Insecticide susceptibility of Ephemera orientalis (Ephemeroptera: Ephemeridae) and two mosquito species,Anopheles sinensis and Culex pipiens in the Republic of Korea

Field-collected populations of mayflies, Ephemera orientalis were tested for susceptibility to 10 different insecticides using a direct-contact mortality bioassay. Ephemera orientalis subimagoes were susceptible to the insecticides chlorpyrifos, fenitrothion and chlorfenapyr with LD₅₀ values of 69.7, 78.8 and 81.9 μg/♀, and adults had LD₅₀ values of 71.9, 78.8 and 85.4 μg/♀, respectively. Susceptibility ratios (SRs) of subimagoes and adults of E. orientalis to the 10 insecticides were 1.0 to1.2 folds. The mayflies showed higher susceptibility to organophosphates than to pyrethroids. The SRs of Anopheles sinensis to E. orientalis were 514 to 1438 folds higher for organophosphates (LD₅₀ values of 0.05 to 0.23 μg/♀) and 62 to 1155 folds higher for pyrethroids (LD₅₀ values of 0.13 to 2.41 μg/♀). The SRs of Culex pipiens to E. orientalis were 606 to 3595 folds higher for organophosphates with LD₅₀ values of 0.02–0.17 μg/♀ and 81 to 1365 folds higher for pyrethroids with LD₅₀ values of 0.11–1.83 μg/♀. These results indicate that the use of ineffective insecticides will result in unsatisfactory control against field populations of the subimagoes and adults of E. orientalis.     

Fenitrothion: an alternative insecticide for the control of deltamethrin‐resistant populations of Triatoma infestans in northern Argentina

Deltamethrin‐based campaigns to control Triatoma infestans (Klug) (Hemiptera: Reduviidae) have decreased in success as a result of the development of insecticide resistance. We compared the in vitro effects of the pyrethroid deltamethrin and two doses of the organophosphate fenitrothion, presented on different materials, on T. infestans from La Esperanza, Argentina. Laboratory tests demonstrated a decrease in susceptibility to deltamethrin in the field population [LD₅₀: 30.32 nanograms per insect (ng/i)] compared with the reference population (LD₅₀: 0.13 ng/i), giving a high resistance ratio of 233.42. By contrast, similar susceptibility to fenitrothion was assessed in both the field and reference populations (LD₅₀: 21.65 ng/i and 21.38 ng/i, respectively). The effectiveness of the formulated insecticides varied according to the surfaces to which they were applied. The application of fenitrothion formulations to glass or brick resulted in mortality of 90–100%. The application of fenitrothion formulations to wood or mud caused mortality in the range of 6.7–56.7%. Resistant insects presented low mortality when exposed to the deltamethrin formulation and high mortality when exposed to fenitrothion formulations. Moreover, the insecticides demonstrated residual activity only when applied to glass. The present work demonstrates that fenitrothion is an alternative to pyrethroids for the management of deltamethrin‐resistant insects in La Esperanza. However, this effectiveness is not sustained over time.     

The Wiggle Index: An Open Source Bioassay to Assess Sub-Lethal Insecticide Response in Drosophila melanogaster

Toxicological assays measuring mortality are routinely used to describe insecticide response, but sub-lethal exposures to insecticides can select for resistance and yield additional biological information describing the ways in which an insecticide impacts the insect. Here we present the Wiggle Index (WI), a high-throughput method to quantify insecticide response by measuring the reduction in motility during sub-lethal exposures in larvae of the vinegar fly Drosophila melanogaster. A susceptible wild type strain was exposed to the insecticides chlorantraniliprole, imidacloprid, spinosad, and ivermectin. Each insecticide reduced larval motility, but response times and profiles differed among insecticides. Two sets of target site mutants previously identified in mortality studies on the basis of imidacloprid or spinosad resistance phenotypes were tested. In each case the resistant mutant responded significantly less than the control. The WI was also able to detect a spinosad response in the absence of the primary spinosad target site. This response was not detected in mortality assays suggesting that spinosad, like many other insecticides, may have secondary targets affecting behaviour. The ability of the WI to detect changes in insecticide metabolism was confirmed by overexpressing the imidacloprid metabolizing Cyp6g1 gene in digestive tissues or the central nervous system. The data presented here validate the WI as an inexpensive, generic, sub-lethal assay that can complement information gained from mortality assays, extending our understanding of the genetic basis of insecticide response in D. melanogaster.     

