Comp. Biochern. Physiol.,7968, Vol.2+, pp.997 to 7002. Pergamon Press. Printed in Great Britain

CSIS? METABOLISM IN BLATTA ORIENTALIS ATYARIOUS TEMPERATURES*

TSIN FU CHUANG,t MORRIS B. SNIPES, CLIFFORD S. CRAWFORDANd MARVIN L. RIEDESEL

Department of Biology, University of New Mexico, Albuquerque, New Mexico, U.S.A.87106

(Receioed 22 August 1967)

Abstract-1. The effect of temperature on Cs13? metabolism in the orientalcockroach, Blatta orimtalz's, was studied following a single ingestion of theisotope.

2. The extension of biological half-time resulting from lowering of tempera-ture was greater than could be predicted from the reduction in metabolic ratewhich accompanied lowering of temperature.

3. The retention of Csrs? in the 10"C environment was in particular greaterthan would be expected from the retention of Cs13? in the 20-30'C temperaturerzutge.

INTRODUCTIONTnr punpose of this study was to observe the effect of environmental temperatureon metabolic rate and on retention of orally administered Cs18? in the cockroach,Blatta orimtalis.

Poikilotherms represent an impoftant portion of the total biomass andundoubtedly some contribute significantly to the movement of Cs18? along foodchains. The relationship between contaminant loss rate and metabolic rate isimportant for estimating rates of radionuclide movement along food chains andfor determination of concentrations of radionuclides in portions of food chains(Crossley, 1964). Insects are of particular interest since they are potential sourcesof contamination by radionuclides produced during nuclear accidents.

Biological half-time (BT1) refers to the time required for the amount of aparticular radionuclide in the body to decrease to one-half of its initial value dueto elimination by natural biological processes. Biological half-times for radio-nuclides in invertebrates have been reported to decrease by one-halffor each 10"Crise in temperature over the 5-30'C range (Crossley, 1964). However, our datademonstrate Cs137 BTg in the oriental cockroach is longer at 10oC than wquld beexpected if elimination of Cs137 paralleled metabolic rate. Odum (1961) reportedBT* values for Zn66 in Tenebrio which suggest a non-linear relationship betweenisotope excretion and temperature similar to our observations.

* Supported in part by A.E.C. research contract AT (29-2)-1629. Taken in part from aM.S. thesis by Tsin Fu Chuang, University of New Mexico, 1967.

t Present address: Department of Biological Sciences, Purdue lJniversity, WestLafayette, Indiana 47907.

998 T. F. CnueNc, M. B. SNIers, C. S. CnawroRD AND M. L. RrroBsrr-

MATERIALS AND METHODSNymphal and adult male cockroaches were the experimental animals. Nymphs

were all within a few days of being 6 months old at the beginning of the experi-ments; adults were collected in the field and were of unknown ages.

The cockroaches were weighed and placed in separate cages (cylindrical card-board containers 8 cm in dia. x 9 cm in length). Animals were kept in a

temperature-controlled environment and deprived of food and water f.or a 6-daystarvation and acclimation period. Following starvation they were weighed,placed in separate feeding cages and allowed t hr to drink all or part of 125 tr ofwater containing 0'1 pc of Cs1s7. Cesium-137 intake ranged from 0'01 to 0'09 prc

per animal. Cockroaches which failed to ingest isotope during the 1-hr feedingperiod were discarded; therefore, experimental groups ranged in number fromseven to thirteen animals. Each cockroach, after feeding, was transferred to a

small wire cage and washed in running distilled water to remove isotope from themouth parts. Whole-body measurements of radioactivity r,l'ere recorded and theanimals placed in the experimental environments with food and water ad libitum.Adult cockroaches had been kept at room temperature prior to feeding. However,each group of nymphs had been exposed during the starvation period to its respec-tive post-feeding thermal environment. Data collected periodically for t}re durationof tJre experiment included weights and whole-body counts. At each counting andweighing the animals were transferred to clean individual cages with food andwater ad libitum.

Radioactivity measurements were made with a Packard Instrument CompanyModel4l0A small-animal whole-body counter. To reduce variation due to dailybiological rhythms all measurements were made between 3.00 and 4.30 p.m. andthe animals were subjected to a 12-hr photoperiod (light from 6.00 a.m. to 6.00 p.m.).

Oxygen consumption was measured with a Gilson Differential Respirometerequipped with a constant temperature bath. After equilibration of the respiro-meter, six 10-min readings were taken for each cockroach with the reaction vessels

shaking at the rate of 72lmn. Carbon dioxide was absorbed in 10o/o KOH solution.Respiratory rates were determined during the third to eighth day after ingestionof the cesium solution.

