Radiac. Phys. Chem. Vol. 34, No. 6, pp. 979-984, 1989 Int. J. Radiat. Appl. Instrum., Parr C Printed in Great Britain

0146-5724/89 $3.00 + 0.00 Pergamon Press plc

GAMMA IRRADIATION: EFFECT OF DOSE AND DOSE RATE ON DEVELOPMENT OF MATURE CODLING

MOTH LARVAE AND ADULT ECLOSION

ARTHUR K. BURDITT JR,‘? FRANK P. HUNGATE* and H. HAROLD TOBA’$

‘Yakima Agricultural Research Laboratory, Agricultural Research Service, U.S. Department of Agricul- ture, Yakima, WA 98902 and ‘Battelle Pacific Northwest Laboratory, Richland, WA 99352, U.S.A.

(Received 10 February 1989; accepted 16 May 1989)

Abstract-Codling moth, CydiupomoneNa (L.), larvae infest apples, pears and many other fruits and nuts. Mature, nondiapausing, cocooned larvae in fiberboard strips were exposed to y-irradiation at applied doses ranging from 0 to 98 Gy and dose rates from 0.77 to 204.4 Gy/min and subsequently held to permit further development, pupation and adult emergence. At or above an applied dose of 58 Gy, many of the adults that emerged were physically deformed and most were males. As the applied dose increased from 44 to 98 Gy, the percentage of normal adults decreased, the primary effect shifting from a higher percentage of abnormal adults, pupa1 mortality, to larval mortality. The effects were more pronounced at higher than at lower dose rates. Insect development apparently was not affected when larvae were irradiated at applied doses up to 3 1.7 Gy. Significantly more adults emerged when larvae were treated at low dose rates (1.0 Gy/min) than at higher dose rates (204 Gy/min). A rate of 52.2 Gy/min was more effective at preventing adult emergence than rates of 1, 4.4 or 201.5 Gy/min.

INTRODUCTION

Extensive research has been conducted over the past 35 yr on the effects of y-irradiation on fruits, vegeta- bles and other food commodities. Much of this research has been to determine if radiation would be an effective technology to reduce or eliminate insect and pathogen infestations. Doses of less than 1000 Gy can be used for insect disinfestation, as well as to prevent sprouting and delay ripening of some commodities. Higher doses are required for control of pathogens. However, doses as low as 100 Gy, or less, when applied to insect eggs or larvae will prevent adult eclosion or result in eclosion of abnormal adults unable to reproduce.

Larvae of the codling moth, Cydin pomonella (L.), infest apples, pears, and many other deciduous fruit and nut crops throughout most of the world, with a few exceptions, two of which are Japan and Korea. Their regulatory agencies have imposed quarantine restrictions against importation of host commodities from infested areas.

In the northwestern United States the codling moth usually has two generations. Mature larvae usually leave the fruit, spin cocoons, pupate and subse- quently emerge as adults. Second generation larvae mature in late summer and leave the fruit in search of a suitable site where they can spin a cocoon and overwinter as larvae in diapause. In the spring larvae form pupae and adults emerge, mate and lay eggs.

TPresent address: 9068-C SW 82nd Terrace, Ocala, FL 32676, U.S.A.

$To whom correspondence and reprint requests should be addressed.

Research on the effects of y-irradiation on codling moth pupae and adults was initiated over 25 yr ago to determine the potential of the Sterile Insect Tech- nique as a method for suppression or eradication of codling moth populations (Proverbs et al., 1966; Butt et al., 1973; White et al., 1976; Proverbs et al., 1982). Recently research was initiated to determine the effects of y-irradiation applied to larvae on subse- quent development, pupation and adult emergence to determine its potential use as a quarantine treatment for infested commodities (Burditt and Moffitt, 1985; Burditt et al., 1985). Most of these studies were conducted using 6oCo sources with doses up to 300 Gy and dose rates ranging from 15 to 20 Gy/min.

