Mosquito Species Composition And Insecticide Resistance Status of Anopheles Arabiensis In Itang Special Woreda, Gambella, Southwestern Ethiopia

Introduction: Anopheles arabiensis, member species of the Anopheles gambiae complex, is the primary vector of malaria widely distributed in Ethiopia. Anopheles funestus, An. pharoensis and An. nili are secondary vectors occurring with limited distribution in the country. Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are pillars for the interventions against malaria control and elimination efforts in Ethiopia. However, the emergence and widespread of insecticide resistance in the major malaria vector, An. arabiensis, might compromise the efforts of the country. The aim of this study was to investigate composition of mosquito species and insecticide resistance status of An. arabiensis in Itang special woreda (district), Gambella, southwestern Ethiopia.Materials and methods: Adult mosquitoes were sampled from September 2020 to Feburary 2021 using Centers for Disease Control and Prevention (CDC) light trap and Pyrethrum Spray Catch (PSC). Moreover, mosquito larvae were also collected from different breeding sites and reared to adults to assess susceptibility status of populations of An. gambiae s.l. in the study area. Susceptibility tests were conducted on two to three days old non blood fed female An. gambiae s.l using insecticide impregnated papers with deltamethrin (0.05%), alpha-cypermethrin (0.05%), propoxur (0.1%), pirimiphos-methyl (0.25%) and bendiocarb (0.1%) following World Health Organization (WHO) standard susceptibility test procedure. Molecular diagnostics were done for the identification of member species of An. gambiae s.l and detection of knockdown resistance (kdr) allele using species specific polymerase chain reaction (PCR) and allele specific PCR. Results: In total, 468 adult mosquitoes were collected from different houses. Culex mosquitoes were the most dominant (80.4%) followed by Anopheles mosquitoes. Three species of Anopheles mosquitoes (An. coustani, An. pharoensis, and An. gambiae (s.l.)) were identified, of which An. coustani was the dominant (8.1%) species. WHO bioassay tests revealed that the populations of An. gambiae s.l in the study area are resistant against alpha-cypermethrin and deltamethrin whereas, susceptible to bendiocarb, pirimiphos-methyl and propoxur. Out of the total 86 An. gambiae s.l specimens assayed, 79 (92%) successfully amplified and identified as An. arabiensis. West African Kdr (L1014F) mutation was detected with high Kdr allele frequency ranging from 67-88%.Conclusion: The detection of target site mutation, kdr L1014F allele, coupled with the phenotypic resistance against alpha-cypermethrin and deltamethrin call for continuous resistance monitoring.

Insecticidal potency of mixtures of plant powders and Actellic SuperTM (Pirimiphos-methyl + Permethrin) on Callosobruchus chinensis F. and Sitophilus zeamais Motch

Insect pests still cause substantial quantitative and qualitative grain loss ranging from 20 to 100% in small holder farming systems in tropical countries. Synthetic pesticides are recommended as stop gap measures for the management of stored product insect pests. However, their application has not been fully exploited in small scale farming due to environmental, health, and economic concerns. As a result, new researches have shifted focus to exploiting pesticidal plants as alternatives to synthetic pesticides. Therefore, the current study evaluated mixtures of plant powders and reduced amount of Actellic superTM (pirimiphos-methyl + permethrin) as alternative insecticide formulation against Callosobruchus chinensis and Sitophilus zeamais. Green grams and wheat grains were mixed with a mixture of plant powders in the ratios of 1:1, 1:3 and 1:9 to obtain four rates (0.0, 2.0, 6.0 and 10%w/w). Grains and plant powders were also mixed with reduced amount (10, 25, and 50 %) of recommended rate of Actellic SuperTM to obtain dosages as above. Twenty unsexed adults, 1-5 day old S. zeamais and C. chinensis were introduced into treated grains. The mixture of C. lusitanica: T. vogelii powders in the ratios of 1:1, 1:3 and 1:9 caused mortality in C. chinensis of 55, 95 and 85%, respectively. At the same ratio, E. saligna: L. camara mixture produced mortality in S. zeamais of 77, 82, and 85% respectively. In mixture of C. lusitanica and T. vogelii and reduced amount of Actellic SuperTM by 50% the mortality of C. chinensis was 85 and 80 % respectively. Similarly, E. saligna and L. camara and reduced amount of Actellic SuperTM by 50% caused a mortality of S. zeamais of 48 and 97% respectively. The application of plant powders and reduced amounts of synthetic insecticide has the potential to be applied in stored product pest control

