J. theor. Biol. (1975) 52, 149-158
Comparative RaQiosensitivity in the Class Insecta WILLIAM K. WILLARD ,+D
DONALD S.CHFBRY~
Department of Zoology, Clemson University, Clemson, South Carolina 29631, U.S.A. (Received 13 May 1974, and in revisedform 7 October 1974) A “radiosensitivity index” (LTJmean longevity) was correlated with the mean longevity and dry weight of 37 insect species(both sexesof 12 species)
representing eight orders. Curvilinear regression analysis reIating radiosensitivity to mean longevity and mean dry weight indicated that 46.3% of the observed variation could be attributed to longevity and 32.6% to the dry weight of the species. In general, large long-lived adults were more radiosensitive than small short-lived ad&s. Correlation of the phylogeny of insect orders and order groupings with the radio-sensitivity index was found to be poor. However, when the index was related to longevity, there was a tendency for species comprising the major orders
investigated to occur in groups along the predicted curve.
There are numerous exceptions to the generalization correlating animal radiosensitivity with phylogeny (Bacq & Alexander, 1955). Variations have been such that the predictive value of the concept has been of little significance. One reason for this lack of predictability is that investigators have utilized such a wide variety of approaches that consolidation of their findings into principles having predictive value has not been possible. The radiosensitivity of organisms has been evaluated mainly in terms of the LD,, (Ives, Heihnan 8z Plough, 1955; Cole, LaBrecque 8~ Burden, 1959; Balock, Burditt & Christenson, 1963; Erdman, 1968) and the LT5,, (Wharton & Wharton, 1959; Clark, 1961; Davich & Lindquist, 1962; Flint, 1965; Menhinick 8i Crossley, 1968, 1969; McMahon, 1969). The disadvantages of these parameters have already been pointed out (Menhinick & Crossley, 1969; Willard, 1970). Willard (1970) suggested a “radio-sensitivity index” (hereafter referred to as R.I.) which expresses a time response to radiation exposure in terms of a species mean longevity R.I. = LT,e/mean longevity. t Ibent IIbtehe
adkss: Vii
Department of Environmental Science,Virginia Polytechnic Institute, 24060, U.S.A. 149
150
W.
K.
WILLARD
AND
D.
S.
CHERRY
The LTS, represents the time required, following irradiation, for 50% of a population to die. This parameter (R.I.), like the LT, has the disadvantage of requiring a single dose (and dose rate); however, it has the advantage of broad applicability for comparative purposes, predictive potential and statistical value. The present study was concerned with (1) the investigation of several parameters (longevity and weight) presently believed to influence the radiosensitivity of organisms, (2) to evaluate their relevance to the R.I., and (3) to apply the R.I. as a “biological tool” in the correlation of radiosensitivity with phylogeny in the class Insecta. 2. Method Each species studied was handled in terms of populations and all treated groups were irradiated as young adults or cohorts. If the species were relatively short-lived (e.g. 1 week), the adults were collected when very young (12+ 8 hr for lepidopterans). In species which were relatively longlived (4 months or longer), cohorts of young adults were treated when 1 week -& 3 days of age. Each lepidopteran species population was organized into six groups (mixed sexes), three control populations and three replicated treated populations. Each orthopteran species population was divided into eight groups; four male populations consisting of one control and three experimental replicates, and four female populations organized in the same manner as the males. All control and experimental replicates contained approximately 50 individuals. Carbon dioxide was used to anesthetize all species to facilitate their separation into control and experimental replicates. The insects were allowed adequate time for complete recovery from the anesthetic prior to irradiation. Moth populations were maintained in containers 2 1 in volume. To avoid overcrowding effects, roaches were maintained in containers ranging from 2-12 1 in volume, depending on the relative size of the roach species. Small roaches, like Blattella germanica, were housed in cages 2 1 in volume; intermediate-sized roaches, such as Peripheta americana, were housed in 7 1 cages, and the largest roaches, Blaberus giganteus, were maintained in 12 1 containers. Food (finely ground Purina Laboratory Chow) and water were provided daily. All populations were maintained at 27 f 2°C and 70 % relative humidity. Dry weights were obtained for each species (according to sex) by exposing 50-100 individuals (depending on relative size) to a temperature of lOOf2”C for 48 hr and then averaging the resulting weights. An Atomic Energy of Canada, Ltd gamma cell “200” containing 2430 Ci of 6oCo was used to irradiate the species studied. A dose rate of 100 rads/sec
