Absoluta Populations Research Articles

Phthalides as promising insecticides against Tuta absoluta (Lepidoptera: Gelechiidae)

ABSTRACTIn this study, the insecticide potential of eight phthalides derived from furan-2(5H)-one was evaluated against Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) larvae. The potency of the most active phthalides and the susceptibility of six different T. absoluta populations to these compounds were determined. The toxicity of these molecules to two non-target species (Solenopsis saevissima Smith and Tetragonisca angustula Latreille) was also evaluated. Two phthalides (3 and 4) presented insecticide potential against T. absoluta. Phthalide 4 was as toxic as piperine (positive control) and both phthalides exhibited rapid action (LT50 < 2 hours). The variation in the susceptibility of T. absoluta populations to the phthalides 3 and 4 was low. Neither phthalide presented physiological selectivity for non-target species.Therefore, the phthalides 3 and 4 are promising molecules, or at least, a starting point for a chemical optimization program leading to formulations for the management of the tomato leafminer. The application of such products should be conducted according to the principles of ecological selectivity.

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

AbstractThe 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.

Rapid spread of the tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), an invasive pest in Sub-Saharan Africa

Abstract The invasive tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera, Gelechiidae) has become a real threat for the continued production of tomatoes across Sub-Saharan Africa since its first detection in Senegal. However, little is known of its geographical expansion, seasonal population dynamics, and damage to crops. A trapping network was deployed in 2014 and 2015 in Senegal to monitor the dynamics of T. absoluta populations at a regional and nationwide scale. A field network was also implemented in the most infested area to get information on the pest incidence during the 2013–2014 cropping season. In 2014, pheromone traps did not detect the presence of T. absoluta moths in remote areas of Eastern Senegal. In 2015, moths were detected in all the fifteen monitored areas deployed throughout the country. Abundance of trapped moths was greatest in 'Niayes', the main tomato-producing area. Unexpectedly, T. absoluta moths were trapped in some areas with few or no tomato crops, including off-season in the 'Vallee du fleuve', hot drylands ('Matam' and 'Kidira') and urban environments ('Dakar'). This suggests high mobility of moth populations and capacity to survive in harsh environments and to persist on alternative host plants. Field monitoring in the main tomato-producing area showed a very low incidence of T. absoluta over the early dry season (0–2% mined leaves), followed by severe outbreaks during the late dry season (up to 60% mined leaves). Results on the invasive pest occurrence will be helpful to decision-makers with a view to develop alternative strategies such as biological control by indigenous natural enemies or collective management strategies based on the temporal or spatial exclusion of host crops. (Resume d'auteur)

Ryanodine receptor point mutations confer diamide insecticide resistance in tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae)

Insect ryanodine receptors (RyR) are the molecular target-site for the recently introduced diamide insecticides. Diamides are particularly active on Lepidoptera pests, including tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae). High levels of diamide resistance were recently described in some European populations of T. absoluta, however, the mechanisms of resistance remained unknown. In this study the molecular basis of diamide resistance was investigated in a diamide resistant strain from Italy (IT-GELA-SD4), and additional resistant field populations collected in Greece, Spain and Brazil. The genetics of resistance was investigated by reciprocally crossing strain IT-GELA-SD4 with a susceptible strain and revealed an autosomal incompletely recessive mode of inheritance. To investigate the possible role of target-site mutations as known from diamondback moth (Plutella xylostella), we sequenced respective domains of the RyR gene of T. absoluta. Genotyping of individuals of IT-GELA-SD4 and field-collected strains showing different levels of diamide resistance revealed the presence of G4903E and I4746M RyR target-site mutations. These amino acid substitutions correspond to those recently described for diamide resistant diamondback moth, i.e. G4946E and I4790M. We also detected two novel mutations, G4903V and I4746T, in some of the resistant T. absoluta strains. Radioligand binding studies with thoracic membrane preparations of the IT-GELA-SD4 strain provided functional evidence that these mutations alter the affinity of the RyR to diamides. In combination with previous work on P. xylostella our study highlights the importance of position G4903 (G4946 in P. xylostella) of the insect RyR in defining sensitivity to diamides. The discovery of diamide resistance mutations in T. absoluta populations of diverse geographic origin has serious implications for the efficacy of diamides under applied conditions. The implementation of appropriate resistance management strategies is strongly advised to delay the further spread of resistance.

