Indiscriminate use of agro-verinary pesticides and susceptibility status of xenopsylla cheopis (family: pulicidae) in plague endemic foci in Tanzania
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Date
2020
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Publisher
Sokoine University of Agriculture
Abstract
The control of rodent-borne fleas, which play major role in the transmission of plague, is
the mainstay of plague control. The application of chemical insecticides forms the most
powerful and widely used control measure. The reliability and continued use of this
approach however is threatened by the development of resistance. The excessive use of
agro-veterinary pesticides is increasingly associated with the development of resistance in
different arthropods; however, such possibility has not been explored in flea vectors of
plague in Tanzania. This study identified injudicious uses and/or malpractices which
potentially enhance exposure of flea vectors to agro-veterinary insecticides and emergence
of resistance thereof. Furthermore, the study assessed susceptibility status of major plague
flea vector, Xenopsylla cheopis, to commonly used agro-veterinary and public health
pesticides. The study was conducted in Lushoto and Mbulu districts, northern Tanzania,
both of which are active plague foci. About 91% of the respondents in Lushoto and 93%
respondents in Mbulu reported using agricultural pesticides during the cropping season.
Excessive and injudicious use of agricultural and veterinary pesticides was common
across the study districts. Most of the farmers reported applying agricultural pesticides for
up to four times per a cropping season. The three out of fourteen most commonly used
agricultural pesticides in Lushoto were master kinga72WP (mancozeb 640g/kg+
cymoxanil 80g/kg) (44%), suracron720EC (profenos 500g/l EC) (25.3%) and Sumo 5EC
(lambda-cyhalothrin) (18.7%). The three out of seventeen most commonly used
agricultural pesticides in Mbulu were Dursban 50W (Chlorpyrifos) (29%), Duduban
450EC (Cypermethrin 10g/lt+chloropyrifos 35g/lt) (18%) and Dursban+farmerzeb
(Chlorpyrifos 48%, Mancozeb 80%WP). Cybadip (Cypermethrin) (≥45%) and paranex
(alphacypermethrin) (≥13%) were the two most commonly used veterinary pesticides
across the districts. Moreover, the susceptibility of Xenopsylla cheopis, originating from
wild population in Mbulu was assessed against nine different agro-veterinary and public
health pesticides via contact bioassays. The percentage mortality after exposure to
recommended doses of eight insecticides tested was strongly suggestive of resistance
(100% 24 h mortality, 93 - 96%). The fleas confirmed resistance to lambdacyhalothrin and
carbaryl, with 90% mortality. The reference ‘susceptible’ colony Xenopsylla Cheopis was
fully susceptible (100% 24 h mortality) to all tested insecticides. Similarly, the field
Xenopsylla Cheopis was fully susceptible (100% 24 h mortality) to 5× and 10× the
recommended doses of all insecticides indicating low resistance intensity. Conclusively,
this study identified a suite of injudicious uses and/or malpractices; excessive use of
agricultural chemicals, maluse of agro-veterinary chemicals as well as poor adherence to
the application and safety procedures, all of which potentiate contamination of
environments/surfaces and exposure of the chemicals to fleas thereof. Furthermore, the
study indicates resistance in the wild population of Xenopsylla cheopis from Mbulu
district. As such, flea vector populations across Lushoto and Mbulu districts are putatively
under intense risk of resistance development, thus warranting further studies across plague
endemic areas in country to understand distribution of the resistance, involved resistance
mechanisms; and confirm the contribution of agro-veterinary insecticides
Description
Masters Thesis
Keywords
Agro-veterinary, Misuse, Malpractices, Resistance, Fleas, Xenopsylla cheopis, Plague