Development and stability of insecticide resistance in the leafminer Liriomyza trifolii (Diptera: Agromyzidae) to cyromazine, abamectin, and spinosad

Three populations of the leafminer, Liriomyza trifolii (Burgess), were collected from commercial ornamental production greenhouses in the United States and tested for susceptibility to three commercial insecticides. A leaf dip bioassay of leaves containing young (1-2-d-old) larvae was used. Based on larval mortality and compared with a susceptible laboratory reference colony, the three strains varied in spectrum and level of resistance to the insecticides. CA-1, collected from Gerbera daisy, was moderately resistant to cyromazine (18.1-fold) and abamectin (22.0-fold), but highly resistant to spinosad (> 188-fold). CA-2, collected from chrysanthemums, was not resistant to abamectin, had a low level of resistance to cyromazine (8.2-fold), but was extremely resistant to spinosad (1,192-fold). GA-1, collected from chrysanthemums, had very low levels of resistance to cyromazine (5.4-fold) and spinosad (1.9-fold) but was moderately resistant to abamectin (30.6-fold). When reared in the absence of insecticide selection pressure, all three strains reverted to approximately the level of the reference strain. The CA-1 strain reverted in nine generations to cyromazine; however, the lowest levels of abamectin and spinosad resistance reverted to was 3.1-fold at F8 and 3.2 at the F10, respectively. The CA-2 strain reverted in five generations to both cyromazine and spinosad. GA-1 reverted in five generations to abamectin. Based on the results, resistance to these three insecticides was unstable. Additionally, there was no cross-resistance among these three insecticides.     

Mortality and knockdown effects of imidacloprid and methomyl in house fly (Musca domestica L., Diptera: Muscidae) populations

In this study, the knockdown and mortality effects of imidacloprid and methomyl were investigated. The residual surface applications were carried out to determine the knockdown effects (KDt₅₀ and KDt₉₅) and mortality (LD₅₀ and LD₉₅) induced by each insecticide. For mortality comparisons, the susceptible house fly (Musca domestica L., Diptera: Muscidae) of a WHO population and three natural field‐collected M. domestica populations from Turkey were used. In conclusion, it was found that the resistance to imidacloprid and methomyl was significantly higher in the field populations when compared to the susceptible population from WHO. The results showed that applicators and pest management decision‐makers should control and conduct an integrated pest management strategy by including biological agents to prevent the development of high levels of resistance in the field populations.     

The impact of insecticides applied in apple orchards on the predatory mite Kampimodromus aberrans (Acari: Phytoseiidae)

Kampimodromus aberrans is an effective predatory mite in fruit orchards. The side-effects of insecticides on this species have been little studied. Field and laboratory experiments were conducted to evaluate the effects of insecticides on K. aberrans. Field experiments showed the detrimental effects of etofenprox, tau-fluvalinate and spinosad on predatory mites. Spider mite (Panonychus ulmi) populations reached higher densities on plots treated with etofenprox and tau-fluvalinate than in the other treatments. Single or multiple applications of neonicotinoids caused no detrimental effects on predatory mites. In the laboratory, spinosad and tau-fluvalinate caused 100 % mortality. Etofenprox caused a significant mortality and reduced fecundity. The remaining insecticides did not affect female survival except for imidacloprid. Thiamethoxam, clothianidin, thiacloprid, chlorpyrifos, lufenuron and methoxyfenozide were associated with a significant reduction in fecundity. No effect on fecundity was found for indoxacarb or acetamiprid. Escape rate of K. aberrans in laboratory was relatively high for etofenprox and spinosad, and to a lesser extent thiacloprid. The use of etofenprox, tau-fluvalinate and spinosad was detrimental for K. aberrans and the first two insecticides induced spider mite population increases. The remaining insecticides caused no negative effects on predatory mites in field trials. Some of them (reduced fecundity and repellence) should be considered with caution in integrated pest management programs.     