Can pyrethroid-piperonyl butoxide (PBO) nets reduce the efficacy of indoor residual spraying with pirimiphos-methyl against pyrethroid-resistant malaria vectors?

As the uptake of pyrethroid-PBO ITNs increases, their combination with IRS insecticides could become an operational reality in many malaria-endemic communities. Pirimiphos-methyl is a pro-insecticide requiring activation by mosquito cytochrome P450 enzymes to induce toxicity while PBO blocks activation of these enzymes in pyrethroid-resistant vector mosquitoes. PBO may thus antagonise the toxicity of pirimiphos-methyl IRS when combined with pyrethroid-PBO ITNs. The impact of combining two major brands of pyrethroid-PBO ITNs (Olyset Plus, PermaNet 3.0) with pirimiphos-methyl IRS (Actellic 300CS) was evaluated against pyrethroid-resistant Anopheles gambiae sl in two parallel experimental hut trials in southern Benin in comparison to bendiocarb IRS and each intervention alone. The wild vector population was resistant to pyrethroids but susceptible to pirimiphos-methyl and bendiocarb. PBO pre-exposure partially restored deltamethrin toxicity but not permethrin. Mosquito mortality in experimental huts was significantly improved in the combinations of bendiocarb IRS with Olyset Plus (33%) and PermaNet 3.0 (38%) compared to bendiocarb IRS alone (14 to 16%, p<0.001), demonstrating an additive effect. Conversely, mortality was significantly reduced in the combinations of pirimiphos-methyl IRS with Olyset Plus (59%) and PermaNet 3.0 (55%) compared to pirimiphos-methyl IRS alone (77 to 78%, p<0.001), demonstrating an antagonistic effect. Combining pirimiphos-methyl IRS with the pyrethroid-PBO ITNs provided significantly improved mosquito mortality (55 to 59%) compared to the pyrethroid-PBO ITNs alone (22 to 26%) and improved blood-feeding inhibition relative to the IRS alone. This study provided evidence of an antagonistic effect when pyrethroid-PBO ITNs were combined with pirimiphos-methyl IRS in the same household resulting in lower levels of vector mosquito mortality compared to the IRS alone. Pirimiphos-methyl IRS also showed potential to significantly enhance malaria control when deployed to complement pyrethroid-PBO ITNs in an area where PBO fails to fully restore susceptibility to pyrethroids.

Influence of Indoor Residual Spay on An. Gambiae S.L. and An. Funestus Abundance, Resting Behavior and Community Perception on Irs Intervention In Kagera-Tanzania

