Evolutionary genomics of three agricultural pest moths reveals rapid evolution of host adaptation and immune-related genes.

BACKGROUND: Understanding the genotype of pest species provides an important baseline for designing integrated pest management (IPM) strategies. Recently developed long-read sequence technologies make it possible to compare genomic features of nonmodel pest species to disclose the evolutionary path underlying the pest species profiles. Here we sequenced and assembled genomes for 3 agricultural pest gelechiid moths: Phthorimaea absoluta (tomato leafminer), Keiferia lycopersicella (tomato pinworm), and Scrobipalpa atriplicella (goosefoot groundling moth). We also compared genomes of tomato leafminer and tomato pinworm with published genomes of Phthorimaea operculella and Pectinophora gossypiella to investigate the gene family evolution related to the pest species profiles. RESULTS: We found that the 3 solanaceous feeding species, P. absoluta, K. lycopersicella, and P. operculella, are clustered together. Gene family evolution analyses with the 4 species show clear gene family expansions on host plant-associated genes for the 3 solanaceous feeding species. These genes are involved in host compound sensing (e.g., gustatory receptors), detoxification (e.g., ABC transporter C family, cytochrome P450, glucose-methanol-choline oxidoreductase, insect cuticle proteins, and UDP-glucuronosyl), and digestion (e.g., serine proteases and peptidase family S1). A gene ontology enrichment analysis of rapid evolving genes also suggests enriched functions in host sensing and immunity. CONCLUSIONS: Our results of family evolution analyses indicate that host plant adaptation and pathogen defense could be important drivers in species diversification among gelechiid moths.

Better Together: Volatile-Mediated Intraguild Effects on the Preference of Tuta absoluta and Trialeurodes vaporariorum for Tomato Plants.

Plant-herbivore interactions have been extensively studied in tomato plants and their most common pests. Tomato plant chemical defenses, both constitutive and inducible, play a role in mediating these interactions. Damaged tomato plants alter their volatile profiles, affecting herbivore preferences between undamaged and damaged plants. However, previous studies on tomato volatiles and herbivore preferences have yielded conflicting results, both in the volatile chemistry itself as well as in the attraction/repellent herbivore response. This study revisits the volatile-mediated interactions between tomato plants and two of their main herbivores: the leafminer Tuta absoluta and the whitefly Trialeurodes vaporariorum. Tomato plant volatiles were analyzed before and after damage by each of these herbivores, and the preference for oviposition (T. absoluta) and settling (T. vaporariorum) on undamaged and damaged plants was assessed both after conspecific and heterospecific damage. We found that both insects consistently preferred damaged plants over undamaged plants. The emission of herbivore-induced plant volatiles (HIPVs) increased after T. absoluta damage but decreased after T. vaporariorum damage. While some of our findings are in line with previous reports, T. absoluta preferred to oviposit on plants damaged by conspecifics, which differs from earlier studies. A comparison of HIPVs emitted after damage by T. absoluta and T. vaporariorum revealed differences in up- or down-regulation, as well as significant variations in specific compounds (12 for T. absoluta and 26 for T. vaporariorum damaged-plants). Only two compounds, ß-caryophyllene and tetradecane, significantly varied because of damage by either herbivore, in line with the overall variation of the HIPV blend. Differences in HIPVs and herbivore preferences may be attributed to the distinct feeding habits of both herbivores, which activate different defensive pathways in plants. The plant's challenge in simultaneously activating both defensive pathways may explain the preference for heterospecific damaged plants found in this study, which are also in line with our own observations in greenhouses.

Probe-based quantitative PCR and RPA-Cas12a molecular diagnostics for detection of the tomato pest Phthorimaea absoluta (Lepidoptera: Gelechiidae).

The tomato pest Phthorimaea absoluta Meyrick is highly invasive but has not yet invaded North America. However, several morphologically similar species are already present, making detection of P. absoluta presence and invasion challenging. We designed a quantitative PCR molecular diagnostic to differentiate P. absoluta, P. operculella (Zeller), or Keiferia lycopersicella (Walsingham) (Lepidoptera: Gelechiidae) DNA. Additionally, we developed an RPA-Cas12a molecular diagnostic that allows for the isothermal detection of P. absoluta DNA, eliminating the need for a thermocycler. The results of the RPA-Cas12a diagnostic can be visualized simply using a UV light source and cell phone camera. We expect these diagnostics to improve quarantine and prevention measures against this serious agricultural threat.

