Geraes, J. - Hindawi Publishing Corporation...column at Minas Geraes, Brazil, by J. F. Zikan and D. nevermanni has been collected twice in Costa Rica: by F. Nevermann frorn an emigration

THE BEHAVIOR OF DIPLOECITON NEYERMANNI,A STAPHYLINID BEETLE

ASSOCIATED WITH ARMY ANTS

BY ROGER D. _A_KRE AND RICHARD L. TORGERSON

INTRODUCTION

The genus Diploeciton of staphylinid beetles contains two knownspecies, D. constrictum Wasmann and D. nevermanni Reichensperger,both collected only with the army ant Neivamyrmex pilosus (F.Smith). D. constrictum has been collected once in an emigrationcolumn at Minas Geraes, Brazil, by J. F. Zikan and D. nevermannihas been collected twice in Costa Rica: by F. Nevermann frorn anemigration column at Harnburgfarrn and in a nest by H. J. C.Schmidt at Farm La Caja (Reichensperger, I939). The literaturecontains taxonomic descriptions and mention of the host ant, but noother information is available.

Diploeciton are unusual rnyrmecoid staphylinids belonging to theAleocharinae: Dorylomimini. They are shiny reddish-brown to. darkbrown in color while their host, N. pilosus, is shiny black; otherwisethe beetles resemble their host. They have "pseudogasters" formedby the enlargement of the 6th-Sth abdominal segments which mimicthe gasters of the army ants, a three segmented, petiole (army antshave two segments), and a iliform process of unknown functionon the renter of the petiole (Seevers, I965). The beetles havefunctional wings and presumably can fly. The legs of the beetlesare clothed with scattered hairs along their entire lengths, withthe hairs becoming longer and denser on the inner surface of thedistal end of the tibiae of the first and second pair of legs. Thestaphylinids do not have tufts of hairs for rubbing their host as dosome of the ecitophilous histerids (Akre, I968).A previous paper concerned with the behavior o.f ecitophilous

staphylinids (Akre and Rettenmeyer, 966) covered methods usedin studying army ants and their guests; additional methods aregiven by Rettenmeye; (963).The findings reported here were conducted at the Smithsonian

Tropical Research Institute (Barro Colorado Island) in the Canal

Scientific Paper Number 3131. Study supported in part by Grant GB-5220 rom the National Science Foundation. Work was conducted underProiect 1802, insect behavior.

2Assistant Professor and Research Assistant, Washington State University,Department of Entomology.

2II

212 Psyche [September

Zone during 1967. Our collections o D. nevermanni in the CanalZone have extended the distribution o this beetle several hundredmiles. This would imply a continuous distribution o the genusDiploeciton rom Costa Rica to Brazil.

ETHOLOGY

On 11 February 1967 we ound a raid column o N. pilosuscrossing a damp stream bed at 3 :oo PM. Upon our return at 7:03PM these same ants were engaged in an emigration. Brood was seenbeing carried, the column was 2-4 ants wide and 90% o the. tratZficwas moving in one direction. Myrmecophiles were continuouslyabundant in the column and between 7:03- 11:45 PM, when theobservations were terminated, a male and a emale D. nevermanniwere taken Jrom the column. The queen passed our stationaryobservation post at 9:24 PM but guests were collected until IO

minutes before observations ended. The specimens o Diploecitonwere taken running in the center o the column and were difficultto distinguish rom the ants except or their color and long hindlegs. The myrmecoid abdomen was held at approximately 45 Jromthe perpendicular while the beetles were running.A large sample oJ ants, still carrying brood, was taken with bottle

aspirators at 11:45 PM. This sample was later Jound to contain4 additional males and emale o Diploeciton.On 12 February all Diploeciton were placed in laboratory nests

with about 2000 N. pilosus workers and were observed or a minimumo( one hour each day until March when the contents o the nestswere preserved.The staphylinids spent nearly all their time in the laboratory

nests grooming worker ants their size or smaller. They were neverseen grooming any oI the major workers present. Grooming consistedo licking the head and thorax o the workers. Although the staphyl-inids groomed workers rom a number oJ positions, Diploeciton hadtheir own unique grooming position that was assumed most Jrequently(Fig. 1). In this behavior the staphylinids are remarkably similarto the staphylinids Probeyeria pulex (Sanderson) and to a lesserextent Ecitophya bicolor Reichensperger (Akre and Rettenmeyer,1966). While Probeyeria and Ecitophya straddled their host acrossthe longitudinal axis o the. body, Diploeciton assume a positionparallel to, but slightly to one side and on top o, the ant. To posi-tion itselt:, a beetle grasps with its mandibles the scape o an antennao an ant close to its base. It then positions its body parallel tothe body oI the ant and uses the (irst and third legs on the lower

1968"] Akre and Torgerson Staphylinid Beetle

Figure 1. Diploeciton neermanni in its unique grooming position on aworker o its host, N. pilosus. Drawing from a photograph.

