C. W. Robey.
Observations on Breeding Behavior of Pachydiplax longipennis (Odonata: Libellulidae).
Psyche 82(1):89-96, 1975.

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OBSERVATIONS ON BREEDING BEHAVIOR OF
PACHYDIPLAX LONGIPENNIS
(ODONATA :LIBELLULIDAE) *
Museum of Comparative Zoology
Cambridge, Mass. 021 38
Pachydiplax longipennis Burmeister is a medium sized dragonfly found throughout the United States. Clifford Johnson ( 1962) has described the general pattern of breeding behavior of this species in North Carolina, Virginia and Texas. In this paper I report my observations of three populations of this species in Massachusetts. While territorial and mating behavior is similar to that described by Johnson, I am able to extend his findings in some areas. In addi- tion, I describe the coloration of this species in ultraviolet light and speculate as to the behavioral significance of the high reflectancy of areas of blue pruinescence.
Observations were made at three ponds near Boston, Massachu- setts, during the period June-August, 1974. Pachydiplax longipennis was relatively abundant at each pond. Observations were made throughout the daily activity period and under a variety of weather conditions.
Initial observations were made at Pickman Pond at the Concord Field Station of Harvard University in Bedford from June 13- July 18. This is a shallow man-made pond of about 1.5 hectares. The banks are thickly vegetated with bushes and sedges; the sur- rounding vegetation has been mapped by Maguire et al. (1973). Water depth within 2 m of the shore was typically 20-50 cm. Fallen branches and emergent vegetation, such as water lilies, lined the periphery. In early July, studies were conducted at a second shallow, artificial pond in Lexington (Five Fields: ca. 0.5 hectares), where the lack of dense fringing vegetation facilitated detailed observations. The pond was bordered on two sides by grassy banks and overhung by trees (mostly Acer rubrum). Emergent vegetation included *Manuscript received by the editor May 19, 1975. Pu&e U:W6 (1975). hup Ytpsychu einclub orgtSV82-OWJ html



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arrow head (Sagittaria latif olia) . Observations were made daily until August 8, by which time the water had dropped to such a level that few emergent perches suitable 'for Pach~diplax longipennis re- mained. On August 12, observations were commenced at a third shallow, artificial pond off Shade Street in Lexington. This 1.2 hectare pond was completely surrounded by trees (Acer rubrum and Ainus sp.) and emergent sticks and logs suitable for perches were plentiful.
At the Five Fields pond, attempts were made to study behavior by marking males. These attempts were largely unsuccessful due primarily to failure to relocate marked individuals. Thereafter, identifications of individuals were made by recording natural vari- ations.
Some preliminary studies were made of the ultraviolet reflectant properties of the blue-grey abdominal pruinescence. With the col-
laboration of Robert E. Silberglied (Department of Biology, Har- vard University) ultraviolet patterns were examined, using a 35mm single-lens-reflex camera with Zeiss F.4, 6omm Ultraviolet Objektiv lens, Zeiss UV 366 filter (=Wratten 18A)) Bowens Texturelight electronic flash, Kodak Tri-X Pan film, and Acufine developer. Although most of my observations confirm those of Johnson ( 1962)) I found that there was a difference in male perching be- havior. These and some additional observations are reported below. From the time of their arrival (approx. 10 a.m.) until their de- parture (approx. 4 p.m.), the males observed defended a defined territory as described by Johnson (1962). The "threat display" (Johnson, 1962) was also frequently seen. Following this display, I observed that the two males engage in further agonistic behavior. One male pursues the other in a horizontal direction with abdomen raised while the leading insect flies with abdomen lowered (Fig. la). The two may repeat this behavior several times, exchanging positions and/or reversing direction after flying a distance of 1-2 meters.
(They may alternatively resume the "threat display." Occasionally this may involve only one male if the other has returned to a perch.) After a variable duration (usually less than a minute) this pursuit behavior is discontinued and the males may begin a third behavior, as Johnson (1962) noted. Then, as I observed, the male who does succeed in getting the lower position, flies upwards, forcing the other up with him as much as 15 meters into the air at an angle of 50-80



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Figure 1. Pachydifhx longipennis: a, male-male chasing behavior; b, male perching position; c, male-female precopula~tory position.



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degrees. Immediately, one male returns directly to defend the terri- tory while the defeated male returns many seconds later to rest or does not return to the area at all. Unfortunately, the flight speed was so great, and the distance so far, that I was unable to determine which male claimed the territory, or whether either regularly did, but I would hypothesize that the lower and therefore faster male usually dominates. As Johnson (1962) stated, this is the final step in establishing territorial dominance between two males. At any time one male may abandon this territorial dispute and retreat out of the area leaving it for the remaining male. In further agreement with Johnson (1962)' I observed that the original owner often retains the territory.
Such disputes gener(a1ly last from 5 to 50 seconds and terminate with territorial possession and perch display by the dominant male.
PERCHING POSITION
The 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 is low, a male in an open situation exposed to full sunlight, usually aligns his body along the length of the perch. He raises his abdomen
only a few degrees and brings his wings forward (Fig. ib). Every 10 to 60 seconds he leaves his perch to patrol but returns directly if undisturbed by intruders. Very rarely did any male raise his abdo- men to the extent illustrated by Johnson (1962: Fig. 2). On windier days, males keep their wings fully outstretched and at right angles to the prevailing wind. Only on hot calm days, when the air temperature rose above 30å¡C did perching males raise their abdo- mens higher.
My observations, coupled with Johnson's ( I 962), suggest that male perching behavior is influenced by at least four factors includ- ing thermoregulation, aerodynamics, predator avoidance, and terri- torial display. It is interesting to note that whereas Johnson (1962) and Williamson
( I 900) reported that males generally perch with their abdomens directed upwards, this behavior was rarely seen in Massachusetts populations. Johnson and Williamson's observations were made on sunny days, at stations where daytime temperatures are typically 2-4OC higher than those prevailing in Massachusetts. This suggests that this behavior may be temperature dependent. As male-male territorial interactions were otherwise fully dmeveloped in the Massachusetts populations, I suspect that the abdomen orienting



