Insecticide resistance status of Aedes aegypti and Aedes albopictus in Malaysia(2010 to 2022):A review

This review aimed to determine the prevalence of the insecticide resistance status of the field-collected Aedes(Ae.)aegypti and Ae.albopictus in Malaysia from 2010 to 2022 towards carbamates,organochlorines,organophosphates and pyrethroids.Biological and environmental controls were summarized with an emphasis on the mosquito vector control strategies in Malaysia.The information in this review was extracted from several databases such as PubMed(MEDLINE),Science Direct and Scopus by using keywords including“insecticide resistance”,“carbamate resistance”,“organochlorine resistance”,“organophosphate resistance”,“pyrethroid resistance”,“Aedes”and“Malaysia”,between January 2022 and December 2022.Distribution of resistant Ae.aegypti and Ae.albopictus in Malaysia was mapped using QGIS software.Insecticide resistance in both Ae.aegypti and Ae.albopictus is widespread in Malaysia,although the rates vary by states.The most notable was the steep increase in permethrin resistance of Ae.aegypti in Selangor,Malaysia,over the past decade.Ae.albopictus also displayed moderate resistance to permethrin,though not as widespread as Ae.aegypti in Selangor,but showed sign of resistance in Sarawak,East Malaysia.Resistance towards four main classes of insecticides have been widely documented in Malaysia.The extensive resistance towards permethrin in Malaysia which is one of the current insecticides used in Malaysia suggested that policies supporting the widespread use of permethrin fogging needs further evaluation.

Characterization of carboxylesterase PxαE8 and its role in multi-insecticide resistance in Plutella xylostella(L.)

Carboxylesterase(CarE)was considered as important phase-I detoxifying enzymes which participated in detoxification of different types of insecticides.Up-regulation of CarE genes has been proved playing a major role in insecticide resistance in many pest insects,but its involvement in resistance to insecticides in Plutella xylostella has been rarely reported.In this study,a CarE cDNA named PxαE8 was identified in P.xylostella,which has an open reading frame of 1599 nucleotides and putatively encodes 532 amino acids.The investigation of spatial expression profiles of PxαE8 revealed that it was expressed in all developmental stages,especially in larvae and adults.The body part/tissue-specific expression profiles showed that the PxαE8 mainly expressed in fat body,malpighian tubule and hemolymph of larvae.Further,the relative expression of PxαE8 in two multi-resistant field populations,Hainan(HN)and Guangdong(GD)populations,was found 24.4-and 15.5-fold higher than that in susceptible population,respectively.Knockdown of PxαE8 by RNA interference dramatically increased the mortalities of larvae of HN population treated with LC_(50) of beta-cypermethrin and phoxim by 25.3 and 18.3%,respectively.These results suggested that up-regulation of PxαE8 was involved in resistance to both beta-cypermethrin and phoxim in P.xylostella,which shed light on further understanding of molecular mechanisms of multi-insecticide-resistance in P.xylostella and other pest insects.

Insecticide resistance status and biochemical mechanisms involved in Aedes mosquitoes: A scoping review

Mosquitoes belonging to the genus Aedes pose a significant threat to human health on a global scenario due to their role in transmission of dengue,chikungunya,zika,and yellow fever.In absence of specific medications and vaccines against these diseases,disease prevention relies on vector control.However,in today’s world,vector control is facing major challenges due to the onset of insecticide resistance in mosquitoes.There are four main mechanisms of insecticide resistance,namely,behavioral resistance,reduced penetration/cuticular resistance,metabolic detoxification,and target site resistance;however,the latter two mechanisms have been studied widely in Aedes mosquitoes.Insecticide resistance in Aedes mosquitoes is widespread throughout the world.This review compiles the degree of insecticide resistance/susceptibility prevailing among different field populations of Aedes mosquitoes worldwide.In addition,the review has detailed the mechanisms providing the resistance phenomenon observed in nature in Aedes mosquitoes.