褐飞虱对五种杀虫剂抗性的快速检测技术

【目的】建立褐飞虱Nilaparvata lugens对常用杀虫剂抗性的快速检测技术,实时掌握田间褐飞虱种群的抗药性水平,以指导褐飞虱防控合理用药。【方法】基于玻璃瓶药膜法,研制褐飞虱3龄若虫对吡虫啉、啶虫脒、醚菊酯、毒死蜱和异丙威5种杀虫剂抗性的快速检测试剂盒;利用试剂盒测定的死亡率与稻苗浸渍法测得的抗性倍数进行相关性分析,并验证利用试剂盒快速测定褐飞虱田间种群对5种杀虫剂 抗性水平的准确性。【结果】处理1 h时吡虫啉、啶虫脒、醚菊酯、毒死蜱和异丙威对褐飞虱室内敏感种群3龄若虫的LD₉₀分别为：30.96, 92.05, 117.24, 514.21和1.24 ng/cm²。在吡虫啉、啶虫脒、醚菊酯、毒死蜱和异丙威相应诊断剂量下,贵州省不同田间种群褐飞虱3龄若虫的校正死亡率分别在23.75%~78.75%, 25.00%~78.75%, 43.75%~88.75%, 36.25%~85.00%和18.75%~67.50%之间。相关性分析表明,上述田间种群褐飞虱3龄若虫的死亡率与稻苗浸渍法测定的抗性倍数呈显著负相关,相关系数在0.8751~0.9754之间。通过快速检测试剂盒获得的死亡率及相关性方程计算得到贵州安龙地区(AL)褐飞虱种群对吡虫啉、啶虫脒、醚菊酯、毒死蜱和异丙威的推测抗性倍数分别为7.23, 3.68, 4.14, 4.12和31.18,采用稻苗浸渍法测得上述5种杀虫剂的实测抗性倍数分别为6.33, 5.24, 3.71, 4.50和26.56,表明推测抗性倍数与实测的抗性倍数结果表现一致。【结论】该快速检测试剂盒可以通过测定褐飞虱田间种群的死亡率,快速评估褐飞虱田间种群对杀虫剂的抗性水平。     

Insecticide Susceptibility of Field‐collected Blattella germanica (Blattaria: Blattalidae) in Busan,Republic of Korea during 2014

The susceptibility values for field‐collected (BG‐BG) and laboratory (KS‐BG) strains of German cockroaches (BS‐BG), Blattella germanica (L.) to five synthetic pyrethroid and three organophosphate insecticides were assessed by topical application. Both KS‐BG and BS‐BG strains demonstrated the highest levels of susceptibility to deltamethrin with LD₅₀ values of 0.0035 μg/female and 1.5744 μg/female, respectively. The KS‐BG strain demonstrated the lowest susceptibility level to fenthion with an LD₅₀ value of 0.0698 μg/female, while the BS‐BG field population showed the lowest susceptibility to bifenthrin with 4.6811 μg/female. The BS‐BG field population showed resistance levels of 50 to 640 fold higher against the eight pesticides evaluated compared to the KS‐BG strain. The resistance ratios (RR) of the eight pesticides were compared using populations of B. germanica that were collected from the same locality during 2007 and 2014. The field population of B. germanica collected during 2014 demonstrated significantly high resistance to an organophosphates and all pyrethroids when compared with those collected during 2007, but RR values were <10 except for chlorpyrifos‐methyl and chlorpyrifos with RR values of 74 and 104, respectively.     

Generating susceptible strain and resistance status of field populations of Spodoptera exigua (Lepidoptera: Noctuidae) against some conventional and new chemistry insecticides in Pakistan

Two field populations of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) from Dera Ghazi Khan (D. G. Khan) and Multan, Pakistan, were tested for resistance to the 10 most commonly used insecticides in Pakistan by using a standard leaf disc bioassay on the F1 progeny. For comparison, a susceptible strain was generated from the Multan strain, which displayed lower LC50 values for most of the insecticides, by either mass rearing without exposure to insecticides or single-pair crosses against selected insecticides. The single-pair crosses generated a more susceptible strain than mass rearing. The D. G. Khan field strain was highly resistant to cypermethrin, profenofos, spinosad, abamectin, and chlorpyrifos and moderately resistant to deltamethrin, indoxacarb, and methoxyfenozide compared with susceptible lab strain. The Multan strain was highly resistant to profenofos and indoxacarb. Both field populations were susceptible to emamectin benzoate and lufenuron. Rotating these two insecticides with others that show very low, low, or moderate levels of resistance and have different modes of action may be useful for the effective management of this pest.     