Few indirect effects of baculovirus on parasitoids demonstrate high compatibility of biocontrol methods against Tuta absoluta.

BACKGROUND: Combining different biocontrol agents, particularly micro- and macroorganisms, can contribute to new and sustainable pest control approaches. Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is one of the most destructive pests of solanaceous crops. An emerging management strategy consists of biological control using microbial insecticides such as baculoviruses, but with limited efficacy. Thanks to their high target specificity, baculoviruses can be used simultaneously with natural enemies such as parasitoids for improved control of T. absoluta. However, potential indirect nontarget effects of baculoviruses on parasitoids can result from overlapping resource requirements. We assessed whether ovipositing parasitoid females discriminated against virus-treated hosts and examined the outcome of within-host competition between the hymenopteran parasitoids Necremnus tutae (Reuter) (Eulophidae) and Dolichogenidea gelechiidivoris Marsch (Braconidae), and the Phthorimaea operculella granulovirus (PhopGV, Baculoviridae) that infects T. absoluta larvae. RESULTS: Female D. gelechiidivoris discriminated against virus-treated hosts, whereas N. tutae did not. We found few indirect virus-related effects depending on the species, the sex, and the time of virus treatment. Effects were ambivalent for D. gelechiidivoris offspring and ranged from increased male longevity when infection occurred before parasitization to reduced emergence and male longevity when infection occurred after parasitization. N. tutae offspring showed a longer development time and shorter male longevity when they developed in virus-treated hosts. CONCLUSION: The virus had a low impact on parasitoid offspring. In rare cases, adverse effects were detected; however, the low magnitude of these effects is unlikely to reduce the fitness of parasitoid offspring, therefore both parasitoids seem compatible with the baculovirus for control of T. absoluta. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Instar Determination for the Tomato Leafminer Tuta absoluta (Lepidoptera: Gelechiidae) Using the Density-Based OPTICS Clustering Algorithm.

The tomato leafminer Tuta absoluta (Meyrick) is one of the most harmful pests of solanaceous crops. Its larval morphological characteristics are similar, making the distinguishing between different larval instars difficult. Accurate identification of T. absoluta instars is necessary either for population outbreak forecasting, or developing successful control programs. Although a clustering algorithm can be used to determine the number of larval instars, little is known regarding the use of density-based ordering points to identify the clustering structure (OPTICS) and determine the number of larvae. In this study, larval instars of 240 T. absoluta individuals were determined by the density-based OPTICS clustering method, based on mandible width, and head capsule width and length. To verify the feasibility of the OPTICS clustering method, we compared it with the density-based spatial clustering of applications with noise (DBSCAN) clustering algorithm, Gaussian mixture models, and k-means. Additionally, the instars determined by the clustering methods were verified using the Brooks-Dyar rule, Crosby rule, and linear regression model. The instars determined by the OPTICS clustering method were equal to those determined by the other types of clustering algorithms, and the instar results were consistent with the Brooks-Dyar rule, Crosby rule, frequency analysis, and logarithmic regression model. These results indicated that the OPTICS clustering method is robust for determining insect larva instar phase. Moreover, it was found that three morphological indices of T. absoluta can be used for determining instars of this pest in the field, which may provide important information for the management of T. absoluta populations.

A DNA Extraction Method for Insects From Sticky Traps: Targeting a Low Abundance Pest, Phthorimaea absoluta (Lepidoptera: Gelechiidae), in Mixed Species Communities.