Modeling Insecticide Resistance in Endemic Regions of Kenya

In this study, we develop an SIS model for two types of mosquitoes, a traditional one and one that is resistant to IRS and ITNs. The resistant mosquito develops behavioral adaptation to control measures put in place to reduce their biting rate. They also bite early before dusk and later after dark when people are outside the houses and nets. We determine the effect of the two types of mosquitoes on malaria transmission in Kenya. The basic reproduction number R 0 is established as a sharp threshold that determines whether the disease dies out or persists in the population. Precisely, if R 0 ≤ 1, the disease-free equilibrium is globally asymptotically stable and the disease always dies out and if R 0 > 1, there exists a unique endemic equilibrium which is globally stable and the disease persists. The contribution of the two types of mosquitoes to the basic reproduction number and to the level of the endemic equilibrium is analyzed.

The insecticide resistance in stripped stem borer,Chilo suppressalis(Walker)

The stripped stem borer (SSB),Chilo suppressalis (Walker) is one ofthe major insect pests of rice in Chi-na. Chemical control has been acommon practice in SSB managementsince 1950s. Insecticides used in-cluded BHC before 1983; organophos-

The insecticide resistance in two planthoppers from three areas to three insecticides

Migrating insects brown planthopper(BPH),Nilaparvata lugens St(?)l andwhite-backed planthopper(WBPH),Sogatella furcifera Horvath are both mostharmful insects on rice in China.Chemical control is thought to be the best wayto manage them,but it may cause insecticide resistance.Methamidophos,buprofezin,and imidacloprid were the three insecticides often used.In 2000and 2001,resistance of the field populations collected from three areas,i.e.Dongtai,Jiangsu Province,Anqing,Anhui Province,and Guilin,GuangxiAutonomous Region,to the three insecticides was monitored.The toxicities ofthe three insecticides were determined with the female adult(3-5 d after e-mergence)and by the topical application method with the hand microapplicator.

Comparison of Insecticide Resistance and Its Enzyme Mechanisms among Aedes aegypti Collected with Three Methods in a Dengue-Endemic City in Southern Mexico

Background: Despite the physical and chemical effort to control Aedes aegypti, the arboviruses transmission in the south of Mexico remains latent. Trying to improve the methods of entomological surveillance routinely used, whether the estimation of resistance to insecticides used for its control, as well as their enzyme mechanisms, were influenced by the phase in which the mosquitoes were collected through three different collection methods was investigated. Materials and Methods: Mosquito collections from the “5 de Febrero” neighborhood in Tapachula, Mexico were obtained by ovitraps, larvitraps, and a CDC backpack aspirator. Insecticide resistance of F1 females was determined by WHO diagnostic doses and resistance ratios (RR50), furthermore, levels of insecticide metabolism enzymes were determined by biochemical assays. Results: Overall, in mosquitoes collected by ovitraps, larvitraps, and CDC backpack aspirator respectively, the low mortalities obtained with the discriminant dose to Malathion (27.57%, 26.97%, and 26.91%), and to Bendiocarb (50.5%, 45.36%, and 54.97%) suggest resistance. However, LC50 for Malathion (0.922, 0.934, and 0.915) and for Bendiocarb (0.112, 0.109, and 0.107);and the low resistance ratios (RR50) for Malathion (3.34, 3.29, and 3.27) and for Bendiocarb (2.15, 2.1, and 2.06) does not suggest resistance. Although a slight numerical variation is observed between the three LC50 values, the overlap observed between their confidence intervals allows us to assume that there were no differences between the three methods. In general, esterases (determined with three substrates), glutathion S-transferases (GST) and cytochromes P450 were statistically higher than those of the susceptible strain;and the three enzyme levels were statistically different among the three collection methods (P Conclusion: Although using a CDC backpack aspirator demonstrated being the best collection method determining a specific resistance mechanism (as elevation at the enzyme level) in the mosquito adult phase, any collection method is reliable to determine whether a field mosquito population is resistant or susceptible to an insecticide.

