Title <綜説>Insecticide-resistance and Darwinism

Author(s) BROWN, A.W.A.

Citation 防虫科学 (1957), 22(2): 277-282

Issue Date 1957-05-31

URL http://hdl.handle.net/2433/157282

Right

Type Departmental Bulletin Paper

Textversion publisher

Kyoto University Insecticide-resistance and Darwinism. * A. W. A; BROWN (Professor and Head of the Department of Zoology, University of Western Ontario, London, Canada. Temporarily, Scientist (Biologist) of W. H. 0., Division of Environmental Sanita- tion). Received May 8, 1957. Botyu-Kagaku 22,277,1957. ' ' 48. *1m~lmmt±c9"?-! ='AA (!'J;m: rJJmWF 22, 282, 1957) Next summer, the International Congress of including Hikone in 1954. Zoology will 'meet in London to celebrate the The housefly has also developed resistance to centenary of"The Origin of Species," and to other insecticides, which like DDT are in the class honour its author Charles Robert Darwin. Darwin known as chlorinated' hydrocarbons, In 1949, stated, 100 years ago, that it was natural selection, BHC-and dieldrin-resistance was reported in Cali­ operating on the normal variation of animals and fornia. Finally resistance has appeared to those plants which Over the course' of time separated insecticides which we at first thought never in­ the subspecies which,' he said, were the origin duce it, namely the organophosphorus compounds; of species. 'Vith that book he made his out­ it was reported from Denmark in 1955 that para­ standing contribution to the progress of science thion, diazinon and Resitox can no longer control and radically changed the thought of man. For houseflies there. proof, Darwin pointed not only to 'what could This resistance is not only confined to the be seen in different parts of the world, but also housefly. DDT-resistance was shown by Culex to what happened in history. In England, during molestus in 1947 in Italy, and in 1948 by two at least the previous 200 years, man had been species of Aede,' salt-marsh mosquitos in Florida; developing the various breeds of domestic.animals it ,also appeared in the bed-bug Cimex in 1948, and cultivated plants which man wanted, by and Pulex fleas in 1949. In the winter of 1950­ selecting those individuals which were desirable 5~, in Korea, it became impossible to control and rejecting those that were substandard. This body lice Pediculus with DDT any more. DDT­ is selection for man's good. resistance in lice is particularly serious in ea,stern During the last twenty years we have succeeded Asia be-cause of the, danger of typhus. In the quite wel1 in doing the reverse, selection for same year it became evident that the lack of con­ man's embarrassment, selection to man's detri­ trol of malaria mosquitos Anopheles in Greece ment. We have brought about the selection of was not dtie to inadequacies in spraying, nor to new strains which are now resistant to the chemi­ the chemicals being substandard, but to a change cals which were used to control them, whether on the part of the insects themselves; they had antibiotics to kill bacteria or insecticides to kill now become resistant to DDT. the insects which compete with man for his food Subsequently DDT-resistance of 'Anopheles' or transmit his diseases. mosquitoes appeared in two other regions, Java The best example of insecticide-resistance, of and Saudi Ambia. At this point the World course, is that of the housefly to DDT. The Health Organization became 'vitally concerned, first discovery was " made in 19,16 at Arnas i~ because one of its main activities has been to northern Sweden, only 2 years after the intro­ promote the control of the insects which transmit duction of DDT for housefly control. DDT-resis­ the great endemic diseases, of which malaria is . tance then appeared in 1947 south of Rome, the greatest. mal~ria Italy, and in 1948 in the state of New York, In addition,.' mosquitoes began to show U. S. A. Since then, the same phenomenon was resistance to dieldrin in 1955 with Anopheles discovered in houseflies in every part of the world, quadrimaculatus in Mississippi in U. S. A. and Anopheles gambiae in Nigeria in Africa. Mean­ * A lecture given at the Kyoto University on 14, while cockroaches have developed chlordane­ II, 1957. resistance, which first appeared in Texas in 1952