Invasive insects can cause catastrophic damage to ecosystems and cost billions of dollars each year due to management expenses and lost revenue. Rapid detection is an important step to prevent invasive insects from spreading, but improvements in detection capabilities are needed for bulk collections like those from sticky traps. Here we present a bulk DNA extraction method designed for the detection of Phthorimaea absoluta Meyrick (Lepidoptera: Gelechiidae), an invasive moth that can decimate tomato crops. We test the extraction method for insect specimens on sticky traps, subjected to different temperature and humidity conditions, and among mock insect communities left in the field for up to 21 d. We find that the extraction method yielded high success (>92%) in recovering target DNA across field and lab trials, without a decline in recovery after three weeks, across all treatments. These results may have a large impact on tomato growing regions where P. absoluta is in the early stages of invasion or not yet present. The extraction method can also be used to improve detection capabilities for other bulk insect collections, especially those using sticky traps, to the benefit of pest surveys and biodiversity studies.

Comparing, evaluating and combining statistical species distribution models and CLIMEX to forecast the distributions of emerging crop pests.

BACKGROUND: Forecasting the spread of emerging pests is widely requested by pest management agencies in order to prioritise and target efforts. Two widely used approaches are statistical Species Distribution Models (SDMs) and CLIMEX, which uses ecophysiological parameters. Each have strengths and weaknesses. SDMs can incorporate almost any environmental condition and their accuracy can be formally evaluated to inform managers. However, accuracy is affected by data availability and can be limited for emerging pests, and SDMs usually predict year-round distributions, not seasonal outbreaks. CLIMEX can formally incorporate expert ecophysiological knowledge and predicts seasonal outbreaks. However, the methods for formal evaluation are limited and rarely applied. We argue that both approaches can be informative and complementary, but we need tools to integrate and evaluate their accuracy. Here we develop such an approach, and test it by forecasting the potential global range of the tomato pest Tuta absoluta. RESULTS: The accuracy of previously developed CLIMEX and new statistical SDMs were comparable on average, but the best statistical SDM techniques and environmental data substantially outperformed CLIMEX. The ensembled approach changes expectations of T. absoluta's spread. The pest's environmental tolerances and potential range in Africa, the Arabian Peninsula, Central Asia and Australia will be larger than previous estimates. CONCLUSION: We recommend that CLIMEX be considered one of a suite of SDM techniques and thus evaluated formally. CLIMEX and statistical SDMs should be compared and ensembled if possible. We provide code that can be used to do so when employing the biomod suite of SDM techniques. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Screening Potential Reference Genes in Tuta absoluta with Real-Time Quantitative PCR Analysis under Different Experimental Conditions.

Tuta absoluta is one of the most significant invasive pests affecting tomato plants worldwide. RT-qPCR has emerged as one of the most sensitive and accurate methods for detecting gene expression data. The screening of stable internal reference genes is the most critical step for studying the molecular mechanisms of environmental adaptability. The stable reference genes expressed in T. absoluta under specific experimental conditions have not yet been clarified. In this study, seven candidate reference genes (RPL27, RPS13, RPS15, EF1-α, TUB, TBP, and ß-actin) and their optimal numbers were evaluated under biotic (developmental stages and adult tissues) and abiotic (insecticide, temperature, and plant VOC) conditions using four software programs. Our results identified the following reference genes and numbers as optimal: three genes (EF1-α, RPS13, and RPL27) for different developmental stages (egg, larva, pupa, unmated adult), two genes (RPS13 and TBP) for adult tissues (antenna, head, thorax, abdomen, leg), two genes (TBP and RPS13) for insecticides (Bacillus thuringiensis, chlorpyrifos, abamectin-aminomethyl, and chlorantraniliprole), two genes (RPL27 and TUB) for temperature-induced stresses (0, 25, and 40 °C), and two genes (RPS13 and TUB) for VOC-induced stresses (nonanal, α-phellandrene, and tomato leaves). Our results provide a reference for selecting appropriate reference genes for further study of the functional genes of T. absoluta under different experimental conditions.

Water Balance and Desiccation Tolerance of the Invasive South American Tomato Pinworm.

