Society Meeting Of March 23, 1994 Hot headed Dragons - Head Temperature Regulation Of Dragonflies PDF
Preview Society Meeting Of March 23, 1994 Hot headed Dragons - Head Temperature Regulation Of Dragonflies
ENTOMOLOGICALNEWS 188 SOCIETY MEETING OF MARCH 23, 1994 HOT-HEADEDDRAGONS:HEADTEMPERATURE REGULATION OFDRAGONFLIES MichaelL. May DepartmentofEntomology, Rutgers University-Cook College Dragonfliesare active predatorson the wingand assuch areexposed toawide range of temperatures. Although the muscles which control their excellent flight abilities are adapted to operate at high temperatures, they still must be able to control their internal thoracic temperatures and indeed show a wide range of behavioral and physiological mechanismstocarryoutthisregulation.These mechanismshave been investigatedovera numberofyearsthrough the research ofDr. Mike May, RutgersUniversity,and hismost recent resultsconcerningdragonflies"hotheads" were explained anddiscussed. Anyonecaneasilyobservethebehavioral regulation oftemperature bydragonfliesat any pond site when adults are present. Different behaviors are used to warm up ordissi- pate heat. For example, basking on a tree trunk in the sun takes advantage of a warm boundary layer ofairand the adult warms up, while raising the body away from the sur- face,orchangingtheangleofthebodytothesuncanreduce unwantedheat. Somespecies evenpointtheabdomenupanddirectlyatthesun(termed"obelisk"position)tominimize exposure. Dr. May focused his research not on "baskers", however, but on Anaxjunius (Drury) acommon pond species that remainsalmost continually active in flight and gen- erates heat internally (endothermy). In early morning, the adult vibrates the wings with simultaneous contractions until the muscles, which are surrounded by heat-trapping air sacsin the thorax,reach flight temperature (about35C). But what ofthe excessheat generated once the insect isin flight?Through the use of thermocouples in the thorax, abdomen and head, Dr. May noted that the three areas showed different trends in temperature increase in both lab and field studies: the thorax reachedamaximumtemperatureattake-offregardlessofoutsidetemperature (indicating active regulation),theabdomentemperatureincreasedonlyaftertake offandwasrelated tooutsidetemperature (indicatingno regulation),andthe head temperature showed fluc- tuations after maximum thorax temperature was reached and appeared somewhat inde- pendent of outside temperature (indicating some regulation mechanism). That some of thisheatisdissipatedfromthethoraxbythe flowofhaemolymph wasclearlydemonstrat- edbyMaywhenheclampedoffthedorsalvesselflowtotheabdomenandhead,andnoted that as thoracic temperature increased, head and abdominal temperature decreased. Yet the fluctuationsofthe head temperature, asopposed to the simple increase in abdominal temperature,indicatethatthe head isnotsimplyaheatdumpforthethoraxasseen in the abdomen. Other reasons may influence why the head temperature is regulated, perhaps dealingwith the dragonfliesincredible visual acuity. AlsodiscussedwasDr. May'sinterestinthe astonishingsouthward migrations(some- timesinthehundredsofthousandsofindividuals)ofAnaxjuniusobservedinthefall.Also intriguingaretherecordsofadultsofthisspeciesinearlyspringinnorthernlocales,appar- ently not due to local emergence,indicatinga return ofsome adultsfrom southern areas. Dr. Mayisinterested inanyearlysightingsofthisspecies. The meetingincludedafewnotesoflocal entomological observations. Discussion ini- tiatedbyHoward Boydcenteredontherecentactivityofinsectsstimulatedbythelastfew daysofover20Cweather,includingthefirstmothsandpaperwaspsseen.About25mem- bersand theirguestsattended the meeting. Jon K. Gelhaus CorrespondingSecretary
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