Efficacy of fipronil gel over imlprothrin +cypermethrin aerosol in control of cockroaches (Field Trial)

Background and Objectives: Cockroaches are offensive pests visually and expel unpleasant smelling secretion that spoils the flavor of food and environment. This trial was done to test Strikeout bait gel (fipronil 0.055%) developed by Parijat Industries (India) Pvt. Ltd. for its efficacy against Periplaneta americana and Blatella germanica, under field conditions in certain catering establishments of a city in Uttar Pradesh. Material and Methods: Ten catering establishments with high infestation based on pretreatment cockroach density assessment (Four for fipronil gel, four for imlprothrin+ cypermethrin aerosol and two without any treatment to act as a control) were considered for inclusion in trial. Single application of fipronil gel/ imlprothrin+ cypermethrin aerosol was used as crack and crevice treatment. The visual assessment data for cockroach density in treatment and control catering establishments were considered for computation of percent reduction of cockroach infestation in the respective catering establishments. Results: Single application of fipronil gel was able to reduce cockroach infestation up to 96.0% at the end of 12 weeks whereas it was 20% in imlprothrin+ cypermethrin aerosol treated areas. Differences were found statistically significant. However, imlprothrin+ cypermethrin aerosol was more effective (52.0%) in reducing the cockroach density by first week in comparison to fipronil gel (47.8%) but its efficacy started declining after 5th week onwards. Interpretation and Conclusion: The study reports the efficacy of Strikeout bait gel (fipronil 0.055%) for control of cockroaches in catering establishments. The application Strikeout bait gel (fipronil 0.055%) was found more convenient to both operators and clients and there was minimal disruption at workplace.

Keywords: Cockroaches, fipronil gel, imlprothrin0.07%+cypermethrin 0.2% aerosol

Cockroaches are offensive pests visually and expel unpleasant smelling secretion that spoils the flavor of food and environment. Its obnoxious behavior and movement while foraging makes it a potential carrier of various pathogenic organisms, as it contaminates food and water either by frequent regurgitation or defecation. ^[1] Periplaneta americana Linnaeus (Dictyoptera: Blattidae), the American cockroach infests kitchen, storeroom, drainage and latrine, while Blatella germanica (Linnaeus) (Dictyoptera: Blatellidae), the German cockroach inhabits peridomestic conditions, especially the garden having piles of garbage. Since control of cockroaches either by space spray or residual application of insecticides did not yield desired result, attention is being focused on the use of toxic food baits for suppression. ^[2],[3],[4] Baits offer the advantage of long-term residual activity, safe application technology, fast action and reduced odor when compared with residual sprays. In addition, baits have also been reported to possess secondary poisoning effect through necrophagy ^[5] and coprophagy. ^[6],[7] Besides chemicals, baits have some inert food substances, which attract cockroaches. A variety of active ingredients such as chlorinated hydrocarbons, carbamates, organophosphates, inorganic compounds including several new classes of insecticides have been incorporated in baits. ^[8] Fipronil, 5-amino-1- [2,6- d i c h l o r o – 4 – (t r i f l u o r o m e t h y l) p h e n y l ] – 4 – [(trifluoromethyl)sulfinyl]-1-pyrazole-3-carbonitrile is one of the newly developed broad-spectrum chemicals from the phenyl pyrazole family, when used as a bait formulation reported to cause mortality among certain species of insects at a low dosage. ^[9] It has moderate toxicity to mammals and in rat the acute oral lethal dose to kill 50% population (LD50) is 97 mg/kg. ^[10] Fipronil, a phenylpyrazole insecticide, was discovered by Rhone-Poulenc Agro in 1987, introduced in 1993, and registered as a pesticide in the U.S. in 1996. ^[11] Various studies have reported the efficacy of fipronil gel treatment over conventional insecticidal formulations in the control of cockroach infestation in cookhouses of urban households. ^{[12],[13],[14]} This study was done to test Strikeout bait gel (fipronil 0.055%) developed by Parijat Industries (India) Pvt Ltd for its efficacy against P. americana and B. germanica, under field conditions in certain catering establishments of a city in Uttar Pradesh.