Could resistance to insecticides in Plutella xylostella (Lep., Plutellidae) be overcome by insecticide mixtures?

Abstract: To investigate if synergism occurs between pyrethroids, organophosphates and new insecticides, we tested representatives of these compounds (bifenthrin, chlorpyrifos, spinosad, indoxacarb and emamectin) against the diamondback moth (Plutella xylostella). Larvicidal activity of these insecticides was assessed separately and together on a susceptible strain (Lab‐UK) of P. xylostella as well as a field population collected from Multan. The field population showed significant resistance to chlorpyrifos (331 100‐fold), bifenthrin (45 200‐fold), emamectin (1800‐fold), spinosad (11‐fold) and indoxacarb (5600‐fold) when compared with the Lab‐UK population. When insecticides were mixed based on LC₅₀ and tested at serial concentrations against Lab‐UK, significant synergy (CI < 1) occurred between bifenthrin, spinosad and emamectin. In contrast, the interaction between bifenthrin and indoxacarb was additive (CI = 1). The toxicity of bifenthrin against the field population increased significantly (P < 0.01) when combined with spinosad, emamectin and indoxacarb. Synergistic effects could be attributed to the complementary modes of action by these insecticide classes acting on different components of nerve impulse transmission (which are not identical for bifenthrin and indoxacarb either). However, chlorpyrifos/bifenthrin mixture was not significantly different either from bifenthrin or chlorpyrifos alone, indicating an additive affect. In combination with spinosad and emamectin, tested against the resistant field population, the toxicity of chlorpyrifos increased significantly and even more so with indoxacarb. Mixtures could also give rise to multiple resistance that may extend across other chemical classes and thus become difficult to manage. Therefore, alternative strategies such as mosaics or rotations should be considered. That is, though synergistic effects have been found, this should not be followed up as a strategy to manage resistant field populations.     

Insecticide susceptibility of Culex pipiens pallens (L.) and Aedes albopictus (Skuke) to five commonly used pesticides in the Republic of Korea

Field collected populations of two mosquito species, Culex pipiens pallens and Aedes albopictus, were tested for susceptibility to five pyrethroid insecticides using a topical application bioassay. The laboratory strain of Cx. pipiens pallens (KS‐CP) demonstrated the most and the lowest susceptibility to deltamethrin and d‐cis/trans prallethrine with LD₅₀ values of 0.00022 μg/♀ and 0.00178 μg/♀, respectively, while Ae. albopictus (KS‐AL) showed the greatest and the lowest susceptibility to phthalethrin and deltamethrin with LD₅₀ values of 0.00015 μg/♀ and 0.00085 μg/♀, respectively. Cx. pipiens pallens (JF‐CP) collected at a nearby rice field in Jeonju showed the greatest susceptibility to deltamethrin (LD₅₀ value of 0.0473 μg/♀) and the resistance ratios (RRs) and compared to the laboratory strain were 215 fold greater. JF‐CP demonstrated the lowest susceptibility to d‐cis/trans phenothrin (0.7697 μg/♀) with RRs 711.0 fold greater than the KS‐CP. An Ae. albopictus (JF‐AL) collected at a nearby forest in Jeonju showed the highest susceptibility to deltamethrin (0.00203 μg/♀) with RRs 2.4 fold greater than the KS‐AL. JF‐AL demonstrated the lowest susceptibility to d‐cis/trans prallethrine (LD₅₀ value 0.00646 μg/♀) with RRs 9.4 fold greater than the KS‐AL. JF‐AL demonstrated the greatest resistance to phthalethrin with RRs 39.3 fold greater than the KS‐AL. Resistance ratios of Cx. pipiens pallens between field and laboratory strains ranged from 215.0 to 711.0 and Ae. albopictus ranged from 2.4 to 39.3. These results indicate that the choice of effective insecticides to selected species of mosquito populations will result in more effective control against field strains of mosquito vectors and decrease environmental pollution.     