There have been limited studies on the effects of dose rate on development of insects. Nair and Subramanyam (1963) reported on viability of red flour beetle, Tribolium castaneum (Herbst), eggs and on fecundity and fertility of adults exposed to ““Co at different dose rates. They found that when 2-day old eggs were exposed to 20 Gy at rates of 0, 10.2, 35.2, 474.2, 815.5 and 1400 Gy/h, viability was 78.3, 55.3, 33.3, 7.0, 24.3 and 35.6%, respectively. When 7-day old adults were exposed to 50Gy at rates of 0, 2.4, 35.2 and 1400 Gy/h, fecundity was 299.3, 155.1, 113.4 and 67.5 eggs/female and egg viability was 50.4, 16.1, 1.0 and O%, respectively. Brown and Davis (1973) reported that mortality of 18 or 42 h-old eggs of the red flour beetle was higher when exposed to 25 Gy from a 6oCo source at the rate of 25.8 Gy/min than at the rate of 3.6 or 10.8 Gy/min. They also reported (Brown and Davis 1972) similar results using grain mite, Acarus siro L., eggs. Nair and Subramanyam (1963) used a pool cobalt irradiator, and achieved

979

980 ARTHUR K. BURDITT JR et al.

different dose rates by placing their samples at differ- ent distances from the sources. Brown and Davis (1972, 1973) used a cobalt console irradiator and lead shields to obtain lower dose rates.

This paper presents the results of studies on the effects of high and low dose rates of y-irradiation from a cobalt source when applied to mature, co- cooned, nondiapausing codling moth larvae. Results were measured in terms of pupation of larvae and emergence of adults. Larvae were reared and results evaluated at the USDA, Yakima Agricultural Re- search laboratory. Treatments were applied at Pacific Northwest Laboratory, using their AECL-650 cobalt source.

MATERIALS AND METHODS

Codling moth rearing

Larvae used in these studies were from a colony maintained on thinning apples for > 20 years (Hamilton and Hathaway, 1966). In 1987 the colony was established and subsequently maintained on an artificial medium (Toba and Howell, 1989). Approx- imately 4 1 of medium was placed in a stainless steel pan ca 30 x 50 x 8 cm. The pans were covered with fine mesh gauze. Codling moth eggs, deposited on waxed paper, were placed on the medium, where the eggs hatched and the larvae entered the medium. Usually 21 pans of medium were placed on a rack of shelves, three pans per shelf, and held in a walk-in environmental room at ca 22-26°C 60% RH and a 168 hour 1ight:dark cycle for larval development.

When mature, the larvae were collected, during a 3 or 4 day period, in strips of fluted fiberboard, 1.9 cm wide and 7.5 cm long, placed on the medium. The strips were removed and randomized in groups by taking one or more strips from each of several pans on a rack to give 14-18 strips per treatment. Each group of strips was randomly assigned to one of the treatment dose rates and applied doses.

Irradiation sources and treatment

The @‘Co irradiation unit used for this research was a Gammabeam- irradiator (Atomic Energy of Canada, Ontario, Canada) in which 12 source tubes are arranged in a circular configuration. In 1986 the unit was recharged and four of the tubes were loaded with 7.7 kCi and two tubes each with 6.5, 2.0, 0.5 and 0.1 kCi of 6oCo placed opposite each other in the configuration. To provide flexibility in dose rate each source could be raised independently, in pairs or in groups, and the tubes could be adjusted from a closed circular position 7 cm in diameter to a fully opened position 80 cm in diameter or any intermediate posi- tion in between.

Strips containing mature cocooned larvae were placed in paperboard cartons 9 cm in diameter and 8.5 cm high and irradiated by placing the carton in the center of the source tubes. All 12 sources were used to expose larvae at the highest dose rates.

Opposing pairs of sources were selected, depending upon the dose rate desired, for exposure of larvae at the lower dose rates. With the dose delivered from opposite sides and with no interposed shielding, a uniform field and uniform quality of radiation was provided at all dose rates. Total applied doses were determined by time of exposure. Dosimetry was confirmed for each carton of strips and larvae by placing 3 or 4 TLD-700 LiF chips (Harshaw/Filtrol, Cleveland, Ohio) in the center of each carton. The chips were read at PNL with direct National Bureau of Standards traceability techniques. Dose rates were determined by measuring the total dose delivered in a set time interval and dividing by the number of minutes exposure. The applied doses and dose rates were averaged for each experiment and exposure time.