Insensitive Acetylcholine Receptor Conferring Resistance of Plutella xylostella to Nereistoxin Insecticides

The combinative rate measurement of （3-[I125] iodotyrosyl） α-bungarotoxin was applied in the analysis of the relation between nerve acetylcholine receptor and three types of insecticide resistance in diamondback moth, Plutella xylostella （L.）. In the dimehypo-resistant strain and in the cartap-resistant strain, the nerve acetylcholine receptor showed the remarkable insensitivity to dimehypo and cartap, of which the binding rate to ligand was approximately 66 and 60%, respectively, of the susceptible strain. The sensitivity to deltamethrin in the deltamethrin-resistant strain did not show visible change. These results indicated that the decline in the sensitivity of nerve acetylcholine receptor to insecticide might be a potential mechanism to nereistoxin insecticides resistance in the diamondback moth.

Levels of insecticide resistance to deltamethrin,malathion,and temephos,and associated mechanisms in Aedes aegypti mosquitoes from the Guadeloupe and Saint Martin islands(French West Indies)

Background:In the Guadeloupe and Saint Martin islands,Aedes aegypti mosquitoes are the only recognized vectors of dengue,chikungunya,and Zika viruses.For around 40 years,malathion was used as a mosquito adulticide and temephos as a larvicide.Since the European Union banned the use of these two insecticide molecules in the first decade of the 21st century,deltamethrin and Bacillus thuringiensis var.israelensis are the remaining adulticide and larvicide,respectively,used in Guadeloupe.In order to improve the management of vector control activities in Guadeloupe and Saint Martin,we investigated Ae.aegypti resistance to and mechanisms associated with deltamethrin,malathion,and temephos.Methods:Ae.aegypti mosquitoes were collected from six different localities of Guadeloupe and Saint Martin.Larvae were used for malathion and temephos bioassays,and adult mosquitoes for deltamethrin bioassays,following World Health Organization recommendations.Knockdown resistance(Kdr)genotyping for V1016I and F1534C mutations,and expression levels of eight enzymes involved in detoxification mechanisms were examined in comparison with the susceptible reference Bora Bora strain.Results:Resistance ratios(RR50)calculated for Ae.aegypti larvae showed high resistance levels to temephos(from 8.9 to 33.1-fold)and low resistance levels to malathion(from 1.7 to 4.4-fold).Adult females displayed moderate resistance levels to deltamethrin regarding the time necessary to affect 50%of individuals,varying from 8.0 to 28.1-fold.Molecular investigations on adult mosquitoes showed high resistant allele frequencies for V1016I and F1534C(from 85 to 96%and from 90 to 98%,respectively),as well as an overexpression of the glutathione S-transferase gene,GSTe2,the carboxylesterase CCEae3a,and the cytochrome genes 014614,CYP6BB2,CYP6M11,and CYP9J23.Conclusions:Ae.aegypti populations from Guadeloupe and Saint Martin exhibit multiple resistance to organophosphates(temephos and malathion),and pyrethroids(deltamethrin).The mechanisms associated with these resistance patterns show strong frequencies of F1534C and V1016I Kdr mutations,and an over-expression of CCEae3a,GSTe2,and four cytochrome P450 genes(014614,CYP9J23,CYP6M11,CYP6BB2).These results will form the baseline for a deeper understanding of the insecticide resistance levels and associated mechanisms of Ae.aegypti populations and will be used to improve vector control strategies in Guadeloupe and Saint Martin.

Identification and characterization of a cytochrome P450 C YP6CX1 putatively associated with insecticide resistance in Bemisia tabaci

The novel full length of cytochrome P450 gene has been isolated in insecticideresistant （named CYP6CXlvl） and -susceptible （named CYP6CXlv2） Bemisia tabaci, which was identified as B biotype, in Shangjie, Fujian, China （Sj）. CYP6CX1 （1 940 bp contained a 1 557 bp open reading frame） included conserved domains common to CYP6 members, such as heme-binding motif PFGEGPRFCIA, putative ＂meander＂-binding sequence ETLR and PERF in helix-K, oxygen-binding motif AGLDPV and conserved sequence PEKFNP near the carboxyl end. There were four different replacements of amino acid residues between R and S B. tabaci （Thr300 Ala, Thr354Pro, Arg486His and Ile503Thr）, among which the substitution Ile503Thr was located in the substrate recognition sites region. The mRNA transcription level of CYP6CXlvl was 2.38-fold as high as that of CYP6CXlv2. The results indicated that the CFP6CX1 from the B biotype B. tabaci in Sj was one of the CYP6 members, and enhanced CYP6CX1 expression and substitute of amino acid residues might be involved in the resistance mechanisms in field B. tabaci.

