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Insect control by radiation sterilization in Australia
International Journal of Applied Radiation and Isotopes, 1962, Vol. 13, pp. 435--439. Pergamon Press Ltd. Printed in Poland
Insect Control by Radiation Sterilization in Australia D. F. W A T E R H O U S E Division of Entomology, C o m m o n w e a l t h Scientific a n d I n d u s t r i a l R e s e a rc h O r g a n i z a t i o n , Canberra, Australia
I HAVE interpreted the title allotted for my talk as a restriction of m y topic to the use of radiation for the production of sterile males and their use for insect control or eradication. However, I should like to broaden it for a moment and say that, although isotopes are being used in quite a number of entomological investigations in Australia, there is no practical application yet of radiation in the field of insect control. Thus no commercial irradiation of grain has yet been carried out, although this course of action will certainly be considered for both wheat and rice if costs of radiation sources, such as the insulating core transformer, fall low enough. Meanwhile, the radiation susceptibility of Australian grain insects is being compared with that of European strains of the same species (x). Consideration is also being given to the use of sterilizing doses to control fruit fly in fruit moving into quarantine areas and of Sirex or Hylotrupes infested timber entering Australia at mainland ports. It is interesting to note that, in the 5-10,000 r range, there are significant effects on fruit fly and apparently no adverse effects on storage life, flavour or ascorbic acid content of oranges (z). There is one commercial source in Australia (a Co-60 source at Dandenong, Victoria) of 600,000 c used by a carpet manufacturing firm for sterilization of imported raw ma435
terials. However, although this will undoubtedly kill any insects which may be present, insect control is entirely secondary to its main purpose. To return to the use of sterile males, we in Australia, like many people in other parts of the world, were much impressed by the success of Dr. Knipling and his colleagues with this method against the screw worm in Curacao and Florida. We have considered several candidate pests in Australia for which the technique might not only be applicable, but for which the costs involved might be commensurate with the reduction in losses due to the pest. We are not at all sure yet that we know of any pest which meets these requirements but there has been, so far, only a relatively small amount of work in this field. More consideration has been given to the use of sterile males against the Queensland fruit fly Dacus tryoni (Frogg.), a major Australian insect pest, than against any other species. The approximate distribution in Australia of D. tryoni is shown in Fig. 1. There does not seem to be much possibility that the portion of the fly population which is more or less continuously distributed along the broad coastal and subcoastal zone in eastern Australia (and this occupies some 400,000 sq. miles) will be controlled by sterile males because of the great areas and large numbers
D. F. Wat~rhous~
436
of flies involved. However, there is some hope that populations on the margins of distribution might be eradicated by this method. In such places the populations
facing us in such semi-isolated areas m a y be illustrated by considering what has happened in the thirteen small isolated outbreaks which have been reported in Adelaide since
DISTRIBUTION OF PEST FRUIT FLIES I N AUSTRALIA S+~OW~NGzoos o; tJ6[~T~ONO~ jMI'OxTfOFARAS~t~
NOgTHERN~R~TORY
WI~TEgN AUSTII,AUA
o-
/
VICTOII.IA
~
M~st~NT PO~JLATIONo, , c ~
V/, m
1;ONESOF UKKAIlON OF t~UlT FgY ~A~A~TEI~-Sl
/
0
~,p.~
E ...............
~COVERYslrEiN I~0
',-'-.-"v TASHANI~
%/
• • • • C~4J~I.ANTINE|AARIEA
FIG. 1. The approximate distribution of the O~ueensland Fruit Fly (Dacus t~yoni) and the Mediterranean Fruit Fly (Ceratitis ¢apilata) in Australia.