151 resulted with an in-out dose of 450 rads. A total dose of 15,000 rads was utilized in making all the LT,, and LTioO determinations. Mortality was recorded at 12 hr intervals. The LTS, and LTloO values were determined from graphic relations or extrapolated from the literature.-The RI. parameter was then calculatedfrom the accumulateddata and employed as a “biological tool” for the investigation of radiosensitivity and subsequent correlation with insect phylogeny. A curvilinear regression analysis was used in the correlation of specieslongevity and dry weight with the R.I. This paper assumesthat survivorship, following irradiation, in species having long longevities is different from that found for specieswith short longevities (i.e. longevity is a valid measure of radiosensitivity), and that the interaction of many parameters (e.g. longevity, weight, stress,diet, etc.) ,resultsin an integrated physiology which manifestsa characteristicresponse to a given radiation dose. We make no claim that the theory presented here applies to all organisms-or even to all Insecta. It is merely another avenue of approach we feel worthy of investigation. Other comparative radiosensitivity theories, such as the nuclear volume approach, the relationship to cyanide resistance, and the protective action of amino acids also merit consideration. COMPARATIVE
RADIOSENSITIVITY
OF
INSECTS
3. Results and Dbcussion Table 1 summarizesR.I. values and associatedparameters for 37 insect speciesrepresenting eight orders. The index values ranged widely (0.20498) between orders and also within the sameorder (e.g. Coleoptera, 0+03483). There was a trend, however, for the R.I. values to be, in general, low in some orders (e.g. Orthoptera), high in some orders (e.g. Lepidoptera), and intermediate in other orders (e.g. Diptera). The R.I. values did not vary widely betweendifferent speciesof the samegenus(see Periplaneta, Tribolium, Cadra, and Drosophila, Table .l). Likewise, the index values for both sexes of the samespecieswere in closeagreementeven though the meanlongevities varied widely in many cases.According to the R.I., for the 12 specieswhere both sexeswere evaluated, males of two specieswere more resistant,females of seven specieswere more resistant, and both sexesof three specieswere equally resistant. Excluding extrapolated data for two species,a statistical analysis indicated there was no difference (0.05 level) in radiosensitivity (using the R.I.) betweensexesfor eight of the ten speciesstudied. However, according to LT,, values, the females of nine specieswere more resistant than males. Statistical analysis revealed (using LT,, values) that seven of these differences between the sexeswere significant (0.05 level). It appears that, according to the RI., there are only small differences in the radio-
Male M&F
Rhodn~us prolixus Crematogaster Iineolata
americana
Hymenoptera
PeripLmeta
Hemiptera
Orthoptera
Collembola Isoptea
Periplaneta americana Bkberus giganteus Bkberus giganteus Acheta domesticus Acheta domesticus Oncopeltus fasCiaus
Sex
M&F M&F M&F M&F Male Female Male Female Male Female Male Female Male Female Male Female Male Female M&F
Species
Onchuirus sp. Nasutitermes costalis Parvitermes discolor Nasutitermes nigriceps SupelIa supellectiiium Supella supellectilium BlatteDa germanica Blattella germanica BIotta orientalis Bkztta orientalis Periplaneta fuliginosa Periplaneta fuI&inosa
Order
Radiosensitivity
1
161-O 82.7
75 10.5 15-4 5.6 1459 165s 17@ 19&i 13@ 1405 1758 2005 3608 4008 40011 40011 26.8 29.1 26-3
Mean longevity (days)
27.5 0.1
18.6 28.6 24.6 28.8 112.2 202.6 143.5 204.6 323.8 4856 1659.2 1691.8 88-O 100.0 14.2
Mean d.wt (m)
15,810 15,000
15,000 12,000 12,000 12,000 15,000 15,000 15,000 15,000 15,cOO 15,ooo 15,000 15,000 15,000 15,000 15,000 15,000 15,000 15,000 15,000
Dose (ads)
46-O 18.3
4.6 3.5 15.0 17.7 15.2 16.5 12.0 12.3 9-o 13.4 7.3 9.2 12.6 16.1 3.7 5.7 8.5
50 0.9
LTco (days)
62.0
23.8 28.8 21.8 22.2 14.8 16.3 13.7 17.0 16.5 17.5 19.8 24.0 9.3 10.0
130
LTIOO (days)
of selected members of the class Znsecta
TABLE
0.29 022
0.67 O-09 0.30 O-63 0.10 0.11 0.09 0*09 0.09 O-09 0.05 0.07 0.02 0.02 o-02 0-W 0.14 0.20 0.32
R**‘t
Willard Willard Willard Menhinick ww Baldwin Menhinick (1969)
Edwards McMahan McMahan McMahan
& Shaver (1963) & Crossley
(1970) (1970) (1970) & Crossley
(1969) (1969) (1969) (1969)
Reference
Lepidoptera
Ghoptera
Hymenoptera
order
M&F M&F M&F M&F Male Female M&F M&F M&F M&F M&F M&F Male
Lasioderma serricorne Sitolphilus oryrae Dermestes ater Attagenus piceus Hatplus pennsylvanicus
Phflonthus sp. Tenebrio molitor
iwtolium castaneum Trtbolium cwnfwum
ComtracheIus nenuphar P[odio interpuncteIla Anagasta kuehniella Ephestia elutelia C&a cautella Cadra jigulilella Sitotroga cerealella Ostrinia nubilais
comtrachehbsnefllphar
Habrobracon juglandis
Male Female Male (haploidveinless) Male (haploid~&W M&F M&F M&F M&F M&F
Habrobracon jugWis Habrobracon juglandis Habrobracon jyglandis
SpecieS
4:; 0.9 2.4 0.7 1.4 1.0 l-5
::: i:; 8-O
0.7 0.9
47.0
15,000 15.000 15,000 15,000 15,000 15,000 15,000 15,000 15,000 15,Ooo 15,000
15,CnO lM@J
15,000 15,000 15,000 15,000 15,000
15,ooo
15,000 15,000 15,000
l-coatinued
111.6 188.2 90*5 574 4.8 5.4
704 29.2
;:i 9.3 224.4
4.7
62
62 92 62
TABLE
;:;
;:; 2.8 1.2 1.8
12.1 17.5 10.3 9.3
40.0 7-7
;:; 6.0
2.8 3.6
36-O
51.5 89-O 34-O
;:; 12.5
;::
;:;
21.3 32-O 15.7 13.3
12.0 12.0
o-74 060 O-64 0.91 0.91
0.11 O-09 0.11 0‘16 o*l?o 0.69
o-57 0.26
oa 0.47 O-83 o-73 0.03
0.38
O-83 o-97 0.55
Walker & Brindley (1963)
Has&t 8c Jenkins (1952) Hassett 8i Jenkins (1952) Hassett 8t Jenkins (1952) Haasett & Jenkins (1952) Me&hick & Crossley (1%9) Pdwards (1969) Menbinick & Crossley W-l Willard (1970) Willard (1970) Willard (1970) Willard (1970)
Clark & Rubin (l%l)
Clark & Rubii (1961) Clark & Rubii (1961) Clark & Rubin (1961)
Hippelates pasio Hippeplates pus121 Drosophila melanogaster Drosophila sabobscura Masca domestica Musca dompstica Aedes aegypti Aedes aegypti
Species Male Female M & F M &F Male Female Male Female
sex .