Field-Evolved Resistance and Cross-Resistance of Brazilian Tuta absoluta (Lepidoptera: Gelechiidae) Populations to Diamide Insecticides.

Tuta absoluta (Meyrick), one of the most important tomato pests worldwide, is heavily controlled by the application of insecticides. Diamide insecticides represent a new class of products recently registered to control T. absoluta After 6 yr of use, control failures have been reported in populations of this pest, suggesting a hypothetical resistance development. Therefore, a resistance survey was performed using nine populations of T. absoluta that were collected in open fields, including from areas with reports of a reduced efficacy of diamides in the Northeast and Central regions of Brazil. Initial surveys with diagnostic and label doses proved the reduced efficacy of diamides against most populations. The LC50 values of chlorantraniliprole varied from 0.0044 (Brasília) to 1,263 (América Dourada) mg AI liter-1 (the resistance ratios [RR50] ranged from 1.0- to 288,995-fold), whereas the LC50 values for cyantraniliprole and flubendiamide, respectively, varied from 0.015 (Brasília) to 281 (América Dourada) mg AI liter-1 and from 0.038 (Guaraciaba do Norte) to 3,018 (Gameleira 1) mg AI liter-1 The resistance ratios (RR50) ranged from 1.0- to 18,423-fold for cyantraniliprole and from 1.0- to 80,413-fold for flubendiamide. The log LC50 values of pairwise diamides were strongly and significantly correlated, which denoted cross-resistance among them. Very high resistance to diamides in T. absoluta was observed in this study, suggesting that strategies to mitigate resistance and thereby control the pest must not include only insecticides. Other control tactics must be carefully implemented over time to increase the life span of diamides, including rotational practices with other molecules.

Mutation (G275E) of the nicotinic acetylcholine receptor α6 subunit is associated with high levels of resistance to spinosyns in Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

The tomato leafminer, Tuta absoluta, now a major pest of tomato crops worldwide, is primarily controlled using chemical insecticides. Recently, high levels of resistance to the insecticide spinosad have been described in T. absoluta populations in Brazil. Selection of a resistant field-collected strain led to very high levels of resistance to spinosad and cross-resistance to spinetoram, but not to other insecticides that target the nicotinic acetylcholine receptor (nAChR). In this study the mechanisms underlying resistance to spinosad were investigated using toxicological, biochemical and molecular approaches. Inhibition of metabolic enzymes using synergists and biochemical assessment of detoxification enzyme activity provided little evidence of metabolic resistance in the selected strain. Cloning and sequencing of the nAChR α6 subunit from T. absoluta, the spinosad target-site, from susceptible and spinosad-resistant strains were done to investigate the role of a target-site mechanism in resistance. A single nucleotide change was identified in exon 9 of the α6 subunit of the resistant strain, resulting in the replacement of the glycine (G) residue at position 275 observed in susceptible T. absoluta strains with a glutamic acid (E). A high-throughput DNA-based diagnostic assay was developed and used to assess the prevalence of the G275E mutation in 17 field populations collected from different geographical regions of Brazil. The resistant allele was found at low frequency, and in the heterozygous form, in seven of these populations but at much higher frequency and in the homozygous form in a population collected in the Iraquara municipality. The frequency of the mutation was significantly correlated with the mortality of these populations in discriminating dose bioassays. In summary our results provide evidence that the G275E mutation is an important mechanism of resistance to spinosyns in T. absoluta, and may be used as a marker for resistance monitoring in field populations.

Enzyme Activities and Analysis of Susceptibility Levels in Turkish Tuta absoluta Populations to Chlorantraniliprole and Metaflumizone Insecticides