probably fluctuate widely and local extinction is likely to occur from time to time. Following extinction, isolated populations may be refounded by larvae introduced in infested fruit or by migration of adults. The areas most likely to come under active consideration are the western towns of New South Wales and Queensland, the irrigation areas of the Murrumbidgee and Murray, east Gippsland and the southern capitals, Adelaide and Melbourne. The problem
1947. These outbreaks were not only localized but also they occurred only in one region of the city. The outbreaks were detected when householders found larvae in their backyard fruit and they were treated by the South Australian authorities for some years by stripping all fruit and spraying over an area of 1 mile radius around the point where infestation was discovered (at a cost of about £ 100,000 an infestation) and, more recently, with a modification of
Insect control by radiation sterilization in Australia
this procedure. The fly populations seem to be small and localized and it can be argued that they might be more cheaply and just as effectively treated with sterile males. T h e problem of detection m a y be made somewhat easier from now on by the grid of male-lure (cue-lure) traps which was used for the first time throughout the city in the 1960/61 season. Gippsland (in north eastern Victoria) presents a rather more difficult problem because of the far larger area involved, but it is fairly isolated and might be treated if costs w e r e low enough. This area is of particular interest because it seems to be a persistent breeding ground for flies of a hardy strain which BATWMANC8) has found to be adapted to withstand southern extremes of temperature. Even if we could use sterile males to eradicate Dacus tryoni in these isolated areas, flies would inevitably be brought in again in infested fruit or possibly adults might fly in. Quarantine is expensive and may not completely exclude the introduction of fresh infestations. Possibly, as suggested by Dr. Knipling for some of his problems, a"caretaker population of sterile males could be maintained in these areas to suppress any fresh outbreaks. The numbers of immigrants would usually be small so that the caretaker population could also be small. The person who has been working actively on this problem for several years is Dr. J. Moz~'a~oof the University of Adelaide who is stationed at the Department of Zoology, University of Sydney. He has published one paper ") dealing with his results and has kindly provided me with further unpubfished information which I am using in this talk. Methods for rearing Dacus tryoni in large numbers are available and these methods could probably be adapted to factory production, so that one of the m a n y requirements of this method can be met
437
from existing knowledge. Laboratory work has been carried out by MorRo in order to estimate the following characteristics of flies given a particular dose of radiation at a particular stage of pupal development: pupal mortality, adult viability, female sterility, male sterility and male efficiency in copulation. His first task was to determine the range of doses which might be given to pupae of different ages without affecting their emergence as adults. There are three stages of susceptibility to radiation during development of the adult within the puparium, an early stage of low resistance, a middle period of rapidly increasing resistance and eventually a period of high resistance. M o ~ a o found that, if 4000 r was given on the 8th day of pupal fife, resulting females did not mature eggs at ages up to 3 months and males were sterile, as tested by caging them with fertile females for 8 weeks after emergence. This dose seems to accord well with results obtained by other workers for a number of other insects, although it is much lower than the 10,000 r used by U.S.D.A. workers in Hawaii on three species of fruit fly. He next found that a trial eradication in the laboratory was successful using this dose and a ratio of sterile to fertile males of 9 to 1. Only one experimental cage out of three produced fertile eggs and these soon ceased to be laid. Although 4000 r would seem to be close to the optimum dose for sterilizing Dacus tryoni there is work in progress to set the dose more accurately in the range 3000--4000 r. Dacus tryoni is fertile following exposure to 2000 r and DO~NV,~LY~5) has observed that Lucilia sericata retains some fertility up to 3000 r. The next step towards field release consisted of an estimation of the relative survival and mating efficiency of sterile males (4000 r on 8th day of pupal life) in corn-
D. F. Waterhouse
438
parison with wild flies when both were exposed together in field cages each of which enclosed a guava or citrus tree. The survival of the sterile males was 83 per cent of that of wild males and their mating
has found that pupae do not survive the winter. In 1960, 85 per cent of the female flies overwintering in some citrus trees were found by MOZ~RO to be unfertilized. It is presumed that these mate in early spring
OCCURRENCE nr LUCILIA CUPI IN AUSTRALI
J
FIG. 2. T h e distribution of the Australian sheep blowfly (Lucilia cuprina) in Australia. Solid black indicates area of continuous distribution. R u l e d lines indicate area where occurrence is sporadic.
