Search

A steric theory of DDT action has led to the design of some new and highly active cyclopropane insecticides. The new compounds suggest a general van der Waals model for diaryl insecticides and support a theory of insecticide action based on the sodium pores of nerve membranes.

Investigations of the properties of ribosomes and polyribosomes isolated from adult houseflies, Musca domestica, throw new light on the part played by these structures in protein biosynthesis and suggest that nascent protein may be an important constituent that holds a polyribosome together.

EXPERIMENTS have been conducted with isodrin and endrin labelled with carbon-14 in the terminal unchlorinated ring1 and with aldrin and dieldrin labelled in the chlorinated ring (from the Radiochemical Centre, Amersham). Adult insects used were of a susceptible strain (S) and dieldrin-resistant strains (R 1) and (R 2). R 1 arose from the S-strain by exposure of the larvae to dieldrin and R 2 from R 1 by removal of the dieldrin pressure after 19 generations2.

IT is now known that a number of insect species which are resistant to insecticides possess effective means of detoxication in order to protect themselves from being exposed to the toxicant at the vital site1–3. One of these insects, Culex tarsalis Fresno strain, was shown to have developed a malathion Carboxyesterase3 with a very narrow substrate specificity against malathion analogues4. This agrees perfectly with the fact that this strain shows little cross-resistance to any other organophosphorus insecticides.

WHEN a glass electrode filled with KCl is placed on the eye of a housefly bursts of nervous activity occurring even in darkness may be observed using an oscilloscope. We present evidence that the diel changes in burst frequency represent a true circadian rhythm. The source of these signals obtained from the housefly eye is as yet unknown. Dethier1 reported two types of electrical activity as recorded externally from the insect eye, the electroretinogram (ERG) and spontaneous nerve firing. The latter activity was related to light intensity and movement in the visual field.

TWENTY different species of insect larvae, distributed among four orders (Orthoptera, Coleoptera, Lepidoptera and Diptera) have been found so far to require sterols as growth factors. All of them, excepting the Dermestidae (Dermestes vulpinus Fabr.1 and Attagenus piceus Oliv.2), can utilize both zoosterols and phytosterols; certain species, however, grow faster with dietary cholesterol than with a phytosterol3. Furthermore, the activity of the intestinal sterol esterase of Periplaneta americana L. was found to be limited to the esters of cholesterol, Δ7-cholestenol and 7-dehydrocholesterol as the substrate4. These observations, together with Bergmann's5 report on the cholesterol content of the phytophagous silkworm Bombyx mori L., led us to suspect that the dietary phytosterols are converted to a zoosterol before utilization. Hence, sitosterol conversion was investigated in the larva of the housefly.

DDT resistance in the housefly (Musca domestica L.) has been known in Australia since 1950 1. In addition, ‘Dieldrin’ resistance was recorded as early as 1956 (Shanahan and Wright, personal communication). During the past year, resistance to organic phosphate has occurred on both the east and west coasts of Australia.

A NUMBER of electrolytes, which are in common use in the fractionation of proteins, have been studied for their effect on choline- and ali-esterase of the housefly. The substrates were acetylcholine and ethylbutyrate, respectively. Enzyme activity was measured by a pH-titrimetric method using barbitone-HCl (pH 7) as buffer.

THE natural pyrethrins (see refs 1 and 2 for references) (for example, pyrethrin I (1)) and related synthetic insecticides3 (allethrin (2), bioallethrin (3), resmethrin (4), bioresmethrin (5), Cismethrin (6) and the ethanochrysanthemate (7)) are unstable in air and light (see refs 1 and 2 for references, and ref. 4). This property restricts their use, particularly against pests of agricultural crops, in spite of other favourable characteristics (see refs 1–3 for references) (outstanding potency against many insect species, rapid action, and low mammalian toxicity5). We describe here new synthetic esters, ten to one hundred times more stable in light than previous pyrethroids, yet as active against insects as bioresmethrin (5) and with low mammalian toxicity.&nbsp

THE effectiveness of repeated small doses of insecticides is of considerable practical importance. For example, mosquitoes and houseflies entering houses treated with residual insecticides make intermittent contacts with deposits, and tsetse flies may receive a succession of doses when applications of insecticides are made from aircraft on a number of parallel runs in each day's sortie, and the area treated at the end of one sortie is re-treated at the beginning of the next. Hoffmann, et al. 1 exposed houseflies intermittently to small amounts of DDT residues and found that the longer the intervals between exposures the greater the number of flies that survived. There is, however, little quantitative information, and the experiments summarized below were designed to determine the cumulative effect of sub-lethal doses of insecticides on houseflies.