Spectrum of cross-resistance to insecticides in field samples of the primary sheep blowfly, Lucilia cuprina

Hughes P. B. (1981) Spectrum of cross-resistance to insecticides in field samples of the primary sheep blowfly, Lucilia cuprina. Internationaljournal for Parasitology11:475–479. Resistance to the organophosphorous (OP) insecticide, diazinon, is due to a major gene on chromosome 4. To examine the spectrum of cross-resistance in field populations of Lucilia cuprina, larvae from 41 field samples were exposed to the susceptible discriminating doses of five insecticides. A comparison of the mortalities produced by diazinon to those caused by the other OPs tested (fenthion-ethyl, chlorfenvinphos and coumaphos) indicates that the diazinon resistance gene may confer cross-resistance to other OPs used for blowfly control. However, two samples were found to be resistant to diazinon but susceptible to coumaphos. The OP resistance gene is present at a high frequency in field populations, with a mean frequency of 0–82. Mortalities produced by the carbamate, butacarb, did not relate to those due to diazinon. It seems that a separate mechanism for carbamate resistance is also present in the field. No indication of resistance was found to the insect growth regulator Vetrazin^® in any sample tested.     

Susceptibility of spinosad in Musca domestica (Diptera: Muscidae) field populations

The toxicity of spinosad was determined in one susceptible and five insecticide-resistant laboratory strains of house fly, Musca domestica L. Spinosad was relatively slow-acting, but highly toxic to house flies. In a feeding bioassay, spinosad LC50 at 72 h was 0.51 microg of spinosad per gram of sugar, making it 6.3- and 3.5-fold more toxic to house flies compared with azamethiphos and methomyl, respectively. In topical application bioassay, the LD50 at 48 h of spinosad in susceptible house flies was 40 ng per 20 mg of house fly, making spinosad less toxic than the pyrethroid bioresmethrin synergized by piperonyl butoxide and the organophosphate dimethoate. The insecticide-resistant laboratory strains had resistance factors to spinosad at LC50 in feeding bioassay from 1.5 to 5.5 and at LD50 in topical application bioassay from 2.5 to 4.7, indicating that in house fly cross-resistance to the major insecticide classes will not initially be of major concern for the use of spinosad for house fly control. The toxicity of spinosad was also evaluated against 31 field populations of house flies collected from livestock farms across Denmark. The field populations were 2.2- to 7.5-fold resistant to spinosad at 72 h in feeding bioassay, but based on steep slopes in the bioassay and the limited variation of spinosad toxicity against the various field populations, we consider the field populations to be spinosad-susceptible. We propose a diagnostic dose of 12 microg of spinosad per gram of sugar in feeding bioassay with impregnated sugar for determination of resistant house flies, which is 10x the LC95 of the susceptible strain WHO and approximately = 2x the LD95 of the field populations. Spinosad showed no substantial cross-resistance to the pyrethroid bioresmethrin synergized by piperonyl butoxide, the anticholinesterases dimethoate, azamethiphos, methomyl, and spinosad in house fly field populations.     

Evaluation of biorational insecticides and DNA barcoding as tools to improve insect pest management in lablab bean (Lablab purpureus) in Bangladesh

Lablab bean (Lablab purpureus) is a popular vegetable crop in Bangladesh, but farmers growing this crop experience significant losses to insect pests despite heavy reliance on conventional insecticides. We conducted field studies to improve pest management in lablab bean by testing biorational insecticides as alternatives to conventional insecticides for the control of pod borers (Maruca vitrata) and aphids (Aphis craccivora), and characterizing flower-inhabiting thrips as an emerging pest in this crop. In field experiments, spinosad was the most promising biorational we tested, suppressing pod-boring caterpillars more effectively than thiamethoxam or quinalphos. In contrast, azadirachtin (neem) did not significantly suppress any of the insect pests we measured, although target aphid populations were generally low at our research site. Using DNA barcoding at the coxI locus combined with morphological identification, we found eight thrips taxa inhabiting lablab bean flowers, dominated by Megalurothrips usitatus and M. distalis/peculiaris. A preliminary regression analysis indicated that these flower-inhabiting thrips reduced lablab bean yield. Our results suggest that spinosad may be useful within lablab bean IPM programs, and that these programs will likely need to incorporate tactics against thrips to effectively protect yield. Finally, we found that DNA barcoding was a valuable tool for pest identification in an understudied crop and region, but that to reach its full potential will require an investment in more comprehensive reference libraries.     