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), tomato leaf miner, is one of the most devastating insect pests that attack tomato crops. T. absoluta larvae destroy tomato plants by producing large galleries in tomato leaves and burrowing stalks, apical buds, green and ripe fruits. This larva causes a major economic effect on tomato industry. Insecticides are commonly used to control this pest in tomato fields. The aim of this study is to determine the susceptibility levels of T. absoluta populations and biochemical analysis of mechanism(s) involved in chlorantraniliprole and metaflumizone metabolism, registered in Turkey for use against T. absoluta. IRAC bioassay method was used to determine the resistance ratios of these insecticides. Resistance ratios ranged between 7.2-and 1.7-folds for chlorantraniliprole, and 4.0- and 1.8-folds for metaflumizone in T. absoluta field populations. NADPH-Cytochrome P450 reductase, glutathione S-transferase, and esterase activities were determined by conducting biochemical assays in field populations of T. absoluta. While NADPH Cytochrome P450 reductase activity showed an increase only in Antalya population (1.9-fold), glutathione S-transferase activity showed an increase only in Adana population (1.2-fold). However, esterase activities were increased both in Adana (1.3-fold) and Ankara (2.2-fold) populations of T. absoluta.

Status of pyrethroid resistance and mechanisms in Brazilian populations of Tuta absoluta

The tomato leafminer, Tuta absoluta, is a major pest of tomato crops worldwide. This study surveyed the resistance of T. absoluta populations from four regions in Brazil to pyrethroid insecticides, the frequencies of L1014F, T929I and M918T Na channel mutations, and the role of detoxification metabolism in the resistance. Resistance ratios varied from 1- to 11-times among populations and insecticides, but control failure likelihood assays showed that all pyrethroids assessed exhibited no efficacy at all (and thus, 98–100% control failure likelihood) against all T. absoluta populations. The activity of glutathione S-transferase and cytochrome P450-mediated N-demethylation in biochemical assays was significantly correlated with the level of resistance to deltamethrin and permethrin suggesting that these enzymes may play a role in resistance. TaqMan assays were used to screen for the presence of knockdown resistance (kdr) mutations and revealed that the L1014F kdr mutation was fixed in all populations and associated with two super-kdr mutations, M918T and particularly T929I, at high frequency. Altogether, results suggest that control failures are because of mutations in the domain II of the sodium channel, as a prevailing mechanism of resistance to pyrethroids in populations of T. absoluta in Brazil. But, enhanced cytochrome P450-dependent monooxygenases and GST activities also play an important role in the resistance of some populations, which reinforce that pyrethroids must not be used overall to control T. absoluta.

Spinosyn resistance in the tomato borer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

Spinosad has been used to control Tuta absoluta in Brazil for more than a decade but will eventually be replaced by spinetoram despite the risk of cross-resistance. Therefore, the susceptibility to both molecules and the activity of detoxification enzymes were determined for eight representative populations of T. absoluta to assess resistance and the risk of cross-resistance. The LC50 values for spinosad varied from 0.007 (Pelotas) to 0.626 mg/L (Sumare); the LC50 values for spinetoram varied from 0.047 (Pelotas) to 0.308 mg/L (Sumare). The LC99 values for spinosad varied from 0.23 (Pelotas) to 11.56 mg/L (Venda Nova do Imigrante); the LC99 values for spinetoram varied from 0.55 (Pelotas) to 6.71 mg/L (Iraquara). The resistance levels ranged from 1.0- to 93.8-fold (RR50) and 1.0- to 51.5-fold (RR99) for spinosad and from 1.0- to 6.5-fold (RR50) and 1.0- to 12.1-fold (RR99) for spinetoram. The concentration-mortality responses to spinetoram were more homogeneous than those to spinosad. A strong correlation between the susceptibilities of T. absoluta populations to spinosad and spinetoram was observed, showing the similarity of the mode of action of both molecules and producing cross-resistance between them. The β–esterase activity of T. absoluta populations was correlated with spinosyn susceptibility, suggesting a potential contribution of the enzyme to evolved spinosyn resistance. The evolution of resistance to spinosyns in T. absoluta observed in this study suggests that strategies to mitigate resistance must be carefully implemented over the short term and that rotation with other products is encouraged.

Susceptibility of Tuta absoluta (Lepidoptera: Gelechiidae) Brazilian populations to ryanodine receptor modulators.

