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Observations on the toxicity of different insecticides to adults and larvae of myiasis-producing diptera
LABORATORY
MEETING
13
R e p r o d u c t i o n o f t h e h e a d louse. ( A s h o r t f i l m ) J. W. M A U N D E R , J. M. C O C K B U R N
Department of Entomology, London School of Hygiene and Tropical Medicine AND A. MAcEWEN
London Film School A 5 minute excerpt from a sound, colour 16 mm. film, " W a r to the last itch", showed aspects of the reproduction of the head-louse, Pediculus humanus capitis. This included copulation, egg laying and the hatching of the egg. This is the first time that details of louse reproduction have been filmed. Several new facts emerged. T h e process of egg hatching differs substantially from published accounts, and the existence of a nocturnal endogenous cycle of egg-laying was observed although previously unsuspected. T h e complete film, which lasts 16 minutes, was made by co-operation of the Entomology Department, London School of Hygiene and Tropical Medicine and the London Film School. T h e film was awarded first prize in the Popular Science Section of the 27th International Festival and Congress of the Scientific Film Association held in October 1973 in Varna, Bulgaria.
O b s e r v a t i o n s o n the t o x i c i t y o f different ~ i n s e c t i c i d e s to a d u l t s a n d l a r v a e o f m y i a s i s - p r o d u c i n g Diptera M. O. I W U A L A
Department of Entomology, London School of Hygiene and Tropical Medicine This investigation was concerned with ascertaining relative effects of different pesticides on the adults and mature larvae of houseflies and blowflies, using the following: (A) Species of Diptera: Musca domestica (Linn.) Lucilia sericata (Meig.) and Chrysomia putoria (Wied.) (B) Types of insecticides : Organochiorines--gamma BHC and D D T Organophosphates--malathion and diazinon Pyrethroids--bioresmethrin and bioallethrin and Carbamates--propoxur and carbaryl (C) Methods of exposure : Contact (by topical application using standard microsyringe equipment) Injection (using microsyringe equipment as above) Oral feeding (using a newly designed glass apparatus) Weight for weight, the mature larvae of the 3 species examined were found to tolerate significantly higher levels of insecticides than their adult equivalents. Both stages were on the average more susceptible to organophosphates and pyrethroids than to the organochiorines and carbamates. T h e lethal dosages by injection were found to be about 40% of those by topical application, and about 60% of the doses by oral feeding. T h e ratio of the LD~0s recorded for the different insecticides, however, did not vary significantly irrespective of the methods of exposure of the insects. M y thanks are due to Professor J. R. Busvine of London School of Hygiene and Tropical Medicine, and to the Scholarship Commission of the Association of Commonwealth Universities (U.K.).
S t a n d a r d i z a t i o n o f a r e s i s t a n c e test for m y i a s l s - p r o d u c i n g l a r v a e M. O. I W U A L A
Department of Entomology, London School of Hygiene and Tropical Medicine Insecticide resistance in sheep blowflies has seriously hampered their control in Australia and may well occur in blowflies elsewhere in the world. Most of the work on detection and measurement of this resistance has been based on tests with adults. Recent Australian work, however, has shown that this is not necessarily a sound guide to resistance in the larvae. While there are several techniques for screening insecticides against myiasis-producing larvae, there is so far no standardized method for detecting their resistance to the pesticides. T h e work displayed was for developing such a test method, to be adopted as a standardized test by a panel of the F o o d and Agriculture Organization. Several methods suggested including those of D u TOIT and FIF_X~L~t(1953), G~m~WOOD and HARRISON (1965), ARNOLD (unpublished, 1970) and ROXBgaGH (1972) have been tried, and a compromise technique has been proposed. This involves the use of triple-layer strips (8 × ~ in. each) of non-woven cellulose fabric (sofnet swab material), roiled into plugs and inserted into 3 × ½ in. test tubes, where they are exposed to a series of insecticide concentrations in acetone (1 ml. of graded solution being pipetted onto each plug), and left to dry properly. T h e plug is then moistened with 1 ml. of nutrient serum and a batch of newly hatched larvae (less than 6 hours old) is placed on its surface, and the tube is sealed with cotton wool.
