Mite Resistance Research Articles

A method to investigate neonicotinoid resistance in mites.

The redlegged earth mite (Halotydeus destructor) is an important agricultural pest in Australia, with a wide range of plant hosts. Halotydeus destructor has developed resistance to pyrethroid and organophosphorus insecticides as a consequence of the widespread use of these chemicals by farmers. Neonicotinoids are one of the few remaining insecticide classes registered against H. destructor in which resistance has not been detected, although there have been occasional reports of control difficulties experienced in the field. There is currently no reliable way to accurately test the response of H. destructor (or indeed any mite species) to neonicotinoid insecticides. Here, we developed a new bioassay to assess the response of mites against the neonicotinoid imidacloprid. The method provided consistent results and showed no variation when used by different operators. We generated base-line sensitivity data for imidacloprid across a number of field-collected populations of H. destructor. This is important for future monitoring of mite responses given the considerable selection pressure now being exerted across large areas of the Australian farming landscape through the widespread use of neonicotinoid seed treatments.

Amidase, a novel detoxifying enzyme, is involved in cyflumetofen resistance in Tetranychus cinnabarinus (Boisduval)

Amidase is an important hydrolytic enzyme in detoxification metabolism. Amidase hydrolyzes a wide variety of nonpeptide carbon‑nitrogen bonds by attacking a cyano group or carbonyl carbon. However, little is known about the relationship between amidase and insecticides. In this study, the amidase activity was significantly higher in cyflumetofen-resistant strain (CyR) than in the susceptible strain (SS) of Tetranychus cinnabarinus, and diethyl-phosphoramidate (an amidase inhibitor) significantly decreased cyflumetofen resistance in T. cinnabarinus. More importantly, an amidase gene, TcAmidase01, was identified in T. cinnabarinus, and the TcAmidase01 overexpression was detected in both two cyflumetofen-resistant strains (CyR and YN-CyR), indicating that it is involved in cyflumetofen resistance in mites. A phylogenetic analysis showed that TcAmidase01 was clustered with deaminated glutathione amidases, which possess hydrolytic activity. The recombinant TcAmidase01 protein showed amidase activity toward succinamate, and the activity could be inhibited by cyflumetofen. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis provided evidence that recombinant TcAmidase01 could decompose cyflumetofen by hydrolysis, and the potential metabolites (2-(4-(tert-butyl) phenyl)-2-cyanoacetate and 2-(trifluoromethyl) benzoic acid) were identified. These results show that TcAmidase01 contribute to cyflumetofen-resistance in T. cinnabarinus by hydrolyzing cyflumetofen, and this is the first study to suggest that amidase has a role in insecticides resistance in arthropods.

Differences in Aceria tosichella population responses to wheat resistance genes and wheat virus transmission

Severe winter wheat yield losses due to infestations of wheat curl mite, Aceria tosichella Keifer, and mite-transmitted viruses occur in wheat production areas of the United States and Canada. Mite infestation alone causes stunted, chlorotic plants in susceptible wheat varieties, and mites transmit Wheat Streak Mosaic (WSMV), High Plains Wheat Mosaic (HPWMoV), and Triticum Mosaic Virus (TriMV). Wheat curl mites were collected from 25 sites in Kansas, Missouri, Nebraska, Texas, North Dakota, and South Dakota in 2014 and 2015. At each site, mite virulence was determined to wheat plants harboring the Cmc2-, Cmc3-, or Cmc4 mite resistance gene; or Cmc4 plus the Wsm2 WSMV resistance gene. Mites collected from 92%, 36%, and 24% of sites were virulent to susceptible Jagger wheat plants (no Cmc), Cmc2, and Cmc3, respectively. The mega-population consisting of all 25 mite sub-populations was avirulent to 80% of plants containing Cmc4 + Wsm2 or Cmc4. WSMV, HPWMoV, or TriMV was present in mites at 76%, 16%, and 8% of the 25 sites, respectively. Our results will enable breeders to increase the efficiency of wheat production by releasing wheat varieties containing wheat curl mite resistance genes that reduce wheat yield losses.

