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.

Laboratory evaluation of fipronil against Periplaneta americana & Blattella germanica.

BACKGROUND & OBJECTIVE: In cockroach control, bait formulations are extensively used. Fipronil is one of the broad spectrum insecticides from phenyl pyrazole family available in bait formulation. The compound has been tested under field conditions. However, information on its effectiveness on different surfaces and at various density levels is not known. Therefore, the efficacy of a new formulation of fipronil 0.03 per cent (Goliath gel) was tested under laboratory conditions. METHODS: The bait formulation was tested against Periplaneta americana at the dosages of 0.025, 0.05, 0.1, 0.15 and 0.2 g/m(2), and Blatella germanica at 0.025, 0.05, 0.075, 0.1 and 0.125 g/m(2) on wood, cement, mud and thatch surface with three density levels of cockroaches viz., 5, 10 and 20 numbers/m(2). Mortality after 24 h of exposure was observed daily for five days. RESULTS: Rate of mortality varied between 16.0 and 96.0 per cent in P. americana and 51.0 and 100.0 per cent in B. germanica on different surfaces tested. The mortality rate of P. americana increased line rarly from the dosage 0.025g to 0.15 g/m(2) and at 0.2 g/m(2), it was independent. The LD(80) values of the gel against P. americana at high density were 0.208, 0.246, 0.361 and 0.466 g/m(2) on wood, cement, mud and thatch surfaces, whereas against B. germanica the values were 0.079, 0.081, 0.089 and 0.055 g/m(2) respectively, indicating a significantly (P<0.001) higher efficacy of Goliath gel against B. germanica than P. americana. The results of fitting logistic regression model to the observed percentage mortality with log dose and cockroach density as explanatory variables satisfactorily described the observations at all densities on each surface. The pattern of response to increasing dosages was similar for all the three density levels on each of the surfaces in P. americana and B. germanica. INTERPRETATION & CONCLUSION: The effectiveness assessed against P. americana and B. germanica using logistic regression model suggested that the gel when applied at the appropriate dosages on wood, cement, mud and thatch surfaces could cause >80 per cent mortality of these species in dwellings having these types of surfaces.

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.

Suceptibility of different field strains of blattella germanica four pyrethroids [orthoptera: blattellidae]

The susceptibility of 5 wild strains of German cockroach collected from five infected flats in Tehran were assessed by tests of surface contact method to cyfluthrin, permethrin, sumithrin and lambdacyhalothrin. Comparison of the result of knockdown tests on the wild strains with a standard susceptible strain indicated that all the strains are resistant to sumithrin, i.e., resistance ratio, the RR, ranged from 309 to 7.75 folds; but susceptible to beta - cyfluthrin [RR < 1.5]. Permethrin tests on the field collected strains revealed that 3 out of 5 strains are resistant [RR = 2.9 to 3 folds] but two are tolerant to permethrin [RR ranged between 2.24 to 2.5 folds]. Further tests on the lambdacyhalothrin showed that 4 out of 5 strains were tolerant and one is susceptible. It could be concluded that development of permethrin and lambdacyhalothrin resistance/tolerance in a number of strains of German cockroach was as the result of direct use of these later insecticides in human dwelling. Sumithrin resistance is unlikely related to use of such small amount of this compound in cockroach control programs; but it is likely related to uses of other pyrethroids and hence developing cross-resistance to sumitlirin