277 and is now very common in the U. S. A. Cattle dane-resistance in the wireworm Conoderus falll, ticks, Boophilus decoloratus and B. microplus, endrln-reslstance in the spiny bollworm Earias, had developed BHC-resistance in South Africa rotenone-resistance in the Mexican bean beetle and Australia around 1948. Epilachna varivestris, and toxaphene-resistance Not only insects of medical 'and veterinary im­ in the cotton leafworm Alabama arglllacea and portance, but also agricultural insects have de­ the bollworm Anthanomus grandis. veloped resistance. In the last few years, DDT­ For some people insect-resistance means simply resistance has appeared in four species of cater-s. figures in account books. To othersTt means a pillars: the codling moth Carpocapsa pomonella change of insecticides: But to biologists, of in the U.S.A. and South"Africa, the diamond-back cource, it means that we must look at the insects moth Plutella maculipennis in Java, the cabbage to sec what makes them resistant, what is it worm Pieris rapae in several states of the U.S.A. about them that is different from the normal and probably in japan, and the cabbage looper susceptible strains: ' T'richoplusia ni in New Y~rk State. DDT­ When DDT-resistance was first discovered in resistance also developed in three species of leaf­ the housefly at Arnas, the difference was con­ hopper Erythraneura, at least one species of sidered to lie in their thicker and darker tarsi. plant bug Lygu« on alfalfa, and the potato flea In fact, when the r,esistant strain was found ncar beetle Epitrix cucumerls, Some agricultural pests Rome in Italy, it was thought to be a subspecies have developed resistance to parathion. No less of Musca domestlca and was described as M. than five species of tetranychid mites have de-. domestica tiberina. But soon afterwards, similar veloped, resistance to parathion in various parts of_ DDT-resistance bagan to be reported from'dif­ the U. S. A. with isolated records from Germany ferent countries and different places. So the, and South Africa. And parathion-resistance has characteristic could not be ascribed to certain been detected in five, species of aphids, including natural subspecies. Many, laboratories found the common Myzus persicae. that if took a normal strain, they could develop, The resistance of insects to insecticides was first 'by selection with DDT, their own resistant strain observed in 1908 and reported in 1914 by Me­ from the normal susceptible strain. It thercf~re lander with the San Jose scale, Aspldiotuspernl­ becomes cleat: how these resistant strains have ciosus, in the state of Washington, U.S.A, with the appeared. They have been produced by a pro­ failure of lime-sulphur sprays to exert the cus­ cess of natural selection, .or rather" unnatural tomary control. He showed that this resistance' selection ". If you, expose a population of flies was a peculiarity i of the strain which had de­ to'DDT, the insecticide kills the most susceptible veloped in the Clarkson valley. Shortly after, ones, and leaves some to mate and lay eggs. If in California between' 1912 and 1925, three you rear, the offspring of the' survivors, it is species of scale on citrus developed resistance to found that this second generation is more resistant hydrogen cyanide fumigation. These are the on the average than the previous 'one, and if you black' scale Salssetia oleae, California red scale repeat the process generation after generation the Aonidiella aurantii and cltricola scale Coccus level of resistance will steadily increase until you pseudomagnoliarum, In 1928 the codling moth, . have a strain which is wholiy resistant. Carpocapsa pomonella, one of the most expensive Usually the average level of resistance increases . ' pests in agriculture, developed resistance to slightly at first and more steeply later, rising in lead arsenate in Colorado. Arsenic-resistance in an exponential curve t~ reach a maximum at per­ both species of cattle ticks and in the peach twig haps the twentieth generation or so. Twenty

