Insecticide resistance of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), in mainland China

BACKGROUND: In order to investigate the extent of resistance of oriental fruit fly, Bactrocera dorsalis (Hendel), which is a widespread pest throughout tropical, subtropical and temperate fruit crops, 25 populations of this insect were collected from 13 sites in mainland China in 2007 and 2008. In addition, resistant strains were established that showed increasing development of resistance. RESULTS: Compared with the susceptible strain, one population of B. dorsalis expressed high resistance (RR = 70.4‐fold), 16 populations expressed medium resistance (11.5‐fold < RR < 25.8‐fold) and eight populations had low resistance or remained susceptible (1.4‐fold < RR < 8.9‐fold) to trichlorphon. As regards β‐cypermethrin, one population showed high resistance (RR = 44.0‐fold), nine populations expressed medium resistance (12.2‐fold < RR < 28.4‐fold), 14 populations expressed low or minor resistance (3.0‐fold < RR < 9.7‐fold) and one population remained susceptible (RR = 1.1‐fold). As regards avermectin, five populations had developed high resistance (44.3‐fold < RR < 104‐fold), seven populations expressed medium resistance (11.4‐fold < RR < 38.6‐fold) and three populations expressed low or minor resistance (3.5‐fold < RR < 5.6‐fold). A continuous resistance selection in the laboratory strain showed that the resistance ratios to trichlorphon, β‐cypermethrin and avermectin were 71.6‐fold, 333‐fold and 70.4‐fold respectively. CONCLUSION: The data provided a comprehensive survey of insecticide resistance in Bactrocera dorsalis in mainland China. All results suggested that early resistance management programmes should be established for restoring the efficacy of pesticide‐based control measures. Copyright © 2010 Society of Chemical Industry     

Susceptibility to neonicotinoids and risk of resistance development in the brown planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae)

BACKGROUND: In recent years, outbreaks of the brown planthopper, Nilaparvata lugens (Stål), have occurred more frequently in China. The objective of this study was to determine the susceptibility of N. lugens to neonicotinoids and other insecticides in major rice production areas in China. RESULTS: Results indicated that substantial variations in the susceptibility to different insecticides existed in N. lugens. Field populations had developed variable resistance levels to neonicotinoids, with a high resistance level to imidacloprid (RR: 135.3–301.3‐fold), a medium resistance level to imidaclothiz (RR: 35–41.2‐fold), a low resistance level to thiamethoxam (up to 9.9‐fold) and no resistance to dinotefuran, nitenpyram and thiacloprid (RR < 3‐fold). Further examinations indicated that a field population had developed medium resistance level to fipronil (up to 10.5‐fold), and some field populations had evolved a low resistance level to buprofezin. In addition, N. lugens had been able to develop 1424‐fold resistance to imidacloprid in the laboratory after the insect was selected with imidacloprid for 26 generations. CONCLUSION: Long‐term use of imidacloprid in a wide range of rice‐growing areas might be associated with high levels of resistance in N. lugens. Therefore, insecticide resistance management strategies must be developed to prevent further increase in resistance. Copyright © 2008 Society of Chemical Industry     

Inheritance mode and realized heritability of resistance to imidacloprid in the brown planthopper,Nilaparvata lugens (Stål) (Homoptera: Delphacidae)

BACKGROUND: The brown planthopper, Nilaparvata lugens (Stål), is a serious pest that causes enormous losses to the rice crop in Asia. The genetic basis of imidacloprid resistance was investigated in N. lugens. RESULTS: The resistant strain, selected for imidacloprid resistance from a field population of N. lugens collected from Nanjing, Jiangsu Province, China, showed a 964‐fold resistance compared with the laboratory strain. Progenies of reciprocal crosses (F₁ and F₁′) showed similar dose–mortality responses (LC₅₀) to imidacloprid, and also exhibited a similar degree of dominance (D), 0.58 for F₁ and 0.63 for F₁′. Chi‐square analyses of self‐bred and backcross progenies (F₂, F₂′ and BC respectively) rejected the hypothesis for a single gene control of the resistance. The estimated realized heritability (h²) of imidacloprid resistance was 0.1141 in the resistant strain of N. lugens. CONCLUSION: The results showed that imidacloprid resistance in N. lugens was autosomal and was expressed as an incompletely dominant trait, probably controlled by multiple genes. Copyright © 2009 Society of Chemical Industry     