The trial was planned as a field study to evaluate the efficacy of the candidate insecticides (0.055% Fipronil gel/ Imlprothrin0.07%+cypermethrin 0.2% aerosol) in control of cockroaches in catering establishments. The institutional Ethical Committee approval was taken before starting the trial. The study included the following:

Study area: The study was carried out in catering establishments in a city at Uttar Pradesh. Catering establishments selected were large in area (approximately 1500 square feet) and were separated from each at a distance of 0.5-1.0 km. Pooled data were used for each catering establishment after estimating cockroach density in kitchen, dining hall, pantry and ration store. Since catering establishments studied were large in size hence total 10 catering establishments were selected for treatment and control by simple random sampling method.

Complaints regarding Cockroach infestation: The individuals whose catering establishments were included in study were briefed about the study to get their full cooperation and participation as well as to get informed consent. They were given a performa which included their subjective assessment of cockroach problem, importance they attach to control and control measures adopted. Ten Catering establishments with high infestation based on pretreatment cockroach density assessment (Four for 0.055% Fipronil gel, four for imlprothrin0.07%+cypermethrin 0.2% aerosol and two without any treatment to act as a control) were considered for inclusion in trial.

Prespray assessment in field: In every catering establishment included in study following pretreatment assessment was done.

1. Visual counts: The visual counts was done in the night after 2200 hrs. The participants whose catering establishments were included in the study were asked to switch off the entire light by 2100 hrs. The lights were switched on after 2200 hrs and cockroaches were counted as they ran about hiding over tables, sink, cooking areas, etc. Light from a torch was thrown behind cabinets, storage areas and dish racks for counting the cockroaches. A 5-minute count of cockroaches was taken. This method has been used by most of the earlier workers. Catering establishments having visual count more than 5.0 per 100 square feet were graded high infestation, 3.0-5.0 per 100 square feet medium infestation and less than 3.0 per 100 square feet as low infestations.
2. Trap count: Sticky cockroach trap were placed around the usual harborages of cockroaches. Twenty to 25 traps were placed to cover the suspected hiding sites in each catering establishment and house. Cockroach traps were removed next morning to estimate the density.
3. Insecticidal spray: Imlprothrin0.07%+cypermethrin 0.2% aerosol available as pressurized can were used for spraying the infested sites as well as potential harborage points once only in selected catering establishments. Imlprothrin0.07%+cypermethrin 0.2% aerosol was applied at rate of 100 ml per 100 square feet. Single application of fipronil gel was used as crack and crevice treatment. Using a bait gun, fipronil gel was applied in the form of spots 3-4 mm in diameter (which weigh approx. 0.03 gm gel per spot). These were distributed in the infested area at a rate of three spots per square meter. No treatment was carried out in control group catering establishments.
4. Post-treatment Density: Post-treatment density was assessed every week by visual count method up to the 12 weeks as it has been found to be better indicator of cockroach infestation in comparison of sticky trap method in earlier studies as well as sticky trap may also affect the results by acting as an intervention for cockroach control. The visual assessment data in treatment and control catering establishments were considered for computation of percent reduction of cockroach infestation in the respective catering establishments. The percent reduction was calculated using the following formula of Mulla: % reduction = 100 – (C1/T1 × T2/C2) × 100, where, C1 is the number of cockroaches in control catering establishments pretreatment; T1 is the number of cockroaches in treatment catering establishments pretreatment; C2 is the number of cockroaches in control catering establishments post-treatment; and T2 is the number of cockroaches in treatment catering establishments post-treatment. Appropriate test of significance was applied to results of 12 ^th week to find out whether the differences in results of test chemicals are significant or not.

Out of 25 catering establishments surveyed, 13 catering establishments had high infestation, 7 catering establishments had medium, 5 catering establishments and 5 had low cockroach infestation.