Temperature and dehydration stress are two major co-occurring environmental stressors threatening the physiology, biochemistry, and ecology of insects. As such, understanding adaptive responses to desiccation stress is critical for predicting climate change impacts, particularly its influence on insect invasions. Here, we assessed water balance and desiccation resistance of the invasive Tuta absoluta (Meyrick, 1917) (Lepidoptera: Gelechiidae), and infer how eco-physiology shapes its niche. We measured basal body water and lipid content, water loss rates (WLRs), and desiccation resistance in larvae (second to fourth instars) and adults. Body -water, -lipid, and WLRs significantly varied across life stages. Second instars recorded the lowest while fourth instars exhibited the highest body water and lipid content. Adult body water and lipid content were higher than second and third instars and lower than fourth instars while proportion of body water and lipid contents were highest in adults and second larval instars respectively. Water loss rates were significantly highest in fourth-instar larvae compared to other life stages, but differences among stages were less apparent at longer exposure durations (48 h). Desiccation resistance assays showed that second instars had greatest mortality while fourth-instar larvae and adults were the most desiccation tolerant. Our results show that T. absoluta fourth-instar larvae and adults are the most resilient developmental stages and potentially contribute most to the invasion success of the pest in arid environments. Incorporation of these species-specific eco-physiological traits in predictive models can help refine invasive species potential spread under changing climates.

The seasonal dynamic of Tuta absoluta in Solanum lycopersicon cultivation: Contributions of climate, plant phenology, and insecticide spraying.

BACKGROUND: A variety of abiotic and biotic factors promoting seasonal variation in the population of insect pests. Knowledge of the timing and magnitude of these factors is important for the study of population dynamics and the development of efficient pest management programs. Currently, there are few studies regarding Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) seasonal dynamics in tomato cultivation under open field conditions, either with or without insecticide application. This study aimed to investigate the effects of tomato phenology, climatic factors, and insecticide spraying on the seasonal dynamics of T. absoluta in tomato cultivation under open field conditions, using data from monitoring performed for 3 years. RESULTS: Insecticide, host plant, and climatic conditions can affect T. absoluta life cycles directly over time, resulting in shifts of peaks of the pest. Insecticides for T. absoluta control reduced injury caused by larvae; however, this was not enough to reduce the density below economic injury levels (EIL) during periods of climatic conditions more suitable for population growth. Tuta absoluta densities surpassed EIL more frequently during the tomato plant fruiting stage. The highest densities of mines and damaged fruits occurred during periods of August to January and September to January in crops without and with the application of insecticides, respectively. Regarding the climatic factors, the highest densities of T. absoluta occurred during periods of increasing air temperature and low rainfall. CONCLUSION: This study provides relevant insights into the factors that regulate the dynamics of T. absoluta in tomato cultivation and the decision-making process of control of this pest. © 2021 Society of Chemical Industry.

Cold hardiness of the South American tomato pinworm Tuta absoluta (Lepidoptera: Gelechiidae): both larvae and adults are chill-susceptible.

BACKGROUND: For many insects, including invasive species, overwintering survival is achieved behaviourally (e.g. through migration) or physiologically by entering diapause, a state of arrested physiological development that may be accompanied with depressed supercooling points (SCPs). Diapause allows in situ adaptation to adverse environmental conditions, providing sufficient parent propagules for insect pest proliferation when optimal conditions resurface. This phenomenon has however not been observed in the invasive South American tomato pinworm Tuta absoluta in its Mediterranean invaded areas. Moreover, no studies have looked at its overwintering survival in sub-Saharan Africa. Here, we thus investigated the cold hardiness of Tuta absoluta larvae and adults to better explain its local overwintering adaptation strategy. RESULTS: Larval lower lethal temperatures ranged from -1 to -17 °C for 0.5 to 4 h durations. Adults showed lower temperature activity limits than larvae albeit freeze strategy experiments showed neither survived internal freezing. Fasting and dehydration pre-treatment generally depressed SCPs, although asymmetrically, conferring more negative SCPs for larvae. Ramping rates, synonymic to diurnal temperature changes also significantly affected SCPs while, inoculative freezing significantly compromised freezing temperatures in both larvae and adults. CONCLUSION: Our results suggest that (i) Tuta absoluta larvae and adults are chill-susceptible and may successfully overwinter, (ii) larvae appear more cold hardy than adults and (iii) ecological factors e.g. inoculative freezing, cooling rates, feeding- and hydration-status may affect cold hardiness. These results are important in determining species range limits, population phenology, modelling pest risk status and allows temporal life-stage specific targeting of management strategies.