Phthalic and anthranilic diamides comprise a new insecticide class recently registered in Brazil to control Lepidoptera such as Tuta absoluta (Meyrick). Therefore, the baseline of susceptibility was determined for eight representative field populations of this species to establish a resistance monitoring programme. The potential for cross-resistance as well as detoxification metabolism was assessed in order to fine-tune the resistance management programme. Brazilian populations were very susceptible to chlorantraniliprole (LC50 values varied from 3.17 to 29.64 µg AI L(-1) ), cyantraniliprole (LC50 values varied from 8.61 to 28.95 µg AI L(-1) ) and flubendiamide (LC50 values varied from 94 to 230 µg AI L(-1) ), with respective resistance ratios of 9.33-, 3.36- and 2.45-fold between most susceptible and tolerant populations. Anthranilic diamides showed significant correlations between log LC50 values among themselves, suggesting a high risk of cross-resistance. However, the log LC50 values of T. absoluta to phthalic diamide did not show any correlation with anthranilic diamides. Cytochrome- P450-dependent monooxygenase activity showed a weak correlation with log LC50 values of T. absoluta populations to anthranilic diamides, which suggests a potential route for evolving resistance to anthranilic diamides. The diamides were highly effective against T. absoluta, with populations showing a homogeneous response to them. Cross-resistance is very likely between anthranilic diamides in T. absoluta. Populations of this pest may evolve resistance by increasing cytochrome- P450-dependent monooxygenases.

Potential for combined use of parasitoids and generalist predators for biological control of the key invasive tomato pest Tuta absoluta

The tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has recently invaded Mediterranean countries and is a major pest in tomato crops. Trichogrammatid oophagous parasitoids have shown promising potential for controlling the pest before the yield decreases in the greenhouse. In protected tomato crops (greenhouse), mirid predators are commonly used for biological control of whiteflies and they also prey on T. absoluta. These predators do not attack Trichogramma adults but they may partially decrease the overall impact of parasitoids on T. absoluta if intraguild predation (IGP) occurs on parasitized eggs. Under laboratory conditions, we tested if the mirid predator Macrolophus pygmaeus shows preference between parasitized and unparasitized T. absoluta eggs. We also tested if the predator reduces the number of parasitized eggs on caged tomato plants (microcosms) and assessed the efficacy of natural enemies used alone or together in limiting T. absoluta populations. We found that IGP is inflicted on the parasitoid Trichogramma achaeae by M. pygmaeus and that the risk of IGP depends on the developmental stage of T. achaeae inside the egg because the larva is at risk mostly early in its development (when parasitized egg is still yellow). In addition, we observed that non-consumptive events, likely probing of the predator on parasitized eggs, may induce mortality in parasitoid offspring without actual feeding on parasitized eggs. However, both IGP and non-consumptive events decreased when the predator was not confined with parasitized eggs in small arenas. Despite negative effects of the predator to the parasitoid, results demonstrate that adding Trichogramma parasitoids may significantly increase the level of control of the pest over what could be attained when only the mirid predator M. pygmaeus is present on tomato. Implications of results are discussed regarding potential of these natural enemies for biological control of T. absoluta in greenhouse tomato crops.

First evidence of deuterotokous parthenogenesis in the tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

The tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), originates from South America and is now considered to be one of the most damaging invasive pests of tomatoes in the Mediterranean Basin countries of Europe and North Africa. The preventing pest mating control methods include: (1) the use of synthetic pheromones for male attraction and annihilation inside insecticide-containing traps; (2) mating disruption by saturating the atmosphere with sex pheromones which alter the ability of males to locate females; and (3) massive applications of sterile males to alter the overall reproductive success of the pest population. However, all these methods achieve only a poor success rate in controlling T. absoluta populations under greenhouse conditions. Sex pheromone management and sterile insect techniques are both based on an important biological trait: the insect must breed through sexual reproduction. Here, we report for the first time laboratory evidence of deuterotokous parthenogenesis, an asexual reproduction where both males and females are produced from unfertilized eggs. We discuss the consequences for T. absoluta control strategies.

