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PubMed2002

Toxaphene and other persistent organochlorine pesticides in three species of albatrosses from the north and south Pacific Ocean.

Toxaphene and other persistent organochlorine (OC) pesticides (chlordane-related compounds [sigmaCHL], DDT-related compounds [sigmaDDT], hexachlorocyclohexanes [sigmaHCH], tris(p-chloro-phenyl)methane, hexachlorobenzene, octachlorostyrene, dieldrin) were determined in fat of Laysan albatross (Diomedea immutabilis) and in fat and eggs of blackfooted albatross (Diomedea nigripes) from the central north Pacific Ocean. The HCH isomers and chlordane- and DDT-related compounds were also determined in eggs of northern royal albatross (Diomedea sanfordi) collected in New Zealand. Toxaphene was detected in fat samples at mean +/- standard deviation (SD) levels ranging from 243 +/- 61 ng/g wet weight in Laysan albatross to 1,020 +/- 237 ng/g wet weight in blackfooted albatross. These levels were higher than sigmaCHL and sigmaHCH but lower than sigmaDDT. In eggs of blackfooted albatross, toxaphene was the major OC pesticide, averaging 513 ng/g wet weight in two pooled samples compared with 293 ng/g wet weight for sigmaDDT. Two toxaphene congeners, the octachloroborane B8-1413 (Parlar 26) and the nonachlorobornane B9-1679 (P50), comprised about 38% of total toxaphene in both albatross species. All OC compounds were present at significantly higher levels in blackfooted than Laysan albatross fat with the exception of sigmaHCH, dieldrin, and octachlorostyrene. Mean levels of sigmaDDT and sigmaHCH in northern royal albatross eggs from New Zealand were 4 and 60 times lower, respectively, than in blackfooted albatross eggs. The pattern of OC pesticide accumulation was consistent with differences in distribution of the three species in the Pacific Ocean, with highest levels in blackfooted albatross, which feed off the west coast of North America, intermediate levels in Laysan albatross, which frequent the western Pacific, and lowest levels in northern royal albatross, which are confined to the southern oceans surrounding the Antarctic.

Adipose Tissue↗
PubMed2005

Residues of endosulfan and other selected organochlorine pesticides in farm areas of the Lower Fraser Valley, British Columbia, Canada.

Crop soils, ditch sediments, and water flowing from several farm areas to salmon tributary streams of the Fraser River in the Lower Fraser Valley (LFV) of British Columbia, Canada, were sampled in 2002-2003 to quantify for residues of an organochlorine cyclodiene pesticide, endosulfan (END = alpha-endosulfan + beta-endosulfan + endosulfan sulfate). Residues from historical use of other selected organochlorine pesticides, namely, cyclodienes (aldrin, alpha-chlordane, gamma-chlordane, dieldrin, endrin, endrin aldehyde, heptachlor, and heptachlor epoxide), hexachlorocyclohexanes [alpha-benzene-hexachloride (alpha-BHC), beta-BHC, delta-BHC, and gamma-BHC (lindane)], and DDT-related compounds (p,p-DDT, p,p-DDD, p,p-DDE, and methoxychlor) were also determined. Reference and background levels of these pesticides in ditches leading to fish streams were obtained from pristine watershed areas. Varying amounts of END residues were detected in soils (<0.02-5.60 mg kg(-1) dry wt.) and ditch sediments (<0.02-3.33 mg kg(-1) dry wt.) in mainly three of five farm areas sampled. Likewise, residues (excluding END) of other selected organochlorine compounds such as aldrin, BHC, chlordane, endrin, p,p-DDT, methoxychlor, and their respective major transformation products (endosulfan sulfate, dieldrin, endrin aldehyde, heptachlor, heptachlor epoxide, p,p-DDD, and p,p-DDE) were found in crop soils (<0.02-16.2 mg kg(-1) dry wt.) and sediments (<0.02-9.73 mg kg(-1) dry wt.). Most of these pesticides (END: <0.01-1.86 microg L(-1); other selected organochlorine pesticides: <0.0.1-1.50 microg L(-1)) were also found in ditch water leading to salmon streams in several farms. The END levels of crop soils from the same LFV study farms in 1994 and 2003 indicated an estimated decline of 22% to 1.35 mg kg(-1) dry wt. during that period. This reduction was probably due to the increasing use of alternate pesticides (e.g., organophosphorus compounds). Some possible biological implications of these pesticide residues on nontarget organisms in the LFV are discussed.

