Absoluta Populations Research Articles

Resistance monitoring of diamide insecticides and characterization of field-evolved chlorantraniliprole resistance among Chinese populations of the tomato pinworm Phthorimaea (=Tuta) absoluta (Lepidoptera: Gelechiidae)

The tomato pinworm, Phthorimaea (=Tuta) absoluta, is considered one of the most destructive and invasive insect pests worldwide, having developed significant resistance to many popular insecticides. In this study, we monitored the field resistance of P. absoluta populations from China to three diamide insecticides: flubendiamide, chlorantraniliprole, and cyantraniliprole. We found that one field population from Wuzhong City (WZ) exhibited high level of resistance to chlorantraniliprole. Using the WZ population and a susceptible reference strain (YN-S), we established a near-isogenic line (WZ-NIL) of P. absoluta with resistance to chlorantraniliprole. This strain also showed substantial cross-resistance to flubendiamide, and cyantraniliprole. Genetic analysis revealed that the inheritance of resistance to chlorantraniliprole in the WZ-NIL strain was autosomal and incompletely dominant. Additionally, the pesticide synergist piperonyl butoxide significantly inhibited chlorantraniliprole resistance by compromising P450 monooxygenase activity, which was significantly higher in the resistant strain. Furthermore, WZ-NIL had significantly prolonged developmental stages, lower pupation rates, reduced female fecundity, and lower egg hatchability than YN-S individuals. The fitness of WZ-NIL relative to YN-S was estimated to be 0.73, indicating significant fitness cost associated with chlorantraniliprole resistance. Rotating chlorantraniliprole with other insecticides that have different modes of action and degradation may be particularly useful for managing chlorantraniliprole resistance in P. absoluta.

Bacterial biota associated with the invasive insect pest Tuta absoluta (Meyrick)

Tuta absoluta (the tomato pinworm) is an invasive insect pest with a highly damaging effect on tomatoes causing between 80 and 100% yield losses if left uncontrolled. Resistance to chemical pesticides have been reported in some T. absoluta populations. Insect microbiome plays an important role in the behavior, physiology, and survivability of their host. In a bid to explore and develop an alternative control method, the associated microbiome of this insect was studied. In this study, we unraveled the bacterial biota of T. absoluta larvae and adults by sequencing and analyzing the 16S rRNA V3-V4 gene regions using Illumina NovaSeq PE250. Out of 2,092,015 amplicon sequence variants (ASVs) recovered from 30 samples (15 larvae and 15 adults), 1,268,810 and 823,205 ASVs were obtained from the larvae and adults, respectively. A total of 433 bacterial genera were shared between the adults and larval samples while 264 and 139 genera were unique to the larvae and adults, respectively. Amplicon metagenomic analyses of the sequences showed the dominance of the phylum Proteobacteria in the adult samples while Firmicutes and Proteobacteria dominated in the larval samples. Linear discriminant analysis effect size (LEfSe) comparison revealed the genera Pseudomonas, Delftia and Ralstonia to be differentially enriched in the adult samples while Enterococcus, Enterobacter, Lactococcus, Klebsiella and Wiessella were differentially abundant in the larvae. The diversity indices showed that the bacterial communities were not different between the insect samples collected from different geographical regions. However, the bacterial communities significantly differed based on the sample type between larvae and adults. A co-occurrence network of significantly correlated taxa revealed a strong interaction between the microbial communities. The functional analysis of the microbiome using FAPROTAX showed that denitrification, arsenite oxidation, methylotrophy and methanotrophy as the active functional groups of the adult and larvae microbiomes. Our results have revealed the core taxonomic, functional, and interacting microbiota of T. absoluta and these indicate that the larvae and adults harbor a similar but transitory set of bacteria. The results provide a novel insight and a basis for exploring microbiome-based biocontrol strategy for this invasive insect pest as well as the ecological significance of some of the identified microbiota is discussed.

