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PubMed1993

Insecticide synergists: role, importance, and perspectives.

Synergists have been used commercially for about 50 years and have contributed significantly to improve the efficacy of insecticides, particularly when problems of resistance have arisen. In the current article we review the nature, mode of action, role in resistance management, natural occurrence, and significance in research of insecticide synergists. These natural or synthetic chemicals, which increase the lethality and effectiveness of currently available insecticides, are by themselves considered nontoxic. The mode of action of the majority of synergists is to block the metabolic systems that would otherwise break down insecticide molecules. They interfere with the detoxication of insecticides through their action on polysubstrate monooxygenases (PSMOs) and other enzyme systems. The role of synergists in resistance management is related directly to an enzyme-inhibiting action, restoring the susceptibility of insects to the chemical, which would otherwise require higher levels of the toxicant for their control. For this reason synergists are considered straightforward tools for overcoming metabolic resistance, and can also delay the manifestation of resistance. However, the full potential of these compounds may not have been realized in resistance management. Synergists have an important role to play in the ongoing investigation of insecticide toxicity and mode of action and the nature of resistance mechanism. They also can be used in understanding the effects of other xenobiotics in non-target organisms. The search for and the need of new molecules capable of synergizing existing or new pesticides has reactivated the identification and characterization of secondary plant compounds possessing such activity. Plants do possess and utilize synergists to overcome the damage produced by phytophages. This has to be exploited in pest management programs. Hopefully, it will lead to a new perspective on the nature and significance of synergism.

Animals↗
PubMed1993

Continuous, alternating, and mixed insecticides affect development of resistance in the horn fly (Diptera: Muscidae).

Susceptible populations of horn flies, Haematobia irritans (L.), were selected with six insecticide treatment regimens: continuous use of permethrin, diazinon, or ivermectin; permethrin/diazinon (1:2) mixture; permethrin-diazinon rotation; and permethrin-ivermectin rotation. Insecticide selection was applied as low-volume sprays on steers infested with horn flies housed in environmentally controlled rooms. During the study period, horn fly populations developed an apparent resistance to all insecticide treatment regimens. Selection with permethrin, diazinon, and ivermectin resulted in development of resistance in generations 21, 31, and 30, respectively. Selection with insecticide mixtures and rotations resulted in the delay of any apparent resistance development for an additional one to seven generations. The magnitude of this resistance ranged from 1,470-fold for the single continuous use of permethrin to < 3-fold for ivermectin in the permethrin-ivermectin rotation. Compared with single continuous insecticide selections, the onset and degree of resistance development was significantly reduced by alternating and mixing insecticides.

Animals↗
PubMed2003

Organophosphorus insecticides synergize pyrethroids in the resistant strain of cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) from West Africa.

Helicoverpa armigera (Hübner) populations from West Africa recently developed resistance to pyrethroid insecticides through enhanced metabolism by mixed-function oxidases. The combination index method was used to study the synergism of pyrethroids by organophosphorus insecticides. Several mixtures of insecticides currently registered to control cotton pest complex in West Africa were tested, including: cypermethrin/ethion, cypermethrin/profenofos, deltamethrin/ triazophos, deltamethrin/chlorpyriphos, cyfluthrin/chlorpyriphos, and betacyfluthrin/chlorpyriphos. In the resistant strain, the organophosphorus insecticides significantly increased the toxicity of pyrethroids suppressing the resistance effect, either by additive or synergistic effects. Significant synergism was shown for the following mixtures: cypermethrin/ethion, deltamethrin/triazophos, and deltamethrin/chlorpyriphos. The use of synergism from these insecticide mixtures should prove to be an additional tool in the overall resistance management strategy because the pyrethroid resistance in H. armigera from West Africa is not yet stable, decreasing between cotton seasons and increasing with treatments. In absence of selection, the susceptibility of H. armigera to insecticides should be restored.

Africa, Western↗
PubMed2000

Assessment of insecticide resistance after the outbreak of diamondback moth (Lepidoptera: Plutellidae) in California in 1997.

