Spatial and temporal variation in the control failure likelihood of the tomato leaf miner,Tuta absoluta

Insecticide resistance is frequently associated with field control failure, but such an assessment of its likelihood seldom occurs. This phenomenon is a potential cause of the control failure of the tomato leaf miner Tuta absoluta (Lepidoptera: Gelechiidae); therefore we surveyed insecticide resistance as the control failure likelihood for a duration of 7 years in 20 field populations of this species. The insecticide label rate was used as the discriminating concentration, and the minimum efficacy threshold required for insecticides in Brazil (i.e. 80% efficacy) was the targeted efficacy. The spatial and temporal variations of the control failure likelihood were also assessed, as was the potential influence of land topography for the area‐wide pattern observed. Most populations of T. absoluta were susceptible to abamectin, chlorfenapyr and spinosad and not to bifenthrin, triflumuron and teflubenzuron. The indoxacarb susceptibility varied in space and time. Spatial dependence was observed for abamectin and indoxacarb. The control failure likelihood of T. absoluta was higher for bifenthrin, triflumuron and teflubenzuron. A flat topography and the wind direction may favour the spread of the control failure likelihood and should be considered in designing pest management programs for T. absoluta.     

Cartap resistance and synergism in populations of Tuta absoluta (Lep., Gelechiidae)

Abstract: Control failures of cartap when used against the tomato leafminer Tuta absoluta (Meyrick) in Brazil and a recent report of cartap resistance in Brazilian populations of this pest species led to the investigation of the possible involvement of detoxification enzymes on this phenomenon using insecticide synergists. The insect populations were collected from seven different sites in the states of Minas Gerais, Rio de Janeiro and São Paulo. These populations were subjected to insecticide-impregnated filter paper assays. The concentration–mortality assays were carried out for cartap alone and in a mixture (1 cartap : 10 synergist) with the synergists diethyl maleate, piperonyl butoxide and triphenylphosphate which, respectively, inhibit the enzymes glutathion-S-transferases, cytochrome P450-dependent monooxygenases and esterases. Resistance to cartap was observed in all populations when compared with the standard susceptible population, with resistance ratios ranging from 2.3- to 21.9-fold. Piperonyl butoxide was the most efficient synergist with cartap synergism ratios ranging from 1.3- to 21.0-fold and nearly completely suppressing the resistance to cartap in all of the populations studied, suggesting a major involvement of cytochrome P450-dependent monooxygenases as a cartap resistance mechanism in these populations of T. absoluta . Diethyl maleate and triphenylphosphate also synergized cartap in nearly every population, and they still provided partial suppression of cartap resistance in the leafminer populations studied. Therefore, glutathion-S-transferases and esterases seem to play a secondary role in cartap resistance in Brazilian populations of T. absoluta .     

Resurgence of the cotton bollworm Helicoverpa armigera in northern Greece associated with insecticide resistance

Helicoverpa armigera has been controlled effectively with chemical insecticides in the major cotton crop production areas of northern Greece for many years. However, a resurgence of the pest was observed in 2010, which significantly affected crop production. During a 4‐year survey (2007 – 2010), we examined the insecticide resistance status of H. armigera populations from two major and representative cotton production areas in northern Greece against seven insecticides (chlorpyrifos, diazinon, methomyl, alpha‐cypermethrin, cypermethrin, gamma‐cyhalothrin and endosulfan). Full dose‐response bioassays on third instar larvae were performed by topical application. Lethal doses at 50% were estimated by probit analysis and resistance factors (RF) were calculated, compared to a susceptible laboratory reference strain. Resistance levels were relatively moderate until 2009, with resistance ratios below 10‐fold for organophosphates and carbamates and up to 16‐fold for the pyrethroid alpha‐cypermethrin. However, resistance rose to 46‐ and 81‐fold for chlorpyrifos and alpha‐cypermethrin, respectively in 2010, when the resurgence of the pest was observed. None of the known pyrethroid resistance mutations were found in the pyrethroid‐resistant insects. The possible association between resistance and H. armigera resurgence in Greece is discussed.     

