Jitka Stará

Efficacy of selected pesticides against synanthropic mites under laboratory assay

BACKGROUND The efficacies of organophosphate pesticides, single-compound versus multicompound pyrethroid formulations and relatively novel unclassified insecticides/acaricides were compared to find the lowest dosage and highest efficacy for the control of Dermatophagoides farina (Hughes), D. pteronyssinus (Trouessart) and Tyrophagus putrescentiae (Schrank). Formulated active ingredients (AIs) were diluted in water and applied onto filter paper in experimental chambers with ten unsexed adult mites in six replicates. Mite mortality was checked after 24 h. The security index (SI) was calculated for all of the AIs by dividing the recommended rate by the LD(90) determined for each species. RESULTS The tested organophosphates had high LD(90) and low SI values. The single-compound pyrethroids were ineffective (deltamethrin and beta-cyfluthrin) or had high LD(90) and low SI values (cyphenothrin, permethrin, pyrethrum and bifenthrin). The multicompound miticides had low LD(90) and high SI values which increased from deltamethrin/S-bioallethrin to permethrin/S-bioallethrin/piperonyl butoxide to permethrin/pyriproxyfen/benzyl benzoate. Abamectin, pyridaben, propargite and flufenoxuron were highly active against Dermatophagoides spp. Neem (Acarosan duo) was highly active against all mite species tested. CONCLUSION The available formulations of multicompound pyrethroids (permethrin/S-bioallethrin/piperonyl butoxide, permethrin/pyriproxyfen/benzyl benzoate), benzyl benzoate, neem and some field acaricides are effective in suppression of synanthropic mites in laboratory assays. Their LD(90) are lower than those of traditionally used organophosphates or single-compound pyrethroid formulations.

Detection of organophosphate and pyrethroid resistance alleles in Czech Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) populations by molecular methods.

BACKGROUND Pyrethroids and organophosphates are the most frequently used insecticides for Colorado potato beetle, Leptinotarsa decemlineata (Say), control in the Czech Republic. Based on molecular methods, organophosphate and pyrethroid resistance alleles have been detected in samples from three sites. The accuracy of restriction fragment length polymorphism (RFLP) and bidirectional polymerase chain reaction amplification of specific alleles (Bi-PASA) for detection of resistance alleles is compared. RESULTS Leptinotarsa decemlineata from three sites showed higher frequencies of resistance alleles to organophosphates than to pyrethroids. The rates of occurrence of individuals homozygous resistant (RR) to pyrethroids ranged from 20.0 to 22.9%, while the rates of occurrence of individuals RR to organophosphates ranged from 52.9 to 66.7%. The incidences of individuals with resistance alleles to both organophosphates and pyrethroids ranged from 8.6 to 13.6%. No relationship was found between incidence of the pyrethroid resistance allele and site, while incidence of the organophosphate resistance allele differed significantly according to site. CONCLUSION Both RFLP and Bi-PASA were suitable for detecting resistance alleles to pyrethroids, and in most cases also for detecting resistance alleles to organophosphates. In contrast to Bi-PASA, RFLP was also suitable for samples with lower DNA quality when testing for the resistance allele to pyrethroids. On the other hand, RFLP was not as accurate as Bi-PASA in detection of the organophosphate resistance allele.

Comparison of the effect of insecticides on three strains of Tyrophagus putrescentiae (Acari: Astigmata) using an impregnated filter paper test and a growth test

BACKGROUND In this study, we compared the efficacy of insecticides against three strains of Tyrophagus putrescentiae using an impregnated filter paper test and a growth test. We tested the suppressive activity of commercial insecticides and their analytical standards (pirimiphos-methyl, cypermethrin, deltamethrin, chlorfenapyr, β-cyfluthrin). METHODS The strains of T. putrescentiae originated from a laboratory, a field and dog food. The mortality of the mites due to active ingredients and analytical standards was tested using an impregnated filter paper test after 24 h. Lethal doses, LD50 , LD95 and LD99 were determined. A growth test was used to observe the suppressive effect of the active ingredients on mites at 21 days after application of the active ingredients to wheat grain. The effective doses ED50 , ED95 and ED99 were determined, indicating the concentration at which the population was reduced by 50, 95 and 99% more than control. RESULTS Cypermethrin, β-cyfluthrin and a formulation of deltamethrin with piperonylbutoxide in the pesticide K-Othrine showed low toxicity to mites. High toxicity was observed for chlorfenapyr (LD50 : 0.1-1 µg cm(-2) ; ED50 : 0.11-1.2 µg g(-1) ) and pirimiphos-methyl (LD50 : 0.01-0.06 µg cm(-2) ; ED50 : 0.2-12 µg g(-1) ). We did not find significant differences among the compared strains in terms of their sensitivity to highly toxic insecticides. CONCLUSION The obtained results showed that a filter paper test is a more sensitive method of identifying differences in pesticide susceptibility among strains, but the efficacy of pesticides against one species should be tested using a growth test.