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19751 Robey - Pachydiplax longipennis 93 behavior may be primarily thermoregulatory in function rather than purely for territorial display as concluded by Johnson (1962). Pachydiplax females were infrequently seen at the three ~onds. During July and August only 25 matings were closely observed. Females appeared between 1300 and I 500 hours (E.S.T.) on warm sunny days
and courtship commenced immediately. A territorial male, upon seeing a female within his territory, would fly directly to a position above her. Hovering a few centimeters above her he would raise his abdomen in a manner similar to that seen in the threat display. (But in a position that makes it difficult for the female to see this display.) He then flaps his wings rapidly in an unusually wide arc. A receptive female will permit the male to align his body directly above hers. The male then descends and the female rises up slightly while lowering her abdomen and presenting her head (Fig IC). In rapid sequence he clasps her with his ab- dominal appendages and they go into copula. Copulation occurs in flight and is brief, lasting 10-40 seconds. Its duration appears to depend, in part, on the number of previous inseminations received by the female, but only by collecting data could this speculation be verified. The pair then separate and the male returns directly to his display perch.
On three occasions the male was seen to transfer sperm to his genitalia during this short postmating flight. Typically, the female also rests for 5-10 seconds on a nearby perch before searching for oviposition sites.
Oviposition was observed as illustrated by Needham and Westfall ( 195 5 ) . 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 defending males was more directed and intense than
that seen in male-male interactions. Nonetheless, in a few cases, when many males were present and/or when the female strayed out of her mate's territory, his fervent defense was inade- quate and oviposition prevented. A behavior, marked in LibeZZuZa incesta Hagen but less common in P. Zongipennis, occurred when unmated males attempted to grasp the female while her head was exposed during oviposition.
The female was usually knocked, tum-
bling, into the water. L. incesta females, being stronger fliers, would attempt to evade such attacks; P. longipennis females usually re- treated to the trees until male excitement diminished. In addition to interference from other males, frogs presented a major threat to females ovipositing near the edge of the ponds.



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Figure 2. Three species of libellulids illuminated under 300-400 nrn U.V. light. Percent reflection indicated in lower left corner: from left to right, @, 2.55, 5.05, 16.0%, > 25.0%.



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19751 Robey - Pachydiplax longipennis 9 5 Pachydiplax longipennis males are unusually aggressive dragon- flies when compared with other Libellulids. They react with par- ticular ferocity to three larger syrnpatric species whose pruinosity color is similar to the grey-blue color of Pachydiplax longipennis. The first, Libellula cyanae Fabricius, most common at Pickman and the Five Fields ponds has a slightly darker pruinescence, cover- ing the entire adult male body. Libellula incesta, common only at the Shade Street pond, has a much darker, almost black, pruinescence. The third, Erythemis simplicicollis Say, has the same color as Pachy- diplax longipennis, covering a teneral green on the dorsal surface of the abdomen and synthorax. It occurred at all three of these ponds. Libellula incesta and L. cyanae sometimes occupy perches and enter the territory of Pachydiplax longipennis. Erythemis simplicicollis usually preferred to perch on an exposed log or rock, situations rarely used by P. longipennis. Despite its smaller size, P. longipennis would display and chase all three of these species that entered its territory. Other dragonflies commonly present at these ponds included: Plathemis lydia, Sympetrum rubicund~l~um, Leucorrhina intacta, Gomphus furcifer, Perithemis tenera, Libellula pulchella, L. luctosa and Ladonia julia. P. longipennis males generally ignore them, pr'e- sumably because of their different appearance'. Coloration patterns of recently dead males (killed by chilling) were compared in visible and ultraviolet light. It was found that the blue pruinose areas on the abdomen though dull under visible light have marked reflectivity in the ultraviolet. Highly reflective prui- nescent areas were also found in males of Libellula cyanae, L. incesta and Erythemis simplicicollis (see Fig. 2), but were absent in females of these species
Some odonates, including a libellulid, have been shown by physio- logical methods to be UV-sensitive (Goldsmith and Bernard, 1974: Table 5). Why is it that these, more stationary, libellulids have pruinescence in similar areas while in others it is a different color, located in different areas or absent all together? Species such as Libellula pdchella have only white pruinescent spots on their wings and are much more mobile than P. longipennis. In light of these preliminary findings, the possible role of ultraviolet patterns in odo- nate behavior deserves careful attention.



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This research was conducted with the aid of NSF Undergraduate Research Participation Grant No. GY-11203 to Concord Field Station, Harvard University. I am indebted to Mary Corn, Paul Miliotis, Robert E. Silberglied, William Stubblefield, and David S. Woodruff for assistance, advice, and encouragement. GOLDSMITH, T. H. AND G. D. BERNARD
1974. The visual system of insects. In The Physiology of Insecta, 2nd ed., 2: 241-246 (M. Rockstein, ed.). Academic Press, New York.
JOHNSON, C.
1962. A study of territoriality and breeding behavior in Pachydiplax longipennis Burmeister (Odonata rLibellulidae). Southwestern Nat., 7: 191-197.
MAGUIRE, L., P. NELSON, W. A. ABRAHAMSON AND D. S. WOODRUFF 1973. 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, E. B.
1900. The dragonflies of Indiana. Ann. Rept. Ind. State Geologist, pp. 233-333, 1003-1010.




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