Efficacy of λ-cyhalothrin, amitraz, and phoxim against the poultry red mite Dermanyssus gallinae De Geer, 1778 (Mesostigmata: Dermanyssidae): an eight-year survey

ABSTRACTDermanyssus gallinae (De Geer, 1778) is a major problem for the poultry industry worldwide, as it negatively affects virtually all kinds of rearing systems. Therefore, the control of infestation has become a routine process, and its economic cost is constantly increasing. Until now, most of the control strategies have relied on the use of synthetic chemical drugs, but their efficacy is often questioned by the emergence and diffusion of resistant mite populations. With this in mind, the efficacy of λ-cyhalothrin, amitraz, and phoxim has been verified by testing them against 86 mite populations collected from the same number of poultry farms in Italy from 2008 to 2015. Assays were performed according to the filter paper method using the recommended, half, quarter, double and quadruple doses. The results showed that phoxim and amitraz were the most effective acaricides (median efficacies 80.35% and 80.83%, respectively), but amitraz exhibited a sharp fall in its efficacy during 2011 and 2012, while phoxim maintained its high effectiveness up to 2015, when it dropped. The overall median efficacy of λ-cyhalothrin was 58.33%. The data also highlighted the importance of the use of the right concentration, as an increase in dosage was not always useful against resistant populations, while its reduction also diminished efficacy, simultaneously increasing the risk for the development of resistance.

Under pressure: force resistance measurements in box mites (Actinotrichida, Oribatida)

BackgroundMechanical defenses are very common and diverse in prey species, for example in oribatid mites. Here, the probably most complex form of morphological defense is known as ptychoidy, that enables the animals to completely retract the appendages into a secondary cavity and encapsulate themselves. The two groups of ptychoid mites constituting the Ptyctima, i.e. Euphthiracaroidea and Phthiracaroidea, have a hardened cuticle and are well protected against similar sized predators. Euphthiracaroidea additionally feature predator-repelling secretions. Since both taxa evolved within the glandulate group of Oribatida, the question remains why Phthiracaroidea lost this additional protection. In earlier predation bioassays, chemically disarmed specimens of Euphthiracaroidea were cracked by the staphylinid beetle Othius punctulatus, whereas equally sized specimens of Phthiracaroidea survived. We thus hypothesized that Phthiracaroidea can withstand significantly more force than Euphthiracaroidea and that the specific body form in each group is key in understanding the loss of chemical defense in Phthiracaroidea. To measure force resistance, we adapted the principle of machines applying compressive forces for very small animals and tested the two ptyctimous taxa as well as the soft-bodied mite Archegozetes longisetosus.ResultsSome Phthiracaroidea individuals sustained about 560,000 times their body weight. Their mean resistance was about three times higher, and their mean breaking point in relation to body weight nearly two times higher than Euphthiracaroidea individuals. The breaking point increased with body weight and differed significantly between the two taxa. Across taxa, the absolute force resistance increased sublinearly (with a 0.781 power term) with the animal’s body weight. Force resistance of A. longisetosus was inferior in all tests (about half that of Euphthiracaroidea after accounting for body weight). As an important determinant of mechanical resistance in ptychoid mites, the individuals’ cuticle thickness increased sublinearly with body diameter and body mass as well and did not differ significantly between the taxa.ConclusionWe showed the feasibility of the force resistance measurement method, and our results were consistent with the hypothesis that Phthiracaroidea compensated its lack of chemical secretions by a heavier mechanical resistance based on a different body form and associated build-up of hemolymph pressure (defensive trade-off).

ACARICIDAL ACTIVITY OF INERT POWDERS AGAINST THE POULTRY RED MITE DERMANYSSUS GALLINAE (DE GEER, 1778) (MESOSTIGMATA: DERMANYSSIDAE)

Dermanyssus gallinae is one of the most important ectoparasite of laying hens. The intensive use of chemicals has led to the selection of resistant mite populations. The difficulty in controlling the mites has promoted the search for alternative products. Thereby, the aim of this study was to assess in laboratory the acaricidal activity of inert mineral powders against D. gallinae , in dust and water suspensions (5 and 10%) treatments. The products were tested against eggs, nymphs and adults of the mite. There were differences in the activity of tested products. Some products based on diatomaceous earth, kaolin and talc, applied in powder form on adults of the mite were more efficient and selected for subsequent tests. In liquid suspension bioassay it was observed no ovicidal activity of any of the tested products. However, the products were efficient on the nymphs with no difference between both products and concentrations. The activity of diatomaceous earth and kaolin 2120 in 5 and 10% water suspension on adults was significatively higher than other treatments against adults. There was no difference between the treatments in residual activity. The morphological characterization and identification of diatom frustules present in the product PosturaSec ® indicated prevalence of the genus Brachysira Kutzing, density of 5.7 x 10 7 valves/g, 200 μm size particles and 86.2% of silicon.