Agriculture↗
PubMed2006

Organochlorine residues in fish and water samples from lake victoria, Uganda.

Nile tilapia and Nile perch samples from Lake Victoria were analyzed for lindane (gamma-1,2,3,4,5,6-hexachlorocyclohexane), aldrin (1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro-1,4:5,8-dimethanonaphthalene), alpha-endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3- benzo(e) dioxathiepin-3-oxide), dieldrin (1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-octahydro-1,4,5,8-dimethanonaphthalene), DDE (p,p'-1,1-dichloro-2,2-bis-(4-chlorophenyl)ethylene), and DDT (p,p'-1,1,1-trichloro-2,2-bis-(4-chlorophenyl)ethane). No significant difference (alpha = 0.05) in the residue levels between fish types for lindane, alpha-endosulfan, p,p'-DDE, p,p'-DDT, and dieldrin was observed. The aldrin levels in Nile perch (Lates niloticus) were significantly higher than the levels in Nile tilapia (Oreochromis niloticus). No difference was observed in the distribution of residues in the different parts of Nile tilapia, although a difference for p,p'-DDE was observed in the Nile perch. No significant difference was observed in the average fat content of the tissue of Nile perch and Nile tilapia; however, the distribution of fat was significantly different in the different parts of the fish, with the abdominal portion having the highest amount of fat. There was no correlation observed in this study between fat content and organochlorine concentration. Lower p,p'-DDT residues levels compared with the p,p'-DDE levels observed in this study indicate that DDT is no longer in use. The levels of organochlorine pesticide residues found in fish samples in this study were below the FAO, U.S. FDA, Australian, and German extraneous residue limits and maximum residue limits. The concentration of organochlorine residues in surface water within the Napoleon Gulf of Lake Victoria was below detection limit (0.1 microg L(-1)).

Animals↗
PubMed1983

Comparative penetration of insecticides in target and non-target species.

Dermal penetration of 14C-labeled carbaryl, parathion, DDT, dieldrin and permethrin was compared in American roaches, tobacco hornworms, Japanese quail, grass frogs and mice. Insecticides were absorbed more quickly in mice (one exception) while entry into insects was generally slow. The half time penetration rates for carbaryl ranged from 6 min for frogs to 4600 min for roaches. Whereas permethrin penetrated easily into insects, other insecticides showed generally slower penetration into target organisms. Carbaryl tended to penetrate most rapidly in all species except roaches, while DDT and dieldrin tended to penetrate slowly in all organisms tested. Distribution of insecticides in the blood and liver of Japanese quail and grass frogs was surprisingly low. Insect species tended to show higher amounts in hemolymph than most other species. Excretion of radioactivity was relatively low in the frog in these experiments but was high in the quail for rapidly-metabolized compounds.

Absorption↗
PubMed1986

Organochlorine pesticide residues in chicken fat: a survey.

One hundred and five chicken fat samples were collected between April, 1980 and February, 1982 from seven geographical locations in Kenya (15 samples/area). The samples were subjected to standard extraction and clean up procedures to recover organochlorine pesticides and were subsequently analysed using gas-liquid-chromatography. alpha-, beta-, and gamma-hexachlorocyclohexane/benzene hexachloride (HCH/BHC; Lindane), aldrin, dieldrin, heptachlor epoxide, [1,1-dichloro-2, 2-bis(p-chlorophenyl) ethylene] (p,p'-DDE), [2-(o-chlorophenyl)-2-(p-chlorophenyl)-1, 1-dichloroethane] (o,p'-DDD/TDE), p,p'-DDD, [2-(o-chlorophenyl)-2-(p-chlorophenyl)-1,1, 1-trichloroethane] (o,p'-DDT), and p,p'-DDT were detected in the samples in varying concentrations. A few samples had lindane, dieldrin, and total DDT residue levels above the respective practical residue limit (PRL) values, but for all pesticides, the mean residue values were below the PRL.

Adipose Tissue↗
PubMed1992

Mortality of workers employed at organochlorine pesticide manufacturing plants--an update.

