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OBSERVATIONS ON BREEDING BEHAVIOR OFPACHYDIPLAX LONGIPENNISODONATA:LIBELLULIDAE *

BY CAROL W’ALSER RoMuseum o: Comparative Zoolog7

Cambridge, Mass. o2I 38

INTRODUCTION

Pachydiplax longipennis Burmeister is a medium sized dragonflyfound throughout the United States. Clifford Johnson (962) hasdescribed the general pattern of breeding behavior of this species, inNorth Carolina, Virginia and Texas. In this paper I report myobservations of three populations of this species in Massachusetts.While territorial and mating behavior is similar to that describedby Johnson, I am able to extend his findings in some areas. In addi-tion, I describe the coloration of this species in ultraviolet light andspeculate as to the behavioral significance of the high reflectancy ofareas of blue pruinescence.

I/IETHODS

Observations were made at three ponds near Boston, Massachu-setts, during the period June-August, I974. Pachydiplax longipenniswas relatively abundant at .each pond. Observations were madethroughout the daily activity period and under a variety o weatherconditions.

Initial observations were made at Pickman Pond at the ConcordField Station of Harvard University in Bedford from June 3-July 8. This is a shallow man-made pond o about 1.5 hectares.The banks are thi.ckly vegetated with bushes and sedges; the sur-rounding vegetation has been mapped by Maguire et al. (973).Water depth within 2 m o the shore was typically 20-50 cm. Fallenbranches and emergent vegetation, such as water lilies, lined theperiphery. In early July, studies were conducted a.t a second shallow,artit%ial pond in Lexington (Five Fields: ca. 0.5 hectares), wherethe lack o dense fringing vegetation facilitated detailed observations.The pond was bordered on two sides by grassy banks and overhungby trees (mostly Acer rubrum). Emergent vegetation included

Manuscript received by the editor May 19, 1975.

89

90 Psyche [March

arrow head (8agittaria lati[olia). Observation’s were made dailyuntil August 8, by which time the water had dropped to such a levelthat few emergent perches suitable for Pachydiplax longipennis re-mained. On August 2, observations were commenced at a thirdshallow, artificial pond off Shade Street in Lexington. This .2

hectare pond was completely surrounded by trees (ztcer rubrumand dlnus sp.) and emergent sticks and logs suitable for percheswere plentiful.At the Five Fields pond, attempts were made to. study behavior

by marking males. These attempts were largely unsuccessful dueprimarily to failure to relocate marked individuals.. Thereafter,identifications of individuals were made by reco.rding natural vari-ations.Some preliminary studies were made of the ultraviolet reftectant

properties of the blue-grey abdominal pruinescence. With the col-laboration o.f Robert E. Silberglied (Department of Biology, Har-vard University) ultraviolet patterns were examined, using a 35mmsingle-lens-reflex camera with Zeiss F.4, 6omm Ultraviolet Objektivlens, Zeiss UV 366 ilte.r (Wratten SA), Bowens Texture.lightelectronic flash, Kodak Tri-X Pan qlm, and Acune developer.Although most o my observations conirm those o. Johnson

(x962), I (ound that there was a difference in male. perching be-havior. These and some additio.nal observations are report.ed belo,w.

MALE-MALE INTERACTIONS

From the time o their arrival (approx. o a.m.) until their de-parture (approx. 4 p.m.), the males observed deended a deqnedterritory as described by Johnson (962). The. "threat display"(Johnson, 9.62) was also requently seen. l’ollowing this. display,I observed that the two males engage in urther agonistic behavior.One male pursues the other in a horizontal direction with abdomenraised while the leading insect flies with abdomen lowered (Fig. a).The two may repeat this behavior several times, exchanging positionsand/or reversing direction ater flying a distance o -2 meters.(They may alternatively resume the "threat display." Occasionallythis may involve only one male i the other has returned to a perch.)Ater a variable duration (usually less than a minute) this pursuitbehavior is discontinued and the males may begin a third behavior,as Johnson (962) noted. Then, as I observed, the male who doessucceed in getting the lower position, flies upwards, o.rcing the otherup with him as much as 5 meters into the air at an angle, o 50-80

Robey Pachydiplax longilennis

Figure 1. Pachydillax longilennis: a, male-male chasing behavior;b, male perching position; c, male-female precopulatory position.

