Pyrethroid resistance in Phytoseiulus macropilis (Acari: Phytoseiidae): cross-resistance, stability and effect of synergists

Prevalence and predictors of adverse events following exposure to long-lasting insecticidal nets used for malaria prevention: a community based cross-sectional study in the Democratic Republic of the Congo

BACKGROUND

Malaria morbidity and mortality increase in the Democratic Republic of the Congo (DRC) may be the consequence of the low utilization rate of long-lasting insecticidal nets (LLINs) resulting from poor compliance due to adverse events (AEs). This study aimed at determining the prevalence and predictors of AEs following the mass distribution of LLINs in the Kisantu Health Zone (KHZ), a high malaria-endemic region in the DRC.

METHODS

A community-based cross-sectional study embedded was conducted within a randomized controlled trial (RCT) after the mass distribution of LLINs in 30 villages located in DRC KHZ. A three-stage sampling method was used without replacement to select 1790 children. Data was collected on adverse events (AEs) using a reporting form and information on demographics, nutritional status, and house characteristics. This was done using a structured questionnaire administered to household heads. Logistic regression models were used to identify predictors of AEs following the mass distribution of LLINs.

RESULT

In a total of 1790 children enrolled, 17.8% (95% CI 16.1-19.7) experienced AEs. The most common AEs were respiratory-related (61%). Around 60% of AEs occurred within 24 h of use, and 51% were resolved without treatment. Sleeping under deltamethrin LLINs (Adjusted OR, 95% CI 5.5 [3.8-8.0]) and zinc roofing (Adjusted OR, 95% CI 1.98 [1.1-3.57]) were associated with the risk of reporting an AE following the mass distribution of LLINs.

CONCLUSION

Approximately 1 out of 5 children had an AE within 24 h following LLIN use. These adverse events were often respiratory-related. LLINs and roofing types were associated with a higher risk of reporting AEs. However, further research using a robust study design is needed to confirm these findings. Future studies should design and implement interventions aiming to reduce AEs and improve compliance with LLINs.

Molecular variation of the cytochrome b DNA and protein sequences in Phytoseiulus macropilis and P. persimilis (Acari: Phytoseiidae) reflect population differentiation

Several phytoseiid mite species are important natural enemies used in biological control strategies. In the present study, Cytb mtDNA sequences of various populations of two species, Phytoseiulus macropolis and P. persimilis, were compared to determine whether the specimens collected in Brazil could belong to P. persimilis as this latter species is reported in South America but not in Brazil. The Cytb marker was used because of its high evolution rate, assumed to capture intraspecific variation. No overlap between intra- and interspecific distances was observed but the distances were quite low for interspecific variation. This can be due to the particular biology of Phytoseiulus species and this shows the difficulty to apply a universal threshold in genetic distances to conclude about the existence of one or several species. Cytb mtDNA sequences were also considered to assess intraspecific variation. The DNA sequences of P. persimilis populations were very similar, probably because they all originated from the West Palearctic region or because of a prevalence of commercialized specimens in natura. For P. macropilis, higher genetic distances were observed and differentiation was noted according to geographic location and, to a smaller extent, pyrethroid resistance. To determine how DNA variation might impact the protein function (CytB fragment considered), the amino acid compositions of the populations studied were compared. No diagnostic mutation was observed between pyrethroid resistant and susceptible populations, whereas four mutations were identified between populations of P. macropilis separated by 1300 km (different climatic conditions). The impact of such mutations is discussed but knowledge is scarce, which makes it difficult to root testable hypotheses. The protein analysis clearly opens new perspectives in Phytoseiidae studies.

From Global to Local-New Insights into Features of Pyrethroid Detoxification in Vector Mosquitoes

The threat of mosquito-borne diseases continues to be a problem for public health in subtropical and tropical regions of the world; in response, there has been increased use of adulticidal insecticides, such as pyrethroids, in human habitation areas over the last thirty years. As a result, the prevalence of pyrethroid-resistant genetic markers in natural mosquito populations has increased at an alarming rate. This review details recent advances in the understanding of specific mechanisms associated with pyrethroid resistance, with emphasis on features of insecticide detoxification and the interdependence of multiple cellular pathways. Together, these advances add important context to the understanding of the processes that are selected in resistant mosquitoes. Specifically, before pyrethroids bind to their targets on motoneurons, they must first permeate the outer cuticle and diffuse to inner tissues. Resistant mosquitoes have evolved detoxification mechanisms that rely on cytochrome P450s (CYP), esterases, carboxyesterases, and other oxidation/reduction (redox) components to effectively detoxify pyrethroids to nontoxic breakdown products that are then excreted. Enhanced resistance mechanisms have evolved to include alteration of gene copy number, transcriptional and post-transcriptional regulation of gene expression, as well as changes to cellular signaling mechanisms. Here, we outline the variety of ways in which detoxification has been selected in various mosquito populations, as well as key gene categories involved. Pathways associated with potential new genes of interest are proposed. Consideration of multiple cellular pathways could provide opportunities for development of new insecticides.

