Performance of <Emphasis Type="Italic">Eriopis connexa</Emphasis> (Coleoptera: Coccinellidae) resistant to lambda-cyhalothrin after extended recovery from knockdown

A population of the predatory lady beetle Eriopis connexa (Germar) (Coleoptera: Coccinellidae) was recorded as resistant to lambda-cyhalothrin. Adults exposed to this insecticide have recovered from knockdown after 72 h. Thus, the performance of resistant (R) and susceptible (S) populations of E. connexa not exposed to insecticide (R0 and S0) and R adults recovering from knockdown 24, 48, and 72 h after exposure (R24, R48, and R72) was studied. In addition, the fertility life table parameters were calculated for one generation considering the progenies from R0, S0, and R24 populations. The recovery rate from knockdown was 69.4% for R-adults, and greater recovery rate was observed within 48 h following lambda-cyhalothrin exposure. The S-females produced about 50% more eggs and lived longer, when compared with R-females irrespective of the recovery periods after knockdown. The R-females produced similar number of eggs and exhibited similar longevity across all treatments (R0, R24, R48, and R72). Progenies produced by R- and S-populations did not exhibit consistent differences in development and survival. The fertility life table parameters showed higher intrinsic rate of population growth (r_m) and lower mean generation time (T) for R0- and R24-females, when compared with those for S0-females. Thus, the time interval needed to recover from knockdown is not related to the adaptive cost of resistance in E. connexa.     

Heterosis and reselection for pyrethroid resistance trait maintenance in the lady beetle Eriopis connexa (Germar)

Exposure of Eriopis connexa (Germar) to pyrethroid residues in agroecosystems has resulted in selection for resistance (R). Pyrethroid resistance allows E. connexa to survive lambda-cyhalothrin applications. Following a field release of E. connexa, development of resistance in an incipient population may depend on three major factors such as the maintenance of: (i) selection pressure, (ii) frequency of mating with susceptible phenotypes (S) and (iii) differential reproductive performance due to the fitness costs associated with resistance. To investigate the potential effects of these three factors on the development of pyrethroid resistance by progeny of field released E. connexa, our experiments included panmictic mating between R and S phenotypes, followed by descendant rearing with and without insecticide selection pressure, reselection and determination of resistance levels. In addition, we measured the reproductive performance of the parental R and S phenotypes and their descendants to assess the cost of resistance after crossing and reselection. Survival of R × S descendants exposed to lambda-cyhalothrin was reduced across successive generations in the absence of selection pressure, but still enhanced after four generations indicating the persistent presence of resistant phenotypes in the population. Under selection pressure with exposure to lambda-cyhalothrin applied at label rates, descendant survival was >50%. Fecundity and survival were higher in the first-generation of crossed R × S females, but higher fecundity was not sustained after reselection. Adults of the R population exhibited a fitness cost, reduced longevity, when compared to S phenotypes and R × S crossed populations. Therefore, resistance maintenance in E. connexa after release will depend on selection pressures imposed by insecticide exposure. In the absence of selection pressure, the phenotype for resistance was reduced, but not completely lost. Further, resistant phenotypes can be reselected following insecticide exposure and this can explain, in part, the high frequency of field-evolved resistance to lambda-cyhalothrin in E. connexa.     

Stability of the resistance to lambda-cyhalothrin in the ladybird beetle Eriopis connexa

