documented for other myrmecophiles (Holl-
dobler, 1970; Blum et. al., 197 I ) and their discovery in other species of Cremastocheihs is' expected.




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Albert and Ritcher - Cremastocheilus armatus 289
ADULT
PUPA
3RD INSTAR
2ND 1NSTAF
1ST INSTAR
EGG
I
I
I
I
I I
APR
MAY JUN
JUL
AUG SEP
Figure 5. Seasonal distribution of the developmental stages of Crema- stocheilus armatus collected from Formica obscuripes ant mounds. During the spring adult beetles were predaceous on both ant larvae and pupae. In the field beetles were found feeding on larvae near the brood chamber while .at the same time beetles in the outer galleries were motionless, suggesting that individuals moved into the center of the nest to feed and returned to the periphery when satiated. In the laboratory predation increased when beetles were deprived of food
for over one month and when containers were darkened. It was not unusual for several beetles to feed on one ant larva at the same time.
Unlike other scarabs, Cremastocheilus has an unusual cupshaped mentum
which prevents ants from contacting the beetle's mouth parts. When feeding, a beetle lowered its mentum and pierced an ant larva with its sharp maxillae. The mandibles are greatly reduced and aid in the transport of fluid.
Feeding lasted from 10 to 30
minutes as the beetle slowly pumped the ant larva dry. Beetles were not disrupted from feeding even when covered with attacking ants.




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290 Psyche
[September-December
C. armatus has fed on the larvae and pupae of the carpenter ant, Camponotus sp. in the laboratory (J. T. Doyen, pers. comm.). The larvae and pupae of other species of non-host Formica sp. have also been consumed. This lack of specificity may account for those species of ants that serve as alternate hosts, and for the wide dis- tribution of armatus.
Holldobler ( I 97 I ) has shown that myrmecophiles have the ability to communicate in the same chemical language as their hosts. Tri- chomes are tufts of hairs that serve to increase the ability of well- integrated ant guests to communicate chemically. They are located on the ventral surface of highly modified anterior and posterior pro- notal projections of Cremastocheilus adults. The pronotal projec- tions have been cited as being modified to fit the mandibles of ants and to contain glands which emit a stimulating and attracting odor (Wheeler, 1908). It has been proposed that these beetles are brought into the nest and held captive by the ants because of this odor (Cazier and Mortenson, I 965 ) .
The role of trichomes in the relationship of C. armatus to its host, 8'. obscuripes, is unknown. The ants do not appear to be specifically attracted to trichome areas nor are the beetles held captive by the ants. C. armatus is usually found unattended by ants within the nest, and is attacked by ants when on the nest surface. The writers extend their appreciation to J. T. Doyen and J. A. Chemsak, U. C. Berkeley for their valuable field and laboratory data. J. T. Doyen also provided data concerning predation on Camponotus so. larvae and pupae, including the suggestion that body fluid was being pumped from the prev. H. F. Howden, Carleton Univ., Canada identified the Cremast~ocheilus, and D. R. Smith, U. S. N. M. identified the ants. We also thank Terri Alpert and Don Frechin for their help in collecting field data. BLUM, M. S., R. M. CREWE, AND J. M. PASTEELS 1971. Defensive secretion of Lomechusa strumosa, a myrmecophilous beetle. Ann. Entom. Soc. Amer. 64 (4) : 975-976. CAZIER, M. A. AND M. STATHAM
1962. The behavior and habits of the myrmecophilous scarab Crema- stocheilus stathamae Cazier, with notes on other species. J. New York Entom. Soc. 70: 125-149.




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19751 Albert and Ritcher - Cremastocheilus armatus 291 CAZIER, M. A. AND M. A. MORTENSON
1965. Bionomical observations on myrmecophilous beetles of the genus Cremastocheilus (Coleoptera : Scarabaeidae) J. Kansas Ent. Soc. 38: 19-44.
HOLLDOBLER, B.
1970. Zur Physiologie der Gast-Wirt-Beziehungen (Myrmecophilie) bei Ameisen 11. Das Gastverhaltnis des imaginalen Atemeles pubi- collis Bris. (Coleoptera: Staphylinidae) zu Myrmica und Formica (Hymenoptera : Formicidae) 2. vergl. Physiol. 66 : 215-250. 1971. Communication between ants and their guests. Scientific Ameri- can, March: 86-91.
HOWDEN, H. F.
1971. Key to the new world Cremastocheilini, with notes and descrip- tion of a new genus. Proc. Entom. Soc. Wash. 73 (2) : 224-230. KING,..R. L. AND F. WALTERS
1950. Population of a colony of Formica rufa melanotica Emery. Iowa
Acad. Sci. 57: 469-473.
MANN, W. M.
1911. On some northwestern ants and their guests. Psyche 18: 102-109.
POTTS, R. W. L.
1945. A key to the species of Cremastocheilini of North America and Mexico (Coleoptera : Scarabaeidae) Bull. Brooklyn Entom. Soc. 40: 72-78.
RITCHER, P. 0.
1966. White Grubs and their Allies, a Study of North American Scarabaeoid Larvae. Oregon State Univ. studies in Entom. 4: 1-219.
WHEELER, W. M.
1908. Studies on myrmecophiles. 1. Cremastocheilus J. New York Entom. SOC. 16: 68-79.
1908a. The ants of Casco Bay, Maine, with observations on two races of Formica sanguinea Latreille. Bull. American Museum of Nat. Hist. 24: 619-645.
WINDSOR, J. K., JR.
1964. Three scarabaeid genera found in nests of Formica obscuripes: Fore1 in Colorado. Bull. So. Calif. Acad. Sci. 63 (4) : 205-209.



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