Tolerance To DDT Research Articles

Cytochrome P450s Cyp4p1 and Cyp4p2 associated with the DDT tolerance in the Drosophila melanogaster strain 91-R

Cytochrome P450s are part of a super-gene family that has undergone gene duplication, divergence, over-expression and, in some cases, loss of function. One such case is the 91-R and 91-C strains of common origin, in Drosophila melanogaster, whereby 91-R (DDT resistant strain) overexpresses Cyp4p1 and Cyp4p2 and both genes are lost in 91-C (DDT susceptible strain). In this study, we used a comparative approach to demonstrate that transcription of Cyp4p1 and Cyp4p2 were constitutively up-regulated in the Drosophila melanogaster strain 91-R as compared to another DDT susceptible strain Canton-S which does not have a loss of function of these genes. Furthermore, significantly increased expression of Cyp4p1 and Cyp4p2 was induced in 91-R in response to sublethal DDT exposure, however, such induction did not occur in the DDT treated Canton-S. Additionally, fixed nucleotide variation within putative transcription factor binding sites of Cyp4p1 and Cyp4p2 promoters were observed between 91-R and Canton-S, however, their impact on transcription remains to be determined. Two GAL4/UAS transgenic strains with integrated heat shock-inducible Cyp4p1- or Cyp4p2-RNAi constructs within wild-type genetic backgrounds were developed. Following heat shock induction of Cyp4p1 and Cyp4p2 knockdown, these transgenic lines showed increased DDT mortality as compared to their corresponding non-heat shock controls. These results provide a functional link of Cyp4p1 and Cyp4p2 in conferring tolerance to DDT exposure.

Pyrethroids and DDT tolerance of Anopheles gambiae s.l. from Sengerema District, an area of intensive pesticide usage in north‐western Tanzania

To assess the susceptibility status of malaria vectors to pyrethroids and dichlorodiphenyltrichloroethane (DDT), characterise the mechanisms underlying resistance and evaluate the role of agro-chemical use in resistance selection among malaria vectors in Sengerema agro-ecosystem zone, Tanzania. Mosquito larvae were collected from farms and reared to obtain adults. The susceptibility status of An. gambiae s.l. was assessed using WHO bioassay tests to permethrin, deltamethrin, lambdacyhalothrin, etofenprox, cyfluthrin and DDT. Resistant specimens were screened for knock-down resistance gene (kdr), followed by sequencing both Western and Eastern African variants. A gas chromatography-mass spectrophotometer (GC-MS) was used to determine pesticide residues in soil and sediments from mosquitoes' breeding habitats. Anopheles gambiae s.l. was resistant to all the insecticides tested. The population of Anopheles gambiae s.l was composed of Anopheles arabiensis by 91%. The East African kdr (L1014S) allele was found in 13 of 305 specimens that survived insecticide exposure, with an allele frequency from 0.9% to 50%. DDTs residues were found in soils at a concentration up to 9.90 ng/g (dry weight). The observed high resistance levels of An. gambiae s.l., the detection of kdr mutations and pesticide residues in mosquito breeding habitats demonstrate vector resistance mediated by pesticide usage. An integrated intervention through collaboration of agricultural, livestock and vector control units is vital.

Metabolic and Target-Site Mechanisms Combine to Confer Strong DDT Resistance in Anopheles gambiae

The development of resistance to insecticides has become a classic exemplar of evolution occurring within human time scales. In this study we demonstrate how resistance to DDT in the major African malaria vector Anopheles gambiae is a result of both target-site resistance mechanisms that have introgressed between incipient species (the M- and S-molecular forms) and allelic variants in a DDT-detoxifying enzyme. Sequencing of the detoxification enzyme, Gste2, from DDT resistant and susceptible strains of An. gambiae, revealed a non-synonymous polymorphism (I114T), proximal to the DDT binding domain, which segregated with strain phenotype. Recombinant protein expression and DDT metabolism analysis revealed that the proteins from the susceptible strain lost activity at higher DDT concentrations, characteristic of substrate inhibition. The effect of I114T on GSTE2 protein structure was explored through X-ray crystallography. The amino acid exchange in the DDT-resistant strain introduced a hydroxyl group nearby the hydrophobic DDT-binding region. The exchange does not result in structural alterations but is predicted to facilitate local dynamics and enzyme activity. Expression of both wild-type and 114T alleles the allele in Drosophila conferred an increase in DDT tolerance. The 114T mutation was significantly associated with DDT resistance in wild caught M-form populations and acts in concert with target-site mutations in the voltage gated sodium channel (Vgsc-1575Y and Vgsc-1014F) to confer extreme levels of DDT resistance in wild caught An. gambiae.