During an outbreak of the diamondback moth, Plutella xylostella (L.), in California in 1997, nine populations were collected from the major broccoli areas throughout the state. Populations were assayed for their susceptibility to currently used materials (Bacillus thuringiensis subsp. kurstaki, permethrin, and methomyl) and to newer materials that had not yet been commercially used in California (spinosad, emamectin benzoate, and chlorfenapyr). For the currently used insecticides, elevated levels of resistance were seen only with permethrin and seven of the nine populations had tolerance ratios (TR) of > 100. With the newer chemistries, TR values were all < 15. To compare potential cross-tolerance, TR values of the currently used insecticides were compared with TR values of the newer insecticides. There were significant relationships found between: methomyl and emamectin benzoate, methomyl and spinosad, and permethrin and spinosad. Further biochemical studies are needed to confirm the actual mechanisms that lead to these relationships and field tests are needed to determine what impact, if any, such TR levels would have on control in the field. These data indicate that resistance to at least one of the commonly used insecticides (permethrin) may have played a role in the outbreak during 1997. However, other factors may have been at least equally important. The winter of 1996-1997 was warmer than normal, and during the period from February through August of 1997 the amount of rainfall was < 50% of normal. Hot and dry conditions are known to be conducive to outbreaks of P. xylostella. These data add to an overall knowledge about the geographic variation of resistance in P. xylostella populations within the United States. They also serve as a baseline for monitoring changes in susceptibility to these newer insecticides and can also help explain the occurrence of outbreaks caused by factors other than insecticide resistance.

Animals↗
PubMed2000

Insecticide resistance and cross-resistance in the house fly (Diptera: Muscidae).

A house fly strain, ALHF, was collected from a poultry farm in Alabama after a control failure with permethrin, and further selected in the laboratory with permethrin for five generations. The level of resistance to permethrin in ALHF was increased rapidly from an initial 260-fold to 1,800-fold after selection. Incomplete suppression of permethrin resistance by piperonyl butoxide (PBO) and S,S,S,-tributylphosphorotrithioate (DEF) reveals that P450 monooxygenase- and hydrolase-mediated detoxication, and one or more additional mechanisms are involved in resistance to permethrin. The ALHF strain showed a great ability to develop resistance or cross-resistance to different insecticides within and outside the pyrethroid group including some relatively new insecticides. Resistance to beta-cypermethrin, cypermethrin, deltamethrin, and propoxur (2,400-4,200-, 10,000-, and > 290-fold, respectively, compared with a susceptible strain, aabys) in ALHF house flies was partially or mostly suppressed by PBO and DEF, indicating that P450 monooxygenases and hydrolases are involved in resistance to these insecticides. Partial reduction in resistance with PBO and DEF implies that multiresistance mechanisms are responsible for resistance. Fifteen- and more than fourfold resistance and cross-resistance to chlorpyrifos and imidacloprid, respectively, were not effected by PBO or DEF, indicating that P450 monooxygenases and hydrolases are not involved in resistance to these two insecticides. Forty-nine-fold cross-resistance to fipronil was mostly suppressed by PBO and DEF, revealing that monooxygenases are a major mechanism of cross-resistance to fipronil. Multiresistance mechanisms in the ALHF house fly strain, however, do not confer cross-resistance to spinosad, a novel insecticide derived from the bacterium Saccharopolyspora spinosa. Thus, we propose that spinosad be used as a potential insecticide against house fly pests, especially resistant flies.

Animals↗
PubMed2002

Susceptibility and detoxifying enzyme activity in two spider mite species (Acari: Tetranychidae) after selection with three insecticides.