Distribution of Pyrethroid Resistant Populations of Triatoma infestans in the Southern Cone of South America

BackgroundA number of studies published during the last 15 years showed the occurrence of insecticide resistance in Triatoma infestans populations. The different toxicological profiles and mechanisms of resistance to insecticides is due to a genetic base and environmental factors, being the insecticide selective pressure the best studied among the last factors. The studies on insecticide resistance on T. infestans did not consider the effect of environmental factors that may influence the distribution of resistance to pyrethroid insecticides. To fill this knowledge gap, the present study aims at studying the association between the spatial distribution of pyrethroid resistant populations of T. infestans and environmental variables.Conclusions/SignificanceThe occurrence of these two groups concentrated over a particular region that coincides with the area where populations of the intermediate cytogenetic group were found might reflect the spatial heterogeneity of the genetic variability of T. infestans, that seems to be the cause of the insecticide resistance in the area, even on sylvatic populations of T. infestans, never before exposed to pyrethroid insecticides, representing natural and wild toxicological phenotypes. The strong linear relationship found between LD₅₀ and RR₅₀ suggest RR₅₀ might not be the best indicator of insecticide resistance in triatomines.     

Effect of rotational use of insecticides on pyrethroids resistance in Helicoverpa armigera (Lep.: Noctuidae)

Abstract:  To investigate fluctuation in susceptibility to insecticides in the field, natural populations of Helicoverpa armigera were collected from the same field in the region of Multan, Pakistan in 2002 and 2003. The populations were examined against pyrethroids (viz. cypermethrin, esfenvalerate and fenpropathrin) and new insecticides (viz. spinosad, abamectin and indoxacarb). In 2002, the resistance ratio (RR) of cypermethrin and esfenvalerate was significantly higher than fenpropahrin compared with susceptible population. The susceptibility to cypermethrin, esfenvalerate and fenpropathrin increased significantly in 2003; however, the RR for cypermethrin was about half the RR (38) of esfenvalerate (101) and fenpropathrin (89). The toxicity of spinosad, abamectin and indoxacarb was identical in both years. In the field experiments, abamectin was more effective than other compounds tested whereas fenpropathrin, cypermethrin and esfenvalerate had similar toxicity. These results might have important implications in resistance management and suggest that the rotational use of spinosad, abamectin and indoxacarb could help to avoid the development of multiple resistant in H. armigera .     

Monitoring and mechanisms of organophosphate resistance in San Jose scale,Diaspidiotus perniciosus (Hemiptera: Diaspididae)

San Jose scale, Diaspidiotus perniciosus (Comstock), is a serious pest in Chilean apple tree orchards, and a number of organophosphate insecticides were used to control them for decades. Recently, control failures with these insecticides were reported and linked to insecticide resistance development. In this study, 40 San Jose scale field populations were collected and their susceptibility to two commonly used organophosphate insecticides, that is chlorpyrifos and methidathion, was assessed. The obtained bioassay data suggest moderate levels of resistance to both insecticides when compared to a reference susceptible strain. The highest resistance ratio (RR) detected for chlorpyrifos and methidathion was 31‐fold and 11‐fold, respectively. The bioassay results suggest the occurrence of a significant cross‐resistance between both compounds. Biochemical measurements revealed a role for esterases in conferring resistance to organophosphates, but not modified acetylcholinesterase. The spatial spread and extend of insecticide resistance were also evaluated. Our result shows that no autocorrelation can be assumed, and then, insecticide resistance is caused by random factors.     

Novel Kdr mutations (K964R and A943V) in pyrethroid‐resistant populations of Triatoma mazzottii and Triatoma longipennis from Mexico and detoxifying enzymes

Although having five different ways of transmission the vector-borne is the principal way of transmission of Chagas disease, which involves insects of the subfamily Triatominae (Hemiptera: Reduviidae). Nineteen of the 31 species that occur in Mexico are associated with humans, and all are capable of transmitting the disease. Pyrethroids are the insecticides recommended for the control of these vectors in Mexico. We determined the susceptibility to the pyrethroids dcltamethrin and permethrin of peridomestic populations of Triatoma mazzottii Usinger and two populations of Triatoma longipetmis Usinger in comparison with a reference strain for each species. Bioassays were performed for the determination of the LD50 for both field populations and reference strains. A maximum of 27 fold resistance to deltamethrin was observed in T. mazzottii, meanwhile, for permethrin, T. longipennis from Jalisco show the highest value of 3.19 fold. There was significantly increased activity of esterases in field populations in comparison with their corresponding reference strain. The results of the search of kdr mutations related to the resistance to deltamethrin and permethrin in the evaluated species show the presence of mutations in the field populations, as is the case with individuals of T. mazzottii, for which the mutation was found A943V, and for the two populations of T. longipennis included in this study, we report the presence of the kdr mutation K964R. Evaluation of the various mechanisms involved in resistance to pyrethroids in triatomines from Mexico could guide us to the real justification for insecticide resistance monitoring.     