As part of a programme designed to test a free-radical hypothesis of insecticidal action for DDT1, a series of new DDT compounds substituted by halogen in the ortho-position was synthesized and the toxicity to normal and to DDT-resistant house-flies (Musca domestica L.) was determined (Table 1). The results are of unusual significance in regard to: (1) the mechanism of DDT resistance, and (2) the relative toxicity of the positional isomers of DDT.

THE decomposition of animals after death is of limited aesthetic appeal but very important. Several recent papers1–5 have described aspects of the ecology of carrion on the soil surface or other exposed locations. With the exception of a few medico-legal papers6–8 that discuss arthropods of tombs and graves, little or nothing is known concerning the processes of decomposition of animal bodies beneath the soil.

THE adult house-fly has been reported to require a dietary source of both protein and carbohydrate for ovarian maturation and to show little or no ovarian growth on an adult diet consisting solely of carbohydrates1–5. This requirement of the adult for protein could not be fulfilled by supplementing the larval diet with additional protein4.

Differences between Rates of Metabolism of Benzene Hexachloride in Resistant and Susceptible Houseflies

SEX is determined by the presence of X and Y sex chromosomes in the house fly, Musca domestica L. (males are heterogametic), and the Y chromosome determines maleness. Aneuploid house flies with from one to six X chromosomes (and with the normal five pairs of autosomes) are females if no Y chromosome is present and males if one or more Y chromosomes are present1.

THE concentrations of blood Na and K in the adult housefly, Musca domestica, fed a normal diet of milk and sugar are fairly constant. The usual amounts are Na, 109–140 mequiv./l., 0.11–0.14 M (2.4–3.2 (µg/µl.); K, 0.0–4 mequiv./l., 0.0–0.004 M (0.0–0.16 µg/µl.). Blood cells contain very small quantities of these ions.

ALTHOUGH synergized pyrethrins have been used for fly control for many years, there is no published record of Musca domestica L. becoming resistant to this insecticide in the field.

SOME initial results of an investigation of insect colour vision carried out by recording the activities of second and higher order neurones are reported here. They are relevant to the question of sensitivity to red light in the Diptera.

STERNBERG and Kearns1 have reported that both γ-benzene hexachloride (γ-BHC)-resistant and susceptible houseflies can dehydrochlorinate γ-BHC to pentachlorocyclohexene (PCCH). Their evidence relied on the formation of 1-chloro-2:4-dinitro-benzene when the method of Schecter and Hornstein2 for the determination of γ-BHC was applied to flies treated with the insecticide. This method involved the reduction with zinc and acetic acid of unchanged γ-BHC and PCCH to benzene and chlorobenzene followed by nitration to form m-dinitrobenzene and 1-chloro-2:4-dinitrobenzene respectively. Bradbury and Standen3, working with a different strain of resistant and susceptible houseflies, used an isotopic dilution technique to determine any γ-PCCH present after γ-BHC treatment but failed to find the large amounts reported by Sternberg and Kearns.

AFTER the discovery that an epoxide derivative of farnesenate esters (1) showed high juvenile hormone (JH) activity1, we undertook to synthesize related compounds in an effort to find the most potent of this class of materials. The elucidation of the structure of two hormones from Hyalophora cecropia (2 (ref. 2) and 3 (ref. 3)) as homologues of the farnesenate structure, and the observation that products obtained from the addition of hydrogen chloride to farnesenate esters (18) also possessed hormone activity4, led to the inclusion of analogous compounds in our programme. Here we describe results with a series of amide derivatives.

THE ability of insects to develop a resistance to an insecticide is now widely acknowledged. It has also been shown that, where resistance to a specific insecticide exists, the toxicity of related compounds can be tolerated also, though probably to a lesser extent. This communication reports the occurrence of a high degree of resistance to dieldrin (an insecticidal product containing not less than 85 per cent of 1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8a-octahydro-1,4,5,8-dimethanonaphthalene, and not more than 15 per cent of insecticidally active related compounds), in a wild strain of Musca domestica L. which had not been exposed to this insecticide prior to this investigation.

Two strains of houseflies (Musca domestica L.) have been derived by selection for a number of generations from a DDT-susceptible colony which originated from wild flies collected in 1939. The colony had been mass-reared in the laboratory for fourteen years without exposure to insecticides. Selection was by two different methods. One strain (D) was derived by incorporating DDT wettable powder in the larval medium at 80 p.p.m. DDT for the first three generations, 160 p.p.m. for generations 4–9, and 320 p.p.m. for all subsequent generations. The other strain (L) was started ten generations later than D; it was selected on the basis of slow preadult development, that is, by breeding only from flies emerging from the cultures towards the end of the emergence period, and its breeding stock was not exposed to insecticides. Pimentel et al.1 had found that late-emerging flies were more tolerant of DDT than early emerging ones, and that, in four DDT-resistant strains, resistance was associated with prolonged larval period.