A previous mortality study among four organochlorine pesticide manufacturers was updated through 1987. The organochlorine pesticides included chlordane; heptachlor and endrin; aldrin, dieldrin and endrin; and dichlorodiphenyltrichloroethane. The mortality for all causes and all malignant neoplasms at each of the plants was lower than expected. There was a statistically significant increase in liver and biliary tract cancer among workers at plant 3 (5 observed, standardized mortality ratio 393, 95% confidence interval 1.27-9.20). These results are somewhat consistent with experimental animal findings showing benign and malignant tumors of the liver after exposure to aldrin and dieldrin. However, the deaths were due to a mixture of intra- and extra-hepatic tumors, and the dose-response analysis was limited because of the small number of deaths and lack of exposure data. Additional study of this group should include continued follow-up of the total cohort and a case-referent analysis of the deaths from liver and biliary tract cancer.

Bile Duct Neoplasms↗
PubMed1997

Entomological and rodent surveillance in plague-suspected areas during September 1994 and thereafter.

Studies carried out in the states of Maharashtra, Gujarat, Uttar Pradesh and Union Territory of Delhi after the bubonic plague outbreak during 1994 revealed the presence of seven species of rodents, viz. Rattus rattus, R. norvegicus, Mus. musculus, Tatera indica, Suncus murinus, Bandicoota bengalensis and B. indica. The flea species encountered were Xenopsylla cheopis and X. astia. The X. cheopis and X. astia index recorded in different areas of Beed district of Maharashtra; Surat, Vadodra and Baruch districts in Gujarat and Varanasi district in Uttar Pradesh and their implications have been discussed. Insecticide suspectibility tests carried out against DDT, dieldrin, malathion and deltamethrin with X. cheopis collected from Maharashtra, Delhi and Varanasi revealed that this vector species is resistant to DDT and dieldrin but susceptible to malathion and deltamethrin. The prevalence and distribution of rodents species, high cheopis index and prevalence of Tatera indica just at the door steps of houses in village Mamla of Beed district provides highly congenital conditions for the intermingling of wild and domestic rodents and transfer of flea population from wild to domestic rodents and vice-versa. These conditions were found to be highly supportive for bubonic plague transmission in the district. The presence of Yersinia pestis antibodies in Rattus rattus collected from Beed, Surat and Varanasi areas are also indicative of bubonic plague in Beed and Varanasi and pneumonic plague in Surat during 1994.

Animals↗
PubMed2000

Insecticide resistance in Anopheles sacharovi Favre in southern Turkey.

We report the resistance to 12 insecticides of specimens of Anopheles sacharovi, both in laboratory cultures and those collected in the malarious areas of Adana, Adiyaman, Antalya, Aydin, and Muğla in southern Turkey. Mortality was higher 24 h after exposure than immediately after exposure but was unaffected by temperature (24 degrees C or 29 degrees C) or the position of the test kit (horizontal or vertical). In Adana, Adiyaman and Antalya, A. sacharovi was susceptible only to malathion and pirimiphos-methyl. In Aydin it was susceptible to both these insecticides as well as to dieldrin, lambda-cyhalothrin, and etofenprox; and in Muğla it was susceptible to dieldrin, fenitrothion, lambda-cyhalothrin, cyfluthrin and etofenprox, as well as to malathion and pirimiphos-methyl.

Animals↗
PubMed2000

Serum organochlorine levels and breast cancer: a nested case-control study of Norwegian women.

This study investigated the potential association between organochlorine exposure and breast cancer using stored sera collected from 1973 through 1991 from the Janus Serum Bank in Norway. Breast cancer cases were ascertained prospectively from among 25,431 female serum bank donors. A total of 150 controls were matched to cases by birth dates and dates of sample collection. One g of serum per subject was analyzed for a total of 71 organochlorine compounds. For 6 pesticides [B-hexachlorocyclohexane, heptachlor epoxide, oxychlordane, trans-nonachlor, p, p'-1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene, and p, p'-2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane] and 26 individual polychlorinated biphenyl (PCB) congeners there were >90% of samples over the limit of detection. There was no evidence for higher mean serum levels among cases for any of these compounds, nor any trend of increasing risk associated with higher quartiles of exposure. The remaining compounds (including dieldrin) were analyzed with respect to the proportion of cancer cases and controls having detectable levels; no positive associations were noted in these analyses. Our study did not confirm the recent findings of a Danish study of increased concentrations of dieldrin in the serum of breast cancer cases. The evidence to date on the association between serum organochlorines is not entirely consistent, but there is accumulating evidence that serum levels of p, p'-1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene and total PCBs are not important predictors for breast cancer in the general population. Studies to date have not been able to evaluate whether exposure to highly estrogenic, short-lived PCB congeners increases breast cancer risk, nor have they fully evaluated the risk associated with organochlorine exposure in susceptible subgroups or at levels above general population exposure, including women with occupational exposure.