P8 nuclear receptor responds to acaricides exposure and regulates transcription of P450 enzyme in the two-spotted spider mite, Tetranychus urticae

Spider mites are destructive arthropod pests on many crops and they have developed resistance to nearly all acaricides. In recent years, along with the application of high throughput sequencing, the molecular mechanisms of mite resistance had made a series of progress. But, the response in molecular level of mite exposure to acaricides, as well as the original mechanism of resistance development was still unclear. To disclose the deeply mechanisms, we used RNA sequencing to analyze the responses of mite exposure to a sublethal concentration (LC30) treatment of the three different action mode acaricides (Abamectin, Fenpropathrin, and Tebufenpyrad). A high number of differentially expressed genes may well be involved in detoxification and regulatory, with extensive overlap in differentially expressed genes between the three insecticide treatments. Two cytochrome P450 genes were co-up-regulated and one glutathione S-transferase genes were co-down-regulated in all the treatments, while carboxylesterase genes only had a response to abamectin. This interesting phenomenon revealed that P450 enzymes play an important role in the early stage of mite exposure to acaricide. Moreover, a P8 nuclear receptor gene was in response to stress caused by exposure to acaricides and RNA interference (RNAi) experiment indicated P8 nuclear receptor regulates the P450 enzyme activity and susceptibility of mites to acaricide. The differential response information of gene expression based on a large-scale sequence would provide some useful clues for studying the molecular mechanisms of mite resistance formation and development.

Disentangling host-parasite-pathogen interactions in a varroa-resistant honeybee population reveals virus tolerance as an independent, naturally adapted survival mechanism

The ectoparasitic mite, Varroa destructor, is unarguably the leading cause of honeybee (Apis mellifera) mortality worldwide through its role as a vector for lethal viruses, in particular, strains of the Deformed wing virus (DWV) and Acute bee paralysis virus (ABPV) complexes. This multi-level system of host-parasite-pathogen interactions makes it difficult to investigate effects of either the mite or the virus on natural host survival. The aim of this study was to remove confounding effects of varroa to examine the role of virus susceptibility in the enhanced survival of a naturally adapted Swedish mite-resistant (MR) honeybee population, relative to mite-susceptible (MS) honeybees. Caged adult bees and laboratory reared larvae, from varroa-free colonies, were inoculated with DWV and ABPV in a series of feeding infection experiments, while control groups received virus-free food. Virus infections were monitored using RT-qPCR assays in individuals sampled over a time course. In both adults and larvae the DWV and ABPV infection dynamics were nearly identical between MR and MS groups, but MS adults suffered significantly higher mortality than MR adults. Results suggest virus tolerance, rather than reduced susceptibility or virus resistance, is an important component of the natural survival of this honeybee population.

Independently evolved and gene flow-accelerated pesticide resistance in two-spotted spider mites.

Pest species are often able to develop resistance to pesticides used to control them, depending on how rapidly resistance can emerge within a population or spread from another resistant population. We examined the evolution of bifenazate resistance in China in the two‐spotted spider mite (TSSM) Tetranychus uticae Koch (Acari: Tetranychidae), one of the most resistant arthropods, by using bioassays, detection of mutations in the target cytb gene, and population genetic structure analysis using microsatellite markers. Bioassays showed variable levels of resistance to bifenazate. The cytb mutation G126S, which confers medium resistance in TSSM to bifenazate, had previously been detected prior to the application of bifenazate and was now widespread, suggesting likely resistance evolution from standing genetic variation. G126S was detected in geographically distant populations across different genetic clusters, pointing to the independent origin of this mutation in different TSSM populations. A novel A269V mutation linked to a low‐level resistance was detected in two southern populations. Widespread resistance associated with a high frequency of the G126S allele was found in four populations from the Beijing area which were not genetically differentiated. In this case, a high level of gene flows likely accelerated the development of resistance within this local region, as well as into an outlying region distant from Beijing. These findings, therefore, suggest patterns consistent with both local evolution of pesticide resistance as well as an impact of migration, helping to inform resistance management strategies in TSSM.