A gene silencing of V-ATPase subunit A interferes with survival and development of the tomato leafminer, Tuta absoluta.

RNA interference (RNAi) technology is not only considered as a tool to analyze gene function, but it is also potentially considered as a strategy to develop novel biopesticide. In the current study, a double-stranded RNA specific to v-ATPase subunit A of the tomato leafminer, Tuta absoluta (Meyrick; Lepidoptera: Gelechiidae), was orally administered. A gradual decrease in the expression of the gene was observed from Day 1 to 3 and resulted in significant larval mortality. These results suggest that v-ATPases A can be considered as a promising target gene by RNAi technology to be used in the management of the tomato leafminer.

Repellence and fumigant toxicity of essential oils of Ocimum gratissimum and Ocimum kilimandscharicum on Tuta absoluta (Lepidoptera: Gelechiidae).

Tuta absoluta Meyrick originates in South America and is now one of the most important insect pests of Solanaceae in different parts of the world, including Africa. Its control has relied primarily on chemical insecticides, which are associated with negative ecological effects. In the present study, essential oils of Ocimum gratissimum and O. kilimandscharicum were tested for repellence and fumigant toxicity on the adult stages under laboratory conditions. The oil of O. gratissimum was more repellent, but its toxicity was comparable with that of O. kilimandscharicum. The major constituents of O. gratissimum were methyl eugenol (39.5%) and eugenol (29.7%). Those of O. kilimandscharicum were camphor (47.1%) and 1.8-cineole (19.3%). Eugenol (LC50 of 0.24 µl/ml, 83.3%, RI50 = 0.15) and camphor (LC50 of 0.23 µl/ml, 89.5%, RI50 = 0.13) were more toxic (at 1 µl/ml for 24 h) and repellent than the other constituents. The results show potential of the essential oils for use in integrated management of the tomato pest.

A Real-Time PCR Assay for Rapid Identification of Tuta absoluta (Lepidoptera: Gelechiidae).

The tomato leafminer, Tuta absoluta (Meyrick), is a highly destructive pest of tomatoes, causing damage to leaves, stalks, buds, and fruits. Native to South America, T. absoluta is now found throughout Europe, South Asia, Africa, parts of Central America, and the Caribbean. Adults are small, with a wingspan of approximately one cm and lack distinctive markings, making morphological identification difficult. Larvae are also difficult to identify and resemble those of many other gelechiids. Due to the extensive time spent and expertise required for morphological identification, and the imminent threat to the North American tomato crop, we have developed a rapid molecular test for discriminating individual specimens of T. absoluta using a probe-based real-time polymerase chain reaction (PCR) assay. The assay is able to quickly distinguish T. absoluta from similar-sized moth specimens that are attracted to T. absoluta pheromone lures in the United States and is also able to identify larvae of T. absoluta. Decreased identification time for this critical pest will lead to more rapid identification at ports of entry and allow for more efficient trap screening for domestic monitoring programs.

Interactions Between the Nematode Heterorhabditis amazonensis JPM4 and the Predator Macrolophus basicornis: Two Natural Enemies of Tuta absoluta Native to South America.

Entomopathogenic nematodes (EPNs) and predatory mirids are among the most effective natural enemies for the control of Tuta absoluta, a key pest of tomato worldwide. In the case of South America, the native EPN Heterorhabditis amazonensis and the predator Macrolophus basicornis (Stal) coexist in tomato. The intraguild interactions of two ENPs, H. amazonensis JPM4 and the widely used Steinernema carpocapsae, with the predator M. basicornis, were studied in laboratory setups with the objective of evaluating the potential interactions between them. We hypothesized that the two natural enemies do not interact negatively. The first nymphal stage of the predator was not affected when exposed to tomato leaves directly sprayed with both EPNs, which we attributed to the small size of its stylet. Individuals treated with H. amazonensis JPM4 had low mortality rates in all developmental stages with a maximum of 1.3%. Mortality was higher when the predator was exposed to S. carpocapsae (28% for adults) and correlated positively with increasing developmental stages. In prey choice tests between larvae infected with H. amazonensis and uninfected larvae, M. basicornis fed indistinctively showing no clear preference. When presented with choice larvae infected with S. carpocapsae, the consumption of healthy larvae was higher. In a no-choice prey acceptance experiment, M. basicornis preyed on both healthy and infected larvae with no difference in larvae consumed. Predators that had fed from infected larvae did not exhibit signs of nematode infection and survived. Our results indicate that the South American native H. amazonensis JPM4 and M. basicornis do not show a negative interaction and are promising candidates for combined use in T. absoluta biological control.