Neonicotinoid resistance in rice brown planthopper, Nilaparvata lugens

BACKGROUND: Rice brown planthopper, Nilaparvata lugens Stål, is a primary insect pest of cultivated rice, and effective control is essential for economical crop production. Resistance to neonicotinoid insecticides, in particular imidacloprid, has been reported as an increasing constraint in recent years. In order to investigate the extent of resistance, 24 samples of N. lugens were collected from China, India, Indonesia, Malaysia, Thailand and Vietnam during 2005 and 2006. Their responses to two diagnostic doses of imidacloprid (corresponding approximately to the LC₉₅ and 5 × LC₉₅ of a susceptible strain) were examined. RESULTS: Ten of the 12 samples collected during 2005 were found to be susceptible to imidacloprid, but two late‐season samples from India showed reduced mortality at both diagnostic doses. All 13 strains collected in 2006 showed reduced mortality at both doses when compared with the susceptible strain. Dose–response lines showed resistance in one of the most resistant field strains to be approximately 100‐fold compared with the susceptible standard. CONCLUSION: The data demonstrate the development and spread of neonicotinoid resistance in N. lugens in Asia and support reports of reduced field efficacy of imidacloprid. Copyright © 2008 Society of Chemical Industry     

Genetic diversity of sulfonylurea-resistant and -susceptible Monochoria vaginalis populations in Japan

Monochoria vaginalis is one of the most serious weeds of rice fields in Asia. The species is predominantly selfing. To reveal the potential for multiple mutational events, outcrossing and gene flow in the sulfonylurea‐resistant (SU‐R) M. vaginalis populations, we investigated (i) if each SU‐R population was a single SU‐R biotype or a mixture of several SU‐R biotypes using restriction analysis or direct sequencing of acetolacatate synthase (ALS) genes and (ii) genetic diversity of SU‐R and ‐susceptible (S) populations using amplified fragment length polymorphism (AFLP) analysis. Nineteen or 20 individuals were sampled from four SU‐R and five SU‐S populations respectively. Amino acid substitutions conferring resistance in the SU‐R populations were Pro₁₉₇Ser in the ALS1 or ALS3, or Asp₃₇₆Glu in the ALS1 and each SU‐R population was composed of a single SU‐R biotype. In cluster analysis each SU‐R individual formed a cluster, whereas the individuals from a SU‐S population belonged to different clusters. Some SU‐R populations showed polymorphic AFLP loci. The results indicated that these SU‐R biotypes emerged from a single mutational event and any gene flow of SU‐R genes from adjacent populations did not occur. A low level of outcrossing and recombinations of SU‐R genes occurred within some SU‐R populations of M. vaginalis.     

Occurrence of sulfonylurea resistance in Sagittaria trifolia,a basal monocot species,based on target‐site and non‐target‐site resistance