Sources of Resistance for Two-spotted Spider Mite (Tetranychus urticae) in Scarlet (Solanum aethiopicum L.) and Gboma (S. macrocarpon L.) Eggplant Germplasms

The two-spotted spider mite, Tetranychus urticae, is a serious global pest of eggplants and other vegetables in the tropics and subtropics. The scarlet (Solanum aethiopicum L.) and gboma (Solanum macrocarpon L.) are two cultivated eggplants indigenous to sub-Saharan Africa. In this study, 120 accessions of S. aethiopicum and five accessions of S. macrocarpon from the World Vegetable Center’s genebank collection were evaluated for spider mite resistance based on leaf damage scores and trichome types and densities. The highest levels of resistance were detected in S. macrocarpon accessions VI050393 and VI050444. In addition, two accessions of S. aethiopicum, VI042749 and VI042753, were moderately resistant. All other S. aethiopicum accessions were susceptible or highly susceptible. Spider mite resistance was significantly associated with the presence of type VII glandular trichome, but nonglandular stellate trichomes were not associated with resistance. The resistant S. macrocarpon accessions can be directly used as resistant cultivars or in prebreeding programs aimed at breeding resistant lines of the most commonly cultivated eggplant (S. melogena).

Comb Irradiation Has Limited, Interactive Effects on Colony Performance or Pathogens in Bees, Varroa destructor and Wax Based on Two Honey Bee Stocks.

Parasitic mites and pathogens compromise honey bee health. Development of sustainable and integrative methods of managing these problems will minimize their detrimental impact on honey bees. Here, we aimed to determine if the combination of using mite-resistant stocks along with gamma-irradiated combs influences colony health and productivity. The major finding concerned honey bee genotype confirming that Russian honey bees are more resistant to Varroa destructor than Italian honey bees. The effect of comb irradiation was inconsistent showing a significant increase in adult bee population and amount of stored pollen in 2015, but not in 2016. The increased amount of stored pollen was probably associated with larger adult population in colonies with irradiated combs in September 2015 regardless of honey bee stock. Nevertheless, the ability of bees to collect and store more pollen in the irradiated group does not appear to compensate the negative impacts of mite parasitism on honey bees especially in the Italian bees, which consistently suffered significant colony losses during both years. Results of viral analyses of wax, newly emerged bees, and Varroa and their pupal hosts showed common detections of Deformed wing virus (DWV), Varroa destructor virus (VDV-1), Chronic bee paralysis virus (CBPV), and Black queen cell virus (BQCV). Wax samples had on average ~4 viruses or pathogens detected in both irradiated and non-irradiated combs. Although pathogen levels varied by month, some interesting effects of honey bee stock and irradiation treatment were notable, indicating how traits of mite resistance and alternative treatments may have additive effects. Further, this study indicates that wax may be a transmission route of viral infection. In addition, pupae and their infesting mites from Italian colonies exhibited higher levels of DWV than those from Russian colonies suggesting potential DWV resistance by Russian honey bees. CBPV levels were also reduced in mites from Russian colonies in general and in mites, mite-infested pupae, and newly emerged bees that were collected from irradiated combs. However, BQCV levels were not reduced by comb irradiation. Overall, the contribution of irradiating comb in improving honey bee health and colony survival appears to be subtle, but may be useful as part of an integrated pest management strategy with the addition of using mite-resistant stocks.

ЗИМОСТОЙКОСТЬ И БИОМЕТРИЧЕСКИЕ ПОКАЗАТЕЛИ ИНТРОДУЦИРОВАННЫХ СОРТОВ ЗЕМЛЯНИКИ В УСЛОВИЯХ ПЛЕНОЧНЫХ ТЕПЛИЦ В ЛЕНИНГРАДСКОЙ ОБЛАСТИ

Background. The intensive inflow of strawberry cultivars from abroad in recent years and a great number of cultivation practices make an accelerated comprehensive study of these cultivars in new soil and climate conditions a high priority for the Northwest of the Russian Federation. Materials and methods. In 2016–2017, 35 newly introduced strawberry cultivars were studied at St. Petersburg State Agrarian University according to the Program and Methodology of Variety Research on Fruit, Berry and Nut Crops. The primary study focused on the biometric characteristics of strawberry cultivars, their winter hardiness, performance of the full cycle of phenological stages in plant development, resistance to spider mite, and productivity. These are the main criteria for cultivars to be grown in plastic film greenhouses in Leningrad Province. Results and conclusion. The primary study of the introduced cultivars under plastic film greenhouse conditions in Leningrad Province and their evaluation for winter hardiness, productivity and spider mite resistance made it possible to identify the cultivars ‘Vechnaya Vesna’, ‘Vystavochnaya’, ‘Yubileynaya Govorovoy’ ‘Jive’, ‘Diamante’ and ‘Elianny’ as promising for cultivation. They require further research targeted at a set of economically important traits.