Background: There has been a persistence of malaria transmission in Kagera Region despite consecutive phases of indoor residual spraying (IRS) targeting malaria vectors. In addition to that, there is limited information on the resting behaviors of An. gambiae s.l. and An. funestus and community perception on IRS in Kagera. Methods: The study was conducted in two districts; Missenyi and Karagwe. Missenyi was IRS sprayed with Pirimiphos methyl insecticide and Karagwe was unsprayed. Mosquito collections were conducted using bucket traps and CDC (Centre for Disease Control) light traps. Mosquitoes were identified morphologically using taxonomical key. Sibling species were identified by polymerase chain reaction (PCR). Interviews and focused group discussions (FGDs) were conducted in order to obtain information on community perception with regard to IRS interventions. Results: A total of 5,777 mosquitoes were collected indoors by CDC light traps. An. gambiae s.l. and An. funestus accounted for 13% (n=749) of all mosquitoes collected. Unexpectedly, large proportions of An. funestus were collected indoors in Missenyi district, despite the fact that, the area was sprayed. In Karagwe district, An. gambiae s.l. was collected in large proportion. Results have showed that, An. arabiensis was the dominant sibling species among the An. gambiae s.l. in Karagwe and Missenyi districts with 82.8% (n=24) and 98.8% (n=166), respectively. Study participants agreed that, IRS campaign is useful for control of malaria vectors. They also reported that, malaria transmission have declined by comparing before and after IRS. Challenges reported which the IRS campaign poses to them, including the emergence of other insects in their houses and increase of mosquitoes later after IRS. They also reported some mosquito resting places which are not a target during spray operations. Conclusion: The present study has revealed the abundance of malaria vectors and community perception on IRS intervention efficacy and sustainability. Surprisingly, large proportions of An. funestus were collected indoors, despite the fact that, Missenyi district was sprayed. This situation calls for further studies on An. funestus behaviors and possible reasons for tolerance in sprayed area. Community sensitization before, during and after IRS application needs to be strengthen for getting intended results.

The effect of some insecticides on the larvae of Aedes aegypti in Jeddah Governorate, Makah Province, Kingdom Saudi Arabia

Mosquitoes can act as vectors for many disease-causing viruses and parasites through carrying these organisms from person to person. The objective of this study was to evaluate the susceptibility of Aedes aegypti larvae to some insecticides in Jeddah Governorate. Mosquito larvae were collected from all the available breeding sites in Jeddah municipalities using standard larval collection kits. The diagnostic doses (LC50 and LC90) were calculated from the mortality and concentration data. The larvicides Pirimiphos methyl, Fenitrothion, Bifenthrin and Cypermethrin were tested against the larvae of Ae. aegypti mosquito. The results showed positive correlation between the concentrations under investigation and mortality% of the treated larvae. Cypermethrin gave strong effect against Ae. aegypti larvae (LD50 0.0015 ml/L) followed by Pirimiphos methyl (LD50 0.0020 ml/L), Bifenthrin (LD50 0.039 ml/L), and at last rank Fenitrothion (0.041 ml/L). The same trend was obtained in LD90s. Ae. aegypti in Jeddah was susceptible to Bifenthrin, Cypermethrin, Pirimiphos methyl and Fenitrothion. Further studies should be run to conduct an intensive and appropriate vector control program in Jeddah Governorate.

The efficacy of insecticide-treated window screens and eaves against Anopheles mosquitoes: a scoping review

Background Female mosquitoes serve as vectors for a host of illnesses, including malaria, spread by the Plasmodium parasite. Despite monumental strides to reduce this disease burden through tools such as bed nets, the rate of these gains is slowing. Ongoing disruptions related to the COVID-19 pandemic may also negatively impact gains. The following scoping review was conducted to examine novel means of reversing this trend by exploring the efficacy of insecticide-treated window screens or eaves to reduce Anopheles mosquito bites, mosquito house entry, and density. Methods Two reviewers independently searched PubMed, Scopus, and ProQuest databases on 10 July, 2020 for peer-reviewed studies using insecticide-treated screens or eaves in malaria-endemic countries. These articles were published in English between the years 2000–2020. Upon collection, the reports were stratified into categories of biting incidence and protective efficacy, mosquito entry and density, and mosquito mortality. Results Thirteen out of 2180 articles were included in the final review. Eaves treated with beta-cyfluthrin, transfluthrin or bendiocarb insecticides were found to produce vast drops in blood-feeding, biting or mosquito prevalence. Transfluthrin-treated eaves were reported to have greater efficacy at reducing mosquito biting: Rates dropped by 100% both indoors and outdoors under eave ribbon treatments of 0.2% transfluthrin (95% CI 0.00–0.00; p < 0.001). Additionally, co-treating window screens and eaves with polyacrylate-binding agents and with pirimiphos-methyl has been shown to retain insecticidal potency after several washes, with a mosquito mortality rate of 94% after 20 washes (95% CI 0.74–0.98; p < 0.001). Conclusions The results from this scoping review suggest that there is value in implementing treated eave tubes or window screens. More data are needed to study the longevity of screens and household attitudes toward these interventions.