Molecular detection of reproductive symbionts and parthenogenesis experiments in Tuta absoluta from Argentina: facing potential for sustainable and specific pest control strategies

AbstractTomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is a key pest of tomato crops. Specific and environmentally friendly control strategies against this pest, such as the sterile insect technique (SIT), are under development and sexual reproduction has emerged as a key focal point to ensure its success. In the present study, we analyzed four representative T. absoluta populations from Argentina, focusing on the molecular detection of endosymbionts potentially associated with reproductive abnormalities and on determining whether parthenogenesis can occur under laboratory conditions. Larvae of T. absoluta were collected in commercial tomato plantations from La Plata and Mar del Plata (both in Buenos Aires province), Bella Vista (Corrientes province), and Yuto (Jujuy province). Tuta absoluta adults were evaluated by standard PCR for the presence of reproductive endosymbionts (Wolbachia sp., Spiroplasma sp., Arsenophonus sp., Cardinium sp., and Rickettsia sp.). For parthenogenesis assays, 20–23 virgin females from each T. absoluta geographic population were life‐long isolated in Petri dishes with a tomato leaf. Fecundity, fertility, and female longevity were estimated and compared with results from mated females from each population. Our results showed the presence of a unique endosymbiont (Wolbachia sp. supergroup B, sequence type 41). Fecundity of the unmated females was significantly lower than fecundity of mated females in all T. absoluta populations. In addition, unmated females only laid infertile eggs. In conclusion, the absence of parthenogenesis in T. absoluta from representative geographic populations supports the implementation of SIT and mating disruption as effective control strategies against this pest in Argentina.

Farklı Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae) popülasyonlarının yerel Bacillus thuringiensis suşlarına duyarlılığı

Tomato leafminer, Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae) is one of the most important tomato pests worldwide and causes 100% product loss if not controlled. Chemical insecticides, which have been overused for many years, have induced resistance in the pests and made it difficult to control their populations in the field. The use of biological agents that express insecticidal proteins, such as Bacillus thuringiensis, is an alternative to conventional insecticides to suppress pest populations. In this study, to recover novel B. thuringiensis strains from soil samples, a survey was conducted in Bilecik province in 2021. Thirteen local B. thuringiensis strains were isolated and the susceptibility of three different field populations (Samsun, İzmir, and Bilecik) of T. absoluta to these strains was evaluated. Bacillus thuringiensis B3 (Bt-B3) strain, which contains lepidopteran-active toxin genes, was more virulent for all T. absoluta populations tested. In addition, Samsun population was more sensitive to the B3 strain than İzmir and Bilecik. The LC50 values of Bt-B3 were determined to be 13.28, 26.06 and 24.24 ppm for Samsun, İzmir and Bilecik populations, respectively. Sequencing of the 16S rRNA gene region confirmed that the isolate was B. thuringiensis, while electron microscopy revealed that the isolate produced bipyramidal, cubic and spherical insecticidal proteins. The results of this study indicate that the isolate Bt-B3 appears to be a promising biocontrol agent for integrated pest management of T. absoluta in Türkiye.

Recent assessment and characterization of Tuta absoluta resistance to cartap hydrochloride

Tuta absoluta can cause 100% loss in tomato yield in Brazil and chemical control, which uses cartap hydrochloride (nereistoxin derivative), is still the most used tactic against T. absoluta populations. Despite the long use of cartap hydrochloride, the genetic and physiological bases underlying the resistance are not known. Resistance to cartap hydrochloride among field populations varied from very low (RR = 2.3 fold) to very high (RR = 537 fold). The Gameleira 2 (GML 2-Res) population was exposed to cartap hydrochloride (up to 500 mg L−1) for few rounds of selection to clean extrinsic factors before used in downstream experiments after 2.5 years without selection in laboratory. Resistance to cartap hydrochloride was autosomal, incompletely recessive, and polyfactorial. The effective dominance (dominance level of survival at a given insecticide dose) at 60 mg of cartap hydrochloride L−1 (which killed 100% of heterozygous individuals) discriminated resistant from susceptible phenotypes. Hydrolases and glutathione S-transferase appear to detoxify cartap hydrochloride as TPP and DEM synergized its toxicity, but CYP450-dependent monooxygenases are as well implicated. Cross-resistance was significant between cartap hydrochloride and methoxyfenozide (RR = 6.99 fold), deltamethrin (RR = 3.57 fold), chlorfenapyr (RR = 3.21 fold), or chlorantraniliprole (RR = 2.83 fold). The characterization of T. absoluta resistance to cartap hydrochloride provides valuable information to refine the management of resistance to insecticides (MRI) program in Brazil with cross resistance pattern very favorable to the rotation of active ingredients that will impair survival of this pest to that insecticide in the field.