Results from three experiments conducted in 1988 are reported in this paper. In one experiment, larvae that had been reared on the medium were treated at dose rates of 0.77 + 0.02 and 36.6 f 1.0 Gy/min to give total doses of 0, 4.3, 8.6, 16.5, 31.7 and 63.4 Gy at each dose rate. Each treatment was replicated four times and contained an average of 82.3 + 16.1 larvae. For the low dose rate two sources, each with an initial load of 0.5 kCi, were used in the fully open (80 cm dia.) position. For the high dose rate all 12 sources were used in the fully open position.

In a second experiment, larvae were treated at dose rates of 1.00 + 0.03 and 204.4 f 2.5 Gy/min and ap- plied doses of 0, 44, 58, 71, 85 or 98 Gy at each rate. Treatments were applied on 5 and 12 April, 1988 with 3 and 4 replications of 91.0 f 11.4 and 124.4 + 13.3 larvae, respectively. For the low dose rate the two 0.1 kCi sources were used and for the high dose rate all 12 sources were used in a partially open (30 cm dia.) position.

In the third experiment five dose rates, 1.0 + 0.02, 4.4 + 0.02, 16.5 +0.4, 52.2 +4.1, and 201.5 & 5.9 Gy/min were tested using the paired sources containing 0.1, 0.5, 2.0 and 6.5 kCi for the four lower dose rates, respectively, and all 12 sources for the 201.5 Gy/min dose rate. The mean applied dose was 67.5 k 2.3 Gy for all five dose rates. In addition, there was an untreated control. Each treatment contained an average of 57.2 + 11 .O larvae and was replicated six times.

Post-treatment evaluation

Following treatment, the strips containing larvae were placed loosely in 3.8 1 telescoping lid paperboard cartons 16 cm dia. and 16 cm high to permit pupation of the larvae and subsequent adult emergence. The cartons were randomly distributed on shelves in a controlled environment room maintained at CQ

22-26°C 50-70% RH and 16:8 hour (L:D) photo- period. A 2 1 clear plastic soft-drink bottle was at- tached to each carton top by a pair of tapered, telescoping plastic tubes. Emerging moths, which were attracted to light, flew or crawled through the

Effect of y-irradiation on codling moth larvae 981

tubes into the bottles. Over 95% of moths emerging from the controls entered the bottles. Bottles were replaced daily and any adults collected in the bottles were removed, sexed, and classified as apparently normal, or abnormal. After emergence was com- pleted, the cartons were opened and the remaining moths were sexed and classified into the same cate- gories. The fiberboard strips were subsequently opened and any remaining larvae and pupae were counted. Live larvae and pupae were held in Petri dishes for further development and examination. Response to treatment effects were recorded based on the following criteria.

1. Mortality as mature larvae: larva died as a mature cocooned larva.

2. Mortality as pupae: larva pupated successfully, although not always normally, and died as a pupa.

3. Emergence as abnormal adults: larva pupated successfully and an adult emerged that was obviously abnormal, primarily due to wing deformities.

4. Emergence as normal adults: larva pupated successfully and an adult emerged that appeared to be normal.

Data on numbers and percentages of insects recov- ered were transformed, using log(x + 1) or arc- sin& transformations, respectively, and subjected to analysis of variance (MSTAT, 1986). Significant differences between treatment means were determined (P > 0.05) by Duncan’s (1955) multiple range test (MSTAT, 1986). Probit analyses were performed using the computer program POLO-PC (Russell, 1987). Throughout this publication data for means f standard deviation (SD) are presented, un- less otherwise designated.

RESULTS

Results of the first experiment (Table 1) showed that there were no significant differences in develop- ment of untreated and irradiated mature codling moth larvae through pupation and adult emergence when larvae were irradiated at doses of 31.7 Gy or less. However, when larvae were treated at 63.4 Gy

significantly fewer adults emerged than when treated at the lower doses. Also, significantly fewer adults developed from larvae receiving 63.4 Gy at the rate of 36.6 Gy per min than from larvae treated at the rate of 0.77 Gy/min. This was primarily due to larvae that had successfully pupated but subsequently failed to eclose (Fig. 1). Over 35% of the larvae treated at 63.4Gy developed into abnormal adults. Over 88% of the emerging adults were males at 63.4 Gy com- pared to 55-62% males for untreated larvae and those treated at doses of 4.3-31.7 Gy, regardless of dose rate.