Adenocarcinoma↗
PubMed1975

Organochlorine residues in starlings, 1972.

During the fall of 1972 starlings were collected from 130 sites in conjunction with the National Pesticide Monitoring Program. They were analyzed for DDT and its metabolites, dieldrin, heptachlor epoxide, benzene hexachloride, polychlorinated biphenyls and, for the first time in the series, oxychlordane and HCB. Mean DDT and dieldrin residue levels have declined significantly since 1967 and a regression analysis suggests that levels of DDT and its metabolites should fall below a mean of 0.1 ppm for the 1974 starling collection.

Animals↗
PubMed2002

Herring gulls and great black-backed gulls as indicators of contaminants in bald eagles in Lake Ontario, Canada.

In 2000, a pair of bald eagles (Haliaeetus leucocephalus) nested successfully along the shorelines of Lake Ontario in North America for the first time since 1957. However, it is a continuing question whether bald eagles will be able to reproduce successfully as they return to nest on Lake Ontario. Great black-backed gulls (Larus marinus) and herring gulls (L. argentatus) were selected as surrogate species to predict contaminant levels in eggs of bald eagles nesting on Lake Ontario. Because of the suspected overlap in the diets of great black-backed gulls and bald eagles (i.e., fish, gull chicks, and waterfowl), the two species probably occupy a similar trophic level in the Lake Ontario food web and, thus, may have similar contaminant levels. Fresh great black-backed gull and herring gull eggs were collected from three study sites in eastern Lake Ontario in 1993 and 1994 and analyzed for contaminants. Average contaminant levels of dichlorodiphenyldichloroethane (p,p'-DDE), total polychlorinated biphenyls (PCBs), and dieldrin in great black-backed gull eggs were 12.85, 26.27, and 0.27 microg/g, respectively. The mean ratio of contaminant levels in great black-backed gull eggs to contaminant levels in herring gull eggs for these three contaminants was 2.09 (range of means, 1.73-2.38). Predicted levels of contaminants in bald eagle eggs in Lake Ontario would be expected to be similar to the mean levels reported for great black-backed gull eggs. As a comparison, contaminant levels in bald eagle eggs collected from other Great Lakes nesting sites were compared to mean levels reported for herring gull eggs collected from nearby sites in 1986 to 1995. The mean ratio of contaminant levels in bald eagle eggs to contaminant levels in herring gull eggs from these sites for DDE, total PCBs, and dieldrin was 2.40 (range of means, 1.73-3.28). These ratios are very similar to those reported using great black-backed gull eggs, illustrating the apparent similarity in trophic status shared by the two top predator species at these Great Lakes sites. Predicted levels of contaminants in bald eagle eggs at Lake Ontario are similar to levels reported for bald eagles breeding at other Great Lakes sites, suggesting that bald eagles may be able to breed on the shores of Lake Ontario. However, it is unclear at this time what level of breeding success should be expected, given that productivity at other similarly contaminated Great Lakes sites may be below that required to sustain a successful breeding population. The absence of an inland bald eagle population from which bald eagles may begin to colonize the shorelines of Lake Ontario may be delaying initiation of nesting site selection; other factors such as habitat and prey availability would likely not limit reproductive success.

Animals↗
PubMed1975

Occurrence of chlorinated hydrocarbon insecticides, southern Florida--1968-72.

The frequency with which chlorinated hydrocarbon insecticides appear in samples of southern Florida surface waters decreased sharply between 1968 and 1972. Sediment analyses attest to the earlier widespread use of chlordane, DDT, and dieldrin. Insecticide residues are more frequently detected in southern Florida than in other U.S. cropland soils. Transport of DDT, DDD, and DDE from the Everglades agricultural area into water conservation areas and undeveloped parts of the Everglades of southeastern Florida is facilitated by a system of water-management canals. Canal sediments within the urban area of southern Florida have high DDD, DDE, and dieldrin residue concentrations which may reflect local use of insecticides rather than their transport from adjacent agricultural areas.

Florida↗
PubMedDate not supplied

Rapid method for trace determination of organochlorine pesticides and polychlorinated biphenyls in yogurt.