Sagittaria trifolia L. is one of the most serious weeds in paddy fields in Japan. Since the late 1990s, severe infestations of S. trifolia have occurred following applications of sulfonylurea herbicides in Akita prefecture. In this study, two accessions of S. trifolia, R1 and R2, were collected from paddy fields with severe infestations and their resistance profiles were determined in comparison to a susceptible accession, S1. R1 and R2 were highly resistant to bensulfuron‐methyl. R1 was also highly resistant to pyrazosulfuron‐ethyl, but R2 was susceptible. Relative to S1, R1 had an amino acid substitution at the Pro₁₉₇ residue of acetolactate synthase (ALS), a well‐known mutation that confers sulfonylurea resistance, suggesting that R1 has a target‐site‐based resistance (TSR) mechanism. The sequence of the ALS gene in R2 was identical to that in S1. A Southern blot analysis indicated that there was only one copy of the ALS gene in S1 and R2. These results suggest that R2 has a non‐target‐site‐based resistance (NTSR) mechanism. R2 was moderately resistant to imazosulfuron but susceptible to thifensulfuron‐methyl. R2 and S1 were susceptible to pretilachlor, benfuresate, MCPA‐ethyl and bentazon. The results reveal the occurrence of two sulfonylurea‐resistant biotypes of S. trifolia that show different mechanisms of cross‐resistance to sulfonylureas related to TSR in R1 and NTSR in R2.     

Assessment of two biotypes of Solanum ptycanthum that differ in resistance levels to imazamox

Glasshouse and laboratory experiments were conducted on acetolactate synthase (ALS) homozygous resistant Solanum ptycanthum biotypes from Illinois (IL‐R) and Indiana (IN‐R), and homozygous susceptible biotypes from Illinois (IL‐S) and Indiana (IN‐S). Genetic similarity of biotypes was assessed by random amplified polymorphic DNA (RAPD) markers, which determined that the Illinois biotypes are more similar to each other than to the IN‐R biotype. ALS enzyme activity from the IL‐R and IN‐R biotypes had I₅₀ values of 362 and 352 μM imazamox respectively. Dose–response experiments using three‐ to four‐leaf‐stage plants of the IL‐R and IN‐R biotypes had GR₅₀ values of 242 and 69 g ae ha⁻¹ imazamox respectively. Whole‐plant and ALS enzyme results are different than previously reported values in the literature, which was attributed in the current study to the original IN‐R population having individuals that were segregating for ALS resistance. Metabolism studies showed no difference in percentage [¹⁴C]imazamox remaining between the IL‐R and IN‐R biotypes up to 72 h after treatment. The IL‐S biotype metabolised [¹⁴C]imazamox approximately two times faster than the IL‐R and IN‐R biotypes and this trait was heritable. Response of F₃ plants containing homozygous ALS‐resistant alleles from the IL‐R biotype in a genetic background of 50% Illinois and 50% Indiana biotypes suggests that genetic factors other than an altered target site or metabolism may also contribute to the magnitude of resistance at the whole‐plant level in resistant biotypes.     

Molecular analysis of pyrethroid resistance conferred by target insensitivity and increased metabolic detoxification in Plutella xylostella

BACKGROUND: The pyrethroid resistance of the diamondback moth Plutella xylostella (L.) is conferred by increased gene expression of cytochrome P450 to detoxify the insecticide and/or through gene mutation of the sodium channel, which makes the individual insensitive to pyrethroids. However, no information is available about the correlation between the increased metabolic detoxification and the target insensitivity in pyrethroid resistance. RESULTS: Frequencies of pyrethroid‐resistant alleles (L1014F, T929I and M918I) and two resistance‐related mutations (A1101T and P1879S) at the sodium channel and expression levels of the cytochrome P450 gene CYP6BG1 were examined individually using laboratory and field strains of P. xylostella. Real‐time quantitative PCR analysis using the laboratory strains revealed that levels of larval expression of the resistant strain, homozygous for the pyrethroid‐resistant alleles other than the M918I, are significantly higher than those of the susceptible strain. In the field strains, the expression levels in insects having the same resistant alleles as those of the resistant strains varied greatly among individuals. The expression levels were not significantly higher than those in the heterozygotes. CONCLUSION: Significant correlation between the target insensitivity and the increased metabolic detoxification in pyrethroid resistance of P. xylostella was observed in the laboratory but not in the field. Copyright © 2010 Society of Chemical Industry     

Characterization of field‐evolved resistance to Bacillus thuringiensis‐derived Cry1F δ‐endotoxin in Spodoptera frugiperda populations from Argentina

BACKGROUND

Transgenic maize (Zea mays L.) event TC1507 (Herculex^® I insect protection), expressing Cry1F δ‐endotoxin derived from Bacillus thuringiensis var. aizawai, was commercialized in 2003 in the Americas. Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) susceptibility to Cry1F was monitored annually across several regions in Argentina using diagnostic concentration bioassays. Reduced performance of TC1507 maize against S. frugiperda was reported in 2013. A resistant population was established in the laboratory and the dominance of Cry1F resistance was characterized.