borer, Anania, and tartar-emetic-rcsistance of 'generations of the fly in most parts'of the world I, the 'citrus thrips Scirtothrips, completed the means about 2 years, and it has been found in­ earlier history. deed that DDT-resist~nce u~ually follows DDT The recent agricultural calamities include chlor- spraying in approximately 2 years. Zi8 , [o-!ll ff ~ m 22 y-I It must bc stressed that the resistant strain can fore now considered that 'the characteristics he only be produced if you' select; in other words; found are probably those of flies from northern you must' kill Some of thc flies. An attempts Sweden and not of the resistant strain. It is to produce a resistant strain by exposing sue­ now concluded that there is no difference in .cesslve generations to truly sub-lethal dosages appearance, in anatomy or morphology between have failed. It is clear that resistance cannot be a resistant strain and a susceptible one. explained by the doctrine of J. B. Lamarck, that Although there is a tendency ,for, .indivlduals a given individual can adapt itself and, having which grow more slowly to be more resistant adapted itself, hand on to its offspring that same than those which grow faster within a group, if adaptation. In fact, it has been found that insects you take a resistant strain as a whole and compare do not adapt themselves to DDT in the first it with a susceptible one, there is no significant place; pretreatment with small doses' does not difference in their bionomics.' They have almost make them any more tolerant of larger doses the same life-cycle. later, Therefore we are forced to the conclusion, There is no difference in the behaviour between. paradoxical at first sight, that the adaptation resistant strains and susceptible ones. There are which causes resistance was not produced by the Some who say that the resistant flies characteristi­ insecticide. There is no post-adaptation as a cally refuse to rise to walls treated with DDT, consequence of the chemical, but rather a pre­ but the fact probably is that the resistant flies are adaptation which the chemical exploited. You seen resting on the untreated ground because they can produce. the resistant strain by killing the are intoxicated but surviving. In short, this most susceptible ones and selecting the less sus­ behaviour is a response to the insecticide, and ceptible ones (in which the pre-adaptation already not a case of difference in the intrinsic behaviour. exists) to produce the next' generation. This is Further~ore, there is no consistent difference in full accord with Darwin's theory ofevolutionary in oxygen consumption, and, no consistent dif­ change through natural selection and survival of ference in cytochromoxid~se content, between the fittest. resistant strains and susceptible'ones. Nor is .When you have succeeded in getting your re­ there any characteristic difference ~n cholinesterase sistant strain of housefly, can you discern any dif­ activity. There is a tendency for resis,tant strains ference between a resistant fly on the one hand . to contain more fat, of a lower melting point" and a susceptible fly on the other? If you make than susceptible ones, and it may be that resis-' studies comparing flies of one resistant strain with tant strains contain more'Cu.than susceptible ones. flies of one susceptible strain, you will probably It might be thought, that flies of resistant st­ detect some differences between them. But if rains absorb less DDT than susceptible ones. you check the result by taking several resistant 'But on the whole resistant strains absorb, DDT strains and several susceptible ones, you will find on the same rate as susceptible strains. In fact, that the differerences which you first thought true if you compare the resistance by Injecting DDT are no longer valid in general. into the body of the fly instead of applying it by Firstly, there is no morphological difference contact, you will find the same difference between characteristically 'distinguishing f~ies of resistant them in their response to DDT; strains from. susceptible ones. \Viesmann di~­ Well, there is one difference which so far has covered morphological peculiarities in the Swe­ proved to be constant. The resistant strain can dish resistant flies found at Arnas in 1946, in detoxify DDT. Houseflies of DDT-resistant st­ that they 'were darker, and had thicker cuticle of rains strip HCI from the molecule ~f DDT, leav-: tarsi and pulvim than h~usefliesat Basle in ing behind DDE; in other words, they dehydro- , Switzerland. The DDT-rcsistant flies which chlorinate DDT to DDE. It Is true that some appeared later in .other parts of the world never susceptible strains can do this too, but only slightly. showed any abnormal morphology. It is there- Of course, susceptible strains can only withstand

