Insecticide resistance compromises the control of Aedes aegypti in Bangladesh

BACKGROUND

With no effective drugs or widely available vaccines, dengue control in Bangladesh is dependent on targeting the primary vector Aedes aegypti with insecticides and larval source management. Despite these interventions, the dengue burden is increasing in Bangladesh, and the country experienced its worst outbreak in 2019 with 101 354 hospitalized cases. This may be partially facilitated by the presence of intense insecticide resistance in vector populations. Here, we describe the intensity and mechanisms of resistance to insecticides commonly deployed against Ae. aegypti in Dhaka, Bangladesh.

RESULTS

Dhaka Ae. aegypti colonies exhibited high-intensity resistance to pyrethroids. Using CDC bottle assays, we recorded 2–24% mortality (recorded at 24 h) to permethrin and 48–94% mortality to deltamethrin, at 10× the diagnostic dose. Bioassays conducted using insecticide–synergist combinations suggested that metabolic mechanisms were contributing to pyrethroid resistance, specifically multi-function oxidases, esterases, and glutathione S-transferases. In addition, kdr alleles were detected, with a high frequency (78–98%) of homozygotes for the V1016G mutation. A large proportion (≤ 74%) of free-flying and resting mosquitoes from Dhaka colonies survived exposure to standard applications of pyrethroid aerosols in an experimental free-flight room. Although that exposure affected the immediate host-seeking behavior of Ae. aegypti, the effect was transient in surviving mosquitoes.

CONCLUSION

The intense resistance characterized in this study is likely compromising the operational effectiveness of pyrethroids against Ae. aegypti in Dhaka. Switching to alternative chemical classes may offer a medium-term solution, but ultimately a more sustainable and effective approach to controlling dengue vectors is required. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Insecticide resistance status of Aedes aegypti (L.) from Colombia

BACKGROUND: To evaluate the insecticide susceptibility status of Aedes aegypti (L.) in Colombia, and as part of the National Network of Insecticide Resistance Surveillance, 12 mosquito populations were assessed for resistance to pyrethroids, organophosphates and DDT. Bioassays were performed using WHO and CDC methodologies. The underlying resistance mechanisms were investigated through biochemical assays and RT‐PCR. RESULTS: All mosquito populations were susceptible to malathion, deltamethrin and cyfluthrin, and highly resistant to DDT and etofenprox. Resistance to lambda‐cyhalothrin, permethrin and fenitrothion ranged from moderate to high in some populations from Chocó and Putumayo states. In Antioquia state, the Santa Fe population was resistant to fenitrothion. Biochemical assays showed high levels of both cytochrome P450 monooxygenases (CYP) and non‐specific esterases (NSE) in some of the fenitrothion‐ and pyrethroid‐resistant populations. All populations showed high levels of glutathione‐S‐transferase (GST) activity. GSTe2 gene was found overexpressed in DDT‐resistant populations compared with Rockefeller susceptible strain. CONCLUSIONS: Differences in insecticide resistance status were observed between insecticides and localities. Although the biochemical assay results suggest that CYP and NSE could play an important role in the pyrethroid and fenitrothion resistance detected, other mechanisms remain to be investigated, including knockdown resistance. Resistance to DDT was high in all populations, and GST activity is probably the main enzymatic mechanism associated with this resistance. The results of this study provide baseline data on insecticide resistance in Colombian A. aegypti populations, and will allow comparison of changes in susceptibility status in this vector over time. Copyright © 2011 Society of Chemical Industry     

Mutated sodium channel genes and elevated monooxygenases are found in pyrethroid resistant populations of Sri Lankan malaria vectors

The present status of pyrethroid resistance in vectors of malaria; Anopheles culicifacies and Anopheles subpictus, was tested in two malarious Districts, Anuradhapura and Trincomalee, of Sri Lanka. Both species were resistant to permethrin and susceptible to cypermethrin and cyfluthrin. An. subpictus were resistant to deltamethrin. λ-Cyhalothrin and etofenprox resistance was shown only by Anuradhapura An. subpictus. Although there were no differences among the populations for esterase and glutathione S-transferase activities, increased monooxygenase levels were found among Trincomalee populations. The voltage-gated sodium channel gene, the target site gene of pyrethroids, was partially sequenced to screen for mutations previously associated with insecticide resistance. The classic leucine to phenylalanine substitution, TTA to TTT, was detected in An. subpictus. It appears that both kdr type and monooxygenase resistance underlie pyrethroid resistance in these two malaria vectors of Sri Lanka.     