Although evidence1, based on laboratory crossing experiments, exists for considering the two forms of housefly which occur in the Ethiopian region to be only subspecifically distinct from each other and from Musca domestica s. str., nothing has been published on how they interact in Nature when they are sympatric. It is important to know this, as it is well known that some species will interbreed in the laboratory whereas they seldom, or never, do so in Nature. The behaviour of M. cuthbertsoni Patton and M. curviforceps Sacca and Rivosecchi1 (vicina auct. not Macquart), both of which occur at Johannes-burg, has therefore been investigated.

THE presence of 2-aminoethylphosphonate has been reported in ciliates1 and in two sea anemones Anthopleura elegantissima2 and Metridium dianthus3. The finding of the phosphonate in hydrolysates of lipid extracts obtained from these sources and the identification of its glyceryl ester in alcoholic extracts of the sea anemone suggest the natural occurrence of a diacylglycerylphosphonolipid. Rouser et al.4 isolated a phosphonolipid from the sea anemone and identified it as a sphingolipid on the basis of its hydrolysis products. Baer and Stanacev5 have synthesized the phosphonic acid analogue of cephalin.

THE recent characterization of DDT dehydrochlorinase in resistant houseflies1 has prompted an investigation of this enzyme and of the production of 2,2-bis(p-chlorophenyl)-1,1-diehloroethylene (DDE) in mosquitoes, in which DDT-resistance is now developing2. As an initial step, two strains of resistant house-flies were assessed for DDT-dehydrochlorinase content. The DDT-45 strain showed no less activity than originally reported1, the DDE production in 3 hr. by the equivalent of six flies averaging 98 µgm. for homogenates and 52 µgm. for acetone powders. The Dilan strain, developed by two years of dilan pressure without any exposure to DDT, showed an enzymic DDE production of 100 µgm. for homogenates and 34 µgm. for acetone powders. This Dilan strain resembled the DDT-45 strain in having an LD90 exceeding 50 µgm. and being able to convert 90 per cent of 10 µgm. of DDT topically applied to DDE in 24 hr.

THE ease with which the chlorinated hydrocarbons give rise to the development of resistance in Musca has led to the use of organo-phosphorus insecticides for controlling flies. However, development of resistance to some of these compounds appears possible also, although at present it seems to be less serious than in the case of the chlorinated compounds. An investigation into the mechanisms causing resistance to these substances has been undertaken.

THE following observations have been made during a study of the mechanisms of resistance to γ-benzene hexachloride in a strain of Musca domestica obtained initially through the kindness of Dr. J. R. Busvine. The flies (S-flies) had a history of dieldrin resistance1; but the first generation of adults at this Laboratory were found to be only slightly more resistant to dieldrin and γ-benzene hexachloride than the normal Laboratory culture of Musca domestica. On incorporation of graded amounts of dieldrin into the larval medium of the S-flies the level of resistance rose rapidly. After six generations a concentration of 150 p.p.m. of dieldrin per wet weight of larval medium had been attained, and this concentration has been maintained during subsequent generations. These flies (R-flies) were highly resistant to both dieldrin and γ-benzene hexachloride although at no time has the latter been used for selection at this Laboratory.

Fertility Reduced in a Caged Native House Fly Strain by the Introduction of Strains bearing Heterozygous Chromosomal Translocations

THERE have been many speculations on the mode of inheritance of resistance to DDT in the housefly (Musca domestica L.), but little scientific evidence in support of one theory or another. In 1950, Bruce and Decker1 reported that it was a multiple gene character and was carried by both male and female flies. Reciprocal crossing experiments between flies of a non-resistant laboratory strain and a DDT-resistant strain resulted in the F1, F2 and F15 generations having a resistance exactly intermediate between that of the parents.

THE widespread occurrence of resistance to present-day insecticides among pest species1,2 has prompted intensive research into alternative means of insect control. The discovery that application of the insect juvenile hormone (JH) or its mimics at certain critical stages of the life cycle leads to developmental abnormalities and death3 has raised hopes of the emergence of a “third generation” of pesticide chemicals4. It has been suggested that insects would be unable to develop resistance to their own juvenile hormone3. Arguments have also been advanced that resistance to hormonal insecticides is not unlikely5,6.

DURING the course of a study on the biochemical changes accompanying ageing in the adult house-fly, the attention of the senior author was directed to the differential longevities of the male and female members of the common house-fly, M. domestica L. Paradoxically enough, a search of the literature revealed only scattered and inconclusive information on the longevity of this species under controlled laboratory conditions. Several authors have been cited by Roubaud1 to the effect that the longevity of the house-fly can be extended to as much as 90 days by exposure to temperatures of 15° C. (59° F.); West, on the other hand2, states in no convincing terms that the longevity of the house-fly varies from two to three weeks, at most, during the summer and up to three months during the winter months. A side study was therefore undertaken to obtain reliable vital statistics for the male and female members of this species, bred, reared and maintained under standardized laboratory conditions. This report will summarize briefly one phase of this study to be published, in extenso, at a later date.