Evidence of insecticide resistance selection in wildmosquitoes due to agricultural pesticide use

Background:The wetlands used for some agricultural activities constitute productive breeding sites for many mosquito species.Thus,the agricultural use of insecticide targeting other pests may select for insecticide resistance in malaria mosquitoes.The purpose of this study is to clarify some knowledge gaps on the role of agrochemicals in the development of insecticide resistance in malaria vectors is of utmost importance for vector control.Methods:Using the CDC bottle test and the log-probit analysis,we investigated for the first time the resistance levels ofAnopheles coluzzii mosquitoes to neonicotinoids,insecticides used exclusively for crop protection in C?te d’Ivoire.The study was conducted in two agricultural regions(Tiassale and Gagnoa)and one non-agricultural region(Vitre)between June and August 2017 using clothianidin,acetamiprid and imidacloprid.Results:Mosquito populations from Tiassale and Gagnoa(agricultural settings)were determined to be resistant to acetamiprid with mortality rates being<85%at 24 h post-exposure.In Vitre(non-agricultural area)however,the mosquito population was susceptible to acetamiprid.In all three localities,mosquito populations were resistant to imidacloprid(mortality rates were 60%in Vitre,37%in Tiassale,and 13%in Gagnoa)and completely susceptible to clothianidin(100%mortality).An.coluzzii represented 100%of mosquito collected in Gagnoa,86%in Tiassale and 96%in Vitre.Conclusions:This study provides strong evidence that agricultural use of insecticides can cause insecticide resistance in malaria vector populations.Insecticide resistance driven by agrochemical usage should be considered when vector control strategies are developed.

Insecticide resistance in malaria-transmitting mosquitoes in Zimbabwe: a review

Malaria is a global public health problem,with about 3.2 billion people at risk of infection.The populations at risk mainly reside in Africa,Asia and America,with African populations accounting for the largest burden of the disease.In 2013,close to 198 million malaria cases were reported,leading to 584,000 deaths.Much(90%)of the mortality rates were recorded from the World Health Organization(WHO)database in the African region and 78%of these occurred in children under the age of five.In Zimbabwe,approximately half of the population is at risk of infection with malaria.Insecticide residual spraying(IRS)has been documented as an effective way to control malaria and has been adopted globally by the WHO and national governments.However,both insecticide resistance and climate change threaten to reverse the progress made by IRS in malaria control.Resistance has been reported in all four classes of insecticides approved by the WHO for vector control intervention.Variability of environmental temperature is suspected to complicate the situation through alteration in the genetic structure,and enzyme and protein profiles of mosquitoes.In Zimbabwe,little research has been done on the interaction between climate change,temperature variability and insecticide resistance in malarial mosquitoes over time.Such information is important for informing policies on insecticide selection for IRS.We reviewed literature on insecticide sensitivity among malarial mosquitoes in Zimbabwe from 1972 to 2014.International peer-reviewed articles on insecticide sensitivity in Zimbabwe,published in English in this time period,were searched using MEDLINE®(PubMed),Google Scholar,Google and grey literature.Eight publications were eligible for the present study,with one of the articles being a review paper.Six articles covered insecticide resistance,while the other two articles,published in 2000,were about the absence of resistance.Contradicting resistance results were reported in 2014.The insecticide sensitivity status and distribution of insecticide resistance in mosquitoes are still under debate in Zimbabwe,as studies report differing results.The resistance trend in Zimbabwe is characterised by fluctuations in the status of the sensitivity of existing insecticides.Inconsistencies in data collection methods may be responsible for the inconsistencies in the results.None of the studies have determined a link between climate/temperature variability and insecticide resistance as yet.The current insecticide sensitivity status of mosquitoes still needs to be verified.

