Diazinon resistant status in Rhipicephalus (Boophilus) microplus collected from different agro-climatic regions of India

Abstract

The resistance status of Rhipicephalus (Boophilus) microplus to “Diazinon” was evaluated in 20 locations situated at various agro-climatic regions of India. Adult immersion test (AIT) was optimized using laboratory reared acaricide susceptible IVRI-I strain of R. (B.) microplus and minimum effective concentration of Diazinon was determined as 635.2 ppm. The discriminating dose (DD) was worked out as 1270.4 ppm and was tested on female ticks collected from organized and unorganized farms located at different agro-climatic regions of India. On the basis of the data generated on three variables viz., mortality, egg masses and reproductive index, the resistance level was categorized as I, II, III and IV. The average resistance factor (RF) of 6.1 (level II) was recorded in the ticks collected from the northern sub-temperate trans-gangetic plains while high average RF values of 26.65 (level III) was recorded in the ticks collected from tropical middle-gangetic plains. The tropical middle gangetic plain has a very high density of animal populations where farmers use Diazinon for tick control, for agricultural practices and for mosquito control. Due to the continuous use of OP compounds the environmental load of Diazinon has become high in the area. This is the first experimental data generated on Diazinon resistant status in ticks of India.

Introduction

Amongst the 106 valid tick species reported from India, Rhipicephalus (Boophilus) microplus is widely prevalent and considered as the most economically important tick infesting livestock (Ghosh et al., 2007). Besides avid blood suckers, this tick species act as the vector of bovine babesiosis and anaplasmosis and also cause 20–30% reduction in the cost of leather due to tick bite marks (Biswas, 2003). Control of ticks is focused on large scale repeated use of acaricides viz., organophosphates (OP), synthetic pyrethroids (SP), amidines and macrocyclic lactones (Khan, 1996, Kemp et al., 1999, Bianchi et al., 2003, Rodriguez-Vivas et al., 2007) with limited success. Repeated application of these chemicals leads to the development of resistance in the ticks which is considered as the main hindrance for successful pest and vector control program in livestock globally (Shidrawi, 1990, FAO, 2004, Graf et al., 2004). According to Whalon et al. (2008), R. (B.) microplus developed resistance to almost every chemicals registered for use against it and ranked sixth amongst the resistant arthropods.

In India, about 60% of livestock is reared by small and marginal farmers and use of OP compounds like diazinon and malathion is very common for the control of agricultural pests including livestock and poultry (Sharma, 2004, Ghosh et al., 2006). Besides their applications against agriculturally important pests, OP compounds are also used for mass eradication of mosquito larvae in the breeding places (ICMR Bulletin, 2002). Although farmers have complaints about lack of efficacy of different chemical acaricides against ticks, validation of acaricide resistance with suitable in vitro bioassays for generating base line informations has not been done. In the present study, the status of acaricide resistance against the organophosphate compound “Diazinon” in targeted populations of R. (B.) microplus infesting cattle in different agro-climatic regions of India was evaluated by standardizing an adult immersion test (AIT).