In the second experiment, when the applied doses as well as the dose rates were increased, differences in development of irradiated larvae that had been reared on artificial medium were statistically significant be- tween the applied doses as well as between dose rates (Table 2). Untreated larvae continued their develop- ment, resulting in over 88% of the larvae forming pupae and emerging as adults. There were significant reductions in emergence of normal adults as the dose applied to the mature larvae was increased from 44 to 98 Gy. These were all significantly less than that from untreated larvae. At each of the five treatment doses significantly more normal adults emerged from larvae that had been treated at the 1.0 Gy/min dose rate than from those treated at the 204.4 Gy/min rate (Fig. 2). The reason for this depended upon the total dose applied as well as the dose rate. At 44 Gy more abnormal moths emerged at the high dose rate than at the low rate. However, at the 58, 71 and 85 Gy doses, differences in adult emergence were due pri- marily to significantly higher pupal mortality at the high dose rate. At the 98 Gy dose, the difference in adult emergence between dose rates was due primar- ily to significantly higher larval mortality at the high dose rate.

Of the adults produced from untreated larvae, 59% were males. The percentage of emerging moths that were males increased with the increase in treatment dose (Table 2). Significantly more males emerged from larvae treated at 44, 58 or 71 Gy when the dose was applied at the high rate compared with the low rate.

Table I. Development of nondiapausing codling moth following irradiation as mature larvae at various doses and at dose rates of 0.77 and 36.6 Gy/min

Dose Applied Larvae Mortality (%) as: Adult emergence (%) rate dose tested

(Gylmin) (GY) (Q Mature larvae Pupae Abnormal Normal Total Males (%)

0 0 79.8 4.1 a 4.4 cd 0.3 c 91.3 a 91.6 ab 55.4 b 36.6 4.3 94.8 5.2 a 9.2 bc 2.9 bc 82.7 b 85.6 bc 55.3 b 36.6 8.6 75.3 5.3 a 4.1 d 1.0 bc 89.7 ab 90.6 ab 57.5 b 36.6 16.5 92.0 3.9 a 3.9 d 1.5 bc 90.7 a 92.2 a 51.4 b 36.6 31.7 81.8 4.2 a 7.1 bed 3.0 b 85.7 ab 88.7 ab 62.2 b 36.6 63.4 71.5 5.9 a 33.2 a 40.2 a 20.7 d 60.9 d 90.9 a

0 0 73.3 7.2 a 5.6 cd 0.6 bc 86.5 ab 87.2 abc 58.6 b 0.77 4.3 92.0 3.8 a 5.3 cd 1.1 bc 89.8 ab 90.9 ab 58.6 b 0.77 8.6 85.0 5.5 a 3.9 d 0.6 bc 90.0 ab 90.6 ab 60.2 b 0.77 16.5 84.5 3.6 a 1.5 bed 2.3 bc 86.7 ab 89.0 ab 55.7 b 0.77 31.7 76.8 6.7 a 6.1 cd 1.6 bc 85.5 ab 87.1 abc 58.6 b 0.77 63.4 80.3 6.4 a 11.9 b 35.9 a 45.9 c 81.8 c 88.1 a

Means within columns followed by the same letter are not significantly different (P = 0.05; Duncan’s, 1955, multiple range test). Data were transformed to arcsin& for ANOVA and Duncan’s test.

982 ARTHUR K. BURDITT JR et al

100 100

80 80

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2 60 60 w

i Y

$ 40 8 s 40 6

3 20 20

0 0

80 i

0 0.0 4.3 6.6 16.5 31.7 63.4 0.0 4.3 E I.6 16

DOSE (GRAY) DOSE (GRAY)

Fig. 1. Effect of y-irradiation on subsequent pupation and adult emergence of mature, cocooned, nondiapausing codling moth larvae reared on media and treated at dose rates of 0.77 and 36.6 Gy/min.