Development of microsatellite markers for the predatory mite Phytoseiulus macropilis and cross-amplification in three other species of phytoseiid mites

Phytoseiid mites are efficient predators of mites and small pest insects. Understanding the dispersion and distribution pattern of phytoseiid mites is essential to promote the conservation of these natural enemies and support their use in biological control. Population genetic studies using molecular markers such as microsatellites have proved to be extremely informative to address questions about population structure and dispersion patterns of predatory mites. The objective of this work was to develop specific microsatellite markers for the predatory mite Phytoseiulus macropilis, aiming at improving field dispersion studies. For this purpose, the genomic DNA was extracted from the whole body of a pool of 260 adult females and used to build the genomic microsatellites-enriched library, using biotinylated probes (CT)₈ and (GT)₈. In total 26 pairs of primers were synthesized and screened across 30 adult females of P. macropilis for characterization. Seven loci were polymorphic, revealing from two to six alleles per locus. Cross amplifications were successfully obtained in the species Phytoseiulus persimilis, Amblyseius swirskii and Proprioseiopsis sp. The molecular markers obtained are the first developed for P. macropilis-they are effective for the detection and quantification of genetic variation, and show high transferability, thus can be used in genetic and molecular studies of this and other species of the same genus and also of close genera.

Effects of Acaricides on the Functional and Numerical Responses of the Phytoseid Predator Neoseiulus idaeus (Acari: Phytoseiidae) to Spider Mite Eggs

Integrated control tactics are often necessary for pest management. This is especially true for organisms such as the two-spotted spider mite, Tetranychus urticae Koch. The management of this mite pest species relies on pesticide use, but its short life cycle associated with high selection pressure results in frequent problems of acaricide resistance and population outbreaks. Therefore, combining acaricides and natural enemies is an appealing strategy for managing this pest species. The predatory mite Neoseiulus idaeus Denmark & Muma (Phytoseiidae) is important in arid environments, where other natural enemies show low efficacy. Thus, we investigated the effects of representative acaricides used for managing spider mites around the world in several crops (i.e., abamectin, fenpyroximate, and azadirachtin), on the functional and numerical responses of the phytoseid predator N. idaeus to increasing egg densities of its prey. Acaricide exposure did not affect the type of N. idaeus functional response or attack rate (a). However, acaricide exposure decreased the amount of consumed prey and increased prey handling time (Th). All acaricides affected the numerical response of the predator, which reduced oviposition rates. Therefore, caution is required in attempts to integrate the control methods.

Improving the compatibility of pesticides and predatory mites: recent findings on physiological and ecological selectivity

Integrated pest management relies upon the application of selective pesticides that do not hinder biological control. Phytoseiid mites represent an interesting case-study: they are amongst the most frequently used biological control agents and often are less affected by pesticides than their prey by natural tolerance or by developing resistance. The selectivity of a pesticide is determined by physiological processes that include metabolism, transport, and the affinity to the target-site. Genomic and transcriptomic studies start to elucidate the genetic and molecular mechanisms of differential toxicity in some phytoseiid species, such as a mutation in the sodium channel conferring pyrethroid resistance. Ecological selectivity is achieved by smart applications of pesticides and management practices that influence the persistence of phytoseiid mites on plants. Although modern pesticides often show lower acute toxicity, there is a need for robust assays and procedures that quantify lethal and sublethal effects, through different routes and times of exposure.

Evidence for Metabolic Pyrethroid Resistance in the Common Bed Bug (Hemiptera: Cimicidae)

Resistance to insecticides, especially the pyrethroids, in the common bed bug, Cimex lectularius L., has been well-documented. However, the presence and relative contribution of metabolic detoxifying microsomal oxidases and hydrolytic esterases to the observed resistance has yet to be fully elucidated. This is due, in part, to the absence of a simple bioassay procedure that appropriately isolates esterases from potentially competing oxidases. Recently, an analogue of piperonyl butoxide (PBO) was developed, EN16/5-1 (6-[2-(2-butoxyethoxy)ethoxymethyl]-5-propyl-2,3-dihydrobenzofuranby), which inhibits esterases but has limited efficacy against the oxidases, whereas PBO inhibits both. The opportunity is now available to use both synergists via established bioassay methodologies and to screen for the potential presence of oxidase- or esterase-derived pyrethroid resistance in insecticide-resistant insects, including bed bugs. In the present study, EN16/5-1 and PBO were assayed in conjunction with deltamethrin against four field strains of C. lectularius collected from independent geographic locations across Australia. All strains expressed a high degree of resistance to deltamethrin and significant inhibition of the observed resistance with preexposure to PBO. Nonsignificant differences between the cumulative mortality values for PBO and EN16/5-1 were then observed in two of the four bed bug strains, which indicate that detoxifying esterases are conferring substantially to the observed resistance in those strains. This study is the first to provide evidence that metabolic detoxification in the form of both hydrolytic esterases and microsomal oxidases is a major contributing factor to pyrethroid resistance in C. lectularius.