Insecticide Resistance in Eggs and First Instars of the Bed Bug, Cimex lectularius (Hemiptera: Cimicidae)

Efficacy of plant-based products and nonconventional pesticides for the management of tropical bed bug

Insecticide resistance is widespread in global bed bug populations. Both common bed bugs and tropical bed bugs are pyrethroid-resistant among most field populations. Plant-based products and nonconventional pesticides offer minimal-risk strategies for managing bed bug resistance, but this strategy has yet to be formally evaluated in Cimex hemipterus (F.) (Hemiptera: Cimicidae). Here, several commercial plant-based formulations (Cedarcide, EcoRaider (also known as EcoVenger), EcoSMART, and Bio-D), a novel product, Provecta, and a pyrethroid insecticide, Pesguard FG161 were tested against pyrethroid-susceptible and resistant strains of C. hemipterus using direct spray, residual exposure, and egg dipping assays. Direct spray treatments outperform residual applications against all tested bed bug strains. Cedarcide exhibits the highest consistency in eliminating bed bugs, followed by EcoRaider, EcoSMART, and Provecta that outperform Bio-D and Pesguard FG161. In comparison to Pesguard FG161, all plant-based insecticide products and Provecta showed higher efficacy against pyrethroid-resistant strains. Although effective, product efficacy varies in terms of speed. Cedarcide kills all bed bugs within 1 min after spraying; however, other products can take up to 9 days to achieve 100% mortality. The efficacy of all products was reduced when evaluated on fabric surface (42%-65% mortality). Cedarcide and EcoRaider reduced egg hatchability by 37%-73% and 47%-70%, respectively. This study suggests that certain plant-based insecticides and an unconventional insecticide can serve as alternative direct spray treatments for managing tropical bed bugs, though their residual effects are limited.

Insecticide Resistance of Cimex lectularius L. Populations and the Performance of Selected Neonicotinoid-Pyrethroid Mixture Sprays and an Inorganic Dust

Insecticide resistance is one of the factors contributing to the resurgence of the common bed bug, Cimex lectularius L. This study aimed to profile the resistance levels of field-collected C. lectularius populations to two neonicotinoids and one pyrethroid insecticide and the performance of selected insecticide sprays and an inorganic dust. The susceptibility of 13 field-collected C. lectularius populations from the United States to acetamiprid, imidacloprid, and deltamethrin was assessed by topical application using a discriminating dose (10 × LD₉₀ of the respective chemical against a laboratory strain). The RR₅₀ based on KT₅₀ values for acetamiprid and imidacloprid ranged from 1.0-4.7 except for the Linden 2019 population which had RR₅₀ of ≥ 76.9. Seven populations had RR₅₀ values of > 160 for deltamethrin. The performance of three insecticide mixture sprays and an inorganic dust were evaluated against three C. lectularius field populations. The performance ratio of Transport GHP (acetamiprid + bifenthrin), Temprid SC (imidacloprid + β-cyfluthrin), and Tandem (thiamethoxam + λ-cyhalothrin) based on LC₉₀ were 900-2017, 55-129, and 100-196, respectively. Five minute exposure to CimeXa (92.1% amorphous silica) caused > 95% mortality to all populations at 72 h post-treatment.

Ovicidal and repellent activities of several plant essential oils against Periplaneta americana L. and enhanced activities from their combined formulation

Natural ovicidal and repellent agents against Periplaneta americana L. are urgently needed, and plant essential oils (EOs) can assume this role quite readily. In this study, ovicidal and repellent activities against Periplaneta americana of EOs from Cymbopogon citratus (Stapf.), Cinnamomum verum (J. Presl.), Eucalyptus globulus (Labill.), Illicium verum (Hook.f.), and Zanthoxylum limonella (Alston) in soybean oil and in ethyl alcohol were determined by topical and dual-choice assays, as well as 10% cypermethrin and a combined formulation of 5% C. verum EO + 5% I. verum EO. Cypermethrin at 10% provided the highest toxicity (100% inhibition rate) against the eggs, but only slightly higher than that (99.3%) provided by the combined EO formulation, while the highest repellent activity against the adults was provided by the combined formulation (89.5% repelled cockroaches at 48 h after treatment). In addition, all EO formulations in soybean oil provided higher ovicidal and repellent activities than those in ethyl alcohol. To conclude, the combined EO formulation in soybean oil can replace cypermethrin because their efficacy was nearly equivalent, but the combination should be much safer to use.