** indicates differences between high and low dose rates significant at the 0.01 levels.

Data from this experiment were used to calculate dose-mortality curves for total adult emergence and for emergence of normal adults from treated larvae. The slope and 50 and 99% mortality levels are summarized in Table 3, along with the standard errors and confidence limits for slope and mortality, respectively. These data confirm that there were significant differences in dose-mortality response de- pendent upon dose rate. The doses required to pre- vent 50 and 99% emergence of adults were calculated to be 65.3 and 115.6 Gy for a dose rate of 204 Gy/min compared to 84.5 and 154.1 Gy for a rate of 1 .O Gy/min, respectively (Table 3). Doses required to prevent 50 and 99% emergence of normal adults were calculated to be 47.5 and 85.4 Gy for a dose rate of 204Gy/min compared to 58.2 and 122.5 Gy for a dose rate of 1.0 Gy/min, respectively.

Results of the third experiment, in which codling moth larvae were treated at an applied dose of

67.5Gy at dose rates of 1.0, 4.4, 16.5, 52.2 or 201.5 Gy/min, are given in Table 4. When treated at 67.5 Gy, 34.3 + 7.6% of the treated and 2.2 + 3.3% of the untreated larvae developed and emerged as abnormal adults. There were significant differences in mortality of pupae, as well as in emergence of normal adults when treated at different dose rates. Signifi- cantly fewer normal adults emerged when the larvae were treated at a dose rate of 52.2 Gy/min than when treated at rates of 1.0 or 4.4 Gy/min (Table 4). This was due to differences in eclosion at the various dose rates.

DISCUSSION

In this study on the effects of irradiation dose rate on insect development we randomized our insect population between dose rates and doses to eliminate possible effects due to differences in insect popula- tion. In all experiments the position of the radiation

Table 2. Development of nondiapausing codling moth following irradiation as mature larvae at various doses and at dose rates of I and 204Gy/min

Dose Applied Larvae Mortality (%) as: Adult emergence (%) rate dose tested

(Gyimin) (GY) (Q Mature larvae Pupae Abnormal Normal Total Males (%)

0 0 114.1 4.8 cde 7.1 ef 1.7 h 86.4 a 88.1 ab 59.9 e 204 44 98.7 5.0 cde 9.9 ef 33.9 bed 51.3 c 85.1 ab 89.2 c 204 58 Ill.1 6.5 cde 33.1 d 38.5 abc 21.9 d 60.4 d 94.0 b 204 71 119.3 8.9 bc 58.7 b 28.0 d 4.4 f 32.4 f 98.6 a 204 85 107.7 14.2 b 71.6 a 13.5 f 0.7 g 14.1 g 100.0 a 204 98 108.4 28.0 a 68.3 a 3.7 g 0.0 g 3.7 h 100.0 a

0 0 107.9 3.6 de 6.2 f 2.0 gh 88.2 a 90.2 a 57.7 e I .o 44 109.1 5.4 cde 6.2 ef 17.3 ef 71.2 b 88.5 ab 71.4 d 1.0 58 113.6 5.6 cde II.6 e 38.8 ab 44.0 c 82.8 b 88.7 c 1.0 71 107.0 3.3 e 27.1 d 44.6 a 25.0 d 69.6 c 96.2 b 1.0 85 115.4 9.5 bc 48.2 c 32.1 cd 10.2 e 42.3 e 98.6 a 1.0 98 109.0 1.9 cd 65.6 ab 21.9 e 4.6 f 26.5 f 98.7 a

Means within columns followed by the same letter are not significantly different (P = 0.05; Duncan’s, 1955, multiple range test). Data were transformed to arcsir& for ANOVA and Duncan’s test.

Effect of y-irradiation on codling moth larvae 983

100.

0 204 Gy/min LARVAE

60. ggS 1.0 Gy/min

E c 60

i

f 40

s

20

DosE (GRAY)

ABNORMAL ADULTS

NORMA,. ADULTS

0 44 56 71 65 96

oosE (GRAY)

100

60

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60 w

4

40 8 6

B

20

60

z?

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Fig. 2. Effect of y-irradiation on subsequent pupation and adult emergence of mature, cocooned, nondiapausing codling moth larvae reared on media and treated at dose rates of 1 and 204 Gy/min. l * and *** indicate differences between high and low dose rates significant at the 0.01 and 0.001 levels,

respectively.

sources and the exposed insects was constant while differences in dose rates were achieved by raising more or fewer paired sources. This assured that the quality of the radiation was uniform. Also, in all instances the doses were delivered simultaneously from opposite sides, assuring a uniform dose to the exposed insects. Therefore, we are relatively sure that differences in pupation and adult emergence from codling moth larvae irradiated at different dose rates were due to dose rate and not some other factor such as distance from the source (Nair and Subramanyam, 1963) or shielding (Brown and Davis, 1972, 1973).