A new multiresidue method was developed for the analysis of 19 organochlorine pesticides and 6 polychlorinated biphenyls in yogurt. The sample was extracted twice with acetone by homogenization with an Ultra-Turrax dispersing unit, and the combined extracts were filtered. The extract was then purified by reversed-phase C18 columns and subjected to further cleanup with neutral alumina columns. The residues were determined by gas chromatography with electron capture detection. After the method was optimized, it was validated by determination of recovery percentages, precision (repeatability and reproducibility), and sensitivity (detection and quantitation limits) with yogurt samples fortified at 10 and 1 microg/kg concentration levels. The recovery of 23 organochlorine residues ranged from 77 to 95% at a level of 10 microg/kg, from 74 to 102% at a level of 1 microg/kg, and between 54 and 61% for dieldrin and alpha-endosulfan. The method is repeatable and reproducible, with relative standard deviation values <19% for all residues except dieldrin. Detection and quantitation limits were between 0.02 and 0.62 microg/kg. The analytical method proposed was quick, accurate, repeatable, and reproducible for the determination of organochlorine residues in yogurt samples.

Chromatography, Gas↗
PubMed1976

Collaborative study of an extension of the Mills et al. method for the determination of pesticide residues in foods.

Fifteen laboratories collaboratively determined parathion, o,p'-DDT, p,p'-DDT, and p,p'-DDE in kale, and lindane, dieldrin, heptachlor epoxide, and p,p'-DDE in eggs, using electron capture gas-liquid chromatography (potassium chloride thermionic detector for parathion). Pesticide levels ranged from 0.033 ppm heptachlor epoxide to 3.32 ppm p,p'-DDT. Mean recoveries (+/- standard deviations) were: parathion 91+/-15%, o,p'-DDT 99+/-8%, P,P'-DDT 97+/-8%, lindane 94+/-4%, dieldrin 106+/-8%, heptachloro epoxide 106+/-5%, p,p'-DDE 94+/-8% in eggs and 101+/-9% in kale. The methods have been adopted as official first action.

Chromatography, Gas↗
PubMed1979

Bioassay of Endrin for Possible Carcinogenicity (CAS No. 72-20-8).

Endrin is an organochlorine pesticide having a structural characteristic of the cyclodiene group, which includes aldrin (CAS No. 309-00-2), dieldrin (CAS No. 60-57-1), chlordane (CAS No. 57-74-9), heptachlor (CAS No. 76-44-8), and endosulfan (CAS No. 115-29-7). It is the most acutely toxic compound in the cyclodiene group but is less persistent in the environment than DDT or dieldrin. As an insecticide, it is currently used for small grains, sugarcane, and cotton; as an avicide, for forest seed and perch applications; and as a rodenticide, for forest seed and orchard soil applications. A bioassay of technical-grade endrin for possible carcinogenicity was conducted by administering the test chemical in feed to Osborne-Mendel rats and B6C3F1 mice. Groups of 50 rats of each sex were administered one of two doses of endrin for 80 weeks, then observed for 31 or 34 weeks. The doses used for the male rats were 2.5 or 5 ppm. The initial doses of 5 or 10 ppm used for the females were not well tolerated and were reduced during the study. The time-weighted average doses used for the females were 3 or 6 ppm. Matched controls consisted of groups of 10 rats of each sex; pooled controls, used for statistical evaluation, consisted of the matched-control groups combined with 40 untreated male and 40 untreated female rats from similar bioassays of other test chemicals. All surviving rats were killed at 110 to 114 weeks. Groups of 50 mice of each sex were administered endrin at one of two doses for 80 weeks, then observed for 10 or 11 weeks. Initial doses of 2.5 or 5 ppm used for the males were not well tolerated and were reduced during the study. The time-weighted average doses used for the males were 1.6 or 3.2 ppm; the doses used for the females were 2.5 or 5 ppm. Matched controls consisted of groups of 10 mice of each sex; pooled controls, used for statistical evaluation, consisted of the matched-control groups combined with 50 untreated male and 50 untreated female mice from similar bioassays of other test chemicals. All surviving mice were killed at 90 or 91 weeks. The clinical signs observed in both rats and mice indicated that the doses of endrin used were near the maximum tolerated doses. In mice these signs includedhyperexcitability, a manifestation of toxicity of the organochlorine pesticides. However, mean body weights of the rats and mice were not affected by administration of endrin. Although the survival of the high-dose male mice at the end of the study was markedly lower than that of the controls, the survivals of the low- and high-dose female mice and male and female rats were unaffected by the endrin. The survival of the low-dose male mice could not be evaluated, due to the accidental administration of excessive quantities of endrin to this group during week 66. However, a substantial portion of all groups of rats and mice survived to an age at which tumors could be expected to occur. In rats, the combination of adenomas and carcinomas of the adrenal occurred at the following incidences -- males: pooled controls 2/44, matched controls 2/9, low-dose 4/46, high-dose 8/44; females: pooled controls 4/46, matched controls 3/9, low-dose 16/49, high-dose 7/47. These incidences did not show consistent statistical significance. Furthermore, the incidences of the tumors in the matched controls of either sex were higher than those of the corresponding pooled controls, and the incidences in the matched controls equaled or exceeded those in any of the respective dosed groups. Thus, these tumors cannot be clearly related to administration of the test chemical. In mice, no tumors occurred in dosed groups at incidences that were significantly higher than those in pooled or matched controls. It is concluded that under the conditions of this bioassay, endrin was not carcinogenic for Osborne-Mendel rats or for B6C3F1 mice.