Identification of mutations associated with pyrethroid resistance in the voltage-gated sodium channel of the tomato leaf miner (Tuta absoluta)

The tomato leaf miner, Tuta absoluta (Lepidoptera) is a significant pest of tomatoes that has undergone a rapid expansion in its range during the past six years and is now present across Europe, North Africa and parts of Asia. One of the main means of controlling this pest is through the use of chemical insecticides. In the current study insecticide bioassays were used to determine the susceptibility of five T. absoluta strains established from field collections from Europe and Brazil to pyrethroids. High levels of resistance to λ cyhalothrin and tau fluvalinate were observed in all five strains tested. To investigate whether pyrethroid resistance was mediated by mutation of the para-type sodium channel in T. absoluta the IIS4–IIS6 region of the para gene, which contains many of the mutation sites previously shown to confer knock down (kdr)-type resistance to pyrethroids across a range of different arthropod species, was cloned and sequenced. This revealed that three kdr/super-kdr-type mutations (M918T, T929I and L1014F), were present at high frequencies within all five resistant strains at known resistance ‘hot-spots’. This is the first description of these mutations together in any insect population. High-throughput DNA-based diagnostic assays were developed and used to assess the prevalence of these mutations in 27 field strains from 12 countries. Overall mutant allele frequencies were high (L1014F 0.98, M918T 0.35, T929I 0.60) and remarkably no individual was observed that did not carry kdr in combination with either M918T or T929I. The presence of these mutations at high frequency in T. absoluta populations across much of its range suggests pyrethroids are likely to be ineffective for control and supports the idea that the rapid expansion of this species over the last six years may be in part mediated by the resistance of this pest to chemical insecticides.

Preplant release of Nesidiocoris tenuis and supplementary tactics for control of Tuta absoluta and Bemisa tabaci in greenhouse tomato

AbstractAn early release system developed for Nesidiocoris tenuis Reuter (Heteroptera: Miridae) could provide a good control of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in tomato. Tuta absoluta and the whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) often appear simultaneously in tomato crops and this might affect control capacity. Therefore, the new approach needs to be tested in a situation with both pests present. In addition, Bacillus thuringiensis Berliner and Trichogramma achaeae Nagaraja &amp; Nagarkatti (Hymenoptera: Trichogrammatidae) have been shown to be effective against T. absoluta and could be a supplement to N. tenuis. Two experiments were carried out to evaluate the potential of this approach and its combination with supplementary control agents against T. absoluta. In the first experiment four treatments were compared (T. absoluta, B. tabaci, T. absoluta + N. tenuis, and T. absoluta + B. tabaci + N. tenuis) and N. tenuis was able to control T. absoluta and B. tabaci either alone or together. In the second experiment, five treatments were compared: T. absoluta, T. absoluta + N. tenuis, T. absoluta + N. tenuis + T. achaeae, T. absoluta + N. tenuis + B. thuringiensis, and T. absoluta + N. tenuis + T. achaeae + B. thuringiensis. Nesidiocoris tenuis again proved capable of significantly reducing T. absoluta populations, and the implementation of additional agents did not increase its effectiveness.

Efficacy of sulphur on Tuta absoluta and its side effects on the predator Nesidiocoris tenuis

AbstractThe South American tomato pinworm, Tuta absoluta (Meyrick), is one of the major pests of tomato crop. Since its detection in the Mediterranean basin, it has been commonly controlled using chemical insecticides. However, inoculation and conservation of predatory mirids, integrated with sprays of selective insecticides, has been demonstrated to be a cost‐effective strategy for controlling this pest. In this work, we tested the efficacy of two sulphur formulations, dustable and wettable powder, for controlling T. absoluta on tomato under greenhouse and open‐field conditions. In addition, the side effects of both sulphur formulations on the predator, Nesidiocoris tenuis (Reuter), were evaluated under laboratory conditions. Dustable sulphur, applied weekly on tomato seedlings artificially infested with T. absoluta in greenhouse conditions, significantly reduced the infestation levels and was demonstrated to have a repellent effect on oviposition. Wettable sulphur was not effective for controlling T. absoluta populations in both greenhouse and open‐field experiments. In the side effect trials conducted with N. tenuis, only dustable sulphur resulted in being moderately harmful as a fresh residue and slightly harmful as a 7‐day‐old residue; no effects were recorded exposing the predator to 14‐day‐old sulphur residues. In contrast, wettable sulphur was classified as harmless to N. tenuis. Our results suggest that the use of sulphur, especially as dustable powder, could be considered as a tool in T. absoluta management strategies, although its side effects on N. tenuis should be taken into account. The implications of these results for the use of sulphur formulations in pest and disease management programmes in tomato crops are discussed.