Can colonization by an endophytic fungus transform a plant into a challenging host for insect herbivores?

Endophytic growth of arthropod pathogenic fungi can parasitize insect herbivores without causing damage to the crop. However, studies addressing this tritrophic interaction are absent. Here, the endophytic arthropod pathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordyciptaceae), the polyphagous two-spotted spider mite Tetranychus urticae Koch (Trombidiformes: Tetranychidae), and its preferred plant host Phaseolus vulgaris L. (Fabales: Fabaceae) were selected to study the multi-kingdom interactions among plants, arthropods, and entomopathogenic fungi. Real-Time PCR analysis of nine defense-related genes revealed that a broad range of plant defense mechanisms is activated in response to the endophytic growth of B. bassiana. Moreover, we studied the molecular mechanism adapted by the two-spotted spider mite that underlies resistance. The analysis of 41 detoxification genes revealed that relatively moderate, high, and few numbers of genes were changed in the adults, nymphs, and eggs stages of T. urticae, respectively, after inoculation on colonized tissues of P. vulgaris. The endophytic growth of B. bassiana can have a negative effect on the growth and performance of the pest, in a developmental stage-dependent manner, by priming plant defense pathways. In parallel, the herbivore induces a broad range of detoxification genes that could potentially be involved in adaptation to endophytically colonized plant tissues.

Assessment of Tropical Bed Bug (Hemiptera: Cimicidae), Infestations in Cape Coast, Ghana: Household Control Practices and Efficacy of Commercial Insecticides and Long-Lasting Insecticidal Nets Against Field Bed Bugs

This study reports the first baseline information on tropical bed bug, Cimex hemipterus (F.) (Hemiptera: Cimicidae), infestations in Ghana. The purpose of this study was to assess bed bug infestation levels, and the efficacy of locally available insecticides and long-lasting insecticidal nets (LLINs) in controlling field bed bugs populations in the Cape Coast region. A survey was undertaken to assess bed bug infestation levels and current control practices by residents. In total, 205 bed bug affected households were identified in 20 communities and live bed bug infestations were associated with most of these premises. Many homeowners knew of other households (from 1 to 3) with a bed bug infestation. Residents reported itching and swelling of the skin from the bed bug bites and the bites were considered severe. The most common household bed bug control strategy was the application of insecticides. However, LLINs and commercially formulated insecticides commonly used by households (notably chloropyrifos and pyrethroid-based formulations) did not efficaciously suppress field collected strains of C. hemipterus. Using a dipping bioassay, mean mortality ranged from 0 to 60% for eggs, nymphs, and adults, and less than 40% mortality was observed in bed bugs placed on insecticide-treated filter paper. Each LLINs (all are pyrethroid based) produced a mean mortality of less than 20% in adult bed bugs. For a more effective response to the global bed bug resurgence in developing countries, government and supporting agencies need to render assistance to bed bug affected residents through the provision of improved pest management strategies.

Bioactivity of Bacillus thuringiensis (Bacillales: Bacillaceae) on Diatraea saccharalis (Lepidoptera: Crambidae) eggs

BACKGROUND

Bacillus thuringiensis (Bt) is a Gram-positive bacterium that synthesizes specific protein toxins, which can be exploited for control of various insect pests, including Diatraea saccharalis, a lepidopteran that severely damages sugarcane crops. Although studies have described the effects of Bt in the larval phases of D. saccharalis, few have examined its effect on insect eggs. Herein, we studied the entomopathogenic potential of Bacillus thuringiensis serovar Aizawai GC-91 (Bta) during D. saccharalis embryo development with the aim of understanding the entomopathogenic mechanism and developing new biological control techniques for target insects.