Journal Article↗
PubMed1953

Dose and cycle of insecticide applications in the control of malaria.

The authors first review the doses and cycles of application normally recommended in different parts of the world for DDT, BHC, and dieldrin in controlling malaria, and then discuss the experimental evidence concerning their actual efficacy in the field. The irritant effect of the various insecticides is compared, DDT being found the most irritant and dieldrin the least. BHC appears to be highly irritant when solid, but not when vaporized. The problem of the application of residual insecticides to absorbent surfaces, such as mud, is considered; the wettable powders are generally accepted as the most efficient formulation for such surfaces, but even with these a marked loss in toxicity may occur, requiring higher initial doses and more frequent application than on non-absorbent surfaces. With volatile insecticides, such as BHC, some degree of absorption slows down the loss by volatilization, but at the usual field dosages of 0.1 g and 0.2 g of gamma-BHC per m(2) the decline in toxicity is still rapid. Experiments have also shown that mixtures of DDT and BHC may, in some circumstances, combine the initial high kill of the latter with the persistent moderate kill of the former.Considering the insecticidal efficiency needed for the control of malaria, the authors find that most natural circumstances would be met by attaining a mortality-rate of about 65% of mosquitos entering treated shelters; 85% mortality would be suitable for the most severe conditions and 65% mortality for controlling moderate transmission by endophilic mosquitos.

Animals↗
PubMed1954

A pilot project of residual-insecticide spraying to control malaria transmitted by the Anopheles punctulatus group in Netherlands New Guinea.

The authors report on preliminary observations carried out in three experimental houses in Netherlands New Guinea, the object of which was to determine whether residual spraying with insecticides might be expected to give good results in the control of malaria transmitted by mosquitos of the Anopheles punctulatus group and by A. karwari. One house was sprayed with DDT, another with dieldrin, and the third was left unsprayed. From the kills recorded of mosquitos entering these houses at night it is apparent that good results can be anticipated with both insecticides, although dieldrin is the more effective.Observations made at the same time on the behaviour of these mosquitos indicate that they have greater contact with the inside walls of houses than was previously thought.

Animals↗
PubMed1957

Laboratory tests on mosquito tolerance to insecticides and the development of resistance by Aedes aegypti.

Three strains of Aëdes aegypti and a strain of Culex molestus were used in tests to determine the relative susceptibility levels of the larvae to various insecticides and to investigate the development of resistance in the laboratory through selection by larval treatment only. The procedures and test methods used are described and the results discussed and set out in tabular and graphic form.It was found, inter alia, that selection of fourth-stage larvae of a laboratory strain of Aëdes and Culex for 15 generations with DDT at the LC(50) level did not induce any appreciable decrease in susceptibility; that with another Aëdes strain, naturally three times as resistant to DDT as the laboratory strain, selection for eight generations further increased this resistance to seven times its natural level; that selection of the laboratory strain of Aëdes with gamma-BHC for 15 generations induced a twofold increase in resistance to this compound, which also extended to DDT and dieldrin; and that selection of the same strain with dieldrin, over 14 generations at a low mortality level to avoid after-effects of this insecticide, did not induce any appreciable decrease in susceptibility.

Aedes↗