61.0 a.0 55.0 . :.; 39.4 30.6 65.4
0.1 0.1 0.2 O-2 2.7 2.9 0.5 O-8
15,000 15,000 15,ooo lS.ooO IS,ooo 15,000 15,009 15,000
Mean
Mean
275 24.0 49.5 88-O 26.3 29-4 18.0 37.0 50.0 51.3 35.0 49 *o
41 .o 54.0 86.0
O-46 0.37 090 O-98 0.70 0.75 O-59 0.57
Flint (1965) Flint (1965) strehlw (1964) Lamb (1964) Willard (1970) Willard (1970) Willard (1970) Willard (1970)
Reference
t Radiosensitivity index (LT,,/mean longevity) from Willard (1970). $ Mixed scx data was composed of termite workers and soldiers, and mean longevity estimated from data through communication. $ Estimated from Gould & Deay (1938, 1940) and from Cherry (unpublished). II Estimated from Piquett & Fales (1953) and Siverly (1962).
Diptera
Order
l-continued
TABLE
personal
COMPARATIVE
RADIOSENSITIVITY
OF
INSECTS
155
sensitivity of many insect specieswhich is attributable to sex. These results contradict the view usually held for mammals that females are more radioresistant than males. Perhaps the order level of taxonomic organization may be the pivotal point where the generalization relating radiosensitivity to phylogeny breaks down and other criteria. become more important as indicators of radiosensitivity. Willard (1970) indicated that the criteria reported to influence the radiosensitivity of organisms (age, weight, sex, diet, environmental factors, endocrine disturbances, etc.) may act; by altering the organisms’ physiology-and it is this interaction of ionizing radiation with the integrated physiology of an organism which results in a given effect. O’Brien k Wolfe (1964) reported that the effectsof ionizing radiation on insectsvary according to the order, genus, species,developmental stages and criteria employed. Weight is foremost of the parameters generally believed to have the greatest influence on radiosensitivity (Wharton & Wharton, 1959; Menhinick & Crossley, 1969; Baldwin & Shaver, 1963; Baxter 8z Tuttle, 1957; Odum, 1959). Although not conclusive, an earlier study (Willard, 1970) suggested a curvilinear relationship between the R.I. and both age and weight. When the mean longevities and dry weights of insectsinvestigated in the present study were plotted against the RI. (Fig. l), curvilinear relationships were obtained for both criteria-indicating a physiological relation. Figure 1 showsthat small, short-lived insectswere more resistantto ionizing radiation than large long-lived insects. Cole et al. (1959) investigated the effects of
50
100
350
40
Fro. 1. Rediosensititity of selef2tai members of the class InsefAa as a 0,longevlty; x --x,welgllt.. adult longevity and weight. O-
functi0n
Mean
150 longevity
200 (days),
250 mwn
300
dry weight
(trql
Of their
156
W.
K.
WILLARD
AND
D.
S.
CHERRY
gamma radiation on seven insect species(using LD50-24hr values)and reported that a lower dose was required to kill the largest insects. Menhiniclc 62 Dodson (1965) found a general trend correlating radiosensitivity with the wet weight of adult insects. They reported further that the larger orthopteran species studied were more radiosensitive than small species; similar results were also noted for three species of coleopterans and two species of hymenopterans. McMahan (1969) studying neotropical termite species, found that radiosensitivity increased with increasing size. Menhinick & Crossley (1969) suggested that radiosensitivity of insects was correlated with size regardless of taxonomic grouping, and further stated that this relationship improved within specific groupings (e.g. within orders). Odum (1959) also suggested that radiosensitivity was correlated with size. A curvilinear regression analysis for the longevity data (in relation to the R.I.) shown in Fig. 1 describes a prediction curve given by the following second degree polynomial equation y = 0~682#-0@416~+0WOOO61x~ where y represents the R.I. and x the mean longevity (days). The coefficient of determination was 46.3 % (i.e. 46.3 % of the observed variation could be attributed to mean longevity). A regression analysis was also performed for the dry weight data (in relation to the R.I.) shown in Fig. 1 which describes a prediction curve given by the following second degree polynomial equation y = 0.45829-O~O019461x+O~OOOO01014x2 where y represents the R.I. and x the mean dry weight (mg). The coefficient of determination was 32.6% (i.e. 32.6% of the observed variation could be attributed to dry weight). These results provide evidence that the radiosensitivity of insects is more readily influenced by longevity than by weight. It is almost certain that other parameters (sex, diet, endocrine disturbances, environmental factors, etc.) also influence radiosensitivity-but probably not to the same degree as longevity and mass (depending on the relative variability of the criterion and the conditions under which it is evaluated). The relationship between the radiosensitivity of organisms and phylogeny is only a “general rule” for the larger taxa (e.g. kingdom or class) and has not been shown to apply to the lower taxonomic categories (e.g. order, family, etc.). The R.I. values obtained in the present study were compared with the phylogeny of insect orders as presented by Ross (1955): although not conclusive, there appeared to be little correlation between radiosensitivity and the phylogeny of insect orders (or major order groupings). These results support the hypothesis made earlier, that the order level of taxonomic organization may be the “pivotal point” where the general-
COMPARATIVE
RADIOSENSITIVITY
OF INSECTS
157
ization relating radiosensitivity to phylogeny begins to break down. However, Fig. 2 shows that when the R.I. was related to mean longevity, a grouping of the species comprising each respective order occurred along the predicted regression curve. The prediction curve for weight is also shown for comparative convenience, although longevity data were used on the abscissa in plotting the observed values. The lepidopterans and dipterans were, in general, the most radiation resistant orders. Orthopterans were among the
0
50
100
150 Mean
200 longewty
250
300
350
,400
(days)
FIG. 2. Relativesensitivityof selected insectordersto i nizingradiationin relationto the predictedresponse curvefor the classinsecta.n , Colleqto la; 0, Isoptera;*, Orthoptera; 0, Hemiptera; x , Hymenoptera;A, Coleoptera;0, Ikpidoptera; v, Diptera; -, predictedcurve (longevity);- - -, predictedcurve(wkght).