Insecticide susceptibility level and control failure likelihood estimation of Sub-Saharan African populations of tomato leafminer: Evidence from Burkina Faso

The South American tomato pinworm, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) is a leafminer species currently considered as one of the major pests of fresh tomatoes around the world. The species settled in north Africa in 2007, before being observed in the entire continent. Widespread insecticide use has led to the emergence of resistant populations in South America and Europe, but no large-scale insecticide resistance assessment has been performed in Sub-Saharan Africa so far. In this study, we collected T. absoluta larvae from locations widely distributed in Burkina Faso, where the pest was first detected in 2016. Acute toxicity of the all available molecules in Burkina Faso was evaluated in the laboratory on F1 individuals, including acetamiprid, abamectin, spinosad, cypermethrin, chlorpyrifos, λ-cyhalothrin, deltamethrin, and Bacillus thuringiensis. No LC50 differences among T. absoluta populations were highlighted, except for Bacillus thuringiensis. Insects were still highly susceptible to abamectin [LC50 < 0.4 mg/L; Control failure likelihood (CFL) = −25%], spinosad (LC50 < 0.6 mg/L; CFL = 25%) and chlorpyrifos-ethyl (LC50 between 254 and 458 mg/L; CFL = −15%), but were less susceptible to acetamiprid (CFL ranging from 72% to 91%), cypermethrin (CFL = 80%), λ-cyhalothrin (CFL =79%), and deltamethrin (CFL ranging from 51% to 66%), with LC50 values for these insecticides ranging between 100 and 525 mg/L. Pending a proper communication strategy, we hope this work could help producers avoiding the most inefficient active substances.     

Insecticide toxicity and walking response of three pirate bug predators of the tomato leaf miner Tuta absoluta

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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.     

Establishing the role of detoxifying enzymes in field‐evolved resistance to various insecticides in the brown planthopper (Nilaparvata lugens) in South India

The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the major pests of rice throughout Asia. Extensive use of insecticides for suppressing N. lugens has resulted in the development of insecticide resistance leading to frequent control failures in the field. The aim of the present study was to evaluate resistance in the field populations of N. lugens from major rice growing states of South India to various insecticides. We also determined the activity of detoxifying enzymes (esterases [ESTs], glutathione S‐transferases [GSTs], and mixed‐function oxidases [MFOs]). Moderate levels of resistance were detected in the field populations to acephate, thiamethoxam and buprofezin (resistance factors 1.05–20.92 fold, 4.52–14.99 fold, and 1.00–18.09 fold, respectively) as compared with susceptible strain while there were low levels of resistance to imidacloprid (resistance factor 1.23–6.70 fold) and complete sensitivity to etofenoprox (resistance factor 1.05–1.66 fold). EST activities in the field populations were 1.06 to 3.09 times higher than the susceptible strain while for GST and MFO the ratios varied from 1.29 to 3.41 and 1.03 to 1.76, respectively. The EST activity was found to be correlated to acephate resistance (r = 0.999, P ≥ 0.001). The high selection pressure of organophosphate, neonicotinoid, and insect growth regulator (IGR) in the field is likely to be contributing for resistance in BPH to multiple insecticides, leading to control failures. The results obtained will be beneficial to IPM recommendations for the use of effective insecticides against BPH.     

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.     

Organophosphate and pyrethroid resistances in the tomato leaf miner Tuta absoluta (Lepidoptera: Gelechiidae) from Iran

The tomato leafminer, Tuta absoluta (Meyrich) (Lepidoptera: Gelechiidae), is a serious pest of tomato crops worldwide. The intensive use of chemical pesticides to control it has led to the selection of resistant populations. This study investigated the resistance of T. absoluta populations to pyrethroid and the organophosphate insecticides from ten regions of Iran. The resistance ratios at LC₅₀ for chlorpyrifos and diazinon varied among populations from 4.3 to 12 and from 1.4 to 9.0, respectively. The resistance ratios of the pyrethroids cypermethrin, deltamethrin and permethrin varied from 1.3 to 3.7, 2.7 to 13 and 1.2 to 4.3, respectively. Inclusion of synergists in toxicological bioassays and the variation observed in the activity of esterases, glutathione S‐transferase and cytochrome P450‐dependent monooxygenase suggest the existence of metabolically based resistance. Esterase and P450 biochemical assays were positively correlated with deltamethrin, and cypermethrin tolerance and diazinon tolerance correlated with esterase activity. The genes encoding the organophosphate and pyrethroid target sites acetylcholinesterase (ace1) and sodium channel (kdr) were partly sequenced. The genotyping revealed mutations in high frequencies in all populations leading to an A201S substitution in ace1 and three substitutions in the sodium channel gene L1014F, M918T, T929I. In summary, our results indicate the presence of organophosphate and pyrethroid resistance in Iranian T. absoluta populations with involvement of both detoxification enzymes and target site alterations. Most likely the populations of T. absoluta imported to Iran were resistant upon arrival.     