Evidence-based insecticide resistance in South American tomato leaf miner,Phthorimaea absoluta(Meyrick) under laboratory selection

The South American tomato moth, Phthorimaea absoluta (Meyrick), is one of the key pests of tomato in India. Since its report in 2014, chemical control has been the main means of tackling this pest, both in the open field and protected cultivation. Despite regular insecticidal sprays, many outbreaks were reported from major tomato-growing regions of South India during 2019-2020. A study was conducted to investigate the effect of insecticide resistance on biology, biochemical enzymes, and gene expression in various P. absoluta field populations viz., Bangalore, Kolar, Madurai, Salem, and Anantapur to commonly used insecticides such as flubendiamide, cyantraniliprole, and indoxacarb. Increased levels of insecticide resistance ratios (RR) were recorded in P. absoluta populations of different locations. A significant increase in cytochrome P450 monooxygenase (CYP/MFO) and esterase levels was noticed in the resistant population compared to susceptible one. Through molecular studies, we identified four new CYP genes viz., CYP248f (flubendiamide), CYP272c, CYP724c (cyantraniliprole), and CYP648i (indoxacarb). The expression levels of these genes significantly increased as the folds of resistance increased from G1 to G20 (generation), indicating involvement of the identified genes in insecticide resistance development in P. absoluta. In addition, the resistant populations showed decreased fecundity, increased larval development period, and adult longevity, resulting in more crop damage. The information generated in the present study thus helps in understanding the development of insecticide resistance by P. absoluta and suggests the farmers and researchers to use insecticides wisely by adopting insecticide resistance management as a strategy under integrated pest management.

Efficacy of vegetable oil extracts for control of insect pests of tomato in Southern Benin

Pests are a menace to production of tomato (Lycopersicon esculentum Mill.) in sub-Sahara Africa. The objective of this study was to evaluate the efficacy of oil extracts of selected common plants for control of pests of tomato in Benin. The study was carried out on the Togba market garden sites in Benin. The botanical pesticides (Tephrosia purpurea, Ricinus communis, Thevetia neriifolia and Cashew Nut Shell Cold Liquid (CNSL cold) were compared with a biological insecticide (Topbio), a synthetic insecticide (Lambda cyhalothrin) and an untreated negative control. The fish model and the generalised linear mixed or fixed effects model were used to explain the number of caterpillars per plot as a function of the products tested during the different plant phases. Tephrosia purpurea oil, cold CNSL, Topbio and lambda cyhalothrin treatments significantly reduced H. armigera, S. littoralis and T. absoluta populations. The average yields of marketable tomato ranged from 7.20 ± 0.89 t ha-1 for the controls and 21.14 ± 3.56 and 20.46±1.98 t ha-1 for the plots treated with Tephrosia purpurea and CNSL cold on tomato, respectively. Plots treated with the synthetic insecticide lambda cyhalothrin gave the best yields (31.15±3.20 t ha-1). Of all the extracts tested, cold extracted CNSL and T. purpurea oil showed very high larvicidal activity at doses of 10%, compared to R. communis and T. neriifolia oil on the farm. The larvicidal activity of the extracts observed at low doses on H. armigera and S. littoralis larvae seems to offer an alternative advantage for the control of tomato pests.

Can the Combined Use of the Mirid Predator Nesidiocoris tenuis and a Braconid Larval Endoparasitoid Dolichogenidea gelechiidivoris Improve the Biological Control of Tuta absoluta?