most radiosensitive orders in which sensitivity appears to increase with increasing longevity (and size). Coleopterans were intermediate in sensitivity at the order level; within the order, however, radiosensitivity was intermediate between the observed longevity and weight curves. In conclusion, a good correlation of radiosensitivity (at the order level or below in the class Insecta) with some parameter or index does not seem likely since many factors (sex, diet, endocrine disturbance, etc.) affecting an organism’s response to ionizing radiation cannot be incorporated into a single index value. However, the R.I. as a “biological tool” did provide some measure of predictive value at the order taxonomic level in the class Insecta. Although the study does not provide the degree of predictability hoped for, it does nevertheless, focus attention on the problem.
158
W.
K.
WILLARD
AND
D.
S.
CHERRY
The authors acknowledge Drs D. A. Crossley and P. E. Hunter of the University of Georgia for technical assistance in the use of the e°Co source. We also thank Dr C. B. Loadholt of Clemson University for advice and assistance on the statistical procedures. This investigation was supported by MH Training grant No. 1Tl ES 60 from the Division of Environmental Health Sciences to Clemson University. REFERENCES BACQ,
Z. M.
& ALEXANDER,
P.
(1955). Fundamentals of Radiobiology. London: Butter-
worthsScientificPublications.
BALDWIN, W. F. & SHAVER, E. L. (1963). Can. J. Zool. 41, 637. BALOCK, J. A., BURDITT, A. K., JR, & CHRISTENSON, L. D. (1963). BAXTER, R. C. & TUTTLE, L. W. (1957). Radiat. Res. 7, 303.
1. econ.
Ent. 52, 42.
CLARK, A. M. (1961).Radiat. Res. 15, 515. CLARK, A. M. & RUBIN, M. A. (1961).Radiat. Res. 15, 244. COLE, M. M., LABRECQUE, G. C. & BURDEN, G. S. (1959). J. econ. Ent. 52, 448. DAVICH, T. B. & LINDQUIST, D. A. (1962). J. econ. Ent. 55, 164. EDWARDS,
C. A. (1969).Proc. 2ndnatn. Symp.Radioecology,Ann Arbor, Michigan.
ERDMAN, H. E. (1968).J. econ.Ent. 61, 123. FLINT, H. M. (1965). J. econ. Ent. 58, 555. GOULD, G. E. & DEAY, H. 0. (1938). Ann. ent. Sot. Am. 31, 489. GOULD, G. E. & DEAY, H. 0. (1940). Indiana agric. exp. Sta. Bull. 451. BASSETT, C. C. & JENKINS, D. W. (1952). Nucleonics 10, 42. Ives, P. T., HEILMAN, R. S. & &OUCH, H. H. (19.55). Genetics 40, 577. LAMB, M. J. (1964). J. Insect Physiol. 10, 487. MCMAHAN, E. (1969). Ann. ent. Sot. Am. 62, 120. MENWICK, E. F. & DODSON, G. J. (1965). In A. Progr. Rep. Period ending Jury 21, 1965.
Envr. Sciences
Div.,
Oak
Ridge
Natn.
Lab.,
Publ.
No.
130, 53.
MENHINICK, E. F. & CROSSLEY,D. A., JR (1968). Ann. ent. Sot. Am. 61, 1359. MENHINICK, E. F. & CROSSLEY,D. A., JR (1969). Ann. ent. Sot. Am. 62, 711. O’BRIEN, R. D. & WOLFE, L. S. (1964).Radiation, Radioactivity and Insects. New York: Academic Press. ODUM, E. P. (1959). Fundamentals of PIQ~IXT, P. G. & FALE.S, J. H. (1953).
Ecology. Philadelphia: W. B. Saunders J. econ. Ent. 46, 1089.
Co.
Ross,H. H. (1955).fir. News66,197.
SIWRLY, R. E. (1962). Rearing Insects in Schools. Dubuque,
Iowa: Wm C. Brown STRBHLER, B. L. (1964). J. Geront. 19, 83. WALKER, J. R. & BRINDLEY, T. A. (1963). J. econ. Ent. 56, 522. WHARTON, D. R. A. & WHARTON, M. L. (1959). Radiat. Res. 11, 600.
WILLARD, W. K. (1970). ASB Bull. 17, 70.