Insecticide resistance in Bemisia tabaci from Cyprus

A comprehensive study on the Bemisia tabaci （biotype B） resistance to neonicotinoid insecticides imidacloprid, acetamiprid and thiamethoxam, and pyrethroid bifenthrin was conducted in Cyprus. The resistance level to eight field-collected B. tabaci populations was investigated. The activities of enzymes involved in metabolic detoxification and the frequencies ofpyrethroid and organophosphates target site resistance mutations were determined. Moderate to high levels of resistance were detected for imidacloprid （re- sistance factor [RF] 77-392） and thiamethoxam （RF 50-164） while low resistance levels were observed for acetamiprid （RF 7-12）. Uniform responses by the Cypriot whiteflies could be observed against all neonicotinoid insecticides. No cross-resistance between the neonicotinoids was detected as well as no association with the activity of the P450 microsomal oxidases. Only imidacloprid resistance correlated with carboxylesterase activity. Low to extremely high resistance was observed for insecticide bifenthrin （RF 49 1 243） which was associated with the frequency of the resistant allele in the sodium channel gene but not with the activity of the detoxification enzymes. Finally, the F331W mutation in the acetylcholinesterase enzyme acel gene was fixed in all B. tabaci populations from Cyprus.

Mathematical assessment of the role of vector insecticide resistance and feeding/resting behavior on malaria transmission dynamics:Optimal control analysis

The large-scale use of insecticide-treated bednets(ITNs)and indoor residual spraying(IRS),over the last two decades,has resulted in a dramatic reduction of malaria incidence globally.However,the effectiveness of these interventions is now being threatened by numerous factors,such as resistance to insecticide in the mosquito vector and their preference to feed and rest outdoors or early in the evening(when humans are not protected by the bednets).This study presents a new deterministic model for assessing the population-level impact of mosquito insecticide resistance on malaria transmission dynamics.A notable feature of the model is that it stratifies the mosquito population in terms of type(wild or resistant to insecticides)and feeding preference(indoor or outdoor).The model is rigorously analysed to gain insight into the existence and asymptotic stability properties of the various disease-free equilibria of the model namely the trivial diseasefree equilibrium,the non-trivial resistant-only boundary disease-free equilibrium and a non-trivial disease-free equlibrium where both the wild and resistant mosquito geneotypes co-exist).Simulations of the model,using data relevant to malaria transmission dynamics in Ethiopia(a malaria-endemic nation),show that the use of optimal ITNs alone,or in combination with optimal IRS,is more effective than the singular implementation of an optimal IRS-only strategy.Further,when the effect of the fitness cost of insecticide resistance with respect to fecundity(i.e.,assuming a decrease in the baseline birth rate of new resistant-type adult female mosquitoes)is accounted for,numerical simulations of the model show that the combined optimal ITNs-IRS strategy could lead to the effective control of the disease,and insecticide resistance effectively managed during the first 8 years of the 15-year implementation period of the insecticides-based anti-malaria control measures in the community.

Insecticide resistance in phlebotomine sandflies in Southeast Asia with emphasis on the Indian subcontinent