Natural enemies resistant to insecticides are expected to help control the remaining arthropod pests after insecticide application and, hence, prevent crop damage, pest resurgence, and resistance selection. Field-evolved resistance to lambda-cyhalothrin and to other pyrethroids exhibited by the neotropical ladybird beetle Eriopis connexa (Germar) (Coleoptera: Coccinellidae) has been characterized and enhanced under laboratory selection. In this study, we investigated the stability of the resistance and its relationship with detoxification enzyme activity and biological performance, which are important for a biocontrol agent. One subgroup of the resistant population of E. connexa was established without selection pressure (R-UNSEL) during eight generations, and compared to either a susceptible (SUS) or its parental resistant (R-SEL) population. The resistance ratio in R-UNSEL was reduced by 50% compared to R-SEL between the first and fourth generation without selection pressure, but stayed stable afterwards, from the fifth to the eighth generation. Despite eight generations without selection pressure and reduction in the resistance level, the resistance ratio in R-UNSEL was still 39× greater than in the SUS population. The reduced resistance in R-UNSEL correlated to reduction in esterase activity, but the R-UNSEL maintained greater activity than the SUS group. The absence of selection pressure and reduction in enzyme activity in R-UNSEL did not mitigate the adaptive costs, with 2.7× lower egg production compared to SUS females. These findings indicate that resistance to lambda-cyhalothrin in R-UNSEL has already stabilized in the population. Although the resistance ratio and detoxifying enzymes were reduced in R-UNSEL, the impact on fecundity was maintained. Furthermore, the absence of crossing with wild SUS individuals will allow the R-UNSEL offspring to retain the resistance allowing survival to lambda-cyhalothrin even when used at the highest recommended field rate.     

Mortality and knockdown effects of imidacloprid and methomyl in house fly (Musca domestica L., Diptera: Muscidae) populations

In this study, the knockdown and mortality effects of imidacloprid and methomyl were investigated. The residual surface applications were carried out to determine the knockdown effects (KDt₅₀ and KDt₉₅) and mortality (LD₅₀ and LD₉₅) induced by each insecticide. For mortality comparisons, the susceptible house fly (Musca domestica L., Diptera: Muscidae) of a WHO population and three natural field‐collected M. domestica populations from Turkey were used. In conclusion, it was found that the resistance to imidacloprid and methomyl was significantly higher in the field populations when compared to the susceptible population from WHO. The results showed that applicators and pest management decision‐makers should control and conduct an integrated pest management strategy by including biological agents to prevent the development of high levels of resistance in the field populations.     

Residual contact vial method for the rapid on-site detection of insecticide resistance in Thrips palmi

A residual contact vial plus water (RCVpW) bioassay method, in which water was supplemented to minimize control mortality, was established to monitor insecticide resistance in field populations of the melon thrips, Thrips palmi. In the RCVpW, median lethal doses (LD₅₀) of six insecticides commonly used in T. palmi control, were determined at 8 h post-treatment, using a susceptible RDA strain according to the RCVpW protocol. Diagnostic doses for on-site resistance monitoring of the six insecticides, which were determined as doses two-fold higher than required to achieve LD₉₀ in the RDA strain, were in the range of 0.299 to 164.3 μg^?1 cm². Insecticide resistance levels in five field populations of T. palmi were evaluated to test the applicability of RCVpW in monitoring the pest. Although the RDA strain exhibited 100% mortality to diagnostic doses, field populations showed a reduced mortality in response to all test insecticides, indicating different degrees of resistance. In particular, all test field populations exhibited a significantly low mortality in response to spinosad, suggesting a wide distribution of spinosad resistance. Synergistic bioassay revealed that cytochrome P450-mediated metabolic factor is involved in spinosad resistance in the Korean population. Interestingly, an apparently reduced mortality to emamectin benzoate and chlofenapyr was observed in some field populations, perhaps suggesting uneven distribution of resistance to these insecticides in field populations. Our study showed that the RCVpW protocol can be employed both as an on-site resistance monitoring method for major thrip species, and in the selection of appropriate insecticides for their control.     