Changes in the susceptibility and detoxifying enzyme activity were measured in laboratory strains of Banks grass mite, Oligonychus pratensis (Banks), and twospotted spider mite, Tetranychus urticae Koch, that were repeatedly exposed to three insecticides. Three strains of each mite species were exposed to one of two pyrethroids, bifenthrin, and lambda-cyhalothrin, or an organophosphate, dimethoate, for 10 selection cycles at the LC60 for each insecticide. A reference or nonselected strain of each mite species was not exposed to insecticides. After 10 cycles of exposure, susceptibility to the corresponding insecticides, bifenthrin, lambda-cyhalothrin, and dimethoate, decreased 4.5-, 5.9-, and 289.2-fold, respectively, relative to the reference strain in the respective O. pratensis strains, and 14.8-, 5.7-, and 104.7-fold, respectively, relative to the reference strain in the respective T. urticae strains. In the bifenthrin-exposed O. pratensis strain, there was a 88.9-fold cross-resistance to dimethoate. In the dimethoate-exposed T. urticae strain, there was a 15.9-fold cross-resistance to bifenthrin. These results suggest that there may be cross-resistance between dimethoate and bifenthrin. The reduced susceptibility to dimethoate remained stable for three months in the absence of selection pressure in both mites. The decrease in susceptibility in the O. pratensis strains exposed to bifenthrin, lambda-cyhalothrin, and dimethoate was associated with a 4.7-, 3.0-, and 3.6-fold increase in general esterase activity, respectively. The decrease in susceptibility in the T. urticae strains exposed to bifenthrin and lambda-cyhalothrin was associated with a 1.3- and 1.1-fold increase in general esterase activity, respectively. The mean general esterase activity was significantly higher in the pyrethroid-exposed O. pratensis and T. urticae strains than in the nonselected strain. There was no significant increase in esterase activity in the dimethoate-exposed T. urticae strain. The decrease in susceptibility to insecticides was also associated with reduced glutathione S-transferase 1-chloro-2, 4-dinitrobenzene conjugation activity, but this did not appear to be related to changes in insecticide susceptibility. These results suggest that in these mites, the general esterases may play a role in conferring resistance to pyrethroids. However, some other untested mechanism, such as target site insensitivity, must be involved in conferring dimethoate resistance.

Animals↗
PubMed2004

Resistance and synergistic effects of insecticides in Bactrocera dorsalis (Diptera: Tephritidae) in Taiwan.

Oriental fruit flies, Bactrocera dorsalis (Hendel), were treated with 10 insecticides, including six organophosphates (naled, trichlorfon, fenitrothion, fenthion, formothion, and malathion), one carbamate (methomyl), and three pyrethroids (cyfluthrin, cypermethrin, and fenvalerate), by a topical application assay under laboratory conditions. Subparental lines of each generation treated with the same insecticide were selected for 30 generations and were designated as x-r lines (x, insecticide; r, resistant). The parent colony was maintained as the susceptible colony. The line treated with naled exhibited the lowest increase in resistance (4.7-fold), whereas the line treated with formothion exhibited the highest increase in resistance (up to 594-fold) compared with the susceptible colony. Synergism bioassays also were carried out. Based on this, S,S,S-tributyl phosphorotrithioate displayed a synergistic effect for naled, trichlorfon, and malathion resistance, whereas piperonyl butoxide displayed a synergistic effect for pyrethroid resistance. All 10 resistant lines also exhibited some cross-resistance to other insecticides, not only to the same chemical class of insecticides but also to other classes. However, none of the organophosphate-resistant or the methomyl-resistant lines exhibited cross-resistance to two of the pyrethroids (cypermethrin and fenvalerate). Overall, the laboratory resistance and cross-resistance data developed here should provide useful tools and information for designing an insecticide management strategy for controlling this fruit fly in the field.

Animals↗
PubMed2006

Comparative susceptibility of sweetpotato weevil (Coleoptera: Brentidae) to selected insecticides.