Co.
Comparative RaQiosensitivity in the Class Insecta WILLIAM K. WILLARD ,+D
DONALD S.CHFBRY~
Department of Zoology, Clemson University, Clemson, South Carolina 29631, U.S.A. (Received 13 May 1974, and in revisedform 7 October 1974) A “radiosensitivity index” (LTJmean longevity) was correlated with the mean longevity and dry weight of 37 insect species(both sexesof 12 species)
representing eight orders. Curvilinear regression analysis reIating radiosensitivity to mean longevity and mean dry weight indicated that 46.3% of the observed variation could be attributed to longevity and 32.6% to the dry weight of the species. In general, large long-lived adults were more radiosensitive than small short-lived ad&s. Correlation of the phylogeny of insect orders and order groupings with the radio-sensitivity index was found to be poor. However, when the index was related to longevity, there was a tendency for species comprising the major orders
investigated to occur in groups along the predicted curve.
There are numerous exceptions to the generalization correlating animal radiosensitivity with phylogeny (Bacq & Alexander, 1955). Variations have been such that the predictive value of the concept has been of little significance. One reason for this lack of predictability is that investigators have utilized such a wide variety of approaches that consolidation of their findings into principles having predictive value has not been possible. The radiosensitivity of organisms has been evaluated mainly in terms of the LD,, (Ives, Heihnan 8z Plough, 1955; Cole, LaBrecque 8~ Burden, 1959; Balock, Burditt & Christenson, 1963; Erdman, 1968) and the LT5,, (Wharton & Wharton, 1959; Clark, 1961; Davich & Lindquist, 1962; Flint, 1965; Menhinick 8i Crossley, 1968, 1969; McMahon, 1969). The disadvantages of these parameters have already been pointed out (Menhinick & Crossley, 1969; Willard, 1970). Willard (1970) suggested a “radio-sensitivity index” (hereafter referred to as R.I.) which expresses a time response to radiation exposure in terms of a species mean longevity R.I. = LT,e/mean longevity. t Ibent IIbtehe
adkss: Vii
Department of Environmental Science,Virginia Polytechnic Institute, 24060, U.S.A. 149
150
W.
K.
WILLARD
AND
D.
S.
CHERRY
The LTS, represents the time required, following irradiation, for 50% of a population to die. This parameter (R.I.), like the LT, has the disadvantage of requiring a single dose (and dose rate); however, it has the advantage of broad applicability for comparative purposes, predictive potential and statistical value. The present study was concerned with (1) the investigation of several parameters (longevity and weight) presently believed to influence the radiosensitivity of organisms, (2) to evaluate their relevance to the R.I., and (3) to apply the R.I. as a “biological tool” in the correlation of radiosensitivity with phylogeny in the class Insecta. 2. Method Each species studied was handled in terms of populations and all treated groups were irradiated as young adults or cohorts. If the species were relatively short-lived (e.g. 1 week), the adults were collected when very young (12+ 8 hr for lepidopterans). In species which were relatively longlived (4 months or longer), cohorts of young adults were treated when 1 week -& 3 days of age. Each lepidopteran species population was organized into six groups (mixed sexes), three control populations and three replicated treated populations. Each orthopteran species population was divided into eight groups; four male populations consisting of one control and three experimental replicates, and four female populations organized in the same manner as the males. All control and experimental replicates contained approximately 50 individuals. Carbon dioxide was used to anesthetize all species to facilitate their separation into control and experimental replicates. The insects were allowed adequate time for complete recovery from the anesthetic prior to irradiation. Moth populations were maintained in containers 2 1 in volume. To avoid overcrowding effects, roaches were maintained in containers ranging from 2-12 1 in volume, depending on the relative size of the roach species. Small roaches, like Blattella germanica, were housed in cages 2 1 in volume; intermediate-sized roaches, such as Peripheta americana, were housed in 7 1 cages, and the largest roaches, Blaberus giganteus, were maintained in 12 1 containers. Food (finely ground Purina Laboratory Chow) and water were provided daily. All populations were maintained at 27 f 2°C and 70 % relative humidity. Dry weights were obtained for each species (according to sex) by exposing 50-100 individuals (depending on relative size) to a temperature of lOOf2”C for 48 hr and then averaging the resulting weights. An Atomic Energy of Canada, Ltd gamma cell “200” containing 2430 Ci of 6oCo was used to irradiate the species studied. A dose rate of 100 rads/sec