efficiency was close to that of normal males. Unlike the Hawaiian species of fruit flies, D. tryoni females mate only once or twice in the first 2 months of adult life which is the most fertile period. In dealing with wild populations of Dacus tryoni, we would be looking for populations which are small and, if possible, which contain a large proportion of virgin females. Near Sydney the population seems to reach lowest numbers in early spring and BATE_~A~r
before dispersing to the first hosts of the season. These results suggest that we should try to get large numbers of sterile flies into the field by early spring. Unfortunately, the males reared in the laboratory at 25 ° C did not survive nearly as well as wild males during winter in field cages, and means of increasing viability are being considered. There is one interesting possibility which has been raised by the observation of B A ~ A _ ~ , that not all male D. tryoni
Insect control by radiation sterilization in Australia
in a population react to the male " c u e " lure. He has started a selection experiment in an endeavour to obtain a strain which does not react to the lure at all. I f this is successful and the strain has otherwise normal characteristics, it will be used for the sterilization experiments since the wild male population can then be reduced during a sterile male campaign by the use of poison lures. It m a y also be possible to introduce a white genetic marker into this strain of flies. I should perhaps mention, very briefly, the Australian sheep blowfly, Ludlia cuprina (Wied.) O n mainland Australia it occupies permanently some 1½ million sq. miles (of a total of about 3 million) and a further 1 million sq. miles wherever breeding material (living sheep or carrion) occurs (Fig. 2) although the population it attains varies
439
greatly over this area. So far as we know it does not disappear each winter from any substantial tract of country. Even Tasmania has an area of some 26,000 sq. miles, not quite half the 60,000 sq. miles of the Florida screw worm campaign. The annual cost of the sheep blowfly to Tasmania appears to be of the order of £ 60,000 and to the rest of Australia, perhaps, £ 5-7 million. A rough comparison with costs of the Florida operation suggests, that unlike that operation which resulted in eradication for less than the annual cost of the screw worm, the costs of a male annihilation campaign might well be at least 15 times (for Tasmania) and several hundred times (for the mainland) the annual cost. Furthermore Lucilia cuprina, although by far the most important, is not the only species involved.
REFERENCES 1. SHIPP E. Unpublished data. 2. MACFM~LANE J.J. The Technological Use of Radiation, p. 137. Australian Atomic Energy Commission (1960). 3. BATEMA~ M. A. Unpublished data.
9*
4. MOI,~ROJ. The Possible Use of Sterile Males in Controlling or Eradicating Queensland Fruit Fly. The Technological Use of Radiation, p. 130. Australian Atomic Energy Commission (1960). 5. DONNELLY J. Eat. exp. Appl. 6, 48 (1960).
Insect Control by Radiation Sterilization in Australia D. F. W A T E R H O U S E Division of Entomology, C o m m o n w e a l t h Scientific a n d I n d u s t r i a l R e s e a rc h O r g a n i z a t i o n , Canberra, Australia
I HAVE interpreted the title allotted for my talk as a restriction of m y topic to the use of radiation for the production of sterile males and their use for insect control or eradication. However, I should like to broaden it for a moment and say that, although isotopes are being used in quite a number of entomological investigations in Australia, there is no practical application yet of radiation in the field of insect control. Thus no commercial irradiation of grain has yet been carried out, although this course of action will certainly be considered for both wheat and rice if costs of radiation sources, such as the insulating core transformer, fall low enough. Meanwhile, the radiation susceptibility of Australian grain insects is being compared with that of European strains of the same species (x). Consideration is also being given to the use of sterilizing doses to control fruit fly in fruit moving into quarantine areas and of Sirex or Hylotrupes infested timber entering Australia at mainland ports. It is interesting to note that, in the 5-10,000 r range, there are significant effects on fruit fly and apparently no adverse effects on storage life, flavour or ascorbic acid content of oranges (z). There is one commercial source in Australia (a Co-60 source at Dandenong, Victoria) of 600,000 c used by a carpet manufacturing firm for sterilization of imported raw ma435
terials. However, although this will undoubtedly kill any insects which may be present, insect control is entirely secondary to its main purpose. To return to the use of sterile males, we in Australia, like many people in other parts of the world, were much impressed by the success of Dr. Knipling and his colleagues with this method against the screw worm in Curacao and Florida. We have considered several candidate pests in Australia for which the technique might not only be applicable, but for which the costs involved might be commensurate with the reduction in losses due to the pest. We are not at all sure yet that we know of any pest which meets these requirements but there has been, so far, only a relatively small amount of work in this field. More consideration has been given to the use of sterile males against the Queensland fruit fly Dacus tryoni (Frogg.), a major Australian insect pest, than against any other species. The approximate distribution in Australia of D. tryoni is shown in Fig. 1. There does not seem to be much possibility that the portion of the fly population which is more or less continuously distributed along the broad coastal and subcoastal zone in eastern Australia (and this occupies some 400,000 sq. miles) will be controlled by sterile males because of the great areas and large numbers
D. F. Wat~rhous~
436
of flies involved. However, there is some hope that populations on the margins of distribution might be eradicated by this method. In such places the populations
facing us in such semi-isolated areas m a y be illustrated by considering what has happened in the thirteen small isolated outbreaks which have been reported in Adelaide since
DISTRIBUTION OF PEST FRUIT FLIES I N AUSTRALIA S+~OW~NGzoos o; tJ6[~T~ONO~ jMI'OxTfOFARAS~t~
NOgTHERN~R~TORY
WI~TEgN AUSTII,AUA
o-
/
VICTOII.IA
~
M~st~NT PO~JLATIONo, , c ~
V/, m
1;ONESOF UKKAIlON OF t~UlT FgY ~A~A~TEI~-Sl
/
0
~,p.~
E ...............