Temporal changes in the viromes of Swedish Varroa-resistant and Varroa-susceptible honeybee populations.

The parasitic mite, Varroa destructor, in combination with the viruses it vectors, is the main cause for global colony losses of the European honeybee, Apis mellifera. However, an isolated honeybee population established in 1999 on the Island of Gotland, Sweden has naturally acquired resistance to the mite, and has survived without mite control treatment for more than 18 years. A recent study has shown that this mite resistant (MR) population also appears to be resistant to Black queen cell virus (BQCV) and Sacbrood virus (SBV) and tolerant to Deformed wing virus (DWV), relative to nearby mite susceptible (MS) honeybee populations. In this study, RNA sequencing was employed to corroborate these previous findings and identify other viral factors that may play a role in the enhanced survival of this mite resistant honeybee population. Two additional honeybee-infecting viruses, Apis rhabdovirus-1 (ARV-1) and Lake Sinai virus (LSV), were identified and near-complete genomes of these two viruses were obtained. Phylogenetic analyses of the assembled virus sequences revealed consistent separation between the MR and MS honeybee populations, although it is unclear whether this is due to pre-existing differences between the viruses in the two populations when they were established, and isolated, or due to virus genetic adaptation towards reduced virulence in the MR population, to promote colony survival. Reverse transcription quantitative polymerase chain reaction(RT-qPCR) analyses show higher ARV and LSV titres in MS colonies compared to MR colonies, gradually increasing from summer to autumn 2009, and reaching maximum titres in the following spring 2010. While the DWV and BQCV titres in MR colonies increased between autumn 2009 and spring 2010, the SBV practically disappeared entirely by spring 2010. Possible explanations for the apparent virus tolerance or resistance in the Gotland mite-resistant honeybee population are discussed.

Spatio-temporal dynamics of Varroa destructor resistance to tau-fluvalinate in Czechia, associated with L925V sodium channel point mutation.

Extensive application of pyrethroids to control Varroa destructor, an invasive mite devastating bee colonies, has resulted in a global spread of resistant mite populations. In this study, we analyzed the spatio-temporal dynamics of resistant V. destructor populations in Czechia, stemming from the L925V mutation. Mites were collected during 2011-2018 directly or from winter beeswax debris, and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and densitometry was used to detect the L925V mutation. Pooled samples of 10 mites were classified, based on their PCR-RFLP patterns, as tau-fluvalinate-sensitive (56%), resistant (9%), or mixed (35%), with the latter including sensitive and resistant homo- and heterozygotes. We identified two zones with higher frequencies of resistance, one in southern Moravia and the other in Bohemia. The mutant populations were evenly distributed throughout the monitored districts, with a few temporal and spatial local fluctuations. The greatest increase in resistance was observed in 2016, following massive losses of bee colonies in the winter of 2015. This event appeared to be closely associated with fluctuations in resistant mite populations and their dispersion. Two outbreaks of resistance were detected in Czechia; however, the amount of applied tau-fluvalinate was not correlated with the frequency of resistance in mites. There was no remarkable increase in mite resistance in 2011-2018, although the use of tau-fluvalinate increased 40-fold between 2011 and 2015. PCR-RFLP analysis, performed on mites present in beeswax debris, is a suitable method for monitoring the L925V mutation in V. destructor. © 2018 Society of Chemical Industry.

Multivariate techniques in the determination of genetic diversity in pest-resistant mini tomato genotypes