Parámetros poblacionales de Tuta absoluta (Lepidoptera: Gelechiidae) y pérdidas asociadas en tomate de invernadero / Population parameters of Tuta absoluta (Lepidoptera: Gelechiidae) and associated losses in greenhouse tomato

Introducción: El minador de hojas de tomate, Tuta absoluta (Meyrick), la plaga más peligrosa para la producción de tomate, Solanum lycopersicum L., en todo el mundo; puede causar pérdidas totales y es difícil de controlar. Por lo tanto, comprender la dinámica de sus poblaciones en el cultivo es una prioridad para mitigar el daño. Objetivo: Aquí, los parámetros de la población de T. absoluta fueron evaluados en tomate var. Sonero en invernadero, en tres sistemas de gestión (comercial, población máxima y control total). Métodos: Durante 25 semanas en La Unión, Antioquia, Colombia, se aplicaron modelos matemáticos para describir las poblaciones de larvas y adultos (machos) en el tiempo, en relación con los parámetros de producción y las pérdidas asociadas. Resultados: La tasa de crecimiento intrínseco fue de 0.4466 larvas por semana. Los modelos gaussianos y exponenciales describieron mejor a la población en el tiempo. Las pérdidas se asociaron con el peso y la cantidad de frutos comercializables, y también con el peso total de producción y la cantidad de racimos y frutos totales. Conclusión: Las larvas de T. absoluta tienen un crecimiento exponencial en invernadero ventilado, con una tasa de crecimiento intrínseca menor que la calculada por las tablas de vida en el laboratorio.

Introduction: The tomato leafminer, Tuta absoluta (Meyrick), the most threatening pest for tomato, Solanum lycopersicum L., production worldwide, may cause total losses, and is difficult to control. Thus, understanding its populations dynamic in the crop is a priority to mitigate damage. Objective: Herein, population parameters of T. absoluta were evaluated in tomato var. Sonero in the greenhouse, in three management systems (commercial, maximum population and total control). Methods: During 25 weeks in La Union, Antioquia, Colombia, mathematical models were applied to describe the populations of larvae and adults (males) in time, as related to production parameters and associated losses. Results: The intrinsic growth rate was 0.447 larvae per week. The Gaussian and exponential models described best the population over time. The losses were associated with weight and number of marketable fruits, and with total production weight, and number of clusters and total fruits. Conclusion: T. absoluta larvae have growth exponentially in a ventilated greenhouse, with a smaller intrinsic growth rate than that calculated by life tables in the laboratory.

Oviposition-Induced Volatiles Affect Electrophysiological and Behavioral Responses of Egg Parasitoids.

In response to an attack by herbivores, plants emit a variety of compounds that may act as semiochemicals. Oviposition-induced volatiles (OIPVs) have been shown to mediate interactions between plants and natural enemies. Here, we investigated the role of OIPVs by Tuta absoluta towards two egg parasitoids, Trichogramma cordubense and T. achaeae. We collected headspace volatiles from tomato plants at 24, 48, and 72 h after oviposition by T. absoluta females and tested the antennographic response of Trichogramma parasitoids to them by means of gas chromatography- electro-antennographical detection (GC-EAD). The response of the parasitoids was also tested in behavioral experiments using a Y-tube olfactometer. Oviposition by T. absoluta females induced qualitative and quantitative changes in the volatiles emitted by tomato plants. Antennae of Trichogramma parasitoids responded to several of the induced volatiles in GC-EAD. T. cordubense females were attracted to tomato plants with T. absoluta eggs 24 h after oviposition. The elucidation of the behavior of egg parasitoids towards OIPVs enhances the development of sustainable management strategies either by selecting species that exploit OIPVs or by manipulating their foraging behavior by utilizing specific OIPVs that are used by parasitoids as a host location.