A total of 10 catering establishments with high cockroach infestation were considered for random sampling for selection of the trial and control sites. The common cockroach hiding places in the study areas were the food cupboards followed by refrigerators or freezers and under the sinks and water pipes. The infestation in the catering establishments and houses was German cockroach B. germanica and P. americana. The pretreatment density observation in various catering establishments’ two sampling techniques (visual count method and sticky trap method) is presented in [Table 1]. It was observed that visual count method is superior to sticky trap method of density assessment and therefore, this method was chosen as the post-treatment sampling technique. The percent reduction in cockroach infestation in comparison to controls is presented in [Table 2].

It was observed that 52.0% reductions were achieved with imlprothrin0.07%+cypermethrin treated catering establishments by 1 ^st week. Percent reduction was 55.2% in catering establishments by 2 ^nd week and it was 27.5% in catering establishments by the end of 8 weeks post-treatment. Post-treatment cockroach density was 20.0% in catering establishments by 12 ^th week.

It was observed that 47.8% reductions were achieved with fipronil-treated catering establishment by 1 ^st week. A 67.9% reduction in catering establishments was observed by 2 ^nd week and it was 91.3% in by the end of 8 weeks post-treatment. Post-treatment cockroach density was 96.1% in catering establishments by 12th week. Z test was applied to results of test chemicals (12 ^th week) and it was found differences in results of two chemicals were significant.

Control of cockroaches relies mainly on the use of synthetic chemicals. Most of the chemicals, when used in the form of either aerosol or spray, did not prevent cockroach infestation in and around human habitations due to increase in the incidence of insecticide resistance. ^[15] The use of baits in cockroach abatement program is now gaining popularity, due to non repellent action, preference even in the presence of food materials, easy application techniques and specific and fast action on target species. ^[16] Hence baits incorporated with active ingredients, i.e., chemicals having moderate mammalian toxicity and safe application techniques are being developed for controlling cockroaches. Performance of such baits in apartments and commercial kitchens infested with cockroaches has been demonstrated. However, the efficacy of baits varies depending on the type of dwelling surfaces and target species. ^[17]

Resistance to deltamethrin in B. germanica has been reported in some studies. ^[18] The use of synthetic pyrethroids of the 2 ^nd type (viz. deltamethrin) against cockroaches has been recommended by workers because they can produce a higher insecticidal effect as well as irreversible knock-down. ^[19] However, in the present study the synthetic pyrethroid combination of imlprothrin 0.07%+cypermethrin 0.2% aerosol could not bring about the desired reduction in cockroach infestation. Single application of Strikeout bait gel (fipronil 0.055%) was able to reduce cockroach infestation up to 96.0% at the end of 12 weeks whereas. However, imlprothrin 0.07%+cypermethrin 0.2% aerosol was more effective in reducing the cockroach density by 1 ^st week in comparison to Strikeout bait gel (fipronil 0.055%) but its efficacy started declining after 5 ^th week onwards.

The study reports the efficacy of Strikeout bait gel (fipronil 0.055%) for control of cockroaches in catering establishments. However, in the present study the synthetic pyrethroid combination of imlprothrin 0.07%+cypermethrin 0.2% aerosol could not bring about the desired reduction in cockroach infestation. Single application of Strikeout bait gel (fipronil 0.055%) was able to reduce cockroach infestation up to 96.0% at the end of 12 weeks whereas. However, imlprothrin 0.07%+cypermethrin 0.2% aerosol was more effective in reducing the cockroach density by first week in comparison to Strikeout bait gel (fipronil 0.055%) but its efficacy started declining after 5 ^th week onwards. The application Strikeout bait gel (fipronil 0.055%) was not only found more convenient to both operators and clients but was also easy to apply and there was minimal disruption at workplace.

Rohilkhand Medical College for infrastructure and Parijat Industry for provision of test chemicals and contingencies.

Source of Support: Rohilkhand Medical College for infrastructure and Parijat Industry for provision of test chemicals and contingencies, Conflict of Interest: None

DOI: 10.4103/1755-6783.105123

[Table 1], [Table 2]