The effect of larval nutritional deprivation on the life history and DDT resistance phenotype in laboratory strains of the malaria vector Anopheles arabiensis

BackgroundAnopheles arabiensis is a major malaria vector in Africa. It thrives in agricultural areas and has been associated with increased malaria incidence in areas under rice and maize cultivation. This effect may be due to increased adult size and abundance as a consequence of optimal larval nutrition. The aim of this study was to examine the effect of larval nutrition on the life history and expression of insecticide resistance in adults of laboratory reared An. arabiensis.MethodsLarvae drawn from an insecticide susceptible An. arabiensis strain (SENN) as well as a DDT-resistant strain (SENN-DDT) were subjected to three fasting regimes: 1 mg of food per larva offered once per day, once every second day and once every third day. Control cohorts included larvae offered 1 mg food thrice per day. The rate of larval development was compared between matched cohorts from each strain as well as between fasted larvae and their respective controls. The expression of DDT resistance/tolerance in adults was compared between the starved cohorts and their controls by strain. Factors potentially affecting variation in DDT resistance/tolerance were examined including: adult body size (wing length), knock-down resistance (kdr) status and levels of detoxification enzyme activity.Results and conclusionAnopheles arabiensis larval development is prolonged by nutrient deprivation and adults that eclose from starved larvae are smaller and less tolerant to DDT intoxication. This effect on DDT tolerance in adults is also associated with reduced detoxification enzyme activity. Conversely, well fed larvae develop comparatively quickly into large, more DDT tolerant (SENN) or resistant (SENN-DDT) adults. This is important in those instances where cereal farming is associated with increased An. arabiensis transmitted malaria incidence, because large adult females with high teneral reserves and decreased susceptibility to insecticide intoxication may also prove to be more efficient malaria vectors. In general, larval nutrient deprivation in An. arabiensis has important implications for subsequent adults in terms of their size and relative insecticide susceptibility, which may in turn impact on their malaria vector capacity in areas where insecticide based control measures are in place.

The insecticide resistance status of malaria vectors in the Mekong region

BackgroundKnowledge on insecticide resistance in target species is a basic requirement to guide insecticide use in malaria control programmes. Malaria transmission in the Mekong region is mainly concentrated in forested areas along the country borders, so that decisions on insecticide use should ideally be made at regional level. Consequently, cross-country monitoring of insecticide resistance is indispensable to acquire comparable baseline data on insecticide resistance.MethodsA network for the monitoring of insecticide resistance, MALVECASIA, was set up in the Mekong region in order to assess the insecticide resistance status of the major malaria vectors in Cambodia, Laos, Thailand, and Vietnam. From 2003 till 2005, bioassays were performed on adult mosquitoes using the standard WHO susceptibility test with diagnostic concentrations of permethrin 0.75% and DDT 4%. Additional tests were done with pyrethroid insecticides applied by the different national malaria control programmes.ResultsAnopheles dirus s.s., the main vector in forested malaria foci, was susceptible to permethrin. However, in central Vietnam, it showed possible resistance to type II pyrethroids. In the Mekong delta, Anopheles epiroticus was highly resistant to all pyrethroid insecticides tested. It was susceptible to DDT, except near Ho Chi Minh City where it showed possible DDT resistance. In Vietnam, pyrethroid susceptible and tolerant Anopheles minimus s.l. populations were found, whereas An. minimus s.l. from Cambodia, Laos and Thailand were susceptible. Only two An. minimus s.l. populations showed DDT tolerance. Anopheles vagus was found resistant to DDT and to several pyrethroids in Vietnam and Cambodia.ConclusionThis is the first large scale, cross-country survey of insecticide resistance in Anopheles species in the Mekong Region. A unique baseline data on insecticide resistance for the Mekong region is now available, which enables the follow-up of trends in susceptibility status in the region and which will serve as the basis for further resistance management. Large differences in insecticide resistance status were observed among species and countries. In Vietnam, insecticide resistance was mainly observed in low or transmission-free areas, hence an immediate change of malaria vector control strategy is not required. Though, resistance management is important because the risk of migration of mosquitoes carrying resistance genes from non-endemic to endemic areas. Moreover, trends in resistance status should be carefully monitored and the impact of existing vector control tools on resistant populations should be assessed.

The production of a DDT-resistant strain of Aedes aegypti marked on all three linkage groups.

DDT-resistant strains marked on all three linkage groups have been produced by selection at the adult stage after outcrossing a resistant strain (BANGKOK-HR) to a marked susceptible strain (64). The most resistant and viable line (BANGKOK-MR) was kept for linkage studies. The production of a marked resistant strain was not entirely straightforward. In the absence of a suitable genetic background, major resistance genes conferred little or no DDT tolerance and could not be selected. Selection at the adult stage produced resistance in larvae as well as in adults. Resistance was achieved more rapidly in larvae than in adults

Host-preference observations on Anopheles culicifacies (Diptera: Culicidae) in Gujarat State, India.