151 resulted with an in-out dose of 450 rads. A total dose of 15,000 rads was utilized in making all the LT,, and LTioO determinations. Mortality was recorded at 12 hr intervals. The LTS, and LTloO values were determined from graphic relations or extrapolated from the literature.-The RI. parameter was then calculatedfrom the accumulateddata and employed as a “biological tool” for the investigation of radiosensitivity and subsequent correlation with insect phylogeny. A curvilinear regression analysis was used in the correlation of specieslongevity and dry weight with the R.I. This paper assumesthat survivorship, following irradiation, in species having long longevities is different from that found for specieswith short longevities (i.e. longevity is a valid measure of radiosensitivity), and that the interaction of many parameters (e.g. longevity, weight, stress,diet, etc.) ,resultsin an integrated physiology which manifestsa characteristicresponse to a given radiation dose. We make no claim that the theory presented here applies to all organisms-or even to all Insecta. It is merely another avenue of approach we feel worthy of investigation. Other comparative radiosensitivity theories, such as the nuclear volume approach, the relationship to cyanide resistance, and the protective action of amino acids also merit consideration. COMPARATIVE
RADIOSENSITIVITY
OF
INSECTS
3. Results and Dbcussion Table 1 summarizesR.I. values and associatedparameters for 37 insect speciesrepresenting eight orders. The index values ranged widely (0.20498) between orders and also within the sameorder (e.g. Coleoptera, 0+03483). There was a trend, however, for the R.I. values to be, in general, low in some orders (e.g. Orthoptera), high in some orders (e.g. Lepidoptera), and intermediate in other orders (e.g. Diptera). The R.I. values did not vary widely betweendifferent speciesof the samegenus(see Periplaneta, Tribolium, Cadra, and Drosophila, Table .l). Likewise, the index values for both sexes of the samespecieswere in closeagreementeven though the meanlongevities varied widely in many cases.According to the R.I., for the 12 specieswhere both sexeswere evaluated, males of two specieswere more resistant,females of seven specieswere more resistant, and both sexesof three specieswere equally resistant. Excluding extrapolated data for two species,a statistical analysis indicated there was no difference (0.05 level) in radiosensitivity (using the R.I.) betweensexesfor eight of the ten speciesstudied. However, according to LT,, values, the females of nine specieswere more resistant than males. Statistical analysis revealed (using LT,, values) that seven of these differences between the sexeswere significant (0.05 level). It appears that, according to the RI., there are only small differences in the radio-
Male M&F
Rhodn~us prolixus Crematogaster Iineolata
americana
Hymenoptera
PeripLmeta
Hemiptera
Orthoptera
Collembola Isoptea
Periplaneta americana Bkberus giganteus Bkberus giganteus Acheta domesticus Acheta domesticus Oncopeltus fasCiaus
Sex
M&F M&F M&F M&F Male Female Male Female Male Female Male Female Male Female Male Female Male Female M&F
Species
Onchuirus sp. Nasutitermes costalis Parvitermes discolor Nasutitermes nigriceps SupelIa supellectiiium Supella supellectilium BlatteDa germanica Blattella germanica BIotta orientalis Bkztta orientalis Periplaneta fuliginosa Periplaneta fuI&inosa
Order
Radiosensitivity
1
161-O 82.7
75 10.5 15-4 5.6 1459 165s 17@ 19&i 13@ 1405 1758 2005 3608 4008 40011 40011 26.8 29.1 26-3
Mean longevity (days)
27.5 0.1
18.6 28.6 24.6 28.8 112.2 202.6 143.5 204.6 323.8 4856 1659.2 1691.8 88-O 100.0 14.2
Mean d.wt (m)
15,810 15,000
15,000 12,000 12,000 12,000 15,000 15,000 15,000 15,000 15,cOO 15,ooo 15,000 15,000 15,000 15,000 15,000 15,000 15,000 15,000 15,000
Dose (ads)
46-O 18.3
4.6 3.5 15.0 17.7 15.2 16.5 12.0 12.3 9-o 13.4 7.3 9.2 12.6 16.1 3.7 5.7 8.5
50 0.9
LTco (days)
62.0
23.8 28.8 21.8 22.2 14.8 16.3 13.7 17.0 16.5 17.5 19.8 24.0 9.3 10.0
130
LTIOO (days)
of selected members of the class Znsecta
TABLE
0.29 022
0.67 O-09 0.30 O-63 0.10 0.11 0.09 0*09 0.09 O-09 0.05 0.07 0.02 0.02 o-02 0-W 0.14 0.20 0.32
R**‘t
Willard Willard Willard Menhinick ww Baldwin Menhinick (1969)
Edwards McMahan McMahan McMahan
& Shaver (1963) & Crossley
(1970) (1970) (1970) & Crossley
(1969) (1969) (1969) (1969)
Reference
Lepidoptera
Ghoptera
Hymenoptera
order
M&F M&F M&F M&F Male Female M&F M&F M&F M&F M&F M&F Male
Lasioderma serricorne Sitolphilus oryrae Dermestes ater Attagenus piceus Hatplus pennsylvanicus
Phflonthus sp. Tenebrio molitor
iwtolium castaneum Trtbolium cwnfwum
ComtracheIus nenuphar P[odio interpuncteIla Anagasta kuehniella Ephestia elutelia C&a cautella Cadra jigulilella Sitotroga cerealella Ostrinia nubilais
comtrachehbsnefllphar
Habrobracon juglandis
Male Female Male (haploidveinless) Male (haploid~&W M&F M&F M&F M&F M&F
Habrobracon jugWis Habrobracon juglandis Habrobracon jyglandis
SpecieS
4:; 0.9 2.4 0.7 1.4 1.0 l-5
::: i:; 8-O
0.7 0.9
47.0
15,000 15.000 15,000 15,000 15,000 15,000 15,000 15,000 15,000 15,Ooo 15,000
15,CnO lM@J
15,000 15,000 15,000 15,000 15,000
15,ooo
15,000 15,000 15,000
l-coatinued
111.6 188.2 90*5 574 4.8 5.4
704 29.2
;:i 9.3 224.4
4.7
62
62 92 62
TABLE
;:;
;:; 2.8 1.2 1.8
12.1 17.5 10.3 9.3
40.0 7-7
;:; 6.0
2.8 3.6
36-O
51.5 89-O 34-O
;:; 12.5
;::
;:;
21.3 32-O 15.7 13.3
12.0 12.0
o-74 060 O-64 0.91 0.91
0.11 O-09 0.11 0‘16 o*l?o 0.69
o-57 0.26
oa 0.47 O-83 o-73 0.03
0.38
O-83 o-97 0.55
Walker & Brindley (1963)
Has&t 8c Jenkins (1952) Hassett 8i Jenkins (1952) Hassett 8t Jenkins (1952) Haasett & Jenkins (1952) Me&hick & Crossley (1%9) Pdwards (1969) Menbinick & Crossley W-l Willard (1970) Willard (1970) Willard (1970) Willard (1970)
Clark & Rubin (l%l)
Clark & Rubii (1961) Clark & Rubii (1961) Clark & Rubin (1961)
Hippelates pasio Hippeplates pus121 Drosophila melanogaster Drosophila sabobscura Masca domestica Musca dompstica Aedes aegypti Aedes aegypti
Species Male Female M & F M &F Male Female Male Female
sex .