Mutation in the ace‐1 gene of the tomato leaf miner (Tuta absoluta) associated with organophosphates resistance

The tomato leaf miner, Tuta absoluta (Lepidoptera: Gelechiidae), is a major invasive pest that has spread throughout many countries in the Mediterranean basin and parts of Asia over the last decade. The control of T. absoluta has relied heavily on the use of chemical insecticides, a strategy that has led to the evolution of resistance. In this study, biological and molecular methods were used to determine the susceptibility of five strains of T. absoluta to the organophosphate chlorpyrifos and to investigate the molecular mechanisms underlying resistance to this class of insecticides. High levels of resistance to chlorpyrifos were observed in all five strains tested. Cloning and sequencing of the gene encoding the organophosphate target site, ace‐1, of T. absoluta revealed the presence of an alanine to serine substitution at a position that has been previously linked with organophosphate resistance across a range of different insect and mite species. The presence of this mutation at high frequency in T. absoluta populations originating from various countries further supports the suggestion that the rapid expansion of this species is, in part, mediated by the resistance of this pest to chemical insecticides.     

Insecticide susceptibility and resistance of Culex tritaeniorhynchus (Diptera: Culicidae) larvae collected from Gwangju,Republic of Korea

The susceptibility of Culex tritaeniorhynchus collected from Gwangju, Jeollabuk Province, Republic of Korea (ROK) to insecticides was evaluated under laboratory conditions using ten insecticides (7 pyrethroids and 3 organophosphates) that are currently applied by local public health centers in the ROK. Based on the values of median lethal concentration (LC₅₀), Cx. tritaeniorhynchus larvae were most susceptible to chlorpyrifos (0.006 ppm), fenitrothion (0.022 ppm), fenthion (0.035 ppm) and bifenthrin (0.038 ppm), and were least susceptible to esbiol (1.722 ppm). In comparative resistance tests, the resistance ratios (RRs) of seven insecticides were compared among each other using two strains of Cx. tritaeniorhynchus that were collected from the same locality during 1992 and 2010. Culex tritaeniorhynchus demonstrated significantly increased RRs to pyrethroids over time, while demonstrating decreased RRs among the organophosphates. Among the pyrethroids, permethrin had the highest RR values of 182.1‐ and 833.3‐fold differences, followed by etofenprox with RRs of 138.4‐ and 224.1‐fold differences in values of LC₅₀ and concentration that produced 90% mortality (LC₉₀), respectively. Culex tritaeniorhynchus strains demonstrated the least amount of change in susceptibility to the organophosphates, chlorpyrifos, fenitrothion and fenthion with 0.020‐, 0.019‐ and 0.001‐fold differences in resistance ratios (RRLC₅₀), respectively.     

Survey of susceptibilities to monosultap, triazophos, fipronil, and abamectin in Chilo suppressalis (Lepidoptera: Crambidae)

To provide a foundation for national resistance management of the Asiatic rice borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae), a study was carried out to determine dose-response and susceptibility changes over a 5-yr period in the insect from representative rice, Oryza sativa L., production regions. In total, 11 populations were collected from 2002 to 2006 in seven rice-growing provinces in China, and they were used to examine their susceptibility levels to monosultap, triazophos, fipronil, and abamectin. Results indicated that most populations had increased tolerance to monosultap. Several field populations, especially those in the southeastern Zhejiang Province, were highly or extremely highly resistant to triazophos (resistance ratio [RR] = 52.57-899.93-fold), and some populations in Anhui, Jiangsu, Shanghai, and the northern rice regions were susceptible or had a low level of resistance to triazophos (RR = 1.00-10.69). Results also showed that most field populations were susceptible to fipronil (RR < 3), but the populations from Ruian and Cangnan, Zhejiang, in 2006 showed moderate levels of resistance to fipronil (RR = 20.99-25.35). All 11 field populations collected in 2002-2006 were susceptible to abamectin (RR < 5). The tolerance levels in the rice stem borer exhibited an increasing trend (or with fluctuation) over a 5-yr period for different insecticides, and they reached a maximal level in 2006 for all four insecticides. Analysis of regional resistance ratios indicated that the history and intensity of insecticide application are the major driving forces for the resistance evolution in C. suppressalis. Strategic development of insecticide resistance management also is proposed.     