The response of sweetpotato weevil, Cylas formicarius (F.) (Coleoptera: Brentidae), to insecticides used for its control was tested in laboratory bioassays. A glass vial bioassay technique was used to determine the susceptibility of two cohorts of sweetpotato weevil to selected insecticides. Vials were treated with methyl parathion, bifenthrin, cyfluthrin, carbaryl, and phosmet. Sweetpotato weevils demonstrated a mortality response to increasing concentrations of all insecticides tested, and our results indicated decreases in susceptibility of the Louisiana cohort of sweetpotato weevil compared with the Texas cohort for all insecticides tested. Methyl parathion was the most toxic chemical tested for both cohorts, followed by the pyrethroids, cyfluthrin and bifenthrin. Phosmet exhibited moderate toxicity compared with other chemicals tested, whereas sweetpotato weevils were least susceptible to carbaryl. Significant differences in lethal concentration (LC)50 and LC90 values for cyfluthrin and bifenthrin, the LC50 values for methyl parathion and phosmet, and the LC90 values for carbaryl were observed between the two cohorts. This study documents baseline toxicological data for five insecticides in two populations of sweetpotato weevil and demonstrates that susceptibility to all insecticides tested is lower for the Louisiana population compared with the Texas population.

Animals↗
PubMed2006

Insecticide resistance in Anopheles arabiensis and Anopheles gambiae from Mozambique.

Malaria control in the southern part of Mozambique is currently by indoor residual spraying with a carbamate insecticide and by pyrethroid-treated bed-nets distributed to pregnant women and children under five in northern Mozambique. The susceptibility of Anopheles gambiae s.s. and Anopheles arabiensis Patton to pyrethroid, carbamate, organochlorine, and organophosphorus insecticides was determined by World Health Organization adult mosquito susceptibility tests at 17 localities in Mozambique, from March 2000 to July 2002. Biochemical assays were carried out on mosquitoes from the same families to detect shifts in the quantity or activity of enzyme families involved in insecticide detoxification. An. gambiae s.s. from all localities remained fully susceptible to DDT and the organophosphorus insecticide malathion. A low level of pyrethroid resistance was detected in populations in southern Mozambique. Populations outside Maputo province were still susceptible to pyrethroids. Low level resistance to the carbamate propoxur also was detected in An. arabiensis from two localities. Mosquitoes from five of the localities had elevated p450 estimates, compared with the insecticide susceptible Durban strain. The lack of cross-resistance between pyrethroids and DDT in Mozambican populations suggests that a kdr-type target site resistance mechanism has not been selected. Increased frequencies of insecticide insensitive acetylcholinesterase, the target site for carbamates and organophosphates, were found in 16 of the populations tested. Although vector control with bendiocarb is not being compromised by the presence of the acetylcholinesterase mechanism alone, the high level of insensitive acetylcholinesterase unless sensibly managed may have long-term implications for malaria control programs in Mozambique.

Acetylcholinesterase↗
PubMed2006

Developing an evidence-based decision support system for rational insecticide choice in the control of African malaria vectors.

The emergence of Anopheles species resistant to insecticides widely used in vector control has the potential to impact directly on the control of malaria. This may have a particularly dramatic effect in Africa, where pyrethroids impregnated onto bed-nets are the dominant insecticides used for vector control. Because the same insecticides are used for crop pests, the extensive use and misuse of insecticides for agriculture has contributed to the resistance problem in some vectors. The potential for resistance to develop in African vectors has been apparent since the 1950s, but the scale of the problem has been poorly documented. A geographical information system-based decision support system for malaria control has recently been established in Africa and used operationally in Mozambique. The system incorporates climate data and disease transmission rates, but to date it has not incorporated spatial or temporal data on vector abundance or insecticide resistance. As a first step in incorporating this information, available published data on insecticide resistance in Africa has now been collated and incorporated into this decision support system. Data also are incorporated onto the openly available Mapping Malaria Risk in Africa (MARA) Web site (http://www.mara.org.za). New data, from a range of vector population-monitoring initiatives, can now be incorporated into this open access database to allow a spatial understanding of resistance distribution and its potential impact on disease transmission to benefit vector control programs.

Africa↗
PubMed2006

Use of bioassay and microplate assay to detect and measure insecticide resistance in field populations of Culex pipiens from filariasis endemic areas of Egypt.