~COVERYslrEiN I~0
',-'-.-"v TASHANI~
%/
• • • • C~4J~I.ANTINE|AARIEA
FIG. 1. The approximate distribution of the O~ueensland Fruit Fly (Dacus t~yoni) and the Mediterranean Fruit Fly (Ceratitis ¢apilata) in Australia.
probably fluctuate widely and local extinction is likely to occur from time to time. Following extinction, isolated populations may be refounded by larvae introduced in infested fruit or by migration of adults. The areas most likely to come under active consideration are the western towns of New South Wales and Queensland, the irrigation areas of the Murrumbidgee and Murray, east Gippsland and the southern capitals, Adelaide and Melbourne. The problem
1947. These outbreaks were not only localized but also they occurred only in one region of the city. The outbreaks were detected when householders found larvae in their backyard fruit and they were treated by the South Australian authorities for some years by stripping all fruit and spraying over an area of 1 mile radius around the point where infestation was discovered (at a cost of about £ 100,000 an infestation) and, more recently, with a modification of
Insect control by radiation sterilization in Australia
this procedure. The fly populations seem to be small and localized and it can be argued that they might be more cheaply and just as effectively treated with sterile males. T h e problem of detection m a y be made somewhat easier from now on by the grid of male-lure (cue-lure) traps which was used for the first time throughout the city in the 1960/61 season. Gippsland (in north eastern Victoria) presents a rather more difficult problem because of the far larger area involved, but it is fairly isolated and might be treated if costs w e r e low enough. This area is of particular interest because it seems to be a persistent breeding ground for flies of a hardy strain which BATWMANC8) has found to be adapted to withstand southern extremes of temperature. Even if we could use sterile males to eradicate Dacus tryoni in these isolated areas, flies would inevitably be brought in again in infested fruit or possibly adults might fly in. Quarantine is expensive and may not completely exclude the introduction of fresh infestations. Possibly, as suggested by Dr. Knipling for some of his problems, a"caretaker population of sterile males could be maintained in these areas to suppress any fresh outbreaks. The numbers of immigrants would usually be small so that the caretaker population could also be small. The person who has been working actively on this problem for several years is Dr. J. Moz~'a~oof the University of Adelaide who is stationed at the Department of Zoology, University of Sydney. He has published one paper ") dealing with his results and has kindly provided me with further unpubfished information which I am using in this talk. Methods for rearing Dacus tryoni in large numbers are available and these methods could probably be adapted to factory production, so that one of the m a n y requirements of this method can be met
437
from existing knowledge. Laboratory work has been carried out by MorRo in order to estimate the following characteristics of flies given a particular dose of radiation at a particular stage of pupal development: pupal mortality, adult viability, female sterility, male sterility and male efficiency in copulation. His first task was to determine the range of doses which might be given to pupae of different ages without affecting their emergence as adults. There are three stages of susceptibility to radiation during development of the adult within the puparium, an early stage of low resistance, a middle period of rapidly increasing resistance and eventually a period of high resistance. M o ~ a o found that, if 4000 r was given on the 8th day of pupal fife, resulting females did not mature eggs at ages up to 3 months and males were sterile, as tested by caging them with fertile females for 8 weeks after emergence. This dose seems to accord well with results obtained by other workers for a number of other insects, although it is much lower than the 10,000 r used by U.S.D.A. workers in Hawaii on three species of fruit fly. He next found that a trial eradication in the laboratory was successful using this dose and a ratio of sterile to fertile males of 9 to 1. Only one experimental cage out of three produced fertile eggs and these soon ceased to be laid. Although 4000 r would seem to be close to the optimum dose for sterilizing Dacus tryoni there is work in progress to set the dose more accurately in the range 3000--4000 r. Dacus tryoni is fertile following exposure to 2000 r and DO~NV,~LY~5) has observed that Lucilia sericata retains some fertility up to 3000 r. The next step towards field release consisted of an estimation of the relative survival and mating efficiency of sterile males (4000 r on 8th day of pupal life) in corn-