Insecticide resistance and control failure likelihood of the whitefly Bemisia tabaci (MEAM1; B biotype): a Neotropical scenario

Insecticide resistance is a standing concern for arthropod pest species, which may result in insecticide control failure. Nonetheless, while insecticide resistance has remained a focus of attention for decades, the incurring risk of insecticide control failure has been neglected. The recognition of both problems is paramount for arthropod pest management and particularly so when invasive species notoriously difficult to control and exhibiting frequent cases of insecticide resistance are considered. Such is the case of the putative whitefly species Middle East‐Asia Minor I (MEAM1) (Bemisia tabaci B‐biotype), for which little information is available in the Neotropics. Thus, the likely occurrence and levels of resistance to seven insecticides were surveyed among Brazilian populations of this species. The likelihood of control failure to the five insecticides registered for this species was also determined. Resistance was detected to all insecticides assessed reaching instances of high (i.e. >100×) to very high levels (>1000×) in all of them. Overall efficacy was particularly low (<60%) and the control failure likelihood was high (>25%) and frequent (70%) for the bioinsecticide azadirachtin, followed by spiromesifen and lambda‐cyhalothrin. In contrast, the likelihood of control failure was low for diafenthiuron, and mainly imidacloprid. As cartap and chlorantraniliprole are not used against whiteflies, but are frequently applied on the same host plants, inadvertent selection probably took place leading to high levels of resistance, particularly for the latter. The resistance levels of cartap and chlorantraniliprole correlated with imidacloprid resistance (r > 0.65, P < 0.001), suggesting that the latter use may have somewhat favoured inadvertent selection for resistance to both compounds not used against the whitefly. A further concern is that chlorantraniliprole use in the reported scenario may allow cross selection to cyantraniliprole, a related diamide with recent registration against whiteflies demanding attention in designing resistance management programmes.     

Susceptibility of Cypriot Tuta absoluta populations to four targeted insecticides and control failure likelihood

Tuta absoluta, known as the South American tomato pinworm, is one of the most disastrous pests of tomato cultivations, presently menacing tomato cultivations worldwide. In 2006, T. absoluta invaded Spain from South America. Since then, it was rapidly spread to most European, African and Asian countries. Such alien invasive species can minimize crop production, whereas the increasing use of insecticides raises various environmental concerns as well as on control costs, control failure and the toxicity to non‐target organisms. The S. American tomato pinworm is mostly controlled by chemical insecticides, and failure to control it is not a rare phenomenon. Resistance to numerous insecticides has been reported and is mainly due to the fact that farmers do not follow a sustainable resistance management scheme. Several examples have been reported from several countries where the tomato pinworm is present. In order to develop a successful insecticide resistance management (IRM) strategy for any major pest, one needs to identify the baseline toxicity to insecticides and then monitor susceptibility levels . In Cyprus, the current status of susceptibility levels to the main insecticides that are used to control T. absoluta has never been studied before. Herein, nine Cypriot populations of the pest were subjected to laboratory bioassays between 2016 and 2018 using the main insecticides applied against it. We found that the insecticides chlorantraniliprole and indoxacarb could not control the Cypriot T. absoluta populations anymore, with a resistance ratio (RR) >28 and 3–23, respectively. Furthermore, mortality achieved by those two insecticides was 20.6%–72% for chlorantraniliprole and 27.5%–78% for indoxacarb. However, the insecticides emamectin benzoate and spinosad are very effective, since mortality to both of them ranged between 99.5% and 100%.     

