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1969
Journal of the Lepidopterists Society
257
as a collector at Sukabumi, south of Djakarta, Java, Indonesia. This specimen is being deposited with the American Museum of Natural History, New York.
I name this species as an expression of my deepest gratitude to Arthur Moeck, of Milwaukee, Wisconsin, U.S.A., for all the co-operation and encouragement received from him over a period of years.
Acknowledgments I am indebted in describing either or both of these specimens to: Captain Henry Pillichody, my brother-in-law, now residing in Switzerland; Dr. Karl Jordan, chief of Tring Museum; Dr. Tarns, director of the Entomological Section of the British Museum of Natural History; Mr. Riley, first assistant of the lepidopterological collections of the British Museum of Natural History.
THE EFFECT OF X-IRRADIATION ON THE LARVAE OF COLIAS PHILODICE (PIERIDAE)
Richard A. Arnold
735 McKinley, Hinsdale, Illinois
Extensive studies on the effects of X-irradiation on Lepidoptera have not been reported. I believe that lack of interest is due to statements in the literature that members of the Lepidoptera are very resistant to radiation. In a series of experiments, I have found that larvae of Lepidoptera are quite sensitive and responsive to moderate dosages of X-rays. In a previous paper, we reported observations on the marked sensitivity of the larvae of Papilio polyxenes asterius Stoll to radiation (Arnold & Arnold, 1968). In the present paper I show that larvae of Colias philodice Godart are somewhat more tolerant to moderate dosages of X-rays. The resulting adults showed a variety of deformities, which are being studied histologically.
Materials and Experimental Methods Females were collected August 16, 1966, near Palos Park, in Cook County, Illinois. They were immediately caged with their foodplant red clover, Trifolium pratense L. A total of 390 ova were deposited by the same evening. On August 22, 265 larvae emerged. The remaining ova hatched on August 23 and 24. The 260 larvae used for the experiment
258 Arnold: X-irradiation effects Colias Vol. 23, no. 4
were reared under identical conditions for two days. Clear plastic boxes, measuring 5" X 5" X 1W\ housed the larvae. Air holes were made to supply sufficient air for the 40 larvae in each box. The foodplant used was Trifolium pratense L.
The larvae were allowed to mature at their normal rate until August 24. The two-day-old larvae were then divided into five groups: four groups of 40 to be irradiated and one group of 100 for a control. All were first instar larvae. On this day, the four groups were irradiated at dosages of 1500r, 3000r, 4500r, and 6000r. Irradiation factors were 250 Kv, 15 MA, no filter, dosage rate = 233r/10 second, target distance = 17 cm. Irradiation was carried out with a Phillips machine and at a temperature of 72°F. Precautions were taken to avoid "backscatter." The four groups of larvae were irradiated in the open, clear plastic boxes and afterwards transferred to new boxes and fresh foodplant.
Results
Thirty-four of the 160 irradiated larvae pupated. This was quite surprising in that none of the irradiated larvae of Papilio polyxenes asterius, living under the same conditions, survived to pupate (Arnold & Arnold, 1968). From these 34 Colias pupae, 24 adults emerged. The greatest loss of larvae in the four irradiated groups occurred within two days following irradiation. The larvae in the irradiated groups continued to expire gradually. Death usually occurred during the process of moulting, and this trend was also noted with irradiated larvae of Papilio polyxenes asterius (Arnold & Arnold, 1968). A large number of the remaining larvae died while preparing for pupation. The larvae were periodically observed with a dissecting microscope at 23x and 30X for external effects of the X-irradiation. There were no signs of radiation burns or any major differences in color, patterns, etc., noted on the larvae. The lengths of the larvae were measured periodically, and variations in length appeared to fall into the normal range of variation. A few larvae of each of the four irradiated groups survived to pupate. More than half the 24 adults were deformed. These deformities were primarily in the wings, but other deformities were observed and are being studied.
By comparison, 77% of the control larvae pupated. Four of the control pupae died. Perfect adults emerged from the remaining 95% of these pupae.