Insecticide resistance in house flies from the United States: Resistance levels and frequency of pyrethroid resistance alleles

Although insecticide resistance is a widespread problem for most insect pests, frequently the assessment of resistance occurs over a limited geographic range. Herein, we report the first widespread survey of insecticide resistance in the USA ever undertaken for the house fly, Musca domestica, a major pest in animal production facilities. The levels of resistance to six different insecticides were determined (using discriminating concentration bioassays) in 10 collections of house flies from dairies in nine different states. In addition, the frequencies of Vssc and CYP6D1 alleles that confer resistance to pyrethroid insecticides were determined for each fly population. Levels of resistance to the six insecticides varied among states and insecticides. Resistance to permethrin was highest overall and most consistent across the states. Resistance to methomyl was relatively consistent, with 65–91% survival in nine of the ten collections. In contrast, resistance to cyfluthrin and pyrethrins + piperonyl butoxide varied considerably (2.9–76% survival). Resistance to imidacloprid was overall modest and showed no signs of increasing relative to collections made in 2004, despite increasing use of this insecticide. The frequency of Vssc alleles that confer pyrethroid resistance was variable between locations. The highest frequencies of kdr, kdr-his and super-kdr were found in Minnesota, North Carolina and Kansas, respectively. In contrast, the New Mexico population had the highest frequency (0.67) of the susceptible allele. The implications of these results to resistance management and to the understanding of the evolution of insecticide resistance are discussed.     

Insecticide resistance in the tropical bedbug Cimex hemipterus

Insecticide resistance in the bedbug Cimex hemipterus was investigated using 4211 bedbugs collected from three districts of Sri Lanka. Insecticide bioassays were carried out with discriminating dosages of deltamethrin, permethrin, DDT, malathion, and propoxur. Activity levels of insecticide metabolizing enzymes and the insecticide target site acetylcholinesterase were monitored using biochemical assays. Percentage survivals after DDT, malathion, and propoxur exposure were 41-88%, 18-64%, and 11-41%, respectively. For deltamethrin and permethrin, KT₅₀/KT₉₀ (time to knock-down 50%/90% of the population) values were 0.5-24/1.0-58 and 1.3-10/2.5-47 h, respectively. Both elevated esterase and malathion carboxylesterase mechanisms were present in bedbug populations. Monooxygenase levels were heterogeneous. Organophosphate and carbamate target site acetylcholinesterase, was insensitive in 29-44% of the populations. High DDT resistance was probably due to glutathione S-transferases. Malathion carboxylesterases are mainly responsible for high malathion resistance. High tolerance to both DDT and pyrethroids suggests the presence of ‘kdr’ type resistance mechanism in one population.     

Selection of Anopheles stephensi with DDT and dieldrin and cross-resistance spectrum to pyrethroids and fipronil

The field strain of Anopheles stephensi, the main malaria vector in south of Iran, was colonized in laboratory and selected with DDT and dieldrin in two separate lines for 3 generations to a level of 19.5- and 14-fold for DDT and dieldrin resistance, respectively. Synergist tests with chlorofenethol (DMC) and piperonyl butoxide (PBO) on the selected strains indicated that dehydrochlorination and oxidative detoxification might be the underlying mechanisms involved in the resistance to dieldrin and DDT in selected strains. DDT selection decreased susceptibility to DDT and pyrethroids including lambdacyhalothrin, permethrin deltamethrin and cyfluthrin. The result also showed that selection with dieldrin caused negative and positive cross-resistance to pyrethroid and fipronil, respectively. Based on these results, it can be concluded that besides metabolic resistance mechanisms, other factors such as mutation in γ aminobutyric acid (GABA) and voltage-gated sodium channels (Kdr) might be involved.     

Field-simulator studies of insecticide resistance to dimethylcarbamates and pyrethroids conferred by metabolic- and target site-based mechanisms in peach-potato aphids,Myzus persicae (Hemiptera: Aphididae)

A range of insecticides was applied at recommended application rates against populations of Myzus persicae (Sulzer) carrying various combinations of three insecticide resistance mechanisms (carboxylesterase-based metabolic resistance and two target-site mechanisms, known as MACE and kdr), supported on either Chinese cabbage or potatoes in field simulator cages. Patterns of response were similar on both host species. MACE conferred extreme resistance to pirimicarb and triazamate (dimethylcarbamate insecticides). The kdr mechanism was associated with resistance to lambda-cyhalothrin, cypermethrin and deltamethrin (pyrethroid insecticides). A mixture of pirimicarb plus lambda-cyhalothrin was only effective against M persicae not carrying kdr or carrying kdr and low carboxylesterase-based resistance. None of the insecticides tested was effective against M persicae carrying both MACE and kdr resistance. The implications of these findings for the formulation of control strategies, based on regular monitoring of resistance genotype frequencies, are discussed.     