Analyses of the host blood of A. culicifacies Giles by the precipitin test were conducted in Panchmahals district of Gujarat State, where resistance of the adults to DDT was encountered in 1959–60. From mixed animal and human habitations 1045 females were collected, 192 females were collected from animal sheds, and 144 females were collected from artificially dug outdoor pit shelters. In all resting places, feedings on animal hosts were most common, with bovine being the preferred host. Of the positive tests, the blood smears were: human 1.92%; bovine 88.96%; sheep or goat 0.56%; dog and horse 0.34% each; and mixed animals 7.88%. All feedings onhumans took place in the mixed animal and human habitations and were recorded during March, April, and July 1959, prior to the detection of increased tolerance toDDT in the mosquito, showing some evidence that tolerance or resistance may be correlated with a change inthe blood-feeding pattern. No feedings on humans were recorded after tolerance or resistance to DDT developed in the mosquito.

APPARENT DDT TOLERANCE IN AN AQUATIC INSECT DISPROVED BY TEST

AbstractCertain mayflies and stoneflies were present in a forest stream in New Brunswick after frequent yearly sprayings with DDT. Tests showed that a stonefly, Nemoura sp., apparently the most likely insect to have developed DDT tolerance, had not done so. Presence of mayflies and stoneflies in the stream was probably because they survived spraying while in the egg stage, or recovered quickly after spraying, or both.

The basis of DDT tolerance in the laboratory mouse.

DDT tolerance in the Macdonald strain of the laboratory mouse is shown to be related to lipid content. Relatively large amounts of sesame oil injected into DDT-treated mice, either with the DDT or up until the symptoms of poisoning appeared, protected the recipients from severe symptoms and death. DDT-tolerant mice excreted 14C-labelled DDT or its metabolites in the urine, at a significantly lower rate than the normal mice. DDT-susceptible mice excreted 8 to 10% of the injected dose of DDT within 12 days. DDT tolerance could not be related to the production of DDE or TDE.

The Influence of Certain Biological and Environmental Factors on Insecticide Tolerance of the Lygus Bug, Lygus hesperus1

Many factors appear to influence DDT tolerance of the lygus bug, Lygus hesperus Knight. Lygus bugs collected from alfalfa seed fields during the period of bloom and seed set are more tolerant of DDT than those collected from alfalfa hay fields. Lygus bugs reared in the laboratory on green string beans are more tolerant of DDT than those from either alfalfa hay or seed fields Adult females are more tolerant than males. Tolerance to DDT increases progressively with each nymphal instar from third instar to adult. DDT is shown to have a negative temperature coefficient of action, while toxaphene has a positive temperature coefficient of action. Increase in DDT tolerance closely parallel increases in total body lipids. Differences in tolerances of two sexes could not be explained on the basis of differences in total body lipids. Analyses of body lipids of L. hesperus have shown that at least 7 fatty acids are present. They are myristic, palmitic, palmitoleic, stearic, oleic, linoleic, and linolenic. No significant qualitative or quantitative differences in fat composition of the two sexes were apparent. Slight difference in amounts of the fatty acids were found in insects taken from different hosts at various times of the year, but it is believed that these differences would not account for the observed differences in susceptibility to DDT.

Stable Fly Tolerance to Residues of DDT, Dieldrin, Malathion and Diazinon1

In tests conducted to determine the insecticide tolerance of a strain of stable flies (Stomoxys calcitrans (L.)) from the U. S. Army Chemical Center, Maryland, females evinced an LC-50 of 1.3 mg. per square foot in the case of DDT, 0.8 mg. per square foot for malathion and 0.23 mg. per square foot for Diazinon® (O,O-diethyl O-(2-isopropyl-4-methyl-6 pyrimidinyl) phosphorothioate) 24 hours after a 15-minute exposure in treated pint Mason jars. A significantly lower tolerance to DDT was demonstrated by females held for 24 hours at 70°F. than was demonstrated by females held at 90. after a 15-minute exposure. This difference was not significant when similar tests were conducted with malathion. The World Health Organization test procedure for determining the susceptibility or resistance of adult mosquitoes to insecticides was highly satisfactory for testing adult stable flies. Groups of both sexes were tested with this procedure. The slightly higher DDT tolerance evinced by the males was not significant Females demonstrated a significantly higher tolerance to dieldrin than the males.

Holly Bud Moth Control1

The holly bud moth, Rhopobota naevana (Hbn.) Kearfott, was introduced into British Columbia before 1923 and has subsequently spread southward through Washington into Oregon. It is now an important pest in Oregon holly plantings. Evaluation of insecticides for holly bud moth control showed that a high degree of control can be obtained with organic phosphate insecticides. Malathion consistently provided excellent control with one spray applied sometime between the opening of the leaf buds and the time of blossoming. Good control was also obtained with methoxychlor. DDT did not give consistent results under the same conditions. The difference between the results with the organic phosphates and with DDT might be explained on the basis of DDT tolerance in the holly bud moth. Another possible explanation is that the organic phosphate insecticides have an ovicidal effect which DDT does not have. The results with methoxychlor make the first explanation more probable.

DDT Tolerance by Lygus Bugs on Seed Alfalfa1

DDT Tolerance by Lygus Bugs on Seed Alfalfa1