Insecticide resistance monitoring in whitefly (Bemisia tabaci) (Hemiptera: Aleyrodidae) in Oman

The sweet potato whitefly, Bemisia tabaci Gennadius, is an important insect pest of many crops including vegetables through direct feeding damage and as a vector of several plant viruses. Intensive use of insecticides has led to the development of insecticide resistance in global B. tabaci populations. This study was conducted to establish susceptibility levels to deltamethrin, thiamethoxam and pyriproxyfen in seven geographically different populations of B. tabaci MEAM1 adults in Oman. All B. tabaci populations showed very low to low level of resistance (2.1–12.3 fold) to deltamethrin. All B. tabaci populations showed no resistance to very low level of resistance to thiamethoxam (2.2–6.2 fold) and pyriproxyfen (2.4–3.5 fold). A likelihood analysis showed the possibility for control failure in two populations (Barka and Salalah) to deltamethrin, however, no possible failure was detected in all populations for thiamethoxam and pyriproxyfen. An insecticide resistance dynamics study in one population (SQU-1) showed a loss in susceptibility to deltamethrin with increase in the LC₅₀ value from 25.1 mg L⁻¹ to 84.5 mg L⁻¹ between 2017 and 2019 resulting in 5.3 fold increase in RF. The study results determined that several B. tabaci populations are at the initial stages of resistance development to deltamethrin and cross-resistance with thiamethoxam and pyriproxyfen. Vegetable farmers in Oman, the Barka and Salalah regions in particular, should be cautious in the repeated use of one class of insecticide alone.     

Using Drosophila melanogaster to validate metabolism-based insecticide resistance from insect pests

Identifying molecular mechanisms of insecticide resistance is important for preserving insecticide efficacy, developing new insecticides and implementing insect control. The metabolic detoxification of insecticides is a widespread resistance mechanism. Enzymes with the potential to detoxify insecticides are commonly encoded by members of the large cytochrome P450, glutathione S-transferase and carboxylesterase gene families, all rapidly evolving in insects. Here, we demonstrate that the model insect Drosophila melanogaster is useful for functionally validating the role of metabolic enzymes in conferring metabolism-based insecticide resistance. Alleles of three well-characterized genes from different pest insects were expressed in transgenic D. melanogaster : a carboxylesterase gene (αE7) from the Australian sheep blowfly Lucilia cuprina, a glutathione S-transferase gene (GstE2) from the mosquito Anopheles gambiae and a cytochrome P450 gene (Cyp6cm1) from the whitefly Bemisia tabaci. For all genes, expression in D. melanogaster resulted in insecticide resistance phenotypes mirroring those observed in resistant populations of the pest species. Using D. melanogaster to assess the potential for novel metabolic resistance mechanisms to evolve in pest species is discussed.     

Distribution of Pyrethroid Resistant Populations of Triatoma infestans in the Southern Cone of South America

BackgroundA number of studies published during the last 15 years showed the occurrence of insecticide resistance in Triatoma infestans populations. The different toxicological profiles and mechanisms of resistance to insecticides is due to a genetic base and environmental factors, being the insecticide selective pressure the best studied among the last factors. The studies on insecticide resistance on T. infestans did not consider the effect of environmental factors that may influence the distribution of resistance to pyrethroid insecticides. To fill this knowledge gap, the present study aims at studying the association between the spatial distribution of pyrethroid resistant populations of T. infestans and environmental variables.Conclusions/SignificanceThe occurrence of these two groups concentrated over a particular region that coincides with the area where populations of the intermediate cytogenetic group were found might reflect the spatial heterogeneity of the genetic variability of T. infestans, that seems to be the cause of the insecticide resistance in the area, even on sylvatic populations of T. infestans, never before exposed to pyrethroid insecticides, representing natural and wild toxicological phenotypes. The strong linear relationship found between LD₅₀ and RR₅₀ suggest RR₅₀ might not be the best indicator of insecticide resistance in triatomines.     