RESULTS

Bta concentrations of 5, 10 and 20 g L^-1 demonstrated the strongest bioactivity, reducing D. saccharalis egg viability by 28.69%, 33.91% and 34.98%, respectively. The lethal concentrations (LCs) were estimated as: LC₅₀ = 28.07 g L^-1 (CI 95% = 1.89-2.38) and LC₉₀ = 65.36 g L^-1 (CI 95% = 4.19-5.26). Alterations in egg coloration, melanization and granule accumulation were observed at 24 h, persisting until 144 h. The embryo digestive systems were severely damaged, including narrowing of the intestinal lumen, vesiculations and degenerated cells, causing embryonic death.

CONCLUSION

The toxicity caused by Bta in D. saccharalis embryos demonstrated its potential as a biological control agent and as a sustainable alternative for integrated management of D. saccharalis infestation. © 2020 Society of Chemical Industry.

Virulence of Metarhizium brunneum (Ascomycota: Hypocreales) Strains Against Stinkbugs Euschistus heros and Dichelops furcatus (Hemiptera: Pentatomidae)

Three strains of fungi belonging to the genus Metarhizium Sorokīn (ARSEF 4556, ARSEF 3297, native strain) were assayed against adults and nymphs of the Neotropical brown stinkbug Euschistus heros (F.) and the green-belly stinkbug Dichelops furcatus (F.). The most virulent strain, ARSEF 4556, caused over 90% mortality. The average survival time of the second and fifth instar nymphs and adults following immersion in 1 × 108 conidia ml-1 was 4.8, 5.7, and 5.2 d, respectively. The second instar nymphs were more susceptible than the adults. The LC50 values and median survival times for second instar and adult E. heros were 1.6 × 107 and 3.1 × 107 conidia ml-1 and 6 and 8 d, respectively. Eggs of E. heros and the closely related stinkbug, D. furcatus, were highly susceptible to ARSEF 4556 with the mean mortality of eggs immersed in 1 × 108 conidia ml-1 being 77.4% and 89.7%, respectively. The strain 3297 showed also good aptitudes for stinkbugs control with mortalities higher than 80% against nymphs and adults and eggs mortalities of 75.5% for E. heros and 79.6% for D. furcatus. This study has shown that it is possible to have a two-pronged control strategy, targeting adults and to reduce oviposition and targeting egg clusters to prevent emergence and dispersal of nymphs. Besides early instars of nymphs have been shown to be more susceptible to the fungal strains than late instars and adults.

Performance of Commercial Insecticide Formulations Against Different Developmental Stages of Insecticide-Resistant Tropical Bed Bugs (Hemiptera: Cimicidae)

This study examined the presence of insecticide resistance in different developmental stages (adults, first instars, and eggs) of the tropical bed bug, Cimex hemipterus (F.) using several insecticide formulations. Adults and first instars of five strains (Queensland, Kuala Lumpur, Bukit Mertajam, Saujana, and Krystal Point) were evaluated using the surface contact method and compared with a susceptible strain (Monheim) of the common bed bug Cimex lectularius L. The insecticide formulations were used at their label rates in this study: Tandem (thiamethoxam [11.6%], lambda-cyhalothrin [3.5%]) at 183.96 mg/m2; Temprid SC (imidacloprid [21%], beta-cyfluthrin [10.5%]) at 106.13 mg/m2; Sumithion 20CS (fenitrothion [20%]) at 250 mg/m2; Pesguard FG161 (d-tetramethrin [4.4%], cyphenothrin [13.2%]) at 110 mg/m2; and Sumithrin 10SEC (d-phenothrin [10%]) at 100 mg/m2. Results showed a very high level of resistance to Pesguard FG161 (388.3 to >605.0 times) and Sumithrin (302.9 to >365.5 times) in all adults of the strains tested, whereas low to high levels of resistance were registered for Tandem (1.4-4.7 times), Temprid (7.3-16.7 times), and Sumithion (1.2-14.6 times) for adults of all bed bug strains. For first instars, resistance to the former two formulations were high to very high (31.4-118.1 times). In contrast, they showed lower resistance to Tandem, Temprid, and Sumithion (1.0-10.2 times). An immersion method used to test on bed bug eggs found high to very high resistance toward all tested formulations. Results demonstrate that the resistance level varies between bed bug developmental stages.