D. F. Waterhouse
438
parison with wild flies when both were exposed together in field cages each of which enclosed a guava or citrus tree. The survival of the sterile males was 83 per cent of that of wild males and their mating
has found that pupae do not survive the winter. In 1960, 85 per cent of the female flies overwintering in some citrus trees were found by MOZ~RO to be unfertilized. It is presumed that these mate in early spring
OCCURRENCE nr LUCILIA CUPI IN AUSTRALI
J
FIG. 2. T h e distribution of the Australian sheep blowfly (Lucilia cuprina) in Australia. Solid black indicates area of continuous distribution. R u l e d lines indicate area where occurrence is sporadic.
efficiency was close to that of normal males. Unlike the Hawaiian species of fruit flies, D. tryoni females mate only once or twice in the first 2 months of adult life which is the most fertile period. In dealing with wild populations of Dacus tryoni, we would be looking for populations which are small and, if possible, which contain a large proportion of virgin females. Near Sydney the population seems to reach lowest numbers in early spring and BATE_~A~r
before dispersing to the first hosts of the season. These results suggest that we should try to get large numbers of sterile flies into the field by early spring. Unfortunately, the males reared in the laboratory at 25 ° C did not survive nearly as well as wild males during winter in field cages, and means of increasing viability are being considered. There is one interesting possibility which has been raised by the observation of B A ~ A _ ~ , that not all male D. tryoni
Insect control by radiation sterilization in Australia
in a population react to the male " c u e " lure. He has started a selection experiment in an endeavour to obtain a strain which does not react to the lure at all. I f this is successful and the strain has otherwise normal characteristics, it will be used for the sterilization experiments since the wild male population can then be reduced during a sterile male campaign by the use of poison lures. It m a y also be possible to introduce a white genetic marker into this strain of flies. I should perhaps mention, very briefly, the Australian sheep blowfly, Ludlia cuprina (Wied.) O n mainland Australia it occupies permanently some 1½ million sq. miles (of a total of about 3 million) and a further 1 million sq. miles wherever breeding material (living sheep or carrion) occurs (Fig. 2) although the population it attains varies
439
greatly over this area. So far as we know it does not disappear each winter from any substantial tract of country. Even Tasmania has an area of some 26,000 sq. miles, not quite half the 60,000 sq. miles of the Florida screw worm campaign. The annual cost of the sheep blowfly to Tasmania appears to be of the order of £ 60,000 and to the rest of Australia, perhaps, £ 5-7 million. A rough comparison with costs of the Florida operation suggests, that unlike that operation which resulted in eradication for less than the annual cost of the screw worm, the costs of a male annihilation campaign might well be at least 15 times (for Tasmania) and several hundred times (for the mainland) the annual cost. Furthermore Lucilia cuprina, although by far the most important, is not the only species involved.
REFERENCES 1. SHIPP E. Unpublished data. 2. MACFM~LANE J.J. The Technological Use of Radiation, p. 137. Australian Atomic Energy Commission (1960). 3. BATEMA~ M. A. Unpublished data.
9*
4. MOI,~ROJ. The Possible Use of Sterile Males in Controlling or Eradicating Queensland Fruit Fly. The Technological Use of Radiation, p. 130. Australian Atomic Energy Commission (1960). 5. DONNELLY J. Eat. exp. Appl. 6, 48 (1960).