Boric acid toxic sugar bait suppresses male Aedes aegypti (Diptera: Culicidae): wing beat frequency and amplitude, flight activity, fecundity, insemination, and mate-finding Allee effect.

BACKGROUND: Controlling the spread of arboviral diseases remains a considerable challenge due to the rapid development of insecticide resistance in Aedes mosquitoes. This study evaluated the effects of boric acid-containing toxic sugar bait (TSB) on field populations of resistant Aedes aegypti mosquitoes. In addition, this study examined the flight activity and wing beat frequency and amplitude of males and the flight activity, fecundity, and insemination of females after pairing with males exposed to TSB. The population dynamics of Aedes mosquitoes under imbalanced sex ratios were examined to simulate realistic field conditions for male suppression under the effect of TSB. RESULTS: The mortality of male mosquitoes was consistently high within 24 h after exposure. By contrast, the mortality of female mosquitoes was inconsistent, with over 70% mortality observed at 168 h. The flight activity and wing beat amplitude of treated males were significantly lower than those of controls, but no significant difference in wing beat frequency was detected. The fecundity and insemination of treated female mosquitoes were lower than those of controls. A simulation study indicated that considerably low male population densities led to mating failures, triggering a mate-finding Allee effect and resulting in persistently low population levels. CONCLUSION: Boric acid-containing TSB could effectively complement current chemical intervention approaches to control resistant mosquito populations. TSB is effective in reducing field male populations and impairing male flight activity and female-seeking behavior, resulting in decreased fecundity and insemination. Male suppression due to TSB potentially results in a small mosquito population. © 2024 Society of Chemical Industry.

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 + ß-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.

Effects of piperonyl butoxide synergism and cuticular thickening on the contact irritancy response of field Aedes aegypti (Diptera: Culicidae) to deltamethrin.

BACKGROUND: Exploiting indoor-resting mosquitoes' innate behavioral responses to commonly used insecticide is crucial in vector control programs. Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) treated with pyrethroids have become widely used for controlling dengue fever vectors. The present study tested the effects of piperonyl butoxide (PBO) synergism and cuticular thickening on the contact irritancy response of field A. aegypti (Diptera: Culicidae) to deltamethrin in Taiwan and Thailand. RESULTS: The escape response of field mosquitoes treated with PBO was significantly elicited, with an escape percentage increase between 2- and 10-fold. In addition, the escape time was significantly lower in PBO-pretreated mosquitoes compared with field mosquitoes treated with deltamethrin alone. PBO-pretreated mosquitoes from seven out of 11 field strains exhibited a knockdown percentage of 11.23-54.91%, significantly higher than that of mosquitoes in corresponding strains treated with deltamethrin only. The Annan, Zhongxi, Sanmin, and North strains exhibited weak knockdown responses (≤3.75%). The mortality of PBO-pretreated field mosquitoes increased 2- to 75-fold compared with those treated with deltamethrin alone (mortality: 0-6.70%). Furthermore, the effect of cuticular thickness on the escape response of field mosquitoes was significant, that is, the escape response marginally increased inversely to cuticular thickness. By contrast, cuticular thickness was not significantly associated with knockdown or mortality percentage. CONCLUSION: Irritant behavior in mosquitoes was significantly elicited by PBO synergism. PBO incorporating deltamethrin IRS or LLINs may be effective for controlling dengue fever vectors. © 2021 Society of Chemical Industry.

Repellency and Contact Irritancy Responses of Aedes aegypti (Diptera: Culicidae) Against Deltamethrin and Permethrin: A Cross-Regional Comparison.

Control strategies exploiting the innate response of mosquitoes to chemicals are urgently required to complement existing traditional approaches. We therefore examined the behavioral responses of 16 field strains of Aedes aegypti (L.) from two countries, to deltamethrin and permethrin by using an excito-repellency (ER) test system. The result demonstrated that the escape percentage of Ae. aegypti exposed to pyrethroids did not vary significantly between the two countries in both contact and noncontact treatment despite the differing epidemiological patterns. Deltamethrin (contact: 3.57 ± 2.06% to 31.20 ± 10.71%; noncontact: 1.67 ± 1.67% to 17.31 ± 14.85%) elicited relatively lower responses to field mosquitoes when compared with permethrin (contact: 16.15 ± 4.07% to 74.19 ± 4.69%; noncontact: 3.45 ± 2.00% to 41.59 ± 6.98%) in contact and noncontact treatments. Compared with field strains, the mean percentage of escaping laboratory susceptible strain individuals were significantly high after treatments (deltamethrin contact: 72.26 ± 6.95%, noncontact: 61.10 ± 12.31%; permethrin contact: 78.67 ± 9.67%, noncontact: 67.07 ± 7.02%) and the escaped individuals spent significantly shorter time escaping from the contact and noncontact chamber. The results indicated a significant effect of resistance ratio on mean escape percentage, but some strains varied idiosyncratically compared to the increase in insecticide resistance. The results also illustrated that the resistance ratio had a significant effect on the mortality in treatments. However, the mortality in field mosquitoes that prematurely escaped from the treated contact chamber or in mosquitoes that stayed up to the 30-min experimental period showed no significant difference.

Effects of local dexmedetomidine administration on the neurotoxicity of ropivacaine for sciatic nerve block in rats.

Dexmedetomidine, used as an adjuvant to local anesthetics (LAs), may prolong the duration of peripheral nerve block. However, the effect of dexmedetomidine on the neurotoxicity of LAs is not completely understood. The present study was designed to investigate the efficacy of two doses of dexmedetomidine as an adjuvant to ropivacaine and its protective effect against the neurotoxicity of LAs. Paw withdrawal thermal latency testing was used to detect the sensory blockade. Extensor postural thrust testing was used to detect the motor blockade. The results demonstrated that the addition of dexmedetomidine to ropivacaine prolonged the duration of sensory and motor blockade in a dose­dependent manner compared with ropivacaine alone. TUNEL staining was performed to examine apoptosis. Western blotting was used to detect the Cleaved caspase­3 expression levels. The results showed that the addition of dexmedetomidine to ropivacaine decreased the rate of apoptosis and caspase­3 expression levels in a dose­dependent manner compared with ropivacaine alone (P<0.05). In addition, the rate of apoptosis and caspase­3 expression levels were significantly lower in the high­dose dexmedetomidine group compared with the low­dose dexmedetomidine group (P<0.05). The results suggested that the addition of dexmedetomidine to ropivacaine for sciatic nerve block in rats not only prolonged the duration of sensory and motor block of the sciatic nerve, but also markedly alleviated ropivacaine­induced neurotoxicity by decreasing caspase­3­dependent sciatic nerve cell apoptosis. Furthermore, the present study indicated that dexmedetomidine was more effective at a dose of 20 µg/kg compared with 6 µg/kg.