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) eggs as alternative food for rearing of lady beetles Eriopis connexa (Germar) (Coleoptera: Coccinellidae)

Eriopis connexa (Germar) (Coleoptera: Coccinellidae) is an important predator with potential for biological control of insect pests. This research evaluated the development of E. connexa larvae fed on fresh eggs of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) without (T1) or with (T2) scales or one-day (T3) or six-month (T4) frozen, or newly-hatched larvae of S. frugiperda (T5). The percentage of E. connexa adults was higher when larvae feeding on fresh S. frugiperda eggs with or without scales, or one-day frozen eggs of this prey and lower with eggs of this Lepidoptera after frozen for six months or with newly-hatched larvae of S. frugiperda. Duration of the larval period of E. connexa was 15.7, 15.8, 16.0, 17.6, and 17.3 days, respectively, with these diets. The high survival of E. connexa fed with eggs of S. frugiperda shows the potential use of this prey in the laboratory to maintain this natural enemy.     

Incidence of resistance to neonicotinoid insecticides in greenhouse populations of the whitefly, Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) from Greece

The greenhouse whitefly, Trialeurodes vaporariorum Westwood, is an important pest of field and greenhouse crops of horticultural and ornamental plants. In integrated pest management programs its control is mainly based on the release of biological control agents and application of chemical insecticides. Neonicotinoids are relatively new chemicals currently applied for the chemical control of T. vaporariorum. However, cases of development of insecticide resistance to neonicotinoids have already been reported. The state of resistance to neonicotinoid insecticides for populations of the greenhouse whitefly in Greece is currently unknown. The objective of our study was to screen a number of whitefly populations for resistance to the neonicotinoids imidacloprid and thiacloprid. Seven whitefly populations were collected from tomato greenhouse crops from different areas of central and northern Greece. LC₅₀ values were estimated for all populations following the method proposed by the Insecticide Resistance Action Committee (IRAC). The development of resistance to both neonicotinoids was confirmed for all tested populations with resistance ratios ranging from 1.5 to 4.4-fold and from 1.4 to 12.2-fold for imidacloprid and thiacloprid, respectively. We discuss our results with regard to the development of neonicotinoid resistance in T. vaporariorum populations and its implications for whitefly control.     

The potential of crop management practices to reduce pollen beetle damage in oilseed rape

A major problem associated with agricultural intensification over recent decades has been the development of insecticide resistance in crop pest populations. This has been a particular issue for control of the pollen beetle (Brassicogethes aeneus syn. Meligethes aeneus), a major pest of oilseed rape throughout Europe. Sustained and often prophylactic use of pyrethroid insecticides has led to the development of insecticide-resistant beetle populations, and alternatively, more environmentally benign integrated pest management strategies are sought for the pest. The population dynamics of pollen beetles and their natural enemies, and the damage caused by the pest, are influenced by processes acting at multiple scales, from the regional or landscape scale down to the local field or within-field scale. In this review, we focus on the within-field scale, and how crop management factors, including tillage, crop plant density, crop nutrition and crop rotations may be optimised and incorporated into integrated pest management strategies for more sustainable and effective control of the pest.     

Susceptibility to deltamethrin in the predatory mites Neoseiulus californicus and Phytoseiulus macropilis (Acari: Phytoseiidae) populations in protected ornamental crops in Brazil

Knowledge of inter and intra-specific variation in the susceptibility of natural enemies to pesticides could help to better design integrated pest management strategies. The objective of this research was to evaluate the susceptibility to deltamethrin in populations of the predatory mites Neoseiulus californicus (McGregor) and Phytoseiulus macropilis (Banks) populations collected from protected ornamental crops in Brazil. The susceptibility to deltamethrin was characterized against immature and adult stages of both species. The impact of this insecticide was also measured by estimating the intrinsic rate of increase (r _i). The immature and adult stages of N. californicus were approximately 3,600 and 3,000-fold more tolerant to deltamethrin than those of P. macropilis. However, high variability in the susceptibility to this insecticide was detected among P. macropilis populations, with resistance ratios of up to 3,500-fold. The selection of deltamethrin-resistant strains of P. macropilis could be exploited in applied biological control programs.     