side of the body to brace against the substrate. The three legs onthe other side of the body then straddle the ant. The mesothoracicleg on the bottom curls under and around the thorax of the ant. Thisplaces the sternum of the beetle’s thorax against the side o thethorax of the ant as though riding "sidesaddle". In this positionthe beetle rubs the ant with its legs. The mesothoracic lower legrubs the bottom of the thorax and the upper legs rub on the dorsalarea of the ant; the pro,thoracic leg usually rubs the head of theant, the mesothoracic leg rubs on the thorax and gaster, while themetathoracic leg is used sparingly to rub the gaster of the ant. Therubbing strokes are rather slow and alternate between stroking thebody o the ant and the staphylinid’s own body. The ront leg isrubbed on the head and thorax, both middle legs are rubbed on theelytra and the globular portion of the myrmecoid abdomen, whilethe metathoracic leg was rubbed only rarely on the abdomen. Thisintimate rubbing has been suggested as a means of acquiring colony

214 Psyche September

odor (Rettenmeyer, I961 and surely must serve some similar usefulfunction because it is practiced by several different species of staphyl-inids (all Dorylomimini) and at least three species o histerids. Therubbing by Diploeciton calmed the ants being groomed and severalants groomed in this manner even seemed partially paralyzed. Thiscondition of paralysis has been reported previously or ants rubbedby histerids (Akre, 1968). Although the beetles were observed orlong periods of time, no unction was found for the filiform processon the petiole.The staphylinid spent an average of 46 seconds grooming each

ant (2o timed observations) and moved constantly rom one ant toanother. During infrequent periods of inactivity, the. beetle wasusually buried nea.r the bottom of a large cluster o.f ants that wasalways present over the brood. The entire cluster remained stationaryfor periods up to several hours during these rare moments.The staphylinids also groomed at intervals by running their

antennae and front legs through their mouth parts. Although theglobular portion of the abdomen was held 45 rom the perpendicularwhen the staphylinids ran, the abdomen was held perpendicular ortilted slightly forward when grooming ants (Fig. I). The 3-seg-

mented petiole gives the abdomen considerable maneuverability andit can be thrust forward a considerable distance. The beetle rubbedthe tip of the abdomen on the elytra quite requently, a practicewhich also seems widespread among the ecitophilous staphylinids(Akre and Rettenmeyer, I966).Like other guests of army ants, Diploeciton fed on the brood of

dolicho.derine ants given to the N. pilosus as food as well as onarmy ant brood. However, the staphylinids were observed eatingN. pilos,us brood only three times, and may eat it only when bootyis not available. They were extremely efficient in cutting open broodand, as reported previously (Akre and Rettenmeyer, I966), thebeetles were usually driven away by worker ants trying to get atthe oozing juices.The captured beetles behaved nonspecifically towards one another,

in that the beetles antennated vigorously upon meeting but theyalways continued on their way. They were never seen grooming oneanother or in any intimate contact.

SUMMARY

The behavior o Diploeciton nevermanni is similar to that reportedor several other ecitophilous staphylinids in that the beetles assumea unique position in grooming their host, Neivamyrmex pilosus.

1968] Akre and Torgerson Staphylinid Beetle :215

Grooming of ants is probably a means of acquiring colony odor.Diploeciton are predaceous on army ant brood.

LITERATURE CITEDzAxKRE, R. D.

1968. The behavior of Euxenister and Pulinister, histerid beetles asso-ciated with army ants. (Coleoptera" Histeridae; Hymenoptera"Formicidae: Dorylinae). Pan. Pac. Ent. 44: 87-101.

JkKRE, R. D..AND C. W. RETTENMEYER1966. Behavior of Staphylinidae associated with army ants (Formi-

cidae" Ecitonini). J. Kansas Ent. Soc. 39" 745-782.REICHENSPERGER, A. YON

1939. Beitrage zur Kenntis der Myrmecophilen- und Termitophilen-fauna Brasiliens und Costa Ricas. VI. (Col. Hist. Staph.)Rev. de Ent. 10(1): 97-137.

RETTENMEYER, C. W.1961. Arthropods associated with Neotropical army ants with a review

of the behavior of these ants. (Arthropoda" Formicidae" Dory-linae). Ph.D. Dissertation, Univ. of Kansas, 605 pp., 77 Figs.

1963. Behavioral studies of army ants. Univ. Kansas Sci. Bull. 44"281-465.

SEEVERS, C. H.1965. The systematics, evolution and zoogeography of staphylinid

beetles .associated with army ants (Coleoptera: Staphylinidae).Fieldiana: Zool., 47(2) 139-351.

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Geraes, J. - Hindawi Publishing Corporation...column at Minas Geraes, Brazil, by J. F. Zikan and D. nevermanni has been collected twice in Costa Rica: by F. Nevermann frorn an emigration