Simple SummaryCombining natural enemies may lead to synergistic, additive, or antagonistic effects on the control of insect pests. An investigation into the nature and outcome of the interaction between a generalist mirid predator, Nesidiocoris tenuis, and a specialist koinobiont larval endoparasitoid, Dolichogenidea gelechiidivoris, in the control of a co-shared host/prey, Tuta absoluta, was undertaken under laboratory conditions. We found that the presence of N. tenuis did not affect oviposition performance or progeny production by D. gelechiidivoris. When both natural enemies were combined, the efficacy in reducing T. absoluta populations was significantly higher than that of either natural enemy used alone. Nesidiocoris tenuis preferentially reduced the densities of T. absoluta eggs, while D. gelechiidivoris reduced the larval stages of the pest. The combined use of N. tenuis and D. gelechiidivoris could potentially help reduce the overall infestation level of T. absoluta in tomato agroecosystems.The koinobiont solitary larval endoparasitoid Dolichogenidea gelechiidivoris (Marsh) (Syn.: Apanteles gelechiidivoris) (Hymenoptera: Braconidae) and the predatory bug Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) are important natural enemies of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), a serious pest of tomato. Although N. tenuis preferentially feeds on T. absoluta eggs, it is also recorded as a predator of first and second instar larval stages. Dolichogenidea gelechiidivoris preferentially seeks these early larval stages of T. absoluta for oviposition. The occurrence of intraguild predation between N. tenuis and D. gelechiidivoris and the consequences on the oviposition performance of D. gelechiidivoris were investigated in the laboratory. Regardless of the manner of introduction (i.e., the sequence of combinations with D. gelechiidivoris) or density (i.e., number of N. tenuis combined with D. gelechiidivoris), the presence of N. tenuis did not affect the oviposition performance of D. gelechiidivoris or the parasitoid’s progeny. Combination assays revealed that the efficacy of the combined use of N. tenuis and D. gelechiidivoris in controlling T. absoluta populations was significantly higher than that of either natural enemy alone. Our results highlight the potential of combining mirid predators and koinobiont larval endoparasitoids to control T. absoluta. The findings further contribute to data supporting the release of D. gelechiidivoris in tomato agroecosystems for the control of T. absoluta in Africa, where N. tenuis is widespread and abundant.

Outbreak of the South American tomato leafminer, Tuta absoluta, in the Chinese mainland: geographic and potential host range expansion.

In 2017 Tuta absoluta was identified as an invasive species in China. Due to its rapid geographic expansion and the severe crop damage it causes, T. absoluta poses a serious threat to China's tomato production industry. To determine its geographic distribution and host range, intensive surveys and routine monitoring were conducted across the Chinese mainland between 2018 and 2019. The population colonization coefficient (PCC; ratio of colonized sites and prefectures) and population occurrence index (POI; ratio of infested host species and PCCs) were calculated. In northwestern China, T. absoluta populations established in Xinjiang exhibited a medium PCC value (~0.03). In southwestern China, populations in Yunnan and its five neighboring provinces exhibited high (~0.50 in Yunnan and Guizhou), or low (<0.02 in Guangxi, Sichuan, Hunan, and Chongqing) PCC values. In the Chinese mainland, infestations of four crop plant species (tomato, eggplant, potato, and Chinese lantern) and two wild plant species (black nightshade and Dutch eggplant) were identified; tomatoes were infested in every colonized province. Chinese lantern and Dutch eggplant are potentially novel hosts. Yunnan, Guizhou, and Xinjiang experienced the most serious damage (POI). In southwestern China, observed damage significantly decreased with increased distance from the first discovery site of T. absoluta to the farthest county of an infested province increased. T. absoluta populations are well-established and could potentially spread to other regions of China. The present study helps to inform the establishment of better pest management guidelines and strategies in China and tomato-producing regions worldwide. © 2021 Society of Chemical Industry.

Population structure and insecticide resistance status of Tuta absoluta populations from Turkey.

Tuta absoluta is a devastating pest in tomato production areas worldwide. After its first introduction to Turkey in 2009, it quickly became the major pest of tomato-growing areas. Although some biocontrol agents have been used, especially in greenhouses, the main control of T. absoluta relies heavily on chemical insecticides. However, failure in chemical control has often been reported due to resistance development. In this study, we investigated (i) the population structure of 22 T. absoluta populations across Turkey by analysing haplotypes, based on the cytochrome oxidase subunit I gene; (ii) the efficacy of three registered insecticides from different classes (metaflumizone, chlorantraniliprole and spinosad) in real field-greenhouse conditions; and (iii) the geographic distribution of target-site mutations associated with insecticide resistance. The efficacy of spinosad was higher than that of chlorantraniliprole and metaflumizone in the greenhouse trials, as documented by the mortality rates obtained, up to 14 days post application. Known resistance mutations in ryanodine receptors (RyR) (i.e. the I4790M/K and G4946E), nicotinic acetylcholine receptors (G275E), acetylcholinesterases (A201S) and voltage-gated sodium channels (F1845Y and V1848I) were found at various frequencies across the populations genotyped. The I4790K diamide resistance mutation in the RyR has been reported for the first time in T. absoluta populations. Although a total of eight haplotypes were found, the overall mean genetic distance was lower than 0.001, indicating the high genetic homogeneity among Turkish T. absoluta populations. The results will contribute to design area-wide resistance management programs in T. absoluta control in Turkey. However, more monitoring studies are needed to implement evidence-based insecticide resistance management strategies in the frame of integrated pest management. © 2021 Society of Chemical Industry.