Insecticide and resistance bioassays and microplate assays were performed on Culex pipiens mosquitoes to determine the level and mechanisms of resistance. Culex pipiens larvae were collected from three filariasis-endemic areas of Egypt and reared to adults for subsequent production and testing of F1 generation larvae and adults. Bioassays were performed using World Health Organization (WHO) methods with the diagnostic doses of 6 organophosphate insecticides for larvae and 1 organochlorine (OC), 4 pyrethroid, 2 organophosphate, and 2 carbamate insecticides for adults. Microplate assays were performed to measure levels of beta esterase, acetylcholinesterase, insensitive acetylcholinesterase, oxidases, and glutathione-S-transferase enzymes. Larval bioassay results showed clear indications of resistance to organophosphate insecticides. Adult bioassays also showed widespread, significant resistance to many insecticides from all four classes, including the OC, DDT. The Qalubiya larval population was susceptible only to malathion, whereas Sharkiya larvae were susceptible to malathion, temephos, and chlorpyrifos. On the other hand, larval specimens from Assiut were resistant to all insecticides tested. Larval bioassay results were supported by those of microplate assays in showing elevated levels of glutathione S-transferase in populations from all three areas. In general, microplate results confirmed patterns of resistance observed using bioassays, and mechanisms of resistance were evident for all three areas sampled. Mechanisms of resistance are discussed in relation to microplate and bioassay results for the areas sampled and pesticides used.

Animals↗
PubMed1999

Susceptibility and resistance to insecticides of Chagas disease vectors.

Chemical control of Chagas disease vectors appears to be the best practical way to reduce the incidence of the disease. DDT was initially tested in the 1950s for the campaigns of control of Chagas disease vectors. Its low level of effectiveness against triatomine caused the failure of these control actions. HCH was then introduced in the southern cone and Dieldrin in the north of Latinoamerica. Starting in the late 1960s anticholinesterasic organophosphorus and carbamate compounds were introduced in the control of Chagas vectors. The use of pyrethroid compounds began in 1980. This family of insecticides is now the most important tool in triatomines control because of its favorable toxicological properties. Other types of insecticides also studied for Chagas vector control were the insect growth regulators and the antifeeding compounds. Because of the mode of action of these insecticides they are now considered just a potential complement of neurotoxic insecticides for integrated programmes of Triatomines control. Innovative formulations such as fumigant canister and insecticidal paints have been successfully developed in Latinoamerica with the World Health Organization support. Resistance to insecticides of triatomines is not yet a great problem in Chagas vectors. However, some resistant strains to pyrethroids have been found in Rhodnius prolixus from Venezuela and in Triatoma infestans from Brazil. Some cases of T. infestans incipient resistance to deltamethrin have been detected in Argentina. According to the control tools now available it is possible to expect the interruption of vector transmission of Chagas disease in the near future.

Animals↗
PubMed1975

Insecticide susceptibility of some vector fleas and mosquitoes in Burma.

Rat fleas and mosquitoes are insect vectors of public health importance in Burma. Plague is endemic in Central Burma and DDT has been the principal insecticide used for its control to date. Dengue haemorrhagic fever, recently introduced and transmitted by Aedes aegypti, has been spreading to major towns since 1971. The rodents, Rattus rattus, R. exulans, Bandicota bengalensis, Mus musculus, as well as shrews were commonly caught during routine trapping in the country. Rattus norvegicus, prevalent in Rangoon City, is not found in Central Burma. The rat fleas, Xenopsylla cheopis and X. astia, were found to be infesting these rodents, the former being the principal vector of plague. Insecticide susceptibility tests have been carried out periodically in plague endemic areas and Rangoon since 1966 and it is now observed that rat fleas in most of these endemic towns and Rangoon Port are no longer susceptible to DDT. Subsequent rechecks in towns where fleas became resistance to DDT show that fleas are persistently resistant to the insecticide. Aedes aegypti is found to be highly prevalent both in rural and urban areas of almost every major town and townships below 900 meters. Insecticide susceptible tests on this mosquito in limited areas show that the mosquito is generally resistant to DDT but susceptible to other insecticides. With the development of DDT resistance in fleas, it is now necessary to change to an effective insecticide in the control of plague in Burma.