Functional and genetic characteristics of Chlorantraniliprole resistance in the diamondback moth,Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth (Plutella xylostella) is a globally distributed and important economic pest, and it has developed resistance to all conventional insecticide classes used in the field. Chlorantraniliprole is a new chemical class of insecticide that acts as a conformation‐sensitive activator of the insect ryanodine receptor (RyR). In the present study, a field strain (16.3‐fold resistance to chlorantraniliprole) was collected in Korea and lab‐selected with chlorantraniliprole for more than one year. The resulting strain presented 2,157‐fold resistance to chlorantraniliprole. A point mutation (G4946E) in the RyR gene was observed at a high frequency in the resistant strain. Enzyme assays indicated that glutathione S‐transferase (GST) and P450 activity in the resistant strain were 2.4‐ and 1.96‐times higher than that of the susceptible strain, respectively. The expression of the RyR, GST (sigma, omega, and zeta) and CYP321E1 gene was higher in the resistant strain than in the susceptible strain. The F₁ progeny resulting from reciprocal crosses did not reveal maternal effects or a diamide‐susceptible phenotype, which suggests an autosomal nearly recessive mode of inheritance. In addition, we surveyed the susceptibility to 13 insecticides (3 diamides, 2 synthetic pyrethroids, 2 spinosyns, 1 organophosphate, 1 oxadiazine, 1 avermectin, and 3 others) in the chlorantraniliprole‐resistant strain. The resistant strain exhibited high cross‐resistance to flubendiamide (5,910 fold) and showed no cross‐resistance to spinetoram, spinosad, indoxacarb, and metaflumizone. These results can serve as an important basis for guiding the use of insecticides in the field.     

Field Evolved Resistance in Helicoverpa armigera (Lepidoptera: Noctuidae) to Bacillus thuringiensis Toxin Cry1Ac in Pakistan

Helicoverpa armigera (Hübner) is one of the most destructive pests of several field and vegetable crops, with indiscriminate use of insecticides contributing to multiple instances of resistance. In the present study we assessed whether H. armigera had developed resistance to Bt cotton and compared the results with several conventional insecticides. Furthermore, the genetics of resistance was also investigated to determine the inheritance to Cry1Ac resistance. To investigate the development of resistance to Bt cotton, and selected foliar insecticides, H. armigera populations were sampled in 2010 and 2011 in several cotton production regions in Pakistan. The resistance ratios (RR) for Cry1Ac, chlorpyrifos, profenofos, cypermethrin, spinosad, indoxacarb, abamectin and deltamethrin were 580-fold, 320-, 1110-, 1950-, 200-, 380, 690, and 40-fold, respectively, compared with the laboratory susceptible (Lab-PK) population. Selection of the field collected population with Cry1Ac in 2010 for five generations increased RR to 5440-fold. The selection also increased RR for deltamethrin, chlorpyrifos, profenofos, cypermethrin, spinosad, indoxacarb, abamectin to 125-folds, 650-, 2840-, 9830-, 370-, 3090-, 1330-fold. The estimated LC_50s for reciprocal crosses were 105 µg/ml (Cry1Ac-SEL female × Lab-PK male) and 81 g µg/ml (Lab-PK female × Cry1Ac-SEL male) suggesting that the resistance to Cry1Ac was autosomal; the degree of dominance (D_LC) was 0.60 and 0.57 respectively. Mixing of enzyme inhibitors significantly decreased resistance to Cry1Ac suggesting that the resistance to Cry1Ac and other insecticides tested in the present study was primarily metabolic. Resistance to Cry1Ac was probably due to a single but unstable factor suggesting that crop rotation with non-Bt cotton or other crops could reduce the selection pressure for H. armigera and improve the sustainability of Bt cotton.