ABSTRACT The objective of this study was to compare methods of multivariate analysis on the evaluation of genetic diversity of mini tomato and to identify promising genotypes with resistance to pests. The experiment was conducted at the Vegetable Experiment Station of the Universidade Federal de Uberlândia, Monte Carmelo campus, from April 2013 to November 2016. The experimental design was a randomized complete block design with 16 treatments and four replications totaling 64 plots, and each plot represented by five plants. Sixteen genotypes were characterized, 12 from the F2RC1 generation, obtained through the interspecific crossing between the wild access LA-716 (Solanum pennellii) and pre-commercial lines of mini tomato (UFU-73 and UFU-2) (Solanum lycopersicum) and the UFU-2 lines. The content of acyl sugar, the amount of glandular trichomes (types I, IV, VI and VII), twospotted spider mite and whitefly resistance were evaluated. We concluded that there exist genetic variability between the genotypes. The number of groups formed by the canonical variated analysis was higher (four groups) than that obtained by the Tocher method (three groups) and UPGMA (three groups), demonstrating a greater discrimination power. The Tocher and UPGMA methods were consistent in the analysis of the genetic divergence in pest resistant germplasm of tomato, with the acyl sugar content being the most important variable. Genotype UFU-73-F2RC1 # 11 is resistant to pest attack, while the other studied lines have intermediate resistance.

Increase of scabies in Germany and development of resistant mites? Evidence and consequences.

Scabies has been diagnosed surprisingly frequently in Germany in recent years, and the use of acaricides has risen markedly. Present figures indicate an increase in the prevalence/incidence of scabies, but do not prove or quantify it for the following reasons: (a) scabies is not a notifiable disease in Germany; (b) the diagnosis is not always confirmed lege artis by means of light microscopy or dermatoscopy (which may lead to a comparatively high proportion of false‐positive diagnoses due to the low overall prevalence of scabies); (c) repeated treatments of the same patient and treatment of contact persons are included in the total number of prescriptions. Therefore, there are no valid data on disease occurrence, either in the current situation or from previous periods. Observations of ineffective treatment with permethrin have led to speculations that Sarcoptes mites are developing resistance to this drug. However, there is little evidence for this assumption. We discuss risk groups (children, elderly people in need of care, migrant health personnel in nursing institutions, refugees, sexually active young adults) and evaluate their possible contribution, albeit in the absence of evidence. None of the groups would be solely responsible for an increased frequency. We have compiled recommendations on how the management of scabies could be improved, and present a way of differentiating permethrin resistance from application errors and/or lack of compliance. The goal is to solve the epidemiological and parasitological questions mentioned above.

Evaluation of some synthetic acaricides against Varroa destructor (Acari: Varroidae) in Turkey: an indication of resistance or misuse of fumigant amitraz?

The parasitic mite, Varroa destructor is one of the most important agents for substantial losses in honeybee colonies throughout the world. Several acaricides consisting of synthetic and organic compounds are being used to combat mite. This study was conducted to determine the efficacies of three synthetic acaricides in naturally infested honeybee colonies at consecutive two autumn seasons. Acaricides were commercial preparations of coumaphos (liquid and plastic strips), amitraz (fumigation and plastic strip) and flumethrin (plastic and wooden strips) as a treatment group consisting of eight hives per drug. A control group was kept in both seasons. All drugs were applied as prescribed to the homogenised Varroa-infested honeybee colonies at consecutive two years. The evaluation of efficacies was based on the collected mite percentage obtained with powdered sugar method and it was calculated through Henderson-Tilton’s formula. Dropped mites onto the pollen drawers were also evaluated statistically and drugs were compared to each other. Results showed us the effective drugs (up to 90%) were amitraz plastic strip, flumethrin wooden strip and coumaphos plastic strip with 98.5%, 96.5%, and 93.2% averages, respectively according to formula if evaluated within two autumn seasons. Fumigation of amitraz is not sufficient if compared to others and the control group. This data is discussed for suspicion of the possible resistance of mites or misuse of the product with this kind of application.

Resistance of Lima Bean (Phaseolus lunatus L.) to the Red Spider Mite Tetranychus neocaledonicus (Acari: Tetranychidae).