Landscape genomics of Colorado potato beetle provides evidence of polygenic adaptation to insecticides

The ability of insect pests to rapidly and repeatedly adapt to insecticides has long challenged entomologists and evolutionary biologists. Since Crow's seminal paper on insecticide resistance in 1957, new data and insights continue to emerge that are relevant to the old questions about how insecticide resistance evolves: such as whether it is predominantly mono‐ or polygenic, and evolving from standing vs. de novo genetic variation. Many studies support the monogenic hypothesis, and current management recommendations assume single‐ or two‐locus models. But inferences could be improved by integrating data from a broader sample of pest populations and genomes. Here, we generate evidence relevant to these questions by applying a landscape genomics framework to the study of insecticide resistance in a major agricultural pest, Colorado potato beetle, Leptinotarsa decemlineata (Say). Genome–environment association tests using genomic variation from 16 populations spanning gradients of landscape variables associated with insecticide exposure over time revealed 42 strong candidate insecticide resistance genes, with potentially overlapping roles in multiple resistance mechanisms. Measurements of resistance to a widely used insecticide, imidacloprid, among 47 L. decemlineata populations revealed heterogeneity at a small (2 km) scale and no spatial signature of origin or spread throughout the landscape. Analysis of nucleotide diversity suggested candidate resistance loci have undergone varying degrees of selective sweeps, often maintaining similar levels of nucleotide diversity to neutral loci. This study suggests that many genes are involved in insecticide resistance in L. decemlineata and that resistance likely evolves from both de novo and standing genetic variation.     

Two novel sodium channel mutations associated with resistance to indoxacarb and metaflumizone in the diamondback moth,Plutella xylostella

Indoxacarb and metaflumizone belong to a relatively new class of sodium channel blocker insecticides (SCBIs). Due to intensive use of indoxacarb, field‐evolved indoxacarb resistance has been reported in several lepidopteran pests, including the diamondback moth Plutella xylostella, a serious pest of cruciferous crops. In particular, the BY12 population of P. xylostella, collected from Baiyun, Guangdong Province of China in 2012, was 750‐fold more resistant to indoxacarb and 70‐fold more resistant to metaflumizone compared with the susceptible Roth strain. Comparison of complementary DNA sequences encoding the sodium channel genes of Roth and BY12 revealed two point mutations (F1845Y and V1848I) in the sixth segment of domain IV of the PxNa_v protein in the BY population. Both mutations are located within a highly conserved sequence region that is predicted to be involved in the binding sites of local anesthetics and SCBIs based on mammalian sodium channels. A significant correlation was observed among 10 field‐collected populations between the mutant allele (Y1845 or I1848) frequencies (1.7% to 52.5%) and resistance levels to both indoxacarb (34‐ to 870‐fold) and metaflumizone (1‐ to 70‐fold). The two mutations were never found to co‐exist in the same allele of PxNa_v, suggesting that they arose independently. This is the first time that sodium channel mutations have been associated with high levels of resistance to SCBIs. F1845Y and V1848I are molecular markers for resistance monitoring in the diamondback moth and possibly other insect pest species.     

Biotype and status of insecticide resistance of whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) in Alhassa oasis,Eastern Province of Saudi Arabia.

The tobacco whitefly, Bemisia tabaci, is one of the major insects infesting vegetable plants. This pest is well known in Alhassa oasis, Saudi Arabia; which is historically agricultural land cultivated with date palm trees and different vegetables. A molecular key based on the sequence of the mitochondrial cytochrome oxidase gene CO1 was used for the identification of strains of the tobacco whitefly Bemisia tabaci collected from farms located in four areas of the Alhassa oasis; Northern, Southern, Eastern and Western. Only one biotype (B‐biotype) of B. tabaci was reported in the oasis. Resistance of B. tabaci was tested against eight insecticides, the results showed moderate to low levels of resistance to the tested insecticides. However, the resistance to neonicotinoid insecticides was low and established at 1.3 fold to both Imidacloprid and Acetamiprid. In addition, medium levels of resistance were detected to the insect growth regulator Pyriproxyfen (30 fold), and the pyrethroid Deltamethrin (30 fold), Bifenthrin (24 fold) and Cypermethrin (13 fold). A medium level of resistance was also detected to the carbamate insecticide Carbosulfan and was 40 fold of the laboratory strains. A low level of resistance to the organophosphorus insecticide was detected to Phenthoate (11 fold). However, these results reflect that the farmers were less dependent on the use of insecticides to control B. tabaci in the oasis and they may be implementing other environmentally sound techniques to keep the pest below the damage threshold.     