279 slight amount of DDT, and if they get a little range is fairly' gradual and docs not' show any more they die and can no longer dehydrochlorinate. segregation into different categories of resistance, But the difference between resistants and sus- it was at first reasonably concluded that DDT 'ceptibJes is a real one, in that at parallel dosages resistance was due to a numbero£ genes acting the resistants can dehydrochlorinate at a much together; in short, that resistance was polygenic. faster rate. However, with more recent improvement in gene­ Dehydrochlorination is an activity of the living tical technique, the use of single-pair mating, organism,- and you can designate it as an enzyme and greater precision in the categorization of the process. Indeed, it has -been possible to separate F 2,segregation has been found to occur in the and purify enzyme preparations about 120 times, F 2, and it is now concluded that one main gene the dehydrochlorination proceeding in vitro. determines DDT-resistance in the housefly. Since This enzyme, was discovered by,Sternburg and this gene is not on the Xvchromosome, it is on Kearns of the University of Illinois, and has one of the other 5 autosomes. Whether the 'been purified and characterized as DDT-dehydro­ same gene is involved everywhere remains to be chlorinase by Moorefield. One of the most seen. remarkable points is that, in the housefly, it re­ Several Vl;'orkers have found that their resistant quires to be activated by glutathlone, Whim so strains contain many individuals with abnormalities activated, it has optimum temperature of 37°C in the wing venation. Some veins may be re­ and an optimum pH of 7.4. It can only utilize ticulated, othe~ interrupted. Certain investigators certain compounds as substrates, namely the p,p'­ have found' that resistant strains have broader 2nd substituted diphenylethane derivatives such as abdominal sternites than susceptible strains. - But DDT, DDD, methoxychlor and DFDT. Moore­ at present, we have no reason to believe that field, has found that this enzyme after purifica­ these characters arc linked with DDT-resistance. tion consists of 4 separate proteins. Certainly we have -no reason to consider that they Resistance to BHC,. on the other hand" follows are an expression of a pleomorphic gene for a different 'mechanism. True, gamina-BHC is DDT-resistance. first dehydrochlorinated to pentachlorocyc1ohexene, The gene for DDT-resistance in the Hikone but the enzyme DDT-dehydrochlorinase is not in­ strain of Drosophila melznogaster has been volved. In this case, the fly tissue rather qui­ shown -by Tsukamoto and Ogaki to derive chiefly ckly metabolizes it further to 'water-soluble com­ from a locus on chromosome II between 66 and pounds. 67. They have also found the gene for nicotine­ Thus there are two diff~rent mechanisms of de­ resistance to reside on chromosome III near the toxification. Indeed, it will be found that if spindle-fibre attachment. These two genes show you induce DDT-resistance, you have no induced an interaction and may play a part in general , BHC-resistance. The DDT-resistant Anopheles resistance. These resistant genes have been- are perfectly susceptible to BHC and dieldrin. . shown by Oshima and Hiroyoshi -to occur in D. DDT~resistance On the other hand, BHC-resistant cattle ticks' virilis also: It is noteworthy that are perfectly susceptible to DDT. Dieldrin­ in Drosophila does not involve dehydrochlori­ resistant Anopheles gambiaeand A.quadrimacu· nation. latus 'are also perfectly susceptible to DDT. )0.other instances, there may ~e small genes If you cross DDT-resistant flies with susceptible which aid up to a resistance which is usually not ones, the Fl hybrid offspring will be on the whole specific in the insecticides it concerns. In other

intermediate in resistance. The' F 2 generation words" these genes altogether produce :.vhat may shows a' wide range of variation all the way f~om' be called "vigor tolerance ". The best .example susceptibility to resistance, some being as sus­ of vigor tolerance is the lead-arsenate resistance ceptible as the susceptible grandparent and some of the codling moth which appeared in Colorado \ ' being as resistant' as the resistant. Since this in 1928. These larvae were resistant 'to lead-

