Novel pyriproxyfen based treatment for Aedes breeding control through a long-lasting formulation: Laboratory and field trials in Western Maharashtra, India

Background & objectives: There is a need to evaluate novel techniques for dengue control in India. Several formulations of pyriproxyfen have been assessed for efficacy and duration of action. Pyriproxyfen is also used as a microencapsulated ready-to-use formulation against the Aedes vector. We evaluated a novel pyriproxyfen-based microencapsulated formulation. This slow-release, ready-to-use aqueous spray is a larvicidal formulation, and we assessed its efficacy and residual action through laboratory and semi-field trials against Aedes immature stages. Methods: The study was carried out as per the guidelines for laboratory and field/small-scale field testing of mosquito larvicides by the World Health Organization. The evaluation was conducted in laboratory and semi-field conditions from August to December 2018. We tested the novel formulation on three materials (plastic, ceramic, and enamel) in the laboratory for its action as an antilarval. Four containers of each kind were sprayed with the formulation and kept as replicates. Four controls were used in the laboratory trials - 120 larvae (third instar) were introduced in the replicates and the controls each. Readings were taken daily till complete adult emergence or larval and pupal mortality. In the semi-field trials, we applied this formulation to the inside of desert coolers and observed larvicidal and pupicidal activity over five months. Data is presented in numbers and percentages, along with mean and standard deviation. Adult emergence and Emergence Inhibition was calculated. Results: There was 100% adult emergence inhibition amongst the exposed larvae in the treated containers in the laboratory trials. In the untreated controls, adult emergence ranged from 80–95% in all types of containers. In the semifield trials, Inhibition Emergence was 100% in the treated desert coolers during the five months of the study period. Interpretation & conclusion: This advancement in insecticide formulation technology promises to make dengue control more effective and efficient

Emergence of Schoengastiella ligula as the vector of scrub typhus outbreak in Darjeeling: Has Leptotrombidium deliense been replaced.

Background: Following a suspected outbreak of scrub typhus in Kurseong, Darjeeling, the Armed Forces Medical College, Pune was requested by the National Institute of Epidemiology and the State authorities to undertake investigation of the ongoing scrub typhus outbreak and suggest containment measures. Materials and Methods:The epidemic team undertook clinical, entomological and serological studies to understand the local disease pattern and delineate high risk areas, host diversity by rodent trapping using Sherman traps, mite fauna diversity, abundance and vector species identification by phase contrast microscopy for preparation of electronic database and rodent and human serological studies by Weil Felix and PCR. Results:The results indicate no association of scrub typhus with age and sex (P=0.37 and 0.74 respectively). The maximum cases occurred amongst the tea garden workers (73%) in the age group of 25-44 years. The predominant clinical presentation was fever (100%) with headache (75%), lymphadenopathy (45%) and presence of eschar (76.7%). The dominant host species (50% of trapped rodents) was shrew Suncus murinus, the index animal for scrub typhus, which contributed maximally to the vector abundance (52.96%) with a chigger index of 61.56. The trombiculid mite Schoengastiella ligula was the vector species much against the expected mite vector Leptotrombidium deliense, in the area. The study found the presence and abundance of vector species which corroborated well with the occurrence of cases in the various localities within the subdivisions. Conclusion:The study thus establishes Schoengastiella ligula as the vector of scrub typhus outbreak in Kurseong, Darjeeling. Preventive and containment measures with emphasis on reduction of man - vector contact were suggested to the state authorities to contain the outbreak.

Effectiveness of Diflubenzuron in the control of houseflies.

Background & objectives: Houseflies are one of the major pest problems worldwide. The current housefly control strategy in the country hinges on the use of Dichlorvos as a housefly larvicide and pyrethrum spray in kitchens/dining areas. The present study was undertaken to evaluate the newer housefly control options in the wake of concerns about human toxicity of Dichlorvos and its continued use in public health. Methods: Efficacy of Diflubenzuron WP and granule formulations (chitin synthesis inhibitor) visà- vis Dichlorvos EC in the control of housefly was assessed in laboratory by adult emergence inhibition after treatment and in field conditions by estimation of density post-application up to three weeks using standard methods. Results: Dichlorvos EC and Diflubenzuron formulations (WP and granule) brought about 100% inhibition of adult emergence under laboratory conditions. However, in the field evaluation, effective suppression of housefly population was brought about by Dichlorvos and Diflubenzuron granule formulation (though delayed). Conclusion: Dichlorvos EC and Diflubenzuron granule formulation are effective housefly larvicides. It is recommended that Diflubenzuron WP formulation be evaluated at a higher frequency to enhance its effectiveness and its use may be considered in conjunction with an initial suppression of housefly adults with an adulticide, e.g. Cyphenothrin, etc.

Insecticide treated bednet strategy in rural settings: can we exploit women's decision making power?