Toxicity of Kadsura coccinea (Lem.) A. C. Sm. Essential Oil to the Bed Bug, Cimex lectularius L. (Hemiptera: Cimicidae)

Kadsura coccinea (Lem.) A.C. Smith is an evergreen, woody climbing plant that is widely distributed throughout southwest mainland China. Extracts of this plant are used in traditional Chinese medicine (TCM) for the treatment of various diseases, like cancer and dermatosis, and as an anodyne to relieve pain, while the leaves are used to treat eczema. In the current study, the toxicity of essential oil from its stem (EOKC) was studied against two strains of bed bugs (Cimex lectularius). Essential oil from the plant was obtained by hydrodistillation and analyzed by GC/MS. The major compound identified was β-caryophyllene (24.73%), followed by caryophyllene oxide (5.91%), α-humulene (3.48%), and β-pinene (2.54%). Preliminary screening was performed by topically delivering a 1 µL droplet of the treatments dissolved in acetone. At 24 h after treatment, the EOKC induced mortality rates of 61.9% and 66.7% in the Bayonne and Ft. Dix strains, respectively, at 100 µg/bug. Four major compounds-β-caryophyllene, caryophyllene oxide, α-humulene, and β-pinene-were selected based on their availability and were subjected to topical, residual, and fumigation methods. When applied topically, only β-caryophyllene induced high toxicity in both strains. None of the selected compounds induced significant toxicity in the residual and fumigation methods.

Essential Oils of Five Baccharis Species: Investigations on the Chemical Composition and Biological Activities

This paper provides a comparative account of the essential oil chemical composition and biological activities of five Brazilian species of Baccharis (Asteraceae), namely B. microdonta, B. pauciflosculosa, B. punctulata, B. reticularioides, and B. sphenophylla. The chemical compositions of three species (B. pauciflosculosa, B. reticularioides, and B. sphenophylla) are reported for the first time. Analyses by GC/MS showed notable differences in the essential oil compositions of the five species. α-Pinene was observed in the highest concentration (24.50%) in B. reticularioides. Other major compounds included α-bisabolol (23.63%) in B. punctulata, spathulenol (24.74%) and kongol (22.22%) in B. microdonta, β-pinene (18.33%) and limonene (18.77%) in B. pauciflosculosa, and β-pinene (15.24%), limonene (14.33%), and spathulenol (13.15%) in B. sphenophylla. In vitro analyses for antimalarial, antitrypanosomal, and insecticidal activities were conducted for all of the species. B. microdonta and B. reticularioides showed good antitrypanosomal activities; B. sphenophylla showed insecticidal activities in fumigation bioassay against bed bugs; and B. pauciflosculosa, B. reticularioides, and B. sphenophylla exhibited moderate antimalarial activities. B. microdonta and B. punctulata showed cytotoxicity. The leaves and stems of all five species showed glandular trichomes and ducts as secretory structures. DNA barcoding successfully determined the main DNA sequences of the investigated species and enabled authenticating them.

Insecticide resistance and resistance mechanisms in bed bugs, Cimex spp. (Hemiptera: Cimicidae)