280 arsenate simply because they did not die so easily Anopheles gamblae and the chemical involved in from desiccation,. not from lead' arsenate, and the resistance is/dieldrin. In 1954 a house-spraying . thus could wander around the apple Iooking for . programme to control this malaria mosquito was an arsenic-free spot for a longer time before started in Northern .Nigeria on 'the southern edge dying. It' is a characteristic of vigor tolerance of the Sahara desert; where nobody had ever seen that the resistance involves insecticides in general, any synthetic chemical, let alone dieldrin. In' not just special insecticides. Conversely, it bears November 1955, these,mosquitoes were observed no specific relation to the chemical that induces surviving on sprayed walls', and a sample was taken it, and may be induced by selection without for test by a standard method. Thetest showed chemicals at all. that the population had become, on the average, It has been shown recently that houseflies can 8 times more resistant than the normal one from develop resistance to organo-phosphorus com­ unsprayed regions. Then, a sample of eggs of pounds, but it is not nearly as strong as' the this strain was collected in the' village of Am­ DDT-resistance we know, the greatest increase bursa in the sprayed area, and they were air­ being only about 20 times the normal. ' It is mailed to London so that Davidson could quite possible that the ,resistance to organophos­ establish a laboratory colony. On arrival, only phorus compounds may be vigor tolerance. In­ about 5% of the eggs hatched, but the larvae deed, organophosphorus-resistant flies have be­ grew well and emerged into very healthy adults. come much more resistant to chlorinated hydro­ When Davidson had obtained a sufficient nurn- carbons, to which they never been exposed. . ber of mosquitoes to test the resistance of this 'Ve have one selective agent, the insecticide S. colony to dieldrin, he fo~nd that instead of 8 17, which does not induce resistance to itself but times they were now 800 times as resistant as induces resistance to organic phosphates and still normal A. gambiae -frorn Lagos in Northern more to chlorinated hydrocarbons, whereas to S. Nigeria. Then Davidson took his resistant' 17 itself the flies remain completely susceptible. Ambursa strain and crossed it with the sus­ It also appears th'at parathion is very good at in­ ceptible Lagos strain. He found that the ducing resistance to other organophosphorus com­ , hybrids showed intermediate resistance. Since F J pounds rather than to itself. hybrid males sterile. Davidson backcrossed the If the resistance is due to a detoxifying en­ FJ females with the resistant parent, and found zyme, and if those individuals which produce that 50;,; of the offspring were as resistant as that enzyme have a particular gene to produce the resistant parent and 50% showed the inter­ the enzyme, where does this gene come from? mediate resistance characteristic of the FJ hybrid. Did DDT itself produce the gene? The answer, He made the other backcross, with the suscep­ is "No". DDT does not, like nitrogen mustard, tible parent and found that 50% of the offspring induce mutations. Fruit-flies which have grown were as susceptible as the susceptible parent and _in sublethal amounts of DDT for 50 generations 50J,i;' .showed the intermediate resistance. .These did not increase their mutation' rate. We are results constituted proof that the dieldrin-resis­ led to the conclusion that presumably the gene tance was monofactorial, that is due to allelism must have been there from the first; in other in a single gene.. words, somewhere among the fly population some , It is now possible to classify any individual A.' flies contained the gene. But they are very gambiae as homozygous resistant (RR)" hetero­ scarce indeed, and you don't know of their zygous hybrid (Rr) or homozygous susceptible existence in the first place; What you arc. up (rr), by using diagnostic mortality-test dosages. against, again, is not post-adaptation but pre­ In September 1956 a party went into Northern adaptation. Nigeria to test the'genotype composition in nature, In the last year, the correctness of this hypo- and found in t~e dieledrin-sprayed zone now that thesis' has been demonstrated. The insect is about 90% of individuals in the population were 281 homozygousvresistant types. But the most in - , Formosa, where DDT-resistance'developed within teresting point of all is that in one of the un­ 2 years in a population' which before spraying sprayed areas, O.04% of the mosquitoes were of contained 1, resistant individual in every'200; and the hybrldtype, and in another as many as 6% evidently the same kind of thing occurred with of the individuals were heterozygous for the resis­ our house£lies. tant gene. And so with the proven pre-existence of resistant Thus we s~e that individuals carrying the genes genes in certain lridivlduals of the population we for. resistll;nce already existed in Northern Nigeria havethe source of that variation in susceptibility before dieldrin .arrived on the scene in 1954. By upon which selection can act to produce a strain killing only the susceptible genotypes the dieldrin with the new characteristic of. resistance: In selection pressure 'increased the proportion of'. insecticide-resistance therefore, 100 years' after resistant individuals, until dieldrin-resistance cha- the publication of "The Origin of Species ", we .mcterlzed the 'entire population. A similar situa­ have a perfect example of. the truth of Darwin's tion existed in the bed-bug Cimex hemlpterus on ' main hypothesis.

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