MEETING
13
R e p r o d u c t i o n o f t h e h e a d louse. ( A s h o r t f i l m ) J. W. M A U N D E R , J. M. C O C K B U R N
Department of Entomology, London School of Hygiene and Tropical Medicine AND A. MAcEWEN
London Film School A 5 minute excerpt from a sound, colour 16 mm. film, " W a r to the last itch", showed aspects of the reproduction of the head-louse, Pediculus humanus capitis. This included copulation, egg laying and the hatching of the egg. This is the first time that details of louse reproduction have been filmed. Several new facts emerged. T h e process of egg hatching differs substantially from published accounts, and the existence of a nocturnal endogenous cycle of egg-laying was observed although previously unsuspected. T h e complete film, which lasts 16 minutes, was made by co-operation of the Entomology Department, London School of Hygiene and Tropical Medicine and the London Film School. T h e film was awarded first prize in the Popular Science Section of the 27th International Festival and Congress of the Scientific Film Association held in October 1973 in Varna, Bulgaria.
O b s e r v a t i o n s o n the t o x i c i t y o f different ~ i n s e c t i c i d e s to a d u l t s a n d l a r v a e o f m y i a s i s - p r o d u c i n g Diptera M. O. I W U A L A
Department of Entomology, London School of Hygiene and Tropical Medicine This investigation was concerned with ascertaining relative effects of different pesticides on the adults and mature larvae of houseflies and blowflies, using the following: (A) Species of Diptera: Musca domestica (Linn.) Lucilia sericata (Meig.) and Chrysomia putoria (Wied.) (B) Types of insecticides : Organochiorines--gamma BHC and D D T Organophosphates--malathion and diazinon Pyrethroids--bioresmethrin and bioallethrin and Carbamates--propoxur and carbaryl (C) Methods of exposure : Contact (by topical application using standard microsyringe equipment) Injection (using microsyringe equipment as above) Oral feeding (using a newly designed glass apparatus) Weight for weight, the mature larvae of the 3 species examined were found to tolerate significantly higher levels of insecticides than their adult equivalents. Both stages were on the average more susceptible to organophosphates and pyrethroids than to the organochiorines and carbamates. T h e lethal dosages by injection were found to be about 40% of those by topical application, and about 60% of the doses by oral feeding. T h e ratio of the LD~0s recorded for the different insecticides, however, did not vary significantly irrespective of the methods of exposure of the insects. M y thanks are due to Professor J. R. Busvine of London School of Hygiene and Tropical Medicine, and to the Scholarship Commission of the Association of Commonwealth Universities (U.K.).
S t a n d a r d i z a t i o n o f a r e s i s t a n c e test for m y i a s l s - p r o d u c i n g l a r v a e M. O. I W U A L A
Department of Entomology, London School of Hygiene and Tropical Medicine Insecticide resistance in sheep blowflies has seriously hampered their control in Australia and may well occur in blowflies elsewhere in the world. Most of the work on detection and measurement of this resistance has been based on tests with adults. Recent Australian work, however, has shown that this is not necessarily a sound guide to resistance in the larvae. While there are several techniques for screening insecticides against myiasis-producing larvae, there is so far no standardized method for detecting their resistance to the pesticides. T h e work displayed was for developing such a test method, to be adopted as a standardized test by a panel of the F o o d and Agriculture Organization. Several methods suggested including those of D u TOIT and FIF_X~L~t(1953), G~m~WOOD and HARRISON (1965), ARNOLD (unpublished, 1970) and ROXBgaGH (1972) have been tried, and a compromise technique has been proposed. This involves the use of triple-layer strips (8 × ~ in. each) of non-woven cellulose fabric (sofnet swab material), roiled into plugs and inserted into 3 × ½ in. test tubes, where they are exposed to a series of insecticide concentrations in acetone (1 ml. of graded solution being pipetted onto each plug), and left to dry properly. T h e plug is then moistened with 1 ml. of nutrient serum and a batch of newly hatched larvae (less than 6 hours old) is placed on its surface, and the tube is sealed with cotton wool.