Use of insecticide treated bednets in prevention of malaria is a widely propagated global strategy, however, its use has been reported to be influenced and limited by many variables especially gender bias. A cross sectional field epidemiological study was conducted in a rural setting with two outcome variables, 'Bednet use'(primary outcome variable) and 'Women's Decision Making Power' which were studied in reference to various predictor variables. Analysis reveals a significant effect on the primary outcome variable 'Bednet use' of the predictor variables- age, occupation, bednet purchase decision, women's decision making power, husband's education and knowledge about malaria and its prevention. The study recommends IEC on treated bednets to be disseminated through TV targeting the elderly women who have better decision making power and mobilizing younger women who were found to prefer bednets for prevention of mosquito bites for optimizing the use of treated bednets in similar settings.

Field performance of imidacloprid gel bait against German cockroaches (Dictyoptera: Blatellidae).

BACKGROUND AND OBJECTIVES: Resistance amongst cockroaches has been reported to most of the spray insecticides. Imidacloprid gel baits, which can be selectively applied at the infested and potential harborages sites have been found effective in control of cockroach infestation in some laboratory studies but very few field studies are available. This study was therefore undertaken to evaluate the efficacy of imidacloprid gel bait in the control of German cockroaches (Blatella germanica) in field. METHODS: A survey was done to find out pre-treatment density in 12 cookhouses by visual count and sticky trap method. A total of four cookhouses having high cockroach infestation were selected by simple random sampling method (two for imidacloprid treatment and two for control). Imidacloprid gel (2.15%) was used as crack and crevices treatment at the infested sites and potential harborages once only during the entire study duration. Post-treatment density was assessed by visual count method every week for nine weeks. RESULTS: Visual count method gave better indications of cockroach infestation as compared to sticky trap method, hence the same was followed for post-treatment evaluation. Reduction of 75.0 - 86.5 per cent was achieved with imidacloprid gel treatment by week 1 post-treatment in comparison to control areas. The reduction in treated areas by 8 wk post-treatment was 96.3-98.8 per cent in comparison to control areas. Residual effect of imidacloprid started declining at 9 wk (91.7 - 96.5% reduction in comparison to control areas). INTERPRETATION AND CONCLUSION: The results of our study report the efficacy of imidacloprid gel bait (2.15%) up to 8 wk against German cockroaches. The gel was safe and environment friendly also.

Efficacy of synthetic pyrethroid and propoxur aerosol in the control of German cockroaches (Dictyoptera: Blatellidae) in cookhouses.

BACKGROUND AND OBJECTIVES: A field trial was carried out in cookhouses in an urban area to evaluate the efficacy of synthetic pyrethroid (0.02% deltamethrin + 0.13% allethrin) and propoxur aerosols (2%) in the control of German cockroaches (Blatella germanica). METHODS: A total of six cookhouses were selected by simple random sampling method (two each for the two insecticide treatments and two for control). RESULTS: It was observed that 89.36-87.8 and 77.95-59.74% reductions were achieved with propoxur and synthetic pyrethroid treatment respectively by first week post-treatment. The reduction in propoxur treated areas by eight weeks post-treatment was 82.98-76.13%, whereas the reduction in the same time period in synthetic pyrethroid treated areas ranged from 14.36% to an increase in density by a phenomenal 157.86% in one of the treated sites. INTERPRETATION AND CONCLUSION: The study reports the efficacy of propoxur aerosol (2%) treatment over synthetic pyrethroid (0.02% deltamethrin + 0.13% allethrin) in the control of cockroach infestation in cookhouses in urban area.

Field performance of cyphenothrin: an integrated insecticide strategy against German cockroaches (Dictyoptera: Blatellidae).

BACKGROUND & OBJECTIVES: Resistance to organophosphorous and carbamate insecticides amongst German cockroaches is widely reported. Cyphenothrin EC, a new synthetic pyrethroid was evaluated in cookhouses in an urban area, with the aim of exploring alternate control option against the German cockroach Blatella germanica. METHODS: Three cookhouses were selected by simple random sampling method, two for treatment and one as control. The impact of treatment on cockroach infestation was monitored weekly by visual assessment sampling technique. RESULTS: Cyphenothrin brought about 95 to 97.5% reduction in cockroach infestation by the end of six weeks post-treatment. INTERPRETATION & CONCLUSION: The study reports the efficacy of cyphenothrin in the control of German cockroaches and recommends an "Integrated insecticide strategy" for the control of cockroaches in urban cookhouses.

Efficacy of Fipronil and Propoxur in the control of German cockroaches (Dictyoptera: Blatellidae).

A field trial for comparative evaluation of chemicals Fipronil gel, Propoxur spray and bait was carried out. The results in the Fipronil treated area indicate a reduction of 89%, 100% and 98% in cockroach infestation by days 7, 30 and 60, whereas the reduction in Propoxur spray treated area during the same period was 88%, 91% and 87% respectively. Propoxur bait was not found to be effective in reducing the cockroach infestation; rather a build up of the cockroach infestation was noticed in the treated site. The study reports the efficacy of Fipronil gel treatment over conventional insecticidal formulations in the control of cockroach infestation in cookhouses of urban households.