The worldwide resurgence of bed bugs [both Cimex lectularius L. and Cimex hemipterus (F.)] over the past two decades is believed in large part to be due to the development of insecticide resistance. The transcriptomic and genomic studies since 2010, as well as morphological, biochemical and behavioral studies, have helped insecticide resistance research on bed bugs. Multiple resistance mechanisms, including penetration resistance through thickening or remodelling of the cuticle, metabolic resistance by increased activities of detoxification enzymes (e.g. cytochrome P450 monooxygenases and esterases), and knockdown resistance by kdr mutations, have been experimentally identified as conferring insecticide resistance in bed bugs. Other candidate resistance mechanisms, including behavioral resistance, some types of physiological resistance (e.g. increasing activities of esterases by point mutations, glutathione S-transferase, target site insensitivity including altered AChEs, GABA receptor insensitivity and altered nAChRs), symbiont-mediated resistance and other potential, yet undiscovered mechanisms may exist. This article reviews recent studies of resistance mechanisms and the genes governing insecticide resistance, potential candidate resistance mechanisms, and methods of monitoring insecticide resistance in bed bugs. This article provides an insight into the knowledge essential for the development of both insecticide resistance management (IRM) and integrated pest management (IPM) strategies for successful bed bug management.

A Method for Evaluating Insecticide Efficacy against Bed Bug, Cimex lectularius, Eggs and First Instars

Standard toxicity evaluations of insecticides against insect pests are primarily conducted on adult insects. Evaluations are based on a dose-response or concentration-response curve, where mortality increases as the dose or concentration of an insecticide is increased. Standard lethal concentration (LC50) and lethal dose (LD50) tests that result in 50% mortality of a test population can be challenging for evaluating toxicity of insecticides against non-adult insect life stages, such as eggs and early instar or nymphal stages. However, this information is essential for understanding insecticide efficacy in all bed bug life stages, which affects control and treatment efforts. This protocol uses a standard dipping bioassay modified for bed bug eggs and a contact insecticidal assay for treating nymphal first instars. These assays produce a concentration-response curve to further quantify LC50 values for insecticide evaluations.

Comparison of ingestion and topical application of insecticides against the common bed bug, Cimex lectularius (Hemiptera: Cimicidae)

BACKGROUND

The global prevalence of Cimex lectularius infestations has challenged current intervention efforts, as pyrethroid resistance has become ubiquitous, availability of labeled insecticides for bed bugs is limited, and non-chemical treatment options, such as heat, are often unaffordable. We evaluated representative insecticides toward the goal of developing a novel, ingestible liquid bait for hematophagous arthropods.

RESULTS

LC₅₀ values were estimated for adult males and first instar nymphs of an insecticide-susceptible strain for abamectin, clothianidin, fipronil and indoxacarb, after ingestion from an artificial feeder. LD₅₀ values were calculated based on the ingested blood volume. Ingested abamectin, clothianidin and fipronil caused rapid mortality in both life stages. Fipronil was ∼43-fold more effective by ingestion than by topical application. Indoxacarb and its bioactive metabolite decarbomethoxylated JW062 (DCJW) were ineffective at causing bed bug mortality even at concentrations as high as 1000 ng mL^-1 blood.

CONCLUSIONS

Fipronil, clothianidin and abamectin have potential for being incorporated into a liquid bait for bed bug control; indoxacarb and DCJW were not effective. Bed bugs are a good candidate for an ingestible liquid bait because systemic formulations generally require less active ingredient than residual sprays, they remain contained and more effectively target hematophagous arthropods. © 2016 Society of Chemical Industry.

Evidence of Tolerance to Silica-Based Desiccant Dusts in a Pyrethroid-Resistant Strain of Cimex lectularius (Hemiptera: Cimicidae)

Insecticide resistance in bed bugs (Cimex lectularius and Cimex hemipterus) has become widespread, which has necessitated the development of new IPM (Integrated Pest Management) strategies and products for the eradication of infestations. Two promising options are the diatomaceous earth and silica gel-based desiccant dusts, both of which induce dehydration and eventual death upon bed bugs exposed to these products. However, the impact of underlying mechanisms that confer resistance to insecticides, such as cuticle thickening, on the performance of these dusts has yet to be determined. In the present study, two desiccant dusts, CimeXa Insecticide Dust (silica gel) and Bed Bug Killer Powder (diatomaceous earth) were evaluated against two strains of C. lectularius; one highly pyrethroid-resistant and one insecticide-susceptible. Label-rate doses of both products produced 100% mortality in both strains, albeit over dissimilar time-frames (3–4 days with CimeXa vs. 14 days with Bed Bug Killer). Sub-label rate exposure to CimeXa indicated that the pyrethroid-resistant strain possessed a degree of tolerance to this product, surviving 50% longer than the susceptible strain. This is the first study to suggest that mechanisms conferring resistance to pyrethroids, such as cuticular thickening, may have potential secondary impacts on non-synthetic insecticides, including desiccant dusts, which target the bed bug’s cuticle.