The red spider mite, Tetranychus neocaledonicus (Acari: Tetranychidae) can be an important pest on lima bean (Phaseolus lunatus L.). Thus, the objective of this work was to assess the antibiosis and antixenosis effects of lima bean genotypes on T. neocaledonicus, through the evaluation of performance parameters as well as the host preference for food and oviposition. Nine lima bean genotypes from the Active Bank of Germplasm of the Federal University of Piauí – BGP / UFPI were screened. To assess antibiosis parameters, eggs of T. neocaledonicus were individually placed on leaf disks of each genotype. The period and survival of the different stages of development (larvae, protonymph, deutonymph and adult), pre-oviposition, oviposition and post-oviposition period, longevity and fecundity of females were evaluated, and fertility life table parameters were calculated. In choice tests, adult females of T. neocaledonicus were used. The numbers of mites and eggs were counted for each genotype. The protonymph, egg-adult, longevity and oviposition period, fertility life table parameters, as well as the food and oviposition preference were affected by lima bean genotypes. We found that some genotypes reduced adult female longevity, increased the larval and egg-adult period, decreased oviposition period, negatively affected the fertility life table parameters, reducing the net reproductive rate (Ro), the intrinsic rate of increase (rm) and the finite rate of increase (λ), while increasing the population doubling time (DT), exhibiting a reliable antibiosis effect upon T. neocaledonicus. Nevertheless, these same genotypes were the most preferred for food and oviposition. By contrast, some other genotypes reduced the adult female longevity and oviposition period, elongated the larval period and affected fertility life table parameters, demonstrating an antibiosis effect upon T. neocaledonicus. Moreover, these other genotypes were among the less preferred for food and oviposition, exhibiting an additional antixenosis effect. Thus, our results demonstrate that the genotypes of lima bean may present distinct levels of resistance to T. neocaledonicus, and this resistance may be an important tool for Integrated Pest Management. This is one of the first studies aiming to describe mite resistance sources in lima bean.

Biological control of spider mites in North-Italian vineyards using pesticide resistant predatory mites

The success of phytoseiid mite releases to control spider mites [Eotetranychus carpini (Oudemans) and Panonychus ulmi (Koch)] on grapevines can be influenced by pesticide use and competition with local predatory mites. In field experiments we evaluated the effect of the release of Kampimodromus aberrans (Oudemans) and Typhlodromus pyri Scheuten strains showing field resistance to organophosphates and dithiocarbamates. Predatory mites were released in two vineyards infested by spider mites despite the occurrence of Amblyseius andersoni (Chant) and/or Phytoseius finitimus Ribaga. Single or mixed releases were planned. Spider mite populations were not effectively controlled by local predatory mites while successful control was achieved by released species. The effects of releases were higher in the second experimental year. In most cases A. andersoni densities were reduced by T. pyri and K. aberrans releases. Ph. finitimus suffered less than A. andersoni from intraguild predation. Among released species, the effect of the presence of a competitor was higher on T. pyri than on K. aberrans. Results suggest that the outcome of intraguild predation is prey-mediated. The equilibrium level between K. aberrans and T. pyri may depend on which spider mite species is the shared prey. The implications in management of spider mites on grapevines are discussed.

Mapping and KASP marker development for wheat curl mite resistance in “TAM 112” wheat using linkage and association analysis

Wheat curl mite (WCM, Aceria tosichella Keifer) and WCM-transmitted wheat streak mosaic virus (WSMV, genus Tritimovirus) are devastating production constraints for wheat in the US Great Plains. Breeding wheat cultivars with genetic resistance to WCM and WSMV is a viable and economically feasible way to reduce yield loss. The objectives of this study were to (a) identify tightly linked markers for WCM resistance in the wheat cultivar TAM 112 (PI 643143) using linkage and association analysis with the 90K Infinium iSelect SNP array and genotyping-by-sequencing, respectively and (b) develop and test kompetitive allele specific PCR (KASP) single-nucleotide polymorphisms (SNPs) for marker-assisted selection (MAS) of WCM resistance. We tested 124 F5:7 recombinant inbred lines (RILs) derived from the cross of TAM 112 and the WCM-susceptible cultivar TAM 111 (PI 631352). All lines were infested with a Texas WCM collection 2 (TWCMC2) that is virulent to resistance found on the wheat-rye 1AL.1RS translocation at the two-leaf stage and were rated for symptoms on the first and second week after infestation. Linkage maps were constructed with 4890 markers, including SNPs, simple sequence repeats (SSRs), and sequence-tagged site (STS) markers covering 21 chromosomes. A WCM resistance gene present in TAM 112 (CmcTAM112) was mapped onto chromosome arm 6DS. A genome-wide association study of wheat streak mosaic (WSM) symptoms from a separate experiment in Colorado showed significant marker-trait associations at the target regions on 6DS where CmcTAM112 was located, which demonstrated the effectiveness of this gene to reduce symptom severity. Four SNPs flanking CmcTAM112 were mapped within 3.6 cM in the biparental mapping population. We developed two KASP markers that are within 1.3 cM distal to CmcTAM112 and tested in diverse germplasm. These two markers can be used in MAS for improving WCM resistance in some wheat genetic backgrounds.