61.0 a.0 55.0 . :.; 39.4 30.6 65.4
0.1 0.1 0.2 O-2 2.7 2.9 0.5 O-8
15,000 15,000 15,ooo lS.ooO IS,ooo 15,000 15,009 15,000
Mean
Mean
275 24.0 49.5 88-O 26.3 29-4 18.0 37.0 50.0 51.3 35.0 49 *o
41 .o 54.0 86.0
O-46 0.37 090 O-98 0.70 0.75 O-59 0.57
Flint (1965) Flint (1965) strehlw (1964) Lamb (1964) Willard (1970) Willard (1970) Willard (1970) Willard (1970)
Reference
t Radiosensitivity index (LT,,/mean longevity) from Willard (1970). $ Mixed scx data was composed of termite workers and soldiers, and mean longevity estimated from data through communication. $ Estimated from Gould & Deay (1938, 1940) and from Cherry (unpublished). II Estimated from Piquett & Fales (1953) and Siverly (1962).
Diptera
Order
l-continued
TABLE
personal
COMPARATIVE
RADIOSENSITIVITY
OF
INSECTS
155
sensitivity of many insect specieswhich is attributable to sex. These results contradict the view usually held for mammals that females are more radioresistant than males. Perhaps the order level of taxonomic organization may be the pivotal point where the generalization relating radiosensitivity to phylogeny breaks down and other criteria. become more important as indicators of radiosensitivity. Willard (1970) indicated that the criteria reported to influence the radiosensitivity of organisms (age, weight, sex, diet, environmental factors, endocrine disturbances, etc.) may act; by altering the organisms’ physiology-and it is this interaction of ionizing radiation with the integrated physiology of an organism which results in a given effect. O’Brien k Wolfe (1964) reported that the effectsof ionizing radiation on insectsvary according to the order, genus, species,developmental stages and criteria employed. Weight is foremost of the parameters generally believed to have the greatest influence on radiosensitivity (Wharton & Wharton, 1959; Menhinick & Crossley, 1969; Baldwin & Shaver, 1963; Baxter 8z Tuttle, 1957; Odum, 1959). Although not conclusive, an earlier study (Willard, 1970) suggested a curvilinear relationship between the R.I. and both age and weight. When the mean longevities and dry weights of insectsinvestigated in the present study were plotted against the RI. (Fig. l), curvilinear relationships were obtained for both criteria-indicating a physiological relation. Figure 1 showsthat small, short-lived insectswere more resistantto ionizing radiation than large long-lived insects. Cole et al. (1959) investigated the effects of
50
100
350
40
Fro. 1. Rediosensititity of selef2tai members of the class InsefAa as a 0,longevlty; x --x,welgllt.. adult longevity and weight. O-
functi0n
Mean
150 longevity
200 (days),
250 mwn
300
dry weight
(trql
Of their
156
W.
K.
WILLARD
AND
D.
S.
CHERRY
gamma radiation on seven insect species(using LD50-24hr values)and reported that a lower dose was required to kill the largest insects. Menhiniclc 62 Dodson (1965) found a general trend correlating radiosensitivity with the wet weight of adult insects. They reported further that the larger orthopteran species studied were more radiosensitive than small species; similar results were also noted for three species of coleopterans and two species of hymenopterans. McMahan (1969) studying neotropical termite species, found that radiosensitivity increased with increasing size. Menhinick & Crossley (1969) suggested that radiosensitivity of insects was correlated with size regardless of taxonomic grouping, and further stated that this relationship improved within specific groupings (e.g. within orders). Odum (1959) also suggested that radiosensitivity was correlated with size. A curvilinear regression analysis for the longevity data (in relation to the R.I.) shown in Fig. 1 describes a prediction curve given by the following second degree polynomial equation y = 0~682#-0@416~+0WOOO61x~ where y represents the R.I. and x the mean longevity (days). The coefficient of determination was 46.3 % (i.e. 46.3 % of the observed variation could be attributed to mean longevity). A regression analysis was also performed for the dry weight data (in relation to the R.I.) shown in Fig. 1 which describes a prediction curve given by the following second degree polynomial equation y = 0.45829-O~O019461x+O~OOOO01014x2 where y represents the R.I. and x the mean dry weight (mg). The coefficient of determination was 32.6% (i.e. 32.6% of the observed variation could be attributed to dry weight). These results provide evidence that the radiosensitivity of insects is more readily influenced by longevity than by weight. It is almost certain that other parameters (sex, diet, endocrine disturbances, environmental factors, etc.) also influence radiosensitivity-but probably not to the same degree as longevity and mass (depending on the relative variability of the criterion and the conditions under which it is evaluated). The relationship between the radiosensitivity of organisms and phylogeny is only a “general rule” for the larger taxa (e.g. kingdom or class) and has not been shown to apply to the lower taxonomic categories (e.g. order, family, etc.). The R.I. values obtained in the present study were compared with the phylogeny of insect orders as presented by Ross (1955): although not conclusive, there appeared to be little correlation between radiosensitivity and the phylogeny of insect orders (or major order groupings). These results support the hypothesis made earlier, that the order level of taxonomic organization may be the “pivotal point” where the general-
COMPARATIVE
RADIOSENSITIVITY
OF INSECTS
157
ization relating radiosensitivity to phylogeny begins to break down. However, Fig. 2 shows that when the R.I. was related to mean longevity, a grouping of the species comprising each respective order occurred along the predicted regression curve. The prediction curve for weight is also shown for comparative convenience, although longevity data were used on the abscissa in plotting the observed values. The lepidopterans and dipterans were, in general, the most radiation resistant orders. Orthopterans were among the
0
50
100
150 Mean
200 longewty
250
300
350
,400
(days)
FIG. 2. Relativesensitivityof selected insectordersto i nizingradiationin relationto the predictedresponse curvefor the classinsecta.n , Colleqto la; 0, Isoptera;*, Orthoptera; 0, Hemiptera; x , Hymenoptera;A, Coleoptera;0, Ikpidoptera; v, Diptera; -, predictedcurve (longevity);- - -, predictedcurve(wkght).