RESULTS

During 2012–2015, high‐survivorship of several populations was observed in the resistance monitoring program. Reciprocal crosses of a Cry1F‐resistant population with a Cry1F‐susceptible population were evaluated to calculate effective dominance (D_ML) based on mortality levels observed at 100 µg/ml Cry1F. Two additional dominance levels (D_LC and D_EC) were calculated using lethal (LC₅₀) or effective concentration (EC₅₀) derived from concentration–response bioassays. Estimates indicated that Cry1F resistance in S. frugiperda in Argentina was either highly recessive (D_ML = 0.005) or incompletely recessive (D_LC < 0.26 and D_EC < 0.19).

CONCLUSION

This study is the first documented confirmation and characterization of S. frugiperda Cry1F field‐evolved resistance in Argentina. The resistance to Cry1F in S. frugiperda populations collected in Argentina, is autosomal and incompletely recessive similar to the resistance reported in Brazil. © 2017 The Authors. Pest Management Science published by John Wiley © Sons Ltd on behalf of Society of Chemical Industry.     

Buprofezin susceptibility survey, resistance selection and preliminary determination of the resistance mechanism in Nilaparvata lugens (Homoptera: Delphacidae)

BACKGROUND: Buprofezin has been used for many years to control Nilaparvata lugens (Stål). Assessment of susceptibility change in the insect is essential for maintaining control efficiency and resistance management. RESULTS: Eleven‐year surveys showed that most field populations were susceptible before 2004. However, substantially higher levels of resistance (up to 28‐fold) were found in most of the rice fields in China after 2004. A field population was collected and periodically selected for buprofezin resistance in the laboratory. After 65 generations (56 were selected), the colony successfully obtained 3599‐fold resistance to buprofezin. Synergism tests showed that O,O‐diethyl‐O‐phenyl phosphorothioate (SV1), piperonyl butoxide (PBO) and diethyl maleate (DEM) increased buprofezin toxicity in the resistant strain by only 1.5–1.6 fold, suggesting that esterases, P450‐monooxygenases and glutathione S‐transferases had no substantial effect on buprofezin resistance development. CONCLUSION: The results from this study indicate that N. lugens has the potential to develop high resistance to buprofezin. A resistance management program with rotation of buprofezin and other pesticides may efficiently delay or slow down resistance development in the insect. Further investigation is also necessary to understand the resistance mechanisms in N. lugens. Copyright © 2008 Society of Chemical Industry     

基于转录组数据的害虫抗药性综合检测方法

为建立基于转录组数据的害虫抗药性检测方法,以3种重要害虫家蝇Musca domestica、白纹伊蚊Aedes albopictus和小菜蛾Plutella xylostella的8个抗性/敏感种群的转录组数据为对象,使用已开发的乙酰胆碱酯酶抗性突变检测程序ACE检测不同种群中的乙酰胆碱酯酶抗药性突变,并使用Bowtie 2软件和R程序包DESeq2检测其解毒酶基因的表达量变化,分析这3种害虫对有机磷类和氨基甲酸酯类杀虫剂的抗性分子基础。结果显示,在家蝇2个抗性种群KS8S3和ALHF中检测到ace2基因上发生了G227A抗药性突变,突变频率分别为0.318和1.000;在白纹伊蚊抗性种群Tem-GR中检测到CCEae3a基因的表达量较敏感种群Par-GR上调了7.175倍;在小菜蛾抗性种群ZZ中检测到ace1基因上发生A201S和G227A抗药性突变,突变频率分别为0.656和0.692。根据上述突变频率和解毒酶基因表达量变化评估的3种害虫种群抗药性情况与其之前的报道基本相符,表明基于转录组数据同时对靶标抗性机制和代谢抗性机制进行检测的害虫抗药性综合检测方法可以很好地反映害虫种群的抗药性状况。     