Background:Visceral leishmaniasis,commonly known as kala-azar in India,is a global public health problem.In Southeast Asia,Bangladesh,Bhutan,India,Nepal,Sri Lanka and Thailand are endemic for visceral leishmaniasis.The role of sandflies as the vector of kala-azar was first confirmed in 1942 in India.Insecticide resistance in Phlebotomus argentipes Annandale and Brunetti,the vector of kala-azar in the Indian subcontinent,was first reported in 1987 in Bihar,India.This article provides a scoping review of the studies undertaken from 1959 to 2015 on insecticide resistance in P.argentipes and P.papatasi(Scopoli),the vectors of visceral and cutaneous leishmaniasis respectively,in Southeast Asia,mainly in Bangladesh,India,Nepal and Sri Lanka.Results:Studies undertaken in areas of Bihar and West Bengal in India where kala-azar is endemic have reported resistance of P.argentipes to DDT,while in non-endemic areas it has been reported to be susceptible.In areas of Nepal bordering India,there are indications of resistance to DDT;biochemical resistance has been reported in Sri Lanka.No laboratory studies have been undertaken in Bangladesh;however,the sandfly vector is reported to be still susceptible to pyrethroids in all kala-azar endemic areas in the aforementioned countries.Conclusions:Studies are needed to determine the resistance of sandfly vectors to all available classes of potential insecticides in kala-azar endemic areas.There is a need to assess the impact of indoor residual spraying with DDT and pyrethroids on the incidence of kala-azar in India where 54 districts remain endemic for the disease,strengthen entomological surveillance capacity,and develop and implement an insecticide management plan.Alpha-cypermethrin indoor residual spraying has been introduced in 33 kala-azar endemic districts in Bihar State of India in a pilot trial;the outcomes should be used to inform decisions on expanding coverage with alpha-cypermethrin in all remaining endemic districts to achieve the revised goal of elimination of visceral leishmaniasis by 2020.

Influence of seasonal migration on evolution of insecticide resistance in Plutella xylostella

The diamondback moth,Plutella xylostella(L.),is one of the most destructive migratory pest species of cruciferous vegetables worldwide and has developed resistance to most of the insecticides used for its control.The migration regularity,migratory behavior,and relationship between flight and reproduction of P.xylostella have been widely reported.However,the effect of migration on insecticide resistance in this pest is still unclear.In this study,the effect of migration on P.xylostella resistance to seven insecticides was investigated using populations across the Bohai Sea that were collected in the early and late seasons during 2017–2019.The bioassay results showed that the early season populations of P.xylostella from south China possessed much higher resistance to insecticides because of intensive insecticide application;alternatively,the late season populations migrated from northeast China,where the insecticides were only used occasionally,showed much lower insecticide resistance.The genome re-sequencing results revealed that,among the eight mutations involved in insecticide resistance,the frequencies of two acetylcholinesterase mutations(A298S and G324A)responsible for organophosphorus insecticide resistance were significantly decreased in the late season populations.The results indicated that P.xylostella migration between tropical and temperate regions significantly delayed the development of insecticide resistance.These findings illustrated the effect of regional migration on the evolution of insecticide resistance in P.xylostella,and provided foundational information for further research on the relationship between migration and insecticide resistance development in other insects.

Population dynamics, pathogen detection and insecticide resistance of mosquito and sand fly in refugee camps, Greece

Background:As of 2015 thousands of refugees are being hosted in temporary refugee camps in Greece.Displaced populations,travelling and living under poor conditions with limited access to healthcare are at a high risk of exposure to vector borne disease(VBD).This study sought to evaluate the risk for VBD transmission within refugee camps in Greece by analyzing the mosquito and sand fly populations present,in light of designing effective and efficient context specific vector and disease control programs.Methods:A vector/pathogen surveillance network targeting mosquitoes and sand flies was deployed in four temporary refugee camps in Greece.Sample collections were conducted bi-weekly during June-September 2017 with the use of Centers for Disease Control(CDC)light traps and oviposition traps.Using conventional and molecular diagnostic tools we investigated the mosquito/sand fly species composition,population dynamics,pathogen infection rates,and insecticide resistance status in the major vector species.Results:Important disease vectors including Anopheles sacharovi,Culex pipiens,Aedes albopictus and the Leishmania vectors Phlebotomus neglectus,P.perfiliewi and P.tobbi were recorded in the study refugee camps.No mosquito pathogens(Plasmodium parasites,flaviviruses)were detected in the analysed samples yet high sand fly Leishmania infection rates are reported.Culex pipiens mosquitoes displayed relatively high knock down resistance(kdr)mutation allelic frequencies(ranging from 41.0 to 63.3%)while kdr mutations were also detected in Ae.albopictus populations,but not in Anopheles and sand fly specimens.No diflubenzuron(DFB)mutations were detected in any of the mosquito species analysed.Conclusions:Important disease vectors and pathogens in vectors(Leishmania spp.)were recorded in the refugee camps indicating a situational risk factor for disease transmission.The Cx.pipiens and Ae.albopictus kdr mutation frequencies recorded pose a potential threat against the effectiveness of pyrethroid insecticides in these settings.In contrast,pyrethroids appear suitable for the control of Anopheles mosquitoes and sand flies and DFB for Cx.pipiens and Ae.albopictus larvicide applications.Targeted actions ensuring adequate living conditions and the establishment of integrated vector-borne disease surveillance programs in refugee settlements are essential for protecting refugee populations against VBDs.