92 Psyche [March

degrees. Immediately, one male returns directly to defend the terri-tory while the defeated male returns many seconds later to rest ordoes not return to the area at all. Unfortunately, the flight speedwas so great, and the distance so far, that I was unable to determinewhich male claimed the territory, or whether either regularly did,but I would hypothesize that the lower and therefore faster maleusually dominates. As Johnson (962) stated, this is the final stepin establishing territorial dominance between two males. At .anytime one male may abandon this territorial .dispute and retreat outof the area leaving it for the remaining male. In further agreementwith Johnson (962), I observed that the original owner oftenretains the territory. Such disputes generally last from 5 to 5oseconds and terminate with territorial possession and perch displayby the dominant male.

PERCHINO POSITIONThe perching position of Pachydiplax longipennis is probably de-

termined by several factors including wind, sun intensity, air temper-ature, the kind of perch, and the behavior of other dragonflies.Under typical summer daytime conditions when the wind speed islow, a male in an open situation exposed to full sunlight, usuallyaligns his body along the length of the perch. He raises his abdomenonly a few degrees and brings his wings forward (Fig. b). Everyo to 60 seconds he leaves his perch to patrol but returns directly ifundisturbed by intruders. Very rarely did any male raise his abdo-men to the extent illustrated by Johnson (962: Fig. 2). Onwindier days, males keep their wings ully outstretched and at rightangles to the prevailing wind. Only on hot calm da.ys, when the airtemperature rose above 3oC, did perching males raise their abdo-mens higher.My observations, coupled with Johnson’s (r962), suggest that

male perching behavior is influenced by at least our actors includ-ing thermoregulation, aerodynamics, predator avoidance, and terri-torial display. It is interesting to note that whereas Johnson (I962)and Williamson (r9oo) reported that males generally perch withtheir abdomens directed upwards, this behavior was rarely seen inMassachusetts populations. Johnson and Williamson’s observationswere made on sunny days, at stations where daytime temperaturesare typically 2-4C higher than those prevailing in Massachusetts.This suggests that this behavior may be temperature dependent. Asmale-male territorial interactions were otherwise ully developed inthe Massachusetts populations, I suspect that the abdomen orienting

1975] Robey Pachydiplax longibennis 93

behavior may be primarily thermoregulatory in unction rather thanpurely or territorial display as concluded by Johnson (1962).

IATING AND OVIPOSITION

Pachydiplax females were infrequently seen at the three ponds.During July and August only 25 matings were closely observed.Females appeared between 3oo and 5oo hours (E.S.T.) on warmsunny days and courtship commenced immediately. A territorialmale, upon seeing a emale within his territory, would fly directlyto a position above her. Hovering a ew centimeters above her hewould raise his abdomen in a manner similar to that seen in thethreat display. (But in a position that makes it difficult (or thefemale to see this display.) He then flaps his wings rapidly in anunusually wide arc. A receptive emale will permit the male toalign his body directly above hers. The male then descends and thefemale rises up slightly while lowering her abdomen and presentingher head (Fig ,c). In rapid sequence he clasps her with his ab-dominal appendages and they go into copula. Copulation occurs inflight and is brief, lasting o-4o seconds. Its durati.on appears todepend, in part, on the number o previous, inseminations receivedby the female, but only by collecting data could this speculation beverified. The pair then separate and the male returns directly to hisdisplay perch. On three occasions the male was seen to transfersperm to his genitalia during this short postmating flight. Typically,the female also rests for 5-o seconds on a nearby perch beforesearching for oviposition sites.

Oviposition was observed as illustrated by Needham and Wesffall(I955). I found that the male defended the female from interfer-ence by other males only as long as she remained within his terri-tory. The flight of these deending males was more directed andintense than that seen in male-male interactions. Nonetheless, in afew cases, when many males were present and/or when the femalestrayed out of her mate’.s territory, his fervent defense was inade-quate and oviposition prevented. A behavior, marked’ in Libellulaincesta Hagen but less common in P. longipennis, occurred whenunmated males attempted to grasp the female while her head wasexposed during oviposition. The female was usually knocked, tum-bling, into the water. L. incesta females, being stronger fliers, wouldattempt to evade such attacks; P. longipennis females usually re-treated to the trees until male excitement diminished. In additionto interference from other males, rogs presented a major threat tofemales ovipositing near the edge of the ponds.