Egg Hatch Rate and Nymphal Survival of the Bed Bug (Hemiptera: Cimicidae) After Exposure to Insecticide Sprays

Few studies have addressed the efficacy of insecticides used against eggs and first-instar nymphs of the bed bug, Cimex lectularius L. (Hemiptera: Cimicidae). Insect eggs are often resistant to insecticides; therefore, information on which products are effective is important. We evaluated the efficacy of four commonly used insecticide sprays applied directly to bed bug eggs. We also evaluated the efficacy of these insecticides to first-instar nymphs exposed to residuals resulting from directly spraying eggs. Temprid SC (beta-cyfluthrin, imidacloprid) was the most effective insecticide at preventing egg hatch (13% hatch rate) for pyrethroid-resistant, field-strain (Jersey City) bed bugs compared with a control (water [99% hatch rate]), Bedlam (MGK-264, sumithrin [84% hatch rate]), Demand CS (lambda-cyhalothrin [91% hatch rate]), and Phantom SC (chlorfenapyr [95% hatch rate]). Demand CS and Temprid SC were most effective at preventing egg hatch (0%) for an insecticide-susceptible (Harold Harlan) strain, followed by Bedlam (28%). Phantom SC produced a hatch rate similar to the control (97% and 96%, respectively). Harold Harlan-strain nymphs showed 100% survival for the control but 0% survival for Bedlam and Phantom SC. Jersey City-strain nymphs showed 100% survival for the control, 99% survival for Bedlam, 0% survival for Demand CS, 4% survival for Phantom SC, and 38% survival for Temprid SC. Demand CS was less effective at preventing hatch (91% hatch rate) of Jersey City-strain nymphs but was the only product to kill all nymphs (0% survival). One of the least effective products for preventing Jersey City-strain egg hatch (Phantom SC, 95% hatch rate) was the second most effective at killing nymphs, leaving only six of 141 alive. These findings indicate that survival of directly sprayed eggs and residually exposed, first-instar nymphs varies by strain, life stage, and product used.

Efficacy of Selected Insecticide Sprays and Aerosols against the Common Bed Bug, Cimex lectularius (Hemiptera: Cimicidae)

We evaluated the residual efficacy of four liquid sprays and four ready-to-use aerosols that are commonly used in the U.S. against a field-collected bed bug, Cimex lectularius L., strain with moderate resistance level to pyrethroids. The four liquid sprays were: Tandem (0.1% thiamethoxam, 0.03% lambda-cyhalothrin), Temprid SC (0.05% imidacloprid, 0.025% cyfluthrin), Transport GHP (0.05% acetamiprid, 0.06% bifenthrin), and Demand CS (0.03% lambda-cyhalothrin). The four aerosols were: Alpine (0.5% dinotefuran), Bedlam (0.4% sumithrin, 1.6% MGK 264), Bedlam Plus (0.4% sumithrin, 1% MGK 264, 0.05% imidacloprid), and Phantom (0.5% chlorfenapyr). Bed bugs were confined for 4 h to treated substrates (aged 24 h). Four substrates were tested: fabric, unpainted wood, painted wood, and vinyl. Bedlam, Demand CS, and Temprid SC resulted in ≤70% mortality on all tested substrates. Among the other five products, substrate type significantly affected their residual efficacy, except for Transport GHP, which caused ≥89.7% mortality regardless of the substrate. The effect of exposure time (5 min, 4 h, and 24 h) on the efficacy of Transport GHP and Phantom aerosol also was evaluated. A 4 h continuous exposure to Phantom aerosol or Transport GHP residue caused similar mortality to 24 h exposure and higher mortality than 5 min exposure.