First Comprehensive Report of Conventional Insecticide Resistance Status of the Mosquito Culex quinquefasciatus Say (Diptera: Culicidae) in Saudi Arabia

Background The mosquito Culex quinquefasciatus Say is a vector of various fatal diseases including West Nile fever, filariasis, and Japanese encephalitis. The major approach in controlling Cx. quinquefasciatus to prevent associated disease transmission has focused on insecticides. However, because of overreliance on such measures, Cx. quinquefasciatus has developed resistance to these insecticides including organophosphates and pyrethroids. Methods We evaluated 10 commonly used conventional insecticides (five OPs and five pyrethroids) for toxicity/resistance in Cx. quinquefasciatus in adults and larvae in eight populations collected from the environs around Riyadh, Saudi Arabia. Results The LC50 values for the tested insecticides in adults did not differ significantly from those of a susceptible strain, except for bifenthrin, deltamethrin, cypermethrin, cyfluthrin, and fenitrothion against populations from Al-Nakhil, Al-Suwaidi, Al-Ghanemiya, Al-Masfa, and Al-Masanie regions. All Cx. quinquefasciatus adult populations exhibited susceptibility/low resistance to the tested organophosphates with resistance ratios of 0.23–0.80 for chlorpyrifos, 0.44–1.97 for malathion, 0.09–3.62 for fenitrothion, 0.05–2.10 for pirimiphos-methyl, and 0.11–0.93 for diazinon. The Cx. quinquefasciatus adult populations exhibited susceptibility/moderate resistance to the tested pyrethroids with resistance ratios of 0.59–2.56 for alpha-cypermethrin, 0.59–2.19 for bifenthrin, 0.60–7.07 for deltamethrin, 0.60–2.66 for cypermethrin, and 0.58–2.39 for cyfluthrin. In Cx. quinquefasciatus larva populations, susceptibility/low resistance to the tested organophosphates was observed with resistance ratios of 0.03–1.75 for chlorpyrifos, 0.19–3.42 for malathion, 0.11–2.78 for fenitrothion, and 0.08–1.15 for pirimiphos-methyl. Conclusions The susceptibility/low resistance of Cx. quinquefasciatus adults to OP and pyrethroid insecticides suggests that they still have good potency against the adults of this species in Riyadh, Saudi Arabia. These results provide a baseline for decision-making in integrated vector management programs for Cx. quinquefasciatus.

Partial indoor residual spraying with pirimiphos-methyl as an effective and cost-saving measure for the control of Anopheles gambiae s.l. in northern Ghana