94. Psyche [March

Figure 2. Three species of libellulids illuminated under 300-400 nmU.V. light. Percent reflection indicated in lower left corner" from leftto right, 1%, 2.5%, 5.0%, 16.0%, > 25.0%.

1975] Robey Pachydillax longilennis 95

INTERSPECIFIC BEHAVIOR

Pachydiklax longikennis males are unusually aggressive dragon-flies when compared with other Libellulids. They react with par-tieular ferocity to three larger sympatric species whose pruinositycolor is similar to the grey-blue color of Pachydillax longipennis.The first, Libellula cyanae Fabricius, most common at Pickmanand the Five Fields ponds has a slightly darker pruinescence, cover-ing the entire adult male body. Libellula incesta, .common only atthe Shade Street pond, has a. much darker, almost black, pruinescence.The third, Erythemis simllicicollis Say, has the same color as Pachy-dillax longipennis, covering a teneral green on the dorsal surface, ofthe abdomen and synthorax. It occurred at all three of these ponds..Libellula incesta and L. cyanae sometimes occupy perches and enterthe territory of Pachydiplax longikennis. Erythemis simllicicollisusually preferred to perch on an e.xpos.ed log or rock, situations rarelyused by P. longilennis. Despite its smatler size, P. longilennis woulddisplay and chase all three of these species that entered its territory.

Other dragonflies commonly present at these ponds included:Plathemis lydia, 8ymetrum rubicundul.um, Leucorrhina intacta,Gomlhus furcifer, Perithemis tenera, Libellula ulchella, L. luctosaand Ladonia julia. P. longikennis males generally ignore them, pre-sumably because of their different appearance.

COLORATION

Coloration patterns o. recently dead males (killed by chilling)were compared in visible and ultraviolet light. It was ound that theblue pruinose areas on the .a’bdomen though dull under visible lighthave marked reflectivity in the ultraviolet. Highly reflective prui-nescent areas were also found in males of Libellula cyanae, L.incesta and Erythemis simlicicollis (see Fig. 2), but were absentin emales of these speciesSome odonates, including a libellulid, have been shown by physio-

logical methods to be UV-sensitive (Goldsmith and Bernard, 974:Table 5). Why is it that these, more. stationary, libellulids havepruinescence in similar areas while in others it is a different color,located in different areas or absent all together? Species such .asLibellula kulchella have only white pruinescent spots on their wingsand are much more mobile than P. longikennis. In light of thesepreliminary findings, the possible role of ultraviolet patterns in odo-nate behavior deserves careful attention.

96 Psyche [March

ACKNOWLEDGMENTS

This research was conducted with the aid of NSF UndergraduateResearch Participation Grant No. GY-zo3 to Concord FieldStation, Harvard University. I am indebted to Mary Corn, PaulMiliotis, Robert E. Silberglied, William Stubblefield, and DavidS. Woodruff for assistance, advice, and encouragement.

BIBLIOGRAPHY

GOLDSMITH, T. H. AND G. D. BERNARD1974-. The visual system of insects. In The Physiology of Insecta,

2nd ed., 2:24-1-246 (M. Rockstein, ed.). Academic Press, NewYork.

JOHrSOS, C.1962. A study of territoriality and breeding behavior in Pachydiplax

longilennis Burmeister (Odonata:Libellulidae). SouthwesternNat., 7: 191-197.

MAGUIRE, L., P. N-LSOS, W. A. ABR&HAMSOS AlqD D. S. WOODRUFF1973. Pickman area map. Concord Field Station, A guide to Resources

No. 2.NEEDHAM, J. G. AND M. J. WESTFALL

1955. Dragonflies of North America. University of California Press,Berkeley, p. 34.

WILLIAMSON, ]. B.1900. The dragonflies of Indiana. Ann. Rept. Ind. State Geologist,

pp. 233-333, 1003-1010.

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