Discussion
The effects of X-irradiation on Lepidoptera have not been adequately studied. There is a general feeling in the literature that the Lepidoptera
1969
Journal of the Lepidopterists Society
259
are quite resistant to irradiation. There have been a few studies of the sterilization effects of gamma radiation (same as X-rays) on Lepidoptera, which are agricultural pests. The dosages used were in the range of 30,000-40,000 rads. Pupae and adults were exposed to such dosages without lethality. Yet in the present experiment and the previous one (Arnold & Arnold, 1968), a dosage of 1500r was sufficient to kill larvae. This may not be the best comparison inasmuch as different stages of development of different species of Lepidoptera were exposed to the dosages of radiation. I have found only one reference to effects of X-irradiation on larvae of Lepidoptera (Whiting, 1950). He showed that a dose of 40,000r of X-rays prevented pupation of the flour moth, Anagasta kiihniella (Zeller), many specimens of which continued to live as larvae up to 40 days, i.e. 37 days after the controls pupated.
In a previous report (Arnold & Arnold, 1968), eight day old larvae of Papilio polyxenes asterius were exposed in groups to dosages of 1500r, 3000r, 4500r, and 6000r and all the exposed larvae succumbed by the 17th day following radiation. In the present study, two day old larvae of Colias philodice were exposed to the same dosages of X-irradiation with the surprising result that 21% of the irradiated larvae survived to pupate. It seemed that irradiation of younger larvae of Colias philodice would be more lethal since younger developing tissues are usually more susceptible to X-irradiation damage. In the case of asterius, the lethal dose would seem to be below 1500r, possibly in the vicinity of 750-1000r. The lethal dose for philodice would appear to be above 6000r. Thus philodice could possibly tolerate up to 10 times as much radiation as asterius.
Both asterius and philodice larvae suffered their greatest loses within a short time after their exposure to X-irradiation. Deaths also occurred at times of moulting. The asterius died while in their second and third moults, philodice expired while in their first, second, third, and fourth moults and while preparing for pupation. Ten of the 34 philodice pupae died as pupae. Thus the radiation responses observed for the two species seem to be of two types, an early and a latent. The early responses appear almost immediately, within a day or two after irradiation, and the latent responses develop when moulting or pupation stages began. The explanation for the latent damage possibly may rest upon the findings of Baldwin and Salthouse (1959a, b; J 961). They found latent effects of radiation sometimes occur during a brief period of intense mitotic activity which takes place when the insects pass from one instar to another by moulting. If the insect is irradiated prior to moulting,
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visible damage and death may not show up until moulting occurs. The larvae of philodice and asterius were irradiated in their first and second instars respectively. None of the larvae had visibly begun the moulting process, though it is likely many had begun the period of intense mitotic activity which precedes moulting. Thus it is quite possible that many of the larvae of the two groups which exhibited an early response may have been exposed to the X-irradiation when in the process of the intense mitotic activity preceding their moult. The latent response, as Baldwin and Salthouse predicted, appeared when moulting occurred.
The question also arises as to why did some of the philodice survive to pupate. Perhaps the answer to this question may be dependent upon which stage of mitosis the philodice was irradiated or whether some of the larvae had probably not advanced to the period of intense mitotic activity. The metaphase is known to be the stage of mitosis to suffer the greatest effects of radiation damage. Thus a philodice larvae irradiated while in telophase could likely have survived to pupate.
This difference in the survival response between philodice and asterius to radiation is being investigated further. Perhaps the different species of Lepidoptera vary in sensitivity to radiation. A comparative analysis utilizing larvae of similar ages of these two species is under study for a more appropriate comparison of sensitivity and the actual changes seen post irradiation.
Summary The present study reports the reaction of the larvae of Colias philodice to moderate doses of X-rays. When exposed to the same doses of X-rays, the philodice proved to be much more resistant than the larvae of Papilio polyxenes asterius. Twenty-one percent of the philodice following radiation survived to pupate, whereas none of the asterius survived. Approximately one-half of the philodice adults which emerged were defolined. Studies will be made to obtain further comparisons of the effects of X-rays on the other members of the Lepidoptera.
Literature Cited
Arnold, R. A., and A. Arnold, 1968. The effect of X-irradiation on the larvae of Papilio polyxenes asterius (Papilionidae). J. Lepid. Soc., 22: 173-177.
Baldwin, W. F., and T. N. Salthouse, 1959. Latent radiation damage and
synchronous cell division in epidermis of an insect. I. Non-reversible effects
leading to local radiation burns. Radiation Research, 10: 387.
1959. Ibid. II. Reversible Effects in Burn Repair. Radiation Research, 10: 397.
1961. Ibid. III. Spontaneous Reversal of Effects Leading to Delay During
Mitosis. Radiation Research, 14: 426.
Whiting, A. R., 1950. Failure of pupation of Ephestia Larvae following exposure to X-irradiation. Anatomical Record, 108: 609.