The scale up of indoor residual spraying (IRS) and insecticide treated nets have contributed significantly to global reductions in malaria prevalence over the last two decades. However, widespread pyrethroid resistance has necessitated the use of new and more expensive insecticides for IRS. Partial IRS with pirimiphos-methyl in experimental huts and houses in a village-wide trial was evaluated against Anopheles gambiae s.l. in northern Ghana. Four different scenarios in which either only the top or bottom half of the walls of experimental huts were sprayed, with or without also spraying the ceiling were compared. Mortality of An. gambiae s.l. on partially sprayed walls was compared with the standard procedures in which all walls and ceiling surfaces are sprayed. A small-scale trial was then conducted to assess the effectiveness, feasibility, and cost of spraying only the upper walls and ceiling as compared to full IRS and no spraying in northern Ghana. Human landing catches were conducted to estimate entomological indices and determine the effectiveness of partial IRS. An established transmission dynamics model was parameterized by an analysis of the experimental hut data and used to predict the epidemiological impact and cost effectiveness of partial IRS for malaria control in northern Ghana. In the experimental huts, partial IRS of the top (IRR 0.89, p = 0.13) or bottom (IRR 0.90, p = 0.15) half of walls and the ceiling was not significantly less effective than full IRS in terms of mosquito mortality. In the village trial, the annual entomological inoculation rate was higher for the unsprayed control (217 infective bites/person/year (ib/p/yr)) compared with the fully and partially sprayed sites, with 28 and 38 ib/p/yr, respectively. The transmission model predicts that the efficacy of partial IRS against all-age prevalence of malaria after six months would be broadly equivalent to a full IRS campaign in which 40% reduction is expected relative to no spray campaign. At scale, partial IRS in northern Ghana would have resulted in a 33% cost savings ($496,426) that would enable spraying of 36,000 additional rooms. These findings suggest that partial IRS is an effective, feasible, and cost saving approach to IRS that could be adopted to sustain and expand implementation of this key malaria control intervention.

Variable residual activity of K-Othrine® PolyZone and Actellic® 300 CS in semi-field and natural conditions in the Democratic Republic of the Congo

Background Indoor Residual Spray (IRS) against vector mosquitoes is a primary means for combating malaria transmission. To combat increased patterns of resistance to chemicals against mosquito vectors, alternative candidate insecticide formulations should be screened. With mortality as the primary endpoint, the persistence of residual efficacy of a polymer-enhanced pyrethroid suspension concentrate containing deltamethrin (K-Othrine® PolyZone—KOPZ) applied at 25 mg active ingredient (ai)/m2 was compared with a microencapsulated organophosphate suspension formulation of pirimiphos-methyl (Actellic® 300CS—ACS) applied at 1 g ai/m2. Methods Following standard spray application, periodic contact bioassays were conducted for at least 38 weeks on four types of wall surfaces (unbaked clay, baked clay, cement, and painted cement) sprayed with either KOPZ or ACS in simulated semi-field conditions. Similarly, two types of existing walls in occupied houses (painted cement and baked clay) were sprayed and examined. A colonized strain of female Anopheles arabiensis mosquitoes were exposed to treated or untreated surfaces (controls) for 30 min. For each wall surface test period, 40 treatment mosquitoes (4 cones × 10) in semi-field and 90 (9 cones × 10) in ‘natural’ house conditions were used per wall. 30 mosquitoes (3 cones × 10) on a matching unsprayed surface served as the control. Insecticide, wall material, and sprayed location on wall (in houses) were compared by final mortality at 24 h. Results Insecticide, wall material, and sprayed location on wall surface produced significant difference for mean final mortality over time. In semi-field conditions, KOPZ produced a 72% mean mortality over a 38-week period, while ACS gave 65% (p < 0.001). Painted cement wall performed better than other wall surfaces throughout the study period (73% mean mortality). In the two occupied houses, KOPZ provided a mean mortality of 88%, significantly higher than ACS (p < 0.001). KOPZ provided an effective residual life (≥ 80% mortality) between 7.3 and 14 weeks on experimental walls and between 18.3 and 47.2 weeks in houses, while ACS persisted between 3 and 7.6 weeks under semi-field conditions and between 7.1 and 17.3 weeks in houses. Household painted cement walls provided a longer effective residual activity compared to baked clay for both formulations. Greater mortality was recorded at the top and middle sections of sprayed wall compared to the bottom portion near the floor. Conclusion KOPZ provided longer residual activity on all surfaces compared to ACS. Painted cement walls provided better residual longevity for both insecticides compared to other surfaces. Insecticides also performed better in an occupied house environment compared to semi-field constructed walls. This study illustrates the importance of collecting field-based observations to determine appropriate product active ingredient formulations and timing for recurring IRS cycles.