Elevated α-esterase levels associated with permethrin tolerance in Aedes aegypti (L.) from Baja California, Mexico

A discriminating dose for permethrin for Aedes aegypti from Baja California, Mexico was determined, and was used to select individuals. Mosquitoes were collected from four different municipalities located in the north and south end of the Baja California Peninsula. Individuals were chosen for further study based on their similar response to the insecticide. We exposed 10 groups of 90 Ae. aegypti females to the discriminating dose (172 μg/ml) and after producing 50% mortality, individuals were divided into two categories: killed and survivors. Each of these groups was dissected to separate the head, thorax, and abdomen. Biochemical tests were performed on the head and thorax to determine resistance-related enzyme activities including: α- and β-esterases, glutathione S-transferase, acetyl cholinesterase, insensitive acetyl cholinesterase, and mixed-function oxidases. The results were compared with those for the susceptible New Orleans strain of Ae. aegypti. All the populations studied showed the consistent presence of α-esterases, with elevated levels in permethrin-selected populations. Although β-esterases and GST levels were present in high proportions, they did not reveal a clear pattern in relation to resistance.     

Involvement of a sodium channel mutation in pyrethroid resistance in Cydia pomonella L, and development of a diagnostic test

Populations of the codling moth, Cydia pomonella L (Lepidoptera, Tortricidae) have developed resistance to several classes of insecticide such as benzoylureas, juvenile hormone analogues, ecdysone agonists and pyrethroids, but the corresponding resistance mechanisms have not been extensively studied. Knockdown resistance (kdr) to pyrethroid insecticides has been associated with point mutations in the para sodium channel gene in a great variety of insect pest species. We have studied two susceptible strains (S and Sv) and two resistant strains (Rt and Rv) of C pomonella that exhibited 4- and 80-fold resistance ratios to deltamethrin, respectively. The region of the voltage-dependent sodium channel gene which includes the position where kdr and super-kdr mutations have been found in Musca domestica L was amplified. The kdr mutation, a leucine-to-phenylalanine replacement at position 1014, was found only in the Rv strain. In contrast, the super-kdr mutation, a methionine-to-threonine replacement at position 918, was not detected in any C pomonella strain. These data allowed us to develop a PCR-based diagnostic test (PASA) to monitor the frequency of the kdr mutation in natural populations of C pomonella in order to define appropriate insecticide treatments in orchards.     

Biochemical and molecular analyses to determine pyrethroid resistance in Aedes aegypti

Dengue fever is an important mosquito-borne viral disease in Taiwan. Insecticide resistance has been shown to significantly reduce the efficacy of vector control interventions. The detection of insecticide resistance is an important component in mosquito abatement programs. In this study, we used the insecticide-impregnated papers bioassay method to reveal high levels of resistance to permethrin in the LYPR and field strains of Aedes aegypti. We used the standard glass cylinder method to observe the knockdown effect of paralysis within 2 to 4 minutes after exposing mosquitoes to pyrethroid vapors. Biochemical assays showed elevated detoxification enzyme activities. Glutathione S-transferases, monooxygenases and β-esterases were the enzymes predominantly responsible for the permethrin resistance of Ae. aegypti in Taiwan. Molecular screening for common insecticide target-site mutations revealed the presence of V1023G and D1794Y mutations. Pearson’s correlation analysis was used to investigate the correlations between the allelic frequency of kdr mutation associated increase with the LC50 values of permethrin and the KT50 values of pyrethroid vaporizers. These findings will be used to assess resistance levels, estimate resistance potential, and formulate monitoring and resistance management strategies.     