Results of our research confirmed those of others (Nair and Subramanyam, 1963; Brown and Davis, 1972,1973) that dose rate, as well as total dose,

affected insect development. Our data removed the possibility that results might have been due to radia- tion quality. We have demonstrated a differential effect when mature, nondiapausing, cocooned codling moth larvae were exposed to y-irradiation from a cobalt source at dose rates from 1 to 204 Gy/min. In our experiments there were significant differences at the high and low dose rates in the percentage of larvae that pupated but were unable to continue their development and emerge as adults. Concurrently there were significant differences in the effect of dose rate on ability of the insects to eclose as normal or abnormal adults. At a total dose of 58 Gy or more, a high dose rate was more effective at preventing adult emergence than a low dose rate.

Table 3. Statistics for dose-mortality probit analysis: irradiation of mature fifth-instar cocooned codling moths to prevent adult emergence

Dose rate (Gy/min) Number tested Slope (*SE) LD, (k95% CL) (Gy) LD, ( f 95% CL) (Gy)

Total adults

Normal adults

204 3817 9.4(0.4) 1.0 3879 8.9(0.5)

204 3817 9. I(O.4) 1.0 3879 7.2(0.3)

65.3(63.1,67.4) 84.5(81.9,87.1)

47.5(43.8,50.4) 58.2(56X, 59.5)

115.6(109.0, 124.5) 154.1(139.8, 177.4)

85.4(78.3,97.3) 122.5(117.4, 128.5)

Table 4. Development of mature, cocooned, fifth instar, nondiapausing codling moth larvae following irradiation at a dose of 67.5 Gy at various dose rates

Dose- Applied Larvae Mortality (%) as: Adult emergence (%) rate dose tested

(Gy/min) (GY) (i) Mature larvae Pupae Abnormal Normal Total Males (%)

0 0 52.3 17.7 a 3.9 d 2.2 b 76.3 a 78.4 a 60.0 c I.0 67.5 56.2 11.6 a 17.9 c 37.1 a 33.4 b 70.5 a 91.4 b 4.4 67.5 56.7 15.1 a 30.5 b 36.7 a 17.7 c 54.4 b 98.9 a

16.5 67.5 58.8 16.8 a 38.4 ab 34.3 a 10.6 cd 44.9 bc 99.5 a 52.2 67.5 64.0 17.1 a 47.7 a 27.7 a 7.4 d 35.1 c 95.5 ab

201.5 67.5 55.5 16.3 a 33.6 b 35.6 a 14.5 cd 50.1 b 95.6 ab

Means within columns followed by the same letter are not significantly different (P = 0.05; Duncan’s, 1955, multiple range test). Data were transformed to arcsin fi for ANOVA and Duncan’s test.

R P.C. 34/&H

984 ARTHUR K. BURDITT JR et al,

However, doses of 32 Gy or less had no effect on development of irradiated codling moth larvae. While it is possible that some of the differences associated with dose rate could be due to secondary conditions such as ozone concentration, it is more likely that the differences derive from the insects ability to repair damaged biological systems or tissue associated with the lower dose rates (Tilton and Brower, 1983).

An earlier study (Burditt et al., 1985) showed that a few normal adults developed from mature larvae that had been exposed to y-irradiation at doses of 100, 120 and 140 Gy applied at the rate of 9 Gy/min. The present study has shown comparable results: exposure of larvae to 98 Gy at a dose rate of 1 Gy/min permitted 4.6% emergence as normal adults but no normal adults emerged at a dose rate of 204 Gy/min.

SUMMARY

Research during the past 35 yr has demonstrated that y-irradiation is an effective method for disinfes- tation of fruits, vegetables and other food commodi- ties. Doses of 10&300Gy applied to eggs or larvae of the codling moth, a serious pest of apples and other deciduous fruit and nuts, will interfere with further development by preventing pupation or adult eclosion, depending upon total applied dose. However, research reported here has demonstrated that both dose and dose rate are factors to consider in determining the response of an insect to radiation from a y-source. Plans for development and construc- tion of commercial food irradiation facilities to be used for insect disinfestation treatment of food, as well as regulatory protocols for use of radiation as a quarantine treatment, must take into consideration effects of dose rate as well as of total dose on insect response.