RESULTSThe mean weights of the nymphs in the 10, 15 and 20'C retention studies are

presented in Fig. 1. At no time was there a significant difference at the 0'05 levelof confidence in the mean weights of the experimental groups. As indicated bythe weight data, mean weights (1) decreased during the 6-day starvation period,(2) increased nearly 100 mg during the day the Cs137 and ad libitum water andfood were available and (3) were nearly constant during the remainder of theexperiment.

The Cs13? retention curves for adult males at 10, 15, 22 and 31"C (Fig. 2) andfor male nymphs at 10, 15 and 20"C (Fig. 3) suggest a non-linear change in cesiumexcretion as a function of temperature. A cornparison between retention values

Cs13? Mpr,rBor,rsM rN BLATTA 1RIENTALT9 999

for nymphs at 10 and 15'C demonstrated a significant difierence at the 0.01 levelof confi.dence at 10, 20, 40 and 60 days after ingestion, whereas there was no sig-nificant difference at the 0'05 level of confidence between retention at 15 and 20"Cat the same time intervals.

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Frc. 2. Retention of Cs137 in adult male cockroaches following single ingestion.

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_ A plot of per cent excretio.n per day as a function of oxygen consumption byadults is presented in Fig. 4. Excretory and metabolic rates were compuied fromdata collected during the third to eighth day after ingestion of the isoiope.

DISCUSSIONMetabolic rate, expressed in pl. of oxygen consumed per g of arrimal per hour,

has been reported to lave a Qn of approximately 2.5 in the physiologicul te*-perature_ range. Variables determining metabolic rate include species, activity,sex, environmental temperature, previous oxygen experience and genetic back-ground (Prosser, 1962). In our studies metabolic rate increased proportionallywith temperature over tlle 10-31'C range.

variables determining BT* in mammals include species, sex, environmentaltemperature, age, size and diet (Richmond et aI., 1964). Similar factors maydetermine biological half-time in insects. Crossley & pryor (1960) presented acurve for retention of Cs13? in the grasshopper Romalea at ZI"C, whiihwas similarto the retention curves for adult B. orientalis at 22"C.

The proportion of ingested radionuclide assimilated frorn the intestine ofill"_"j. is not known (crossley, 1963). However, Hamilton (1947), Hood & comar(1953) and weeks & oakley (1954) have reporred nearly too per cent absorptionof orally administered cesium in mammals. According to Crossley (1963) theassimilation factor is probably lower in insects than in mammals.

our cockroaches retained -or" cesium at 10'C than would be predicted ifcesium excretion paralleled metabolic rate. The data suggest that metabolic ratealone was not the primary factor determining retention of Csls? at 10oc. onepossible explanation for these results concerns the probability of a considerabledecrease in functional contact between Malpighian tubules and circulating fluidsin the hemocoel at 10"c. A very slow rate of hemolymph movement could resultin a greatly reduced amount of potential excretory product, cesium ions includ.ed,being brought in contact with the Malpighian tubules. Jones (1964) suggests thaihemolymph flow can slow or possibly stop altogether in insects with alow iretabolicrate.

_ Another possible explanation is that the presumably increased time spent bythe cesium in the ion-absorbing areas of the rectum at 10'C may have increa..ithe probability of the isotope's transport back into the hemolymph.

REFERENCESCnossr-nv D. A., Jn. (1963) Movement and accumulation of radiostrontium and radiocesium

in insects. rn Radioecology (Edited by Scnwrz v. & Kr.rnrsNr. A. w., Jr.) pp. 103-105. Reinhold, New York and American Institute of Biological Sciences, Washington,D.C.

Cnossr,rv D. A., Jn. (1964) Biological elimination of radionuclides. Nucl. Safety 5,265-268.cnossr-nv D. A., Jn. & Pnvon M. E. (1960) The uptake and elimination of

"eri.rm- l3z by a

grasshopper, Romalea mic-roptera. Health phys. 4, 16-20.Harrrr,roN J. G. (1947) The metabolism of the fission products and the heaviest elements.

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1002 T. F. CnueNc, M. B. SNrrrs, C. S' CnewroRD AND M. L. Rrronsrr-

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Pnosssn C. L. (1962) Oxygen: respiration and metabolism. In Comparatfute AilrnalPhysiology (Edited by Pnossnn C. L. & Bnowx F. A:, Jn.) Second edn. pp. 153-L97.Saunders, Philadelphia, Penn.

RrcnvroNo C. R., LoNooN J. E.& FuncnNnn J. E. (1964) Metabolism of radiocesium byman and selected laboratory mammals. Radiatinn Res. 22,226-227.

Wenxs M. H. & Oerr.ny W. D. (L954) Gastro-intestiltal Absorptinn, Disaibution, andRetmti.on of Ceshtm fed. chronically in Vafious Forms to Rafs. Hanford Works ReportHW-35917. pp. 50-55. General Electric Hanford Atomic Products Operation,Richland, Washington.