High resistance to insect growth disruptors and control failure likelihood in Brazilian populations of the tomato pinworm Tuta absoluta

This study aimed to compare the susceptibility of tomato pinworm, Tuta absoluta, from four Brazilian regions to insect growth disruptor (IGD) insecticides by tomato leaf-dip bioassays. Larval mortality was assessed seven days after exposure to insecticide-treated leaves. The control failure likelihood (CFL) was estimated after larval bioassays with IGDs recommended label rate. Mortality data were subjected to Probit and variance analysis. All populations of tomato pinworm showed significant resistance to one or more insecticides. The LC50 values ranged from 0.34 to 0.63 g L−1 (chlorfluazuron), 0.17 to 0.92 g L−1 (teflubenzuron), 0.13 to 1.28 g L−1 (novaluron), 0.29 to 0.46 g L−1 (lufenuron), and 0.71 to 4.60 g L−1 (methoxyfenozide). The resistance ratios varied from 1.2 to 1.8-fold (chlorfluazuron), 1.4 to 5.5-fold (teflubenzuron), 1.2 to 9.9-fold (novaluron), 1.0 to 1.6-fold (lufenuron), and 1.5 to 6.5-fold (methoxyfenozide). Despite the low resistance ratios ( 54%, indicating likely control failure at the IGD label rates. We detected significant variations among populations of T. absoluta for activity of enzymes glutathione S-transferases (GST), cytochrome P450-dependent monooxygenases (MFO) and α-esterase (EST), however there was no significant difference between the populations for activity of β-esterase (EST). The evolution of resistance in T. absoluta populations to IGDs observed in this study is likely due to high selection pressure, demanding insecticide resistance management practices and environmentally sustainable tactics to obtain a more effective control of this pest.

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

AbstractThe 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 &lt; 0.4 mg/L; Control failure likelihood (CFL) = −25%], spinosad (LC50 &lt; 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.

Combining Host Plant Resistance, Selective Insecticides, and Biological Control Agents for Integrated Management of Tuta absoluta

Combination of pest management strategies that minimize pesticide use and conserve natural enemies is important for a sustainable environment. Overreliance on synthetic insecticides in the management of Tuta absoluta has led to pesticide resistance leading to difficulties in managing the pest. In this regard, alternative measures need to be put in place to reduce the effects of this pest. The objective of this study was, therefore, to assess the effectiveness of host plant resistance, biological control, and selective insecticides when used in combination, in the management of T. absoluta in tomato production. The study was set up in a greenhouse in a completely randomized design involving two tomato varieties, an insecticide (chlorantraniliprole), and a biological control agent(Macrolophus pygmaeus), applied singly or in combination. Data were collected on T. absoluta damage from the lower, intermediate, and upper leaves. The results from this study show that a combination of insecticide with a moderately resistant variety had a significantly lower T. absoluta damage as compared with a susceptible variety combined with an insecticide. However, the moderately resistant variety when combined with insecticide showed no effect when the biological control agent was added. The susceptible variety significantly reduced T. absoluta damage when combined with the biological control agent. These results indicate that treatment combinations in insect pest management can be utilized. The present study results indicate that using a moderately resistant variety (Riogrande VF) in combination with the insecticide chlorantraniliprole (Coragen®) and a susceptible variety (Pesa F1) in combination with the biological control agent (M. pygmaeus) can improve T. absoluta management. Under good habitat management, the susceptible variety will perform equally as the moderately resistant variety due to suppression of the T. absoluta populations by natural enemies. These findings show the importance of environmental conservation both by enhancing natural enemy abundance and use of selective insecticide in the management of T. absoluta in tomato production. Combinations in this present study are likely to reduce insecticide doses, thereby reducing the cost of production and enhancing environmental compatibility with natural enemies.