Field-evolved resistance to Bt toxin Cry1Ac in the pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), from India

BACKGROUND: The pink bollworm is one of the most destructive pests of cotton. Transgenic cotton producing Bt toxin Cry1Ac or a combination of Cry1Ac and Cry2Ab2 has been used effectively against this pest. However, some other insects have evolved resistance to Bt toxins in the field. During the 2007–2008 and 2008–2009 seasons, pink bollworm populations in India were surveyed to evaluate their responses to Cry1Ac and seed powder containing Cry1Ac and Cry2Ab2. RESULTS: The results provide evidence that resistance to Cry1Ac had evolved by 2008 in a population sampled from non‐Bt cotton in the Amreli district of Gujarat in western India. The median lethal concentration of Cry1Ac for five‐day‐old larvae (LC₅₀) was significantly higher for insects derived in 2008 from Amreli than for any of the other field populations tested from four locations in India. For Cry1Ac, the mean LC₅₀ for the strain derived from Amreli in 2008 was 44 times higher than for the most susceptible population. However, for seed powder of Bollgard II containing primarily Cry2Ab2, the 2008 Amreli population was only slightly less susceptible than the most susceptible population. CONCLUSIONS: The data reported here constitute the first evidence of field‐evolved resistance of pink bollworm to Cry1Ac. This initial evidence spurred more extensive evaluations during the 2009–2010 growing season, which confirmed field‐evolved resistance to Cry1Ac in Amreli. The lack of cross‐resistance to Cry2Ab2 suggests that plants producing this toxin are likely to be more effective against resistant populations than plants producing only Cry1Ac. Copyright © 2011 Society of Chemical Industry     

Inheritance of resistance in <Emphasis Type="Italic">Solanum nigrum</Emphasis> to <Emphasis Type="Italic">Phytophthora infestans</Emphasis>

Solanum nigrum, black nightshade, is a wild non-tuber bearing hexaploid species with a high level of resistance to Phytophthora infestans (Colon et al. 1993), the causal agent of potato late blight, the most devastating disease in potato production. However, the genetic mode of resistance in S. nigrum is still poorly understood. In the present study, two S. nigrum accessions, 984750019 (N19) and #13, resistant (R) and susceptible (S), respectively, to three different isolates of P. infestans, were sexually crossed. The various kinds of progeny including F1, F2, F3, and backcross populations (BC₁; F1 × S), as well as two populations produced by self-pollinating the R parent and S parent, were each screened for susceptibility to P. infestans isolate MP 324 using detached leaf assays. Fifty seedling plant individuals of the F1 progeny were each resistant to this specific isolate, similarly to the seedling plants resulting from self-pollination of the resistant R parent. Thirty seedling plants obtained from self-pollination of the S parent were susceptible. Among a total of 180 F2 plants, the segregation ratio between resistant and susceptible plants was approximately 3: 1. Among the 66 seedling plants of the BC₁ progeny originating from crossing an F1 plant with the susceptible S parent, there were 26 susceptible and 40 resistant plants to P. infestans. The segregation patterns obtained indicated monogenic dominant inheritance of resistance to P. infestans isolate MP 324 in S. nigrum acc. 984750019. This gene, conferring resistance to P. infestans, may be useful for the transformation of potato cultivars susceptible to late blight.     