Acknowledgments-We want to thank Jeanne Morton and Patsy Wilson (Agricultural Research Service, U.S. Depart- ment of Agriculture, Yakima, Wash.) for their patience in examining the insects. The radiation exposure and related dosimetry were supported by the U.S. Department of Energy under contract DE-AC06-76RLO-1830.

REFERENCES

Brown G. A. and Davis R. (1973) Sensitivity of red flour beetle eggs to gamma radiation as influenced by treatment age and dose rate. J. Georgia Entomol. Sot. 8, 153.

Brown G. A. and Davis R. (1972) Sensitivity of grain mite eggs to gamma radiation as influenced by dose rate and treatment age. J. Econ. Entomol. 65, 1619.

Burditt A. K. Jr and Moffitt H. R. (1985) Irradiation as a quarantine treatment for fruit subject to infestation by codling moth larvae. In Proc. Ini. Conf. Radiation Disin- festation of Food and Agricultural Products (Edited by Moy J. H.), p. 87. University of Hawaii, Honolulu, Hawaii, U.S.A.

Burditt A. K. Jr, Moffitt H. R. and Hungate F. P. (1985) Effects of gamma irradiation as a quarantine treatment on the development of codling moth larvae. In International Atomic Energy Agency/Food and Agriculture Organization Int. Symo. Food Irradiation Processin*. Washington. 4-8 March, b. 3. IAEA, Vienna, Austria- -

Butt B. A., White L. D., Moffitt H. R., Hathaway D. 0. and Schoenleber L. G. (1973) Integration of sanitation, insec- ticides, and sterile moth releases for suppression of popu- lations of codling moths in the Wenas Valley of Washington. Environ. Entomol. 2, 208.

Duncan D. B. (1955) Multiple range and multiple F tests. Biomefrics 11, 1.

Hamilton D. W. and Hathaway D. 0. (1966) Codling moths. In Insect Colonization and Mass Production (Ed- ited by Smith C. N.), p. 339. Academic Press, New York.

MSTAT (1986) MSTAT Distribution Package User’s Guide (Version 4.0). Michigan State University, East Lansing.

Nair K. K. and Subramanyam G. (1963) Effects of variable dose-rates on radiation damage in the rust-red flour beetle, Tribolium castaneum Herbst. In Radiation and Radioisotopes Applied to Insects of Agricullural Impor- tance: Proc. Symp. Use and Application of Radioisotopes and Radiation in the Control of Plant and Animal Insect Pesfs, Athens, 22-26 April, p. 425. International Atomic Energy Agency/Food and Agriculture Organization. IAEA, Vienna, Austria.

Proverbs M. D., Newton J. R. and Logan D. M. (1966) Orchard assessment of the sterile male technique for control of the codling moth Carpocapsa pomonella (Lep- idoptera: Olethreutidae). Can. Entomol. 98, 90.

Proverbs M. D., Newton J. R. and Campbell C. J. (1982) Codling moth: a pilot program of control by sterile insect release in British Columbia. Can. Entomol. 114, 363.

Russell R. M. (1987) POLO-PC, Le Ora Software Inc., Berkeley, California.

Tilton E. W. and Brower J. H. (1983) Radiation effects on arthropods. In Preservation of Food by Ionizing Radiation (Edited by Josephson, E. S. and Peterson, M.S.), Vol. II. p, 269. CRC Press, Boca Raton, Florida.

Toba H. H. and Howell J. F. (1989) Modification of a soy-wheat germ formulated diet for improved mass-rear- ing of codling moths (Lepidoptera: Tortricidae). Can. Enromol., in press.

White L. D., Butt B. A., Moffitt H. R., Hutt R. B., Winterfeld R. G., Schoenleber L. G. and Hathaway D. 0. (1976) Codling moths: suppression of populations from releases of sterile insects in the Wenas Valley of Washing- ton, 1972. J. Econ. Entomol. 69, 319.