Toxicity of Insecticides to Tomato Pinworm, Tuta absoluta (Meyrick) Populations from Tamil Nadu

Tomato pinworm, Tuta absoluta is a serious and notorious pest on tomato. Control mainly relies on insecticides because of their high infestation levels on all plant parts and life stages of the crop. This study, investigated the efficacy of different insecticides, against Tuta absoluta for different populations in laboratory conditions. The LC50 ranged from 0.27 to 2.0 ppm for chlorantraniliprole, from 1.01 to 2.25 ppm for flubendiamide, from 0.32 to 0.90 ppm for spinosad, from 0.98 to 6.52 ppm for imidacloprid, from 0.82 to 6.38 ppm for indoxacarb, from 967.32 to 1911.98 ppm, for chlorpyriphos, The resistance ratios ranged from 1.1 to 7.7-fold difference in all six cases. The laboratory experimental results showed that chlorantraniliprole and spinosad were the most toxic insecticides as compared to other chemicals and showed homogenous response to them.

Molecular characterisation of tomato leaf miner Tuta absoluta populations obtained from different geographical locations of India

The tomato leaf miner, Tuta absoluta (Meyrick) is one of the major invasive insect pests on solanaceous crops. T. absoluta distribution is observed in European, North African Mediterranean basin and Asian countries. The tomato leaf miner is spreading fast and affecting tomato production in both closed and open-field conditions. This insect pest has recently reported in various tomato growing regions of India and causing significant loss of production. In the present study, occurrence of a tomato leaf miner was studied by undertaking an extensive survey in tomato growing regions of India during September 2017 to May 2018. The infestation of T. absoluta was recorded in Maharashtra, Karnataka, Telangana, Tamil Nadu, Haryana and Himachal Pradesh. Severe incidence of T. absoluta infestation was recorded in Maharashtra (Nashik district) and Telangana (Mahabubnagar district) followed by Karnataka (Kalaburgi and Raichur districts). The moths collected during the survey were characterized using mitochondrial cytochrome c oxidase subunit I (COI) gene analysis. The T. absoluta samples showed maximum genetic similarity with KU565720 Kenya, KT452897 Oman, KY212128 South Africa, KY619687 India, KP814057 India and KJ657679 Florida. Nine T. absoluta populations were grouped under a single clade revealing no genetic variation within populations and showed high genetic homogeneity thereby the ideal candidate for sterile insect technique application. Further studies are required on population dynamics, host range, local and area-wide biological control management strategies for the effective management of T. absoluta .

Assessing inoculative releases of Pseudapanteles dignus (Hymenoptera: Braconidae) for the biological control of Tuta absoluta (Lepidoptera: Gelechiidae)

Augmentative biocontrol implemented through inoculative seasonal releases of one or more biological control agents has proven to be a reliable crop protection approach in greenhouse and open field crops. The South American tomato pinworm, Tuta absoluta, is a key tomato pest worldwide. In this context, the effectiveness of the American-native larval endoparasitoid Pseudapantales dignus in reducing T. absoluta populations, in a semi-field set-up under greenhouse crop conditions, was assessed. In individual plants enclosed in cages, five host (T. absoluta):parasitoid (P. dignus) relative densities (2:1; 4:1; 4:2; 10:3 and 10:5) were evaluated through inclusion techniques. Controls for each treatment were included. Parasitization was allowed for 48 h; then leaves with signs of moth injury were removed and taken to the laboratory for rearing the host larvae until its pupation or the formation of P. dignus cocoons. Percentages of parasitism were calculated for each treatment and compared using a generalized linear model (GLM) with binomial link function. Pseudapanteles dignus females failed to parasitize at a host density of 2 larvae per plant; meanwhile at the other host densities tested, it reached from 23 to 61% parasitism. The greater percentage of parasitism was observed at host:parasitoid relative densities of 10:3. This field experiment showed evidence that the efficiency of this biocontrol agent decreases at low host densities, probably influenced by a reduction in host localization stimuli. Besides, at higher P. dignus release rates, parasitism decreased due to self-limitation of adult females by mutual interference when searching for hosts. Pseudapantales dignus has a significant potential for use in biological control programs.