Aedes↗
PubMed1965

A STUDY OF THE CHRONIC EFFECTS OF INSECTICIDES IN MAN.

Signs of possible chronic intoxication due to insecticides were sought among 441 apple-growers. A group of 170 persons living in the same environment and 162 other persons having no contact with insecticides were used as controls. It was the first attempt to determine signs of chronic intoxication by organic phosphate and chlorinated hydrocarbon insecticides. The greater incidence of leukopenia and of neurologic manifestations found among the subjects suggest that insecticides may have some chronic effects in man. This assumption is reinforced by the similarities in the findings between the subjects and the environments, and by the parallelism between the duration of exposure to insecticides and the number of affected subjects. The repetition of this study at five-year intervals seems desirable until a sufficient number of apple-growers have been studied who have been exposed to large doses of insecticides for 10, 15 or 20 years.

DDT↗
PubMed2006

High Wolbachia density correlates with cost of infection for insecticide resistant Culex pipiens mosquitoes.

In the mosquito Culex pipiens, insecticide resistance genes alter many life-history traits and incur a fitness cost. Resistance to organophosphate insecticides involves two loci, with each locus coding for a different mechanism of resistance (degradation vs. insensitivity to insecticides). The density of intracellular Wolbachia bacteria has been found to be higher in resistant mosquitoes, regardless of the mechanism involved. To discriminate between costs of resistance due to resistance genes from those associated with elevated Wolbachia densities, we compared strains of mosquito sharing the same genetic background but differing in their resistance alleles and Wolbachia infection status. Life-history traits measured included strength of insecticide resistance, larval mortality, adult female size, fecundity, predation avoidance, mating competition, and strength of cytoplasmic incompatibility (CI). We found that: (1) when Wolbachia are removed, insecticide resistance genes still affect some life-history traits; (2) Wolbachia are capable of modifying the cost of resistance; (3) the cost of Wolbachia infections increases with their density; (4) different interactions occurred depending on the resistance alleles involved; and (5) high densities of Wolbachia do not increase the strength of CI or maternal transmission efficiency relative to low Wolbachia densities. Insecticide resistance genes generated variation in the costs of Wolbachia infections and provided an interesting opportunity to study how these costs evolve, a process generally operating when Wolbachia colonizes a new host.

Animals↗
PubMed1982

The scope and limitations of insecticide spraying in rural vector control programmes in the states of Karnataka and Tamil Nadu in India.

The resurgence of malaria in India began in 1966 and the states of Karnataka and Tamil Nadu were no exception to this phenomenon. In both states the peak occurrence came in 1976. Malaria was largely confined to highly vulnerable and receptive areas. The problem of increased incidence was particularly associated with the development of several irrigation and hydro-electric schemes. Improperly maintained irrigation systems and reservoirs provided ideal breeding grounds. The present paper examines the scope and limitations of a major anti-malaria activity, namely residual insecticide spraying as adopted and practised in rural vector control programmes in irrigation development project areas. Past experiences (as during the National Malaria Eradication programme, 1958-1965) and current practices are reviewed on the basis of selected examples. Eradication programme, 1958-1965) and current practices are reviewed on the basis of selected examples. In view of the current re-emergence of the disease, the states are faced with new obstacles to residual insecticide spraying such as (a) the development of resistance of malaria vectors to DDT and other alternative compounds like BHC (benzene hexachloride), changing vector behaviour with avoidance of contact with indoor insecticide deposits on walls, (c) environmental contamination (risks of chemicals), (d) extensive use of insecticides and pesticides for crop protection under an expanding green revolution agricultural technology, particularly in irrigated areas and (e) the existence of outdoor resting populations of the major vector Anopheles culicifacies and their role in extra-domiciliary transmission, making residual insecticide spray less effective. Spraying operations are also hindered by the persistence of certain social and cultural factors. The custom of mud plastering, white-washing and rethatching rural houses, for example, results in the loss of insecticide-treated surfaces. Other outdoor rural activities persist as obstacles in attempts to break the transmission cycle; washing, bathing and sleeping outdoors; illegal fishing and woodcutting at night; poorly constructed make-shift structures;housing project labourers near water sources; cattle grazing in nearby forests and human population movements related to seasonal migrants. The chain and extent of the transmission is dependent upon the malaria parasite carriers in the community (both indigenous and imported types) and the degree of contact of the community with those sites where people carry on the above activities, and on the effectiveness of surveillance operations.