Evaluation of field resistance in field-collected mosquito Culex quinquefasciatus Say through quantification of ULV permethrin/PBO formulation in field bioassays

BACKGROUND

Pyrethroids are among the most applied adulticides worldwide to control mosquito vectors for prevention of arboviral diseases transmission. However, pesticide resistance development in a mosquito population could lead to decreased control efficacy. While most studies investigate the resistant genotype (i.e. kdr, CYP450, etc.) as explanatory variables, few field efficacy studies have measured pesticide quantities deposited at different distances from the sprayer in association with observed mosquito mortality. The current study determined field delivered amounts of an applied ULV permethrin/PBO formulation (31% permethrin + 66% piperonyl butoxide) by GC/MS and estimated practical resistance ratios using caged mosquito females.

RESULTS

For field samples, the extraction method recovered 78 ± 3.92–108 ± 8.97% of the permethrin/PBO formulation when utilizing the peaks of PBO from GC/MS to estimate the concentrations of adulticide deposited near the mosquito cages. The field bioassay showed that the spatial distribution of permethrin/PBO formulation was heterogeneous among three pseudo-replicates within the same distance. Within the quantifiable permethrin/PBO range of 15.7–51.4 ng/cm², field-collected mosquito mortalities started at 64% and linearly increased reaching 100% only in two areas, while all Sebring susceptible mosquitoes died. The field LC₉₅ resistance ratio (RR) of F₀ Cx. quinquefasciatus ranged from 2.65–3.51, falling within the 95% CI of RR₉₅ estimated by laboratory vial assays. Tests with and without PBO indicated P450's enzymes contributed to field resistance.

CONCLUSION

Results showed the suitability of the collection and quantification method to estimate the field resistance ratio at the applied pesticide rate. Pesticide quantification would also allow the association of the known frequencies of resistance mechanisms (e.g. kdr, CYP450) with field mortalities to estimate the resistance level conferred by such mechanisms. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Multifactorial resistance to transpermethrin in field-collected strains of the tobacco budworm Heliothis virescens F.

The penetration, degradation and excretion of [³H]transpermethrin were examined in susceptible and field-collected pyrethroid-resistant strains of the tobacco budworm Heliothis virescens. No consistent differences in labelled materials excreted or recovered in cuticle rinses were found between the resistant (R) and susceptible (S) larvae. Considerably lower levels of the parent compound were present internally in R compared with S larvae after 24h (P <0.01), clearly identifying a metabolic resistance mechanism in Meloland and Westmorland larvae. Moderate levels of absorbed permethrin accompanied by an absence of poisoning symptoms were observed in certain individuals of both R strains, suggesting a second resistance mechanism. Neurobioassays of R larvae showed a consistently lower sensitivity of the neuromuscular system to pyrethroids when compared with the S larvae, thus confirming the indication from metabolic studies of the additional (site-insensitive) mechanism. Toxicity values suggest a cross-resistance to other pyrethroids.     

Microarray analysis of global gene regulation in the Cry1Ab-resistant and Cry1Ab-susceptible strains of Diatraea saccharalis

BACKGROUND: Extensive adoption of transgenic Bt corn in recent years for stalk borer control has increased risk of resistance evolution in the target pest populations. A Bt‐resistant strain of the sugarcane borer, Diatraea saccharalis, was approximately 100‐fold more tolerant to Cry1Ab toxin than the susceptible counterpart. To gain a better understanding of the molecular mechanisms of Bt resistance, the Cry1Ab‐susceptible (Cry1Ab‐SS) and Cry1Ab‐resistant (Cry1Ab‐RR) strains of D. saccharalis were subjected to a microarray analysis. RESULTS: Results showed that the expression levels of many genes were significantly different between the Cry1Ab‐RR and Cry1Ab‐SS strains. Microarray analysis of 7145 cDNAs revealed 384 differentially expressed genes. A total of 273 genes were significantly upregulated 2–51.6‐fold, and 111 genes were significantly downregulated 2–22.6‐fold in the Cry1Ab‐RR strain. The upregulation of three potential resistance‐related genes, coding for a glutathione S‐transferase (GST), a chymotrypsin‐like protease (CHY) and a lipase (LP), was confirmed using real‐time PCR, indicating a reproducibility of the microarray data. Ontology analysis revealed that more than twice the number of metabolic‐related genes were upregulated compared with downregulated genes with the same biological function. Up to 35.2% of the upregulated genes in the resistant strain were associated with catalytic activity, while only 9.5% of the downregulated genes were related to the same catalytic molecular function. CONCLUSION: The large portion of metabolic‐ or catalytic‐related genes with significant upregulations indicated a potential large increase in metabolic or catalytic activities in the Cry1Ab‐RR strain. This cDNA microarray gene expression data could be used to characterize and identify new genes that may be associated with Bt resistance in D. saccharalis. Copyright © 2012 Society of Chemical Industry     