High pyrethroid-resistance intensity in Culex quinquefasciatus (Say) (Diptera: Culicidae) populations from Jigawa,North-West,Nigeria

This study examined pyrethroid resistance intensity and mechanisms in Culex quinquefasciatus (Say) (Diptera: Culicidae) populations from Jigawa, North-West Nigeria. Resistance statuses to permethrin, lambda-cyhalothrin and alphacypermethrin were determined with both WHO and CDC resistance bioassays. Synergist assay was conducted by pre-exposing the populations to Piperonyl butoxide (PBO) using the WHO method. Resistance intensities to 2x, 5x and 10x of diagnostic concentrations were determined with the CDC bottle method. Species analysis and presence of knockdown mutation (Leu-Phe) were done using Polymerase Chain Reaction (PCR). Results showed that Cx. quinquefasciatus was the only Culex spp. present and “Kdr-west” mutation was not detected in all analyzed samples. Using WHO method, Cx. quinquefasciatus resistance to permethrin was detected in Dutse (12.2%) and Kafin-Hausa (77.78%). Lambda-cyhalothrin resistance was recorded only in Kafin-Hausa (83.95%) with resistance suspected in Ringim (90%). Resistance to alphacypermethrin was recorded in all locations. Pre-exposure to PBO led to 100% mortality to alphacypermethrin and lambda-cyhalothrin in Ringim while mortality to permethrin and alphacypermethrin in Dutse increased from 12.2% to 97.5% and 64.37% to 79.52% respectively. Using CDC bottle bioassay, resistance was also recorded in all populations and the result shows a significant positive correlation (R² = 0.728, p = 0.026) with the result from the WHO bioassay. Results of resistance intensity revealed a very high level of resistance in Kafin-Hausa with susceptibility to lambda-cyhalothrin and alphacypermethrin not achieved at 10x of diagnostic doses. Resistance intensity was also high in Dutse with susceptibility to all insecticides not achieved at 5x of diagnostic doses. Widespread and high intensity of resistance in Cx. quinquefasciatus from North-West Nigeria is a major threat to the control of diseases transmitted by Culex and other mosquito species. It is a challenge that needs to be adequately addressed so as to prevent the failure of pyrethroid-based vector control tools.     

Insecticide resistance in populations of Tuta absoluta (Lepidoptera: Gelechiidae)

1 Control failures of insecticides used against the tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in Brazil led to the investigation of the possible occurrence of resistance of this insect pest to abamectin, cartap, methamidophos and permethrin. 2 The insect populations were collected from seven sites in the states of Minas Gerais, Rio de Janeiro, and São Paulo. These populations were subjected to concentration–mortality bioassays using insecticide‐impregnated filter papers. 3 We were unable to obtain a single population which provided a susceptibility standard for all insecticides tested. Therefore, the resistance levels were estimated in relation to the most susceptible population to each insecticide. Resistance to abamectin and cartap were observed in all populations when compared with the susceptible standard population, with resistance ratios ranging from 5.2‐ to 9.4‐fold and from 2.2‐ to 21.9‐fold for abamectin and cartap, respectively. Resistance to permethrin was observed in five populations with resistance ratios ranging from 1.9‐ to 6.6‐fold, whereas resistance to methamidophos was observed in four populations with resistance ratios ranging from 2.6‐ to 4.2‐fold. 4 The long period and high frequency of use of these insecticides against this insect pest suggest that the evolution of insecticide resistance on them has been relatively slow. Alternatively, the phenomenon might be widespread among Brazilian populations of T. absoluta making the finding of suitable standard susceptible populations difficult and leading to an underestimation of the insecticide resistance levels in this pest. 5 Higher levels of resistance to abamectin, cartap and permethrin are correlated with greater use of these compounds by growers. This finding suggests that local variation in insecticide use was an important cause of variation in susceptibility.     