most radiosensitive orders in which sensitivity appears to increase with increasing longevity (and size). Coleopterans were intermediate in sensitivity at the order level; within the order, however, radiosensitivity was intermediate between the observed longevity and weight curves. In conclusion, a good correlation of radiosensitivity (at the order level or below in the class Insecta) with some parameter or index does not seem likely since many factors (sex, diet, endocrine disturbance, etc.) affecting an organism’s response to ionizing radiation cannot be incorporated into a single index value. However, the R.I. as a “biological tool” did provide some measure of predictive value at the order taxonomic level in the class Insecta. Although the study does not provide the degree of predictability hoped for, it does nevertheless, focus attention on the problem.
158
W.
K.
WILLARD
AND
D.
S.
CHERRY
The authors acknowledge Drs D. A. Crossley and P. E. Hunter of the University of Georgia for technical assistance in the use of the e°Co source. We also thank Dr C. B. Loadholt of Clemson University for advice and assistance on the statistical procedures. This investigation was supported by MH Training grant No. 1Tl ES 60 from the Division of Environmental Health Sciences to Clemson University. REFERENCES BACQ,
Z. M.
& ALEXANDER,
P.
(1955). Fundamentals of Radiobiology. London: Butter-
worthsScientificPublications.
BALDWIN, W. F. & SHAVER, E. L. (1963). Can. J. Zool. 41, 637. BALOCK, J. A., BURDITT, A. K., JR, & CHRISTENSON, L. D. (1963). BAXTER, R. C. & TUTTLE, L. W. (1957). Radiat. Res. 7, 303.
1. econ.
Ent. 52, 42.
CLARK, A. M. (1961).Radiat. Res. 15, 515. CLARK, A. M. & RUBIN, M. A. (1961).Radiat. Res. 15, 244. COLE, M. M., LABRECQUE, G. C. & BURDEN, G. S. (1959). J. econ. Ent. 52, 448. DAVICH, T. B. & LINDQUIST, D. A. (1962). J. econ. Ent. 55, 164. EDWARDS,
C. A. (1969).Proc. 2ndnatn. Symp.Radioecology,Ann Arbor, Michigan.
ERDMAN, H. E. (1968).J. econ.Ent. 61, 123. FLINT, H. M. (1965). J. econ. Ent. 58, 555. GOULD, G. E. & DEAY, H. 0. (1938). Ann. ent. Sot. Am. 31, 489. GOULD, G. E. & DEAY, H. 0. (1940). Indiana agric. exp. Sta. Bull. 451. BASSETT, C. C. & JENKINS, D. W. (1952). Nucleonics 10, 42. Ives, P. T., HEILMAN, R. S. & &OUCH, H. H. (19.55). Genetics 40, 577. LAMB, M. J. (1964). J. Insect Physiol. 10, 487. MCMAHAN, E. (1969). Ann. ent. Sot. Am. 62, 120. MENWICK, E. F. & DODSON, G. J. (1965). In A. Progr. Rep. Period ending Jury 21, 1965.
Envr. Sciences
Div.,
Oak
Ridge
Natn.
Lab.,
Publ.
No.
130, 53.
MENHINICK, E. F. & CROSSLEY,D. A., JR (1968). Ann. ent. Sot. Am. 61, 1359. MENHINICK, E. F. & CROSSLEY,D. A., JR (1969). Ann. ent. Sot. Am. 62, 711. O’BRIEN, R. D. & WOLFE, L. S. (1964).Radiation, Radioactivity and Insects. New York: Academic Press. ODUM, E. P. (1959). Fundamentals of PIQ~IXT, P. G. & FALE.S, J. H. (1953).
Ecology. Philadelphia: W. B. Saunders J. econ. Ent. 46, 1089.
Co.
Ross,H. H. (1955).fir. News66,197.
SIWRLY, R. E. (1962). Rearing Insects in Schools. Dubuque,
Iowa: Wm C. Brown STRBHLER, B. L. (1964). J. Geront. 19, 83. WALKER, J. R. & BRINDLEY, T. A. (1963). J. econ. Ent. 56, 522. WHARTON, D. R. A. & WHARTON, M. L. (1959). Radiat. Res. 11, 600.
WILLARD, W. K. (1970). ASB Bull. 17, 70.
Co.
