The Mode of Action of DDT

Wigglesworth, V. B.

doi:10.1007/978-3-0348-6997-3_3

Cited by 3 publications

(1 citation statement)

References 94 publications

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“…There is an extensive literature on the histological and cytological effects of insecticides (Brown, 1963), mostly with lethal doses, but in general these observations give little insight into sublethal or lethal mechanisms. This is not surprising, for only advanced degenerative changes produce visible effects (Wigglesworth, 1955). Periplaneta americana fed an almost lethal dose of chlordane does show obvious effects in the mid-gut epithelium, but there are few if any significant effects on blood cells (Gupta & Sutherland, 1968).…”

Section: ( 5 ) Miscellanymentioning

confidence: 99%

The Sublethal Effects of Synthetic Insecticides on Insects

Moriarty

1969

Biological Reviews

100

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Summary The synthetic insecticides have been used in steadily increasing quantities since the Second World War and are non‐specific poisons, and so pose the possibility of sublethal effects on wild populations of animals. The organochlorine insecticides in general, and some of the cyclodienes in particular, are usually much more persistent than the organophosphorus and carbamate insecticides, both in the environment and within individual insects. Analyses of samples suggest that traces of the organochlorines are widely dispersed over the entire globe. Although the evidence is incomplete, all of these synthetic insecticides appear to exert their primary toxic lesion by interference with the conduction of impulses in the nervous system. The complete pattern of events that ends in death includes the release of secondary toxins into the blood. These are probably physiologically active compounds, normally present, but liberated in excessive amounts by excessive nervous stimulation. A condition similar to the late, paralytic, stage of insecticidal poisoning can also be produced, in Periplaneta americana, by excessive physical stimulation and there are similarities in the physiological changes caused by both types of stimuli. This suggests that a generalized stress syndrome develops after excessive nervous stimulation. However, this similarity has so far only been demonstrated for this one insect species. Sublethal effects have so far only been looked for cursorily. Interpretation of sublethal effects is sometimes difficult; apparent differences between dosed and control individuals may sometimes be caused by selective mortality of the dosed individuals. Four main types of effect have been found. Latent toxicity, which is evident as a reduction of longevity or of death at particular developmental stages, has been found only with organochlorines, appears to be linked with fat metabolism, and shows clearly that sublethal effects may be produced a long time after acquiring a dose of a persistent insecticide. All types of synthetic insecticide can affect reproductive potential, and may increase or decrease the number of eggs produced. Egg fertility or development of offspring may also be affected. Reductions are sometimes caused directly by inhibition or distortion of ovary development, sometimes indirectly by reduced feeding. The few studies on behaviour have shown that activity may increase, feeding decrease, and the acceptance threshold of sucrose be lowered. DDT induces the formation of more detoxifying microsomal enzyme in Triatoma infestans. I suggest that latent toxicity and some behavioural changes are probably caused by direct effects on the nervous system, but that some of the other results may be secondary effects associated with the stress syndrome. There is also the possibility of direct insecticidal action on other systems. It is a pleasure to thank our librarian, Mrs Jean King, for her unfailing help in tracing references.

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Section: ( 5 ) Miscellanymentioning

confidence: 99%

The Sublethal Effects of Synthetic Insecticides on Insects

Moriarty

1969

Biological Reviews

100

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Effects of DDT on oxygen consumption of Rhodnius prolixus Stål

Spiller

1966

Bull. Entomol. Res.

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Insecticides: Their Route of Entry, Mechanism of Transport and Mode of Action

Gerolt

1983

Biological Reviews

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Summary (1) The assumption that the circulatory system of the insect is instrumental in transporting insecticides to their site of action appeared not to be based on good evidence. On the contrary, experiments specifically designed to test the hypothesis provided ample evidence to refute the idea. Salient points to disprove the haemolymph route of entry can be summed up as follows: (a) A topically applied dose of insecticide does not readily penetrate the insect and the minor fraction that does so is largely retained in the body wall. The small amount that actually passes into the blood is too small to cause symptoms of toxicity if injected into the haemocoel. (b) The amount of insecticide present in the haemolymph (and CNS) does not appear to have any bearing on toxicity ‐ internally introduced insecticides are, in fact, basically very much less toxic than those externally applied. Where injected doses appear to be more toxic than equal amounts topically applied, this is due to the boosting effect of organic solvent carriers. Tests with parabiotically joined insects provide support for the view that haemolymph‐borne insecticide is of no consequence. (c) The topographical proximity of the locus of external application with the site of action (the thoracic ganglia) seems to be important irrespective of the general direction of the blood flow, and this should not be so if the circulatory system was instrumental in the transport of insecticide. (d) The introduction into the haemocoel of material such as olive oil, which is an excellent absorbent for insecticides, does not affect the toxicity (speed of action) of externally applied compounds to a significant extent. It should have a pronounced effect if haemolymph‐borne insecticide were an essential element in the process of poisoning. (e) As judged by speed of action, blocking of the blood circulation does not hamper the insecticide's movement to the site of action. (2) Only two other feasible routes remain. (a) The insecticide might reach the CNS via peripheral nerves and nerve cord, but the results of histochemical assays of cholinesterase inhibition in the insect's CNS make the idea improbable for organo‐phosphates. The nerve route is also incompatible with the observation that a wax barrier blocked the movement in and over the body wall so as to delay the onset of symptoms of toxicity, as such a barrier would not hinder movement into lateral nerves near the locus of application. (6) The only other feasible alternative, i.e. entry by means of lateral transport via the integument of the body wall and tracheae, is supported by autoradiographic and other evidence which showed the insecticide to accumulate in the tracheal system. It is further supported by the fact that inter‐tracheal introduction is faster acting than topical treatment, indicating that the tracheal system offers a very effective pathway to the internal organs. (3) Regarding the mechanism of entry, earlier reviews and text books maintain this to be associated exclusively with penetration into and thr...

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The Mode of Action of DDT

Cited by 3 publications

References 94 publications

The Sublethal Effects of Synthetic Insecticides on Insects

The Sublethal Effects of Synthetic Insecticides on Insects

Effects of DDT on oxygen consumption of Rhodnius prolixus Stål

Insecticides: Their Route of Entry, Mechanism of Transport and Mode of Action

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