Use of mathematical models to estimate characteristics of pyrethroid resistance in tobacco budworm and bollworm (Lepidoptera: Noctuidae) field populations

Genetic models have been used to examine the evolution of insecticide resistance in pest species subject to data and assumptions regarding genetic, biological, and operational parameters. We used time-series data on pyrethroid tolerance and simple genetic models to estimate underlying genetic and biological parameters associated with resistance evolution in tobacco budworm, Heliothis virescens (F.), and bollworm, Helicoverpa zea (Boddie), Louisiana field populations. Assuming pyrethroid resistance is conferred by one gene at one locus in both species, inheritance of pyrethroid resistance was partially dominant in the tobacco budworm and partially recessive in the bollworm. Relative fitness estimates indicated that fitness costs associated with resistance selected against resistance alleles in the absence of selection pressure in the tobacco budworm, but not in the bollworm. In addition, relative fitness estimates obtained using the indirect method outlined in this study were similar in magnitude to estimates obtained using traditional direct approaches.     

Landscape genomics of Colorado potato beetle provides evidence of polygenic adaptation to insecticides

The ability of insect pests to rapidly and repeatedly adapt to insecticides has long challenged entomologists and evolutionary biologists. Since Crow's seminal paper on insecticide resistance in 1957, new data and insights continue to emerge that are relevant to the old questions about how insecticide resistance evolves: such as whether it is predominantly mono‐ or polygenic, and evolving from standing vs. de novo genetic variation. Many studies support the monogenic hypothesis, and current management recommendations assume single‐ or two‐locus models. But inferences could be improved by integrating data from a broader sample of pest populations and genomes. Here, we generate evidence relevant to these questions by applying a landscape genomics framework to the study of insecticide resistance in a major agricultural pest, Colorado potato beetle, Leptinotarsa decemlineata (Say). Genome–environment association tests using genomic variation from 16 populations spanning gradients of landscape variables associated with insecticide exposure over time revealed 42 strong candidate insecticide resistance genes, with potentially overlapping roles in multiple resistance mechanisms. Measurements of resistance to a widely used insecticide, imidacloprid, among 47 L. decemlineata populations revealed heterogeneity at a small (2 km) scale and no spatial signature of origin or spread throughout the landscape. Analysis of nucleotide diversity suggested candidate resistance loci have undergone varying degrees of selective sweeps, often maintaining similar levels of nucleotide diversity to neutral loci. This study suggests that many genes are involved in insecticide resistance in L. decemlineata and that resistance likely evolves from both de novo and standing genetic variation.     

Side-effects of insecticides on two erigonid spider species

The current rearing technique forErigone atra (Blackwall) andOedothorax apicatus (Blackwall) (Araneae, Erigonidae) was improved. To reduce time spent rearing on live fruit flies the spiders were kept on a culture of the Collembola speciesLepidocyrtus lanuginosus (Gmelin) (Entomobryidae). Side-effects on spiders of two pyrethroid insecticides (fenvalerate and lambda-cyhalothrin) and one carbamate insecticide (pirimicarb) were tested. Sensitivity of adults of both sexes and juveniles to insecticides and their influence on the rate of emergence of spiderlings from cocoons were investigated using topical application, spraying or residual contact. LD₅₀ values for adults ranged from 0.49 to 2.52 ng a.i./spider for lambda-cyhalothrin and from 5.75 to 98.20 ng a.i./spider for fenvalerate. Topical application also resulted in up to a week's delay of web-building. A moving laboratory spraying equipment was used to spray spiders with different insecticide dosages and water volumes. Pyrethroids sprayed onto adults in webs had stronger effects than pyrethroids sprayed onto sitting or walking spiders on the soil surface. Residual contamination caused higher mortality of spiders after contact with lambda-cyhalothrin than fenvalerate. In all tests, males were more susceptible to pyrethroids than females; this difference was related to body weight. Mortality rate was higher forE. atra than forO. apicatus. Both pyrethroids were also toxic to spiderlings. Lambda-cyhalothrin inhibited emergence ofE. atra spiderlings from cocoons. Pirimicarb was harmless to both spider species.