Tuta absoluta (Lepidoptera: Gelechiidae) Success on Common Solanaceous Species from California Tomato Production Areas.

Tuta absoluta (Meyrick) is a devastating pest of tomato that has invaded many regions of the world. To date, it has not been detected in North America, but the pest reached Costa Rica in 2014 and seriously threatens the southern, southwestern, and western United States including California. Although the primary host of T. absoluta is tomato, several other species of Solanaceae may serve as alternative hosts. In our study, we aimed to assess the potential risk that other solanaceous crops and wild species that are often present in and around California tomato fields could serve as hosts. To accomplish this, we conducted greenhouse and laboratory studies to determine whether two common cultivars of fresh market tomato, two common cultivars of tomatillo, and the wild plants, Solanum nigrum L., Solanum sarrachoides (Sendtner), and Datura stramonium L., are suitable hosts for reproduction and development of the pest. According to our results, D. stramonium and tomatillo were unable to sustain T. absoluta larval development in either greenhouse studies or laboratory studies, and therefore, they are not likely to contribute to T. absoluta establishment during an invasion. On the contrary, the two other solanaceous weeds, S. nigrum and S. sarrachoides, share a similar potential as tomato to be reproductive and developmental hosts of T. absoluta, and might play an important role in the establishment of the pest in California.

Influence of Age, Host Plant and Mating Status in Pheromone Production and New Insights on Perception Plasticity in Tuta Absoluta.

The tomato leafminer Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) is one of the most important pests of tomato worldwide. However, in spite of its tremendous economic importance, the success of environmentally friendly measures to control the pest is still limited. Study of physiological and behavioral parameters that affect pheromone production has provided useful information for pest management. Our results show no clear difference in pheromone production by females over the period from 2 h before to 2 h after the scotophase. However, pheromone production was clearly dependent on female age, with young females producing the highest amount of each pheromone component 10 days after emergence. In the presence of the host plant (physical contact and olfaction of the plant volatiles), virgin and mated females produced higher amounts of the major component of the pheromone (TDTA) than those in the absence of plant and those devoid of olfaction (antennectomized) but in physical contact with the plant. In electrophysiological experiments, TDTA elicited slightly lower responses on male antennae than the pheromone mixture. When stimulated at certain time intervals after the first exposure to TDTA, male antennae became more sensitive to the stimulus (sensitization effect). For the first time in an insect of the family Gelechiidae, we have found that females are able to detect their own pheromone (autodetection). Altogether, our results may represent a step forward in the knowledge of the chemical communication of this important pest.

The evolution of multiple-insecticide resistance in UK populations of tomato leafminer, Tuta absoluta.

BACKGROUND: The tomato leafminer, Tuta absoluta, is an economically important pest of tomatoes in Europe, Africa, Asia and South America. In the UK this species is controlled using an integrated pest management (IPM) programme which incorporates the insecticides spinosad and chlorantraniliprole. In response to UK grower concerns of loss of efficacy of these compounds at certain sites, insecticide bioassays were performed on five populations collected from four commercial glasshouses and potential mechanisms of resistance investigated. RESULTS: We observed high levels of resistance to spinosad in four of the strains, and in two of these tolerance to chlorantraniliprole. Selection of one of these strains with chlorantraniliprole rapidly resulted in a line exhibiting potent resistance to this compound. Sequencing of messenger RNA encoding the nicotinic acetylcholine receptor (nAChR) α6 subunit, target of spinosad, revealed Taα6 transcripts in the spinosad-resistant strains that lack exon 4 and encode a highly truncated protein, or contain a triplet deletion in the predicted first transmembrane domain resulting in the loss of a highly conserved amino acid. Sequencing of the ryanodine receptor gene, encoding the target of diamide insecticides, of the chlorantraniliprole-selected line revealed an amino acid substitution (G4903V) that has been previously linked to diamide resistance in populations of T. absoluta in the Mediterranean and South America. CONCLUSION: Taken together our results reveal emerging resistance in UK populations of T. absoluta to two of the most important insecticides used as part of IPM, with significant implications for the control of this species in the UK. © 2019 Society of Chemical Industry.