Acarus siro and Tyrophagus putrescentiae (Acari: Acarididae) transfer of Fusarium culmorum into germinated barley increases mycotoxin deoxynivalenol content in barley under laboratory conditions

The possibility of transferring Fusarium poae ((Peck) Wollenw.) and Fusarium culmorum ((W. G. Sm.) Sacc.) via mites into germinating barley was tested under laboratory conditions. The mites Acarus siro Linnaeus, 1758 and Tyrophagus putrescentiae (Schrank, 1781) were preincubated on fungal cultures and then introduced into germinated barley in two mite population densities: 10 and 50 individuals per 20 g of barley. The negative controls were germinated barley without added mites and barley with mites not preincubated on the fungal cultures. The mycotoxin deoxynivalenol (DON) content in germinated barley was used as the marker of successful fungal transfer and colonization. DON concentrations were analysed 5 days after mite colonization. The mite preincubation on F. poae did not significantly increase DON concentration in barley. However, preincubation of mites on F. culmorum increased DON concentration in germinated barley by 5 and 8 times for A. siro and T. putrescentiae, respectively. The population density of mites showed no significant effect on DON concentration in germinated barley. The results of the experiments are discussed as a possible means of mite transfer of mycotoxin-producing fungi.

Beyond the survival and death of the deltamethrin-threatened pollen beetle Meligethes aeneus: An in-depth proteomic study employing a transcriptome database

Insecticide resistance is an increasingly global problem that hampers pest control. We sought the mechanism responsible for survival following pyrethroid treatment and the factors connected to paralysis/death of the pollen beetle Meligethes aeneus through a proteome-level analysis using nanoLC coupled with Orbitrap Fusion™ Tribrid™ mass spectrometry. A tolerant field population of beetles was treated with deltamethrin, and the ensuing proteome changes were observed in the survivors (resistant), dead (paralyzed) and control-treated beetles. The protein database consisted of the translated transcriptome, and the resulting changes were manually annotated via BLASTP. We identified a number of high-abundance changes in which there were several dominant proteins, e.g., the electron carrier cytochrome b5, ribosomal proteins 60S RPL28, 40S RPS23 and RPS26, eIF4E-transporter, anoxia up-regulated protein, 2 isoforms of vitellogenin and pathogenesis-related protein 5. Deltamethrin detoxification was influenced by different cytochromes P450, which were likely boosted by increased cytochrome b5, but glutathione-S-transferase ε and UDP-glucuronosyltransferases also contributed. Moreover, we observed changes in proteins related to RNA interference, RNA binding and epigenetic modifications. The high changes in ribosomal proteins and associated factors suggest specific control of translation. Overall, we showed modulation of expression processes by epigenetic markers, alternative splicing and translation. Future functional studies will benefit. BIOLOGICAL SIGNIFICANCE Insects develop pesticide resistance, which has become one of the key issues in plant protection. This growing resistance increases the demand for pesticide applications and the development of new substances. Knowledge in the field regarding the resistance mechanism and its responses to pesticide treatment provides us the opportunity to propose a solution for this issue. Although the pollen beetle Meligethes aeneus was effectively controlled with pyrethroids for many years, there have been reports of increasing resistance. We show protein changes including production of isoforms in response to deltamethrin at the protein level. These results illustrate the insects survival state as a resistant beetle and in its paralyzed state (evaluated as dead) relative to resistant individuals.

Evaluation of pesticide residue dynamics in Chinese cabbage, head cabbage and cauliflower

ABSTRACT Pesticide residues from the time of application until harvest were analysed for 20, 17 and 18 active insecticidal and fungicidal substances in Chinese cabbage, head cabbage and cauliflower, respectively. In total, 40 mathematical models of residue degradation were developed using a first-order kinetic equation, and from these models it was possible to forecast the action pre-harvest interval for a given action threshold for low-residue production in Brassica vegetables as a percentage of the maximum residue level. Additionally, it was possible to establish an action pre-harvest interval based on an action threshold of 0.01 mg kg‒1 for the production of Brassica vegetables for baby food. Among the evaluated commodities, the speed of residue degradation was highest in head cabbage, medium in Chinese cabbage and lowest in cauliflower. The half-lives of pesticide in various vegetables were also determined: they ranged from 1.55 to 5.25 days in Chinese cabbage, from 0.47 to 6.54 days in head cabbage and from 1.88 to 7.22 days in cauliflower.

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

BACKGROUND 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. RESULTS 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. CONCLUSION 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.

Seven‐year monitoring of pyrethroid resistance in the pollen beetle (Brassicogethes aeneus F.) during implementation of insect resistance management

BACKGROUND An increase in the spread of pyrethroid resistance in the pollen beetle has been documented in many European countries. Pyrethroid resistance in the pollen beetle in the Czech Republic has been detected using a topical application bioassay. Resistance monitoring has been carried out during the implementation of insect resistance management. RESULTS The susceptibilities of nine pollen beetle populations to four pyrethroids in 2009 - 2015 in the Czech Republic are presented in this paper. The highest resistance ratio (RR) values [based on the lethal dose for 50% of the population (LD50 )] obtained for deltamethrin, lambda-cyhalothrin, tau-fluvalinate and etofenprox were 500, 299, 108 and 66.9, respectively. Pollen beetle mortality after application of deltamethrin or lambda-cyhalothrin gradually decreased from 2009 to 2013. High cross-resistance between lambda-cyhalothrin and deltamethrin and low cross-resistance between lambda-cyhalothrin and etofenprox were demonstrated. A kdr mutation known to cause resistance in the pollen beetle was not detected. CONCLUSION A high level of resistance was recorded in most of the nine populations of the pollen beetle in 2013. In the following 2 years, a decrease in resistance associated with a population density decrease of the pollen beetle was observed in all nine populations as a result of insect resistance management based on pyrethroid reduction in winter oilseed rape.