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

AbstractTuta 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) &gt;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%.

Baseline susceptibility and assessment of resistance risk to flubendiamide and chlorantraniliprole in Tuta absoluta (Lepidoptera: Gelechiidae) populations from Kuwait

The tomato leafminer, Tuta absoluta (Meyrick), is one of the most destructive pests of tomato worldwide. T. absoluta has developed resistance to a wide range of insecticides in the field. This study aimed to assess the baseline toxicity of field populations of T. absoluta to flubendiamide and chlorantraniliprole, diamide insecticides recently registered to control the pest in Kuwait. Subsequently, the risk of resistance evolving as well as inheritance of resistance to the insecticides was investigated. The susceptibility variation among the populations tested was low (threefold for flubendiamide and fourfold chlorantraniliprole). The LC50 values for flubendiamide ranged from 0.04 to 0.11 mg L−1, whereas the LC50 values for chlorantraniliprole ranged from 0.29 to 1.13 mg L−1. After 34 generations of selection, 750- and 860-fold increases in resistance were recorded for flubendiamide and chlorantraniliprole, respectively. The realized heritability (h2) of resistance was estimated as 0.21 for flubendiamide and 0.29 for chlorantraniliprole, using threshold trait analysis. The values of the response quotient (Q) for resistance against flubendiamide and chlorantraniliprole were 0.11 and 0.13, respectively. We discussed our results with regard to the development of diamide resistance in T. absoluta, the potential spread of resistance, and strategies to mitigate the evolution of resistance.

Natural mortality factors of tomato leafminer Tuta absoluta in open-field tomato crops in South America.

Little importance has been given to the role of natural mortality factors (biotic and abiotic) in the regulation of tomato leafminer Tuta absoluta (Lepidoptera: Gelechiidae) populations. The present study determined the action of mortality factors on T. absoluta populations infesting cultivated tomato crops. Eighty ecological life tables for T. absoluta in field cultivated tomato plants were constructed and analyzed. Total T. absoluta mortality was 99.08%, with 38.76% mortality during the egg phase, 57.20% in the larva phase and 3.12% in the pupal phase. The main mortality factors during the egg stage were predation, parasitism and egg inviability. In the larval stage, the main mortality factors were predation, parasitism, entomopathogenic agents and physiological disorders. In the pupal stage, the main mortality factor was predation. The larvae of the third and fourth instar were more susceptible to the action of mortality factors and the predatory wasp, Protonectarina sylveirae, was the main insect predator of these larvae. The T. absoluta population is regulated under field conditions by the action of natural enemies of the larvae. The predatory wasp P. sylveirae is very important in the regulation of T. absoluta populations in open-field tomato crops in Brazil. © 2018 Society of Chemical Industry.

Labeling membrane receptors with lectins and evaluation of the midgut histochemistry of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) populations with different levels of susceptibility to formulated Bt.

Studies show that insects can adapt to the toxins of Bacillus thuringiensis under field and laboratory conditions through the development of resistance to the bacterium and its formulations. This has been demonstrated in the failure to control Tuta absoluta populations in Brazil. This study evaluated membrane receptors using peroxidase-labeled lectins and the midgut histochemistry of T. absoluta populations to assess susceptibility to the insecticides Bt fomulations. The histochemistry analysis used Periodic Acid-Schiff for glycogen and Ponceau Xylidine for total proteins. The presence of glucose/mannose and N-acetylgalactosamine (GalNAc) was analyzed using specific lectins. One susceptible and one tolerant population were used in the study; insects were exposed to the insecticide concentrations recommended by the manufacturers. The midgut was collected after an interval of 20 min and analyzed using optical microscopy. Bt fomulation interferes with the glycogen content, whereas XenTari® interferes with the protein content, irrespective of the level of susceptibility. High expression of GalNAc residues was observed using soybean lectin labeling, indicating a direct relationship between the glycosylation pattern and susceptibility to Bt fomulation in the Pelotas population. The use of Bt fomulation caused greater alterations in the larval intestinal histophysiology compared to the use of XenTari® . © 2018 Society of Chemical Industry.