Resistance to paraquat in Mazus pumilus

Mazus pumilus is an annual self‐pollinating weed that is commonly found in arable land, vegetable gardens and roadsides. This weed harbours insects and pathogens that attack vegetables. The mechanism of resistance to paraquat of M. pumilus found in Ohita, Japan, was studied. Whole plant bioassays revealed that the resistant (R) biotypes were four to six times less susceptible than controls. Chlorophyll destruction of leaf discs by paraquat treatment in R biotypes was 4–20 times lower than those of susceptible (S) biotypes. Ferric reducing antioxidant power (FRAP) values in R biotypes were higher than those of S biotypes before and after paraquat treatments. The activity of superoxide dismutase (SOD) was also higher in R biotypes than those of S biotypes before and after treatment with paraquat, but the activities of ascorbate peroxidase (APX) and catalase (CAT) were not different between R and S biotypes. Change of ascorbate (AsA) contents before and after paraquat treatment was equivalent in both biotypes. These results indicate that the increased SOD activity and antioxidant capacity in R biotypes contribute to the resistance to paraquat of M. pumilus.     

Metabolic resistance mechanisms to phosalone in the common pistachio psyllid, Agonoscena pistaciae (Hem.: Psyllidae)

The common pistachio psyllid, Agonoscena pistaciae, is the most damaging pest of pistachio in Iran, and is generally controlled by insecticides belonging to various classes especially, phosalone. The toxicity of phosalone in nine populations of the pest was assayed using the residual contact vial and insect-dip methods. The bioassay results showed significant discrepancy in susceptibility to phosalone among the populations. Resistance ratio of the populations to the susceptible population ranged from 3.3 to 11.3. The synergistic effects of TPP, PBO and DEM were evaluated on the susceptible and the most resistant population to determine the involvement of esterases, mixed function oxidases and glutathione S-transferases in resistance mechanisms, respectively. The level of resistance to phosalone in the resistant population was suppressed by TPP, PBO and DEM, suggesting that the resistance to phosalone is mainly caused by esterase detoxification. Biochemical enzyme assays revealed that esterase, glutathione S-transferase and cytochrome P450 monooxygenase activities in the resistant population was higher than that in the susceptible. Glutathione-S-transferases play a minor role in the resistance of the pest to phosalone.     

Fitness costs of laboratory-selected imidacloprid resistance in the brown planthopper, Nilaparvata lugens Stål

Imidacloprid has been used as a key insecticide to control the brown planthopper, Nilaparvata lugens Stål, for several years, but no obvious resistance has been identified in field populations as yet. To evaluate the risk, a field population was collected and selected with imidacloprid in the laboratory. After 37‐generation selection a strain with 250‐fold resistance had been successfully achieved. Fitness analysis by constructing life tables demonstrated that resistant hoppers had obvious disadvantages in their reproduction. The fitness of highly resistant hoppers had decreased dramatically (0.169 and 0.104) to only one‐fifth to one‐tenth of that of the susceptible strain. Hence it was concluded that the brown planthopper had the potential to develop high resistance to imidacloprid but that the lower fitness of resistant hoppers could result in a quick recovery of sensitivity when the population did not come into contact with imidacloprid. This means that a reasonable resistance management programme with less imidacloprid use may efficiently delay or even stop resistance development. Copyright © 2006 Society of Chemical Industry