Cytochrome P450 monooxygenase-mediated permethrin resistance confers limited and larval specific cross-resistance in the southern house mosquito, Culex pipiens quinquefasciatus

The cytochrome P450-dependent monooxygenases (P450s) are an important enzymatic system that metabolizes xenobiotics (e.g., pesticides), as well as endogenous compounds (e.g., hormones). P450-mediated metabolism can result in detoxification of insecticides such as pyrethroids, or can be involved in the bioactivation and detoxification of insecticides such as organophosphates. We isolated (from the JPAL strain) a permethrin resistant strain (ISOP450) of Culex pipiens quinquefasciatus, having 1300-fold permethrin resistance using standard backcrossing procedures. ISOP450 is highly related to the susceptible lab strain (SLAB) and the high resistance to permethrin is due solely to P450-mediated detoxification. This is the first time in mosquitoes that P450 monooxygenase involvement in pyrethroid resistance has been isolated and studied without the confounding effects of kdr. Resistance in ISOP450 is incompletely dominant (D = +0.3), autosomally linked, and monofactorally inherited. It is expressed in the larvae, but not in adults. Cross-resistance to pyrethroids lacking a 3-phenoxybenzyl moiety (tetramethrin, fenfluthrin, bioallethrin, and bifenthrin) ranged from 1.5- to 12-fold. ISOP450 had only limited (6.6- and 11-fold) cross-resistance to 3-phenoxybenzyl pyrethroids with an α-cyano group (cypermethrin and deltamethrin, respectively). Examination of cross-resistance patterns to organophosphate insecticides in ISOP450 showed an 8-fold resistance to fenitrothion, while low, but significant, levels of negative cross-resistance were found for malathion (RR = 0.84), temephos (RR = 0.73), and methyl-parathion (RR = 0.55). The importance and uniqueness of this P450 mechanism in insecticide resistance is discussed.     

Pyrethroid insecticide resistance and treated bednets efficacy in malaria control

Most of the studies on insecticide impregnated bednets efficacy in malaria control have been undertaken in areas where mosquitoes are pyrethroid susceptible. The efficacy of pyrethroid-treated bednets was not compromised even when mosquitoes were kdr resistant. Here, we evaluate a case in which mosquitoes have kdr-like pyrethroid resistance coupled with metabolic mechanisms. Metabolic and kdr-resistance mechanisms in Anopheles stephensi were characterised in our previous study and this easily colonised species was used as a model to examine the efficacy of pyrethroid-treated bednets in the laboratory. Bioassays performed on adults of susceptible (Beech) and resistant (DUB-S) strains using WHO 0.75% permethrin-impregnated papers showed a resistance ratio of 9.75. The recovery rate of the mosquitoes of the DUB-S strain was significantly higher than that of the susceptible strain Beech. The overall permethrin metabolism rates by DUB-S, measured by HPLC method, were 1.5-fold more than by Beech strain. Bioassays performed on DUB-S mosquitoes using different pyrethroid-treated bednets showed that only deltamethrin at 25 mg/m² and α-cypermethrin at 40 mg/m² produced adequate mortality rates. Four other pyrethroids, including permethrin, were ineffective. The deterrency test performed on susceptible and resistant An. stephensi showed that there are significant differences between the entry rates of susceptible and resistant mosquitoes into the exposure tube containing permethrin-treated bednet. These data show that when mosquitoes have both kdr-type and metabolic resistance mechanisms, the efficacy of pyrethroid-treated bednets is questionable.     

Pyrethroid resistance and cross‐resistance in the German cockroach,Blattella germanica (L)

A German cockroach (Blatella germanica (L)) strain, Apyr‐R, was collected from Opelika, Alabama after control failures with pyrethroid insecticides. Levels of resistance to permethrin and deltamethrin in Apyr‐R (97‐ and 480‐fold, respectively, compared with a susceptible strain, ACY) were partially or mostly suppressed by piperonyl butoxide (PBO) and S,S,S,‐tributylphosphorotrithioate (DEF), suggesting that P450 monooxygenases and hydrolases are involved in resistance to these two pyrethroids in Apyr‐R. However, incomplete suppression of pyrethroid resistance with PBO and DEF implies that one or more additional mechanisms are involved in resistance. Injection, compared with topical application, resulted in 43‐ and 48‐fold increases in toxicity of permethrin in ACY and Apyr‐R, respectively. Similarly, injection increased the toxicity of deltamethrin 27‐fold in ACY and 28‐fold in Apyr‐R. These data indicate that cuticular penetration is one of the obstacles for the effectiveness of pyrethroids against German cockroaches. However, injection did not change the levels of resistance to either permethrin or deltamethrin, suggesting that a decrease in the rate of cuticular penetration may not play an important role in pyrethroid resistance in Apyr‐R. Apyr‐R showed cross‐resistance to imidacloprid, with a resistance ratio of 10. PBO treatment resulted in no significant change in the toxicity of imidacloprid, implying that P450 monooxygenase‐mediated detoxication is not the mechanism responsible for cross‐resistance. Apyr‐R showed no cross‐resistance to spinosad, although spinosad had relatively low toxicity to German cockroaches compared with other insecticides tested in this study. This result further confirmed that the mode of action of spinosad to insects is unique. Fipronil, a relatively new insecticide, was highly toxic to German cockroaches, and the multi‐resistance mechanisms in Apyr‐R did not confer significant cross‐resistance to this compound. Thus, we propose that fipronil could be a valuable tool in integrated resistance management of German cockroaches. © 2001 Society of Chemical Industry     