Genetic study of Mediterranean and South American populations of tomato leafminer Tuta absoluta (Povolny, 1994) (Lepidoptera: Gelechiidae) using ribosomal and mitochondrial markers

Before its introduction into Europe at the end of 2006, Tuta absoluta (Povolny, 1994) was confined solely to South America. Currently, this invasive pest is well established in various European and Mediterranean countries, causing important economic losses to tomato (Lycopersicon esculentum Mill.) crops. In order to study the genetic variability of this pest, 23 Mediterranean and ten native South American populations were analysed with nuclear ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) markers. The internal transcribed spacers 1 (ITS1) and 2 (ITS2) of rDNA and a fragment in the mtDNA gene encoding cytochrome oxidase I (COI) were PCR amplified and sequenced in T. absoluta. Sequence analyses consistently revealed neither intrapopulation nor interpopulation variation in either genomic region. High genetic homogeneity was detected in T. absoluta populations from the Mediterranean Basin and South America, based on mtCOI and ITS rDNA sequence analysis. A single genetic type was identified in this pest.

Divergência genética entre acessos de tomateiro infestados por diferentes populações da traça-do-tomateiro

Neste trabalho estudou-se a divergência genética entre acessos de Lycopersicon spp. com relação à resistência a populações da traça-do-tomateiro, Tuta absoluta, e verificou-se a importância relativa dos caracteres da traça-do-tomateiro para a divergência. Foi conduzido experimento envolvendo quatro populações do inseto procedentes de Uberlândia (MG), Viçosa (MG), Camocim de São Félix (PE) e Santa Teresa (ES) e cinco acessos de tomateiro, 'Santa Clara', 'Moneymaker', TOM-601, PI 126445 (L. hirsutum f. typicum) e PI 134417 (L. hirsutum f. glabratum). Foram realizados testes de médias de Tukey e método de agrupamento de Tocher, e verificada a importância relativa dos caracteres da traça-do-tomateiro para a divergência entre acessos por meio do método de Singh. Verificou-se a existência de variabilidade genética entre os acessos de tomateiro quando infestados pelas populações da traça-do-tomateiro provenientes das diferentes regiões do Brasil. O acesso Santa Clara foi o mais suscetível à população de Santa Teresa. 'Moneymaker' e 'TOM-601' foram mais resistentes às populações provenientes de Camocim de São Félix e Santa Teresa, respectivamente. PI 126445 foi mais resistente às populações de Santa Teresa e Viçosa. PI 134417 foi mais resistente à população de Viçosa. 'Moneymaker' e TOM-601 mostraram-se boas fontes a serem utilizadas em programas de melhoramento que visem à obtenção de cultivars de tomate resistentes à traça-do-tomateiro. Os caracteres que mais contribuíram para a divergência entre os acessos de tomateiro foram mortalidade larval, número de pupas fêmea e número de pupas macho. Os caracteres período larval e peso de pupas macho não podem ser eliminados em futuras avaliações de resistência à população da traça-do-tomateiro proveniente de Uberlândia.

How Much Safety Is Too Much Danger?

The tomato leafminer, Tuta absoluta, is a major pest of tomato crops worldwide. This study surveyed the resistance of T. absoluta populations from four regions in Brazil to pyrethroid insecticides, the frequencies of L1014F, T929I and M918T Na channel mutations, and the role of detoxification metabolism in the resistance. Resistance ratios varied from 1- to 11-times among populations and insecticides, but control failure likelihood assays showed that all pyrethroids assessed exhibited no efficacy at all (and thus, 98–100% control failure likelihood) against all T. absoluta populations. The activity of glutathione S-transferase and cytochrome P450-mediated N-demethylation in biochemical assays was significantly correlated with the level of resistance to deltamethrin and permethrin suggesting that these enzymes may play a role in resistance. TaqMan assays were used to screen for the presence of knockdown resistance (kdr) mutations and revealed that the L1014F kdr mutation was fixed in all populations and associated with two super-kdr mutations, M918T and particularly T929I, at high frequency. Altogether, results suggest that control failures are because of mutations in the domain II of the sodium channel, as a prevailing mechanism of resistance to pyrethroids in populations of T. absoluta in Brazil. But, enhanced cytochrome P450-dependent monooxygenases and GST activities also play an important role in the resistance of some populations, which reinforce that pyrethroids must not be used overall to control T. absoluta.