Anopheles↗
PubMedDate not supplied

Insecticide-induced changes in secretory activity of the thyroid gland in rats.

The present study was conducted to examine the effect of organochlorine (Heptachlor, Benzene hexachloride (BHC)), organophosphorus (Malathion, Monitor) and pyrethroid (Karate, Talstar) insecticides on the thyroid secretory function in rats. Heptachlor (0.5 mg per rat), BHC (0.66 mg per rat) Malathion (0.06 mg per rat), Monitor (0.2 mg per rat), Karate (0.2 mg per rat), Talstar (0.5 mg per rat) were orally administered to young adult rats for 21 days. Serum concentrations of triiodothyronine (T3), thyroxine (T4) and thyrotrophin (TSH) were determined by using specific radioimmunoassays. Body weight was not affected by treatment with any insecticide except Talstar (P < 0.01). Among organochlorine and organophosphorus insecticides, treatment with BHC and Malathion, respectively, led to a significant decrease (P < 0.01) in serum concentration of T3 and T4. Administration of BHC and Malathion also increased (P < 0.01) TSH secretion. Treatment with both of the pyrethroid insecticides similarly induced significant suppression (P < 0.01) of serum T3 and T4 levels, and concomitant stimulation (P < 0.01) of TSH concentrations. The T4/T3 ratio was decreased (P < 0.05) in rats treated with Karate but not with any other insecticide. These data indicate that immense care is warranted in the use of insecticides, because they not only affect the liver, kidney and other organs but also may alter the activity of the endocrine glands.

Animals↗
PubMed2002

Activation of a stress-induced gene by insecticides in the midge, Chironomus yoshimatsui.

Stress proteins (heat shock proteins, HSPs) have been proposed as general biomarkers for environmental monitoring. In the present study, we evaluated the environmental stress-burden on the aquatic midge Chironomus yoshimatsui using hsp70 expression. Larvae collected from streams receiving polluted runoff (field strain) were resistant to the organophosphorus insecticide, fenitrothion (F), and the synthetic pyrethroid, ethofenprox (E), whereas a strain originally collected from an unpolluted area (susceptible strain) showed low resistance to insecticide exposure. To examine the expression of an HSP70 gene in C. yoshimatsui, an hsp70 cDNA probe was prepared using RNA obtained from the field strain larvae and used for Northern blot analyses. The expression of this HSP70 gene in larvae collected from two field sites in May about 1 week after insecticide spraying in the fields was 2.3 (p = 0.018) to 3.3 fold higher than that in the susceptible strain and was also 4.6 and 1.4 (p = 0.033) fold higher than those collected in November 3 months after the cessation of insecticide spraying. In order to identify potential inducers of the HSP70 gene of the field strain, larvae of the susceptible strain were exposed to F or E for 24 h and hsp70 mRNA levels determined. Exposures to F at 0.4 microg/L and E at 1.1 microg/L increased hsp70 mRNA levels 2.7 (p = 0.049) and 4.4 (p = 0.043) fold over controls, respectively. These results suggest that larvae collected from polluted areas are burdened by environmental stressors and the tested insecticides are potential inducers of HSP70. The results also support the suggestion that HSP70 gene expression is a sensitive indicator of low level (nonlethal) exposures to certain insecticides.

Amino Acid Sequence↗