Control failure likelihood and spatial dependence of insecticide resistance in the tomato pinworm, Tuta absoluta

BACKGROUND: Insecticide resistance is a likely cause of field control failures of Tuta absoluta, but the subject has been little studied. Therefore, resistance to ten insecticides was surveyed in seven representative field populations of this species. The likelihood of control failures was assessed, as well as weather influence and the spatial dependence of insecticide resistance. RESULTS: No resistance or only low resistance levels were observed for pyrethroids (bifenthrin and permethrin), abamectin, spinosad, Bacillus thuringiensis and the mixture deltamethrin + triazophos (<12.5‐fold). In contrast, indoxacarb exhibited moderate levels of resistance (up to 27.5‐fold), and chitin synthesis inhibitors exhibited moderate to high levels of resistance (up to 222.3‐fold). Evidence of control failures was obtained for bifenthrin, permethrin, diflubenzuron, teflubenzuron, triflumuron and B. thuringiensis. Weather conditions favour resistance to some insecticides, and spatial dependence was observed only for bifenthrin and permethrin. CONCLUSION: Insecticide resistance in field populations of the tomato pinworm prevails for the insecticides nowadays most frequently used against them—the chitin synthesis inhibitors (diflubenzuron, triflumuron and teflubenzuron). Local selection favoured by weather conditions and dispersal seem important for pyrethroid resistance evolution among Brazilian populations of T. absoluta and should be considered in designing pest management programmes. Copyright © 2011 Society of Chemical Industry     

Frequency and intensity of pyrethroid resistance through the CDC bottle bioassay and their association with the frequency of kdr mutations in Aedes aegypti (Diptera: Culicidae) from Mexico

BACKGROUND

The control of Aedes aegypti (L.), the main urban vector that causes arboviral diseases such as dengue, Chikungunya and Zika, has proved to be a challenge because of a rapid increase in insecticide resistance. Therefore, adequate monitoring of insecticide resistance is an essential element in the control of Ae. aegypti and the diseases it transmits. We estimated the frequency and intensity (Resistance Frequency Rapid Diagnostic Test [F‐RDT] and Resistance Intensity Rapid Diagnostic Test [I‐RDT]) of pyrethroid resistance in populations of Ae. aegypti from Mexico using the bottle bioassay and results were related to the frequencies of knockdown resistance (kdr) mutations V1016I and F1534C.

RESULTS

All populations under study were resistant to the pyrethroids: bifenthrin (99%), d‐(cis–trans)‐phenothrin (6.3% cis, 91.7% trans) and permethrin (99.5%) according to F‐RDT, and showed moderate to high‐intensity resistance at 10× the diagnostic dose (DD) in I‐RDT. Frequencies of the kdr mutation V1016I in Ae. aegypti populations were correlated with moderate permethrin resistance at 10× DD, whereas F1534C mutation frequencies were correlated with high bifenthrin resistance at 5× DD. Both I1016 and C1535 were highly correlated with high‐intensity phenothrin resistance at 1× to 10× DD.

CONCLUSIONS

This study showed that high frequencies of kdr mutations V1016I and F1534C are reflected in the results of F‐RDT and I‐RDT tests. Bioassays in conjunction with the characterization of genetic resistance mechanisms are indispensable in the strategic and rational management of resistance in mosquitoes. © 2018 Society of Chemical Industry

     

Insecticide resistance and,efficacy of space spraying and larviciding in the control of dengue vectors Aedes aegypti and Aedes albopictus in Sri Lanka

Unprecedented incidence of dengue has been recorded in Sri Lanka in recent times. Source reduction and use of insecticides in space spraying/fogging and larviciding, are the primary means of controlling the vector mosquitoes Aedes aegypti and Ae. albopictus in the island nation. A study was carried out to understand insecticide cross-resistance spectra and mechanisms of insecticide resistance of both these vectors from six administrative districts, i.e. Kandy, Kurunegala, Puttalam, Gampaha, Ratnapura and Jaffna, of Sri Lanka. Efficacy of the recommended dosages of frequently used insecticides in space spraying and larviciding in dengue vector control programmes was also tested.     