The Relationship Between Resistance to Controlled Atmosphere and Insecticides of Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae)

The cross resistance of four resistant strains of Liposcelis bostrychophila Badonnel, an important stored-product insect pest, was investigated. These four strains included the HCO2-R (hypercarbia-resistant strain), HCLO-R (hypoxia and hypercarbia resistant strain), DDVP-R (DDVP-resistant strain) and PH3-R (PH3-resistant strain). The results indicated that there were cross-resistances between CA and insecticides, and the quantities of the cross-resistance were different. The cross-resistance factor (RF) of HCO2-R to hypoxia and hypercarbia was 3.2458, whilst, that of HCLO-R to hypercarbia was 1.8280. The RF of DDVP-R to PH3 was 3.9614, whilst, that of PH3-R to DDVP was 2.7852. The RF values of DDVP- R and PH3-R to hypercarbia were 1.3550 and 1.1816, respectively. However, the RF of HCO2- R to DDVP was 2.1372. There also was a low cross-resistance between DDVP-R and HCO2-R. The RF of HCO2-R to PH3 was 3.3698. This suggested that the insects resistant to high CO2 concentration atmosphere would develop significant resistance to PH3. However, the insects resistant to PH3 remain sensitive to hypercarbia atmosphere. Both DDVP-R and PH3- R developed resistance to high CO2 treatment. There was a low cross-resistance between DDVP-R and HCLO-R. The insects resistant to hypoxia and hypercarbia were very sensitive to DDVP. There also was cross-resistance between HCLO-R and PH3-R, but the resistance of PH3-R to hypoxia and hypercarbia was lower than that of HCLO-R to PH3. The difference of the overlapping and separate values indicated that there were differences in the intercross-resistance of four resistant strains.

Geographic variation in cypermethrin insecticide resistance and morphometry in Spodoptera litura(Fabricius)(Lepidoptera:Noctuidae)

Objective:To find out the most resistant strain of Spodoptera litura(S.litura)from Tamil Nadu,Kerala and Karnataka by synthetic insecticide treatment.Methods:Using leaf disc no-choice method,the insects were tested with different doses for pesticides.The LC_(50)and LC_(90)values were calculated by probit analysis.Results:In the insect bioassay,the cypermethrin insecticide showed significantly higher LC_(50)values of 14.699 g/L and 15.738 g/L against the Tamil Nadu and Kerala S.litura insect cultures respectively.The body length of 2nd,3rd and 4th instar larvae were significantly higher(P≤0.05)in TTP insect population[(19.2±2.3)mm,(28.05±3.20)mm,(36.1±2.0)mm],when compared with KTK[(18.5±2.7)mm,(23.38±2.00)mm,(31.75±2.70)mm]and control,KBB[(15.65±2.30)mm,(23.65±2.70)mm,(33.2±2.2)mm]populations.The body breadth of 3rd instar larvae was significantly higher(P≤0.05)in TTP insect population(4.9±1.1)mm,when compared with KTK(3.93±0.80)mm and control,KBB(3.65±0.70)mm populations.Conclusions:The present study clearly showed that field collected strains were highly resistant when compared to control.Based on our study,we conclude that reduced use of synthetic pesticides is necessary and IPM is a better way to reduce the development of pesticide resistance among strains of S.litura.