IT has been known for some time that with very few exceptions1 insects require only the unsaponifiable, not the saponifiable, fractions of lipids. According to Hobson, for example, the larvae of Lucilia sericata require cholesterol as an extraneous growth factor, and they are capable of synthesizing neutral fat from a lipid-free peptone diet under sterile conditions. Since then, many insects have been found to require a sterol (zoosterol, phytosterol or mycosterol) as growth factor.

THERE have recently been several reports which indicate that the oxidative metabolism of drugs by liver microsomes involves a eytoehrome-like pigment usually referred to as P-450 (refs, 1 and 2). This pigment, which is characterized by the difference spectrum observed when microsomal suspensions reduced either with hydrosulphite or with NADPH are saturated with carbon monoxide, has recently been found in microsomes from the housefly Musca domestica (vicina strain)3. Furthermore, the inhibition by carbon monoxide of the epoxidation of aldrin and the partial reversal of this inhibition by light supports the view that P-450 is involved in epoxidation by fly microsomes in vitro. Similar evidence has been produced to support the view that this pigment is involved in the metabolism of drugs by microsomes from rat liver2. Evidence for the role of a reaction in the metabolism of insecticides in vivo which is sensitive to carbon monoxide has not, however, been reported.

IT has been known for a long time that the application of a ligature posterior to the brain in the larva of the blowfly, Calliphora erythrocephala Meig., prevents the pupation of the posterior part, provided that the ligature is applied before a “critical period” in the development of the larva has been reached1. If the ligature is applied after the critical period has passed then the whole larva darkens and forms a puparium.

OUR previous work on the metabolism of isomers of benzene hexachloride by a resistant strain of houseflies showed that the α- and γ-isomers are rapidly converted to water-soluble metabolites1–3, and in the course of the reaction chloride ions are formed in the proportion of four or more per molecule of benzene hexachloride metabolized4. We have now found that alkaline hydrolysis of the metabolic products produces dichlorothiophenols.

TRANSPLANTATION and parabiotic experiments have shown that, in irradiated embryos of vertebrates, direct damage to organ rudiments is primarily responsible for developmental abnormalities1–4. Although the irradiated environment per se does not adversely influence the development of normal organ transplants, it does seem to enhance the damage in irradiated organ primordia5,6. We have carried out similar experiments in housefly pupae and observed that normal imaginal disks transplanted in irradiated pupae developed poorly. Besides, the epidermis of the irradiated host inhibited the development of transplants when they were in contact with each other.

ALTHOUGH considerable information has been published on the nutritional requirements of fly larvae (refs. 1–5 and Mer, G. G., personal communication) the actual natural food of these insects has never been unequivocally described. The biotopes of housefly larvae consist of a variety of materials which by themselves appear nutritionally inadequate, but which have dense microbial floras (for example, animal excrements).

THE hypothesis that the organophosphate insecticides kill insects by inhibiting the cholinesterase of the nervous system has been questioned, partly on the grounds that acetylcholine has not been demonstrated in insects1. That insects contain a substance with pharmacological activity similar to acetylcholine has been amply demonstrated2; but the identity of this substance remains in doubt. Chemical methods have indicated that the substance is not acetylcholine3; on the other hand, combined chromatography and pharmacological methods have indicated that the substance is acetylcholine4. We have used the chemical method, chromatography and electrophoresis to examine the pharmacologically active substance extracted from the housefly, Musca domestica L. The results show consistently that the acetylcholine-like substance in the housefly is identical with acetylcholine itself.

ANTENNAL receptors which mediate various stimuli are concentrated on three segments in higher Diptera1–3. The scanning electron microscope (Cambridge Stereoscan) has now disclosed previously undetected structures on the pedicel or second antennal segment of a number of common flies (Figs. 1a, b). (Specimens were gold coated at 200 A and the microscope was operated at from 3 to 10 kV with an aperture of 200µ.)

THE fungus Amanita muscaria has been the object of intensive investigations for many years, and two of its constituents, muscarine and acetylcholine, are of fundamental importance in pharmacology. The elucidation of the structure of muscarine in the classical researches of Kogl et al.1–3 and Eugster4 and Waser5 has overshadowed the existence in the plant of other interesting substances. The fungus has long had a reputation for insecticidal properties in folk-lore as the names ‘muscaria’, ‘fly agaric’ and ‘fliegenpilz’ imply. Ramsbottom6 describes its use—broken up in milk or sprinkled with sugar—as a fly trap in various parts of Europe.