小菜蛾对九种杀虫剂的抗药性

采用叶片药膜法测定了9种杀虫剂对海南、山东、广东、湖北武汉和襄樊等5个地区小菜蛾Plutella xylostella(L.)田间种群的毒力,和室内相对敏感品系比较。结果显示,5个地区的小菜蛾种群都对氯氰菊酯产生了10倍以上的抗性,广东和山东种群达到30倍以上的抗性。对阿维菌素的抗性山东小菜蛾种群达到135倍,广东种群达到30倍,其他地区均在10倍以下。但是,作用机制与阿维菌素类似的药剂,氟虫腈的抗性5个地区均在5倍或5倍以下。对昆虫生长调节剂定虫隆和氟虫脲的抗性除广东种群分别在10倍和20倍以上外,其他地区均在5倍以下。广东种群对多杀菌素的抗性为7.8倍,其他地区的种群没有产生抗性,多杀菌素和杀虫双均为作用于乙酰胆碱受体的药剂,但是作用的位点不同。杀虫双对5个种群的LC50值均是比较大的(>800 mg/L),尽管没有明显的抗性,不适宜用于小菜蛾田间防治。对呼吸链电子转移抑制剂溴虫腈的抗性均在10倍以下。对辛硫磷的抗性在2~5倍。     

Insecticide susceptibility of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae) in China

Insecticide control is the major measure for suppression of Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae) damage, and a few insecticides used for long time have proved to fail to control this pest in China. Several new chemicals have been introduced for control of C. medinalis. However, there was no baseline susceptibility data of C. medinalis to insecticides used or will be in use. In this study, a seedling dipping method was developed for bioassay of insecticide susceptibility of C. medinalis. Dose responses of C. medinalis to 11 insecticides were tested. Interpopulation sensitivity to insecticides was compared. Based on LC50 values, C. medinalis was most susceptible to antibiotic insecticides (abamectin, emamectin benzoate, and spinosad) and least sensitive to monosultap and a Bacillus thuringiensis (Bt) product. Chlorantraniliprole and insect growth regulator (IGR) insecticides (tebufenozide and hexaflumuron) exhibited great efficacy against C. medinalis. No susceptibility difference was observed for antibiotic insecticide and IGR insecticides among three populations. Narrow variation in tolerant level was detected for organophosphates insecticides, chlorantraniliprole, monosultap, and Bt. The results in this study provided baseline susceptibility data of C. medinalis to 11 insecticides and also offered useful information for choice of alternative insecticide and for integrated resistance management of C. medinalis.     

Positive correlation of methamidophos resistance between Lipaphis erysimi and Diaeretilla rapae and effects of methamidophos ingested by host insect on the parasitoid

Temporal and spatial correlated variations on the methamidophos resistance and biomolecular rate constant of acetylcholinesterase to insecticides were found between the turnip aphid, Lipaphis erysimi and its endoparasitoid, Diaeretilla rapae , collected from field colonies and an insecticide-free field insectarium in Fujian, China. Compared to the related susceptible insectarium population, L. erysimi and D. rapae displayed 7.4–29.2- and 2.6–9.2-fold resistance ratios, respectively. In addition, two populations of L. erysimi with different methamidophos resistance levels, that is, a field (with 5.8-fold resistance ratio) and an insectarium population, were used to study the effects of methamidophos ingested by the host insect on D. rapae development. The percentage of D. rapae cocoon formation decreased significantly when the parasitized L. erysimi were fed on cauliflower leaves treated with methamidophos at lethal concentration dosages 10 (LC₁₀) or LC₅₀. At LC₅₀ dosages the percentage of D. rapae cocoon formation and adult emergence decreased significantly. When the parasitized L. erysimi were fed on methamidophos at LC₉₀ dosage, no D. rapae cocoons were found. When the field or insectarium L. erysimi were treated with methamidophos at LC₁₀, the susceptibility to methamidophos in the adult D. rapae emerged from the treated host insect was similar to the control. However, the susceptibility to methamidophos in the adult D. rapae became lower than the control when the host insects were treated at LC₅₀ dosages. The data thus suggested that the methamidophos ingested by the host insect L. erysimi could be an important factor in the endoparasitoids' insecticide resistance development. The natural selectivity would favor the parasitoids that had developed an insensitivity to the insecticide(s).