Field-simulator study of insecticide resistance conferred by esterase-, MACE- and kdr-based mechanisms in the peach-potato aphid,Myzus persicae (Sulzer)

Insecticide sprays were applied to Myzus persicae (Sulzer) populations carrying various combinations of three insecticide resistance mechanisms (esterase-based metabolic resistance and two target site mechanisms, known as MACE and kdr), supported on host plants growing in field simulator cages. The study showed that MACE confers extreme resistance to pirimicarb and triazamate (carbamate insecticides) but not to deltamethrin + heptenophos (16 + 1) (Decisquick) or dimethoate (an organophosphorus insecticide). Resistance to dimethoate depends solely on levels of esterase-based resistance, while resistance to Decisquick depends on kdr and esterase. None of the four insecticides is effective against aphids carrying MACE combined with extreme esterase-based resistance. This knowledge, in association with current monitoring of the mechanisms, will play an important role in making decisions on insecticide use against M persicae in the UK. © 1999 Society of Chemical Industry     

Cross-resistance to pyrethroids and other insecticides in Aedes aegypti

Two substrains of Aedes aegypti, already resistant to DDT and pyrethroids, were further selected using either DDT or permethrin by mass exposure of the females only. DDT selection over 14 generations raised the resistance to DDT so far that no accurate LC₅₀ values could be determined. Selection with permethrin raised the tolerance to an irregular plateau 7–10 times the original. DDT selection in the adults raised the DDT resistance of the larvae, but this could be partly overcome using a dehydrochlorinase inhibitor. The resistance to pyrethroids was increased but tolerance of dieldrin, malathion and propoxur compounds was little changed. Permethrin selection of the adults raised resistance to pyrethroids more than DDT selection but also increased DDT resistance. Similar patterns were found for the larval insects. A strain from Demerara in Guyana showed both DDT and pyrethroid resistance, including strong resistance to pyrethrins together with dieldrin and propoxur. It was concluded that two major independent resistance mechanisms existed in the selected strains, a dehydrochlorinase affecting DDT alone, and an unknown mechanism, probably nerve insensitivity (kdr) affecting both DDT and pyrethroids.     

Synergism by Propynyl Aryl Ethers in Permethrin-Resistant Tobacco Budworm Larvae,Heliothis virescens

Synergists were used to diagnose possible mechanisms of permethrin resistance in permethrin-selected strains of the tobacco budworm, Heliothis virescens (F.). In addition to permethrin, these strains of the tobacco budworm were resistant to α-cyano-pyrethroid insecticides, organophosphorus insecticides and DDT. The monooxygenase-inhibiting prop-2-ynyl aryl ethers were the only effective synergists of permethrin among 16 candidates tested. The most effective synergist was 1,2,4-trichloro-3-(2-propynyloxy)benzene. Piperonyl butoxide, a common monooxygenase-inhibiting synergist in other species and tobacco budworm strains, was inactive. These results suggested the presence and contribution of an unusual monooxygenase in the enzymatic detoxication of permethrin. DDT cross-resistance, which was not synergized, and broad pyrethroid cross-resistance supported previous evidence for target site insensitivity as a second pyrethroid-resistance mechanism in these strains. The actions of S,S,S-tributyl phosphorotrithioate (TBPT) and triphenyl phosphate (TPP) suggested that hydrolytic detoxication, important in methyl parathion-resistance tobacco budworm strains, had little or no role in conferring pyrethroid resistance in these strains.     

Hyper-susceptibility to deltamethrin in para DDT resistant Drosophila melanogaster

The extensively studied para gene encodes a α-subunit of the voltage-activated sodium channel in Drosophila melanogaster, which is the documented target site of DDT and pyrethroid insecticides. The para^ts-1 fruit fly line carries a recessive sex-linked insecticide-resistance trait (para^ts-1 allele) that has been defined on the basis of the behavioral phenotype of temperature-sensitive paralysis. We have determined that para^ts-1 confers hyper-susceptibility to deltamethrin in addition to the previously annotated resistance to DDT, revealing the presence of negative cross-resistance. We investigated the potential use of negative cross-resistance shifting para^ts-1 gene frequencies in D. melanogaster populations. After five generations of selection, the para^ts-1 allele, respectively, became more or less frequent whether Drosophila populations were selected with DDT or deltamethrin.