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Resting behaviour of Anopheles stephensi type form to assess its amenability to control malaria through indoor residual spray

Author(s): B.N. Nagpal, Aruna Srivastava & A.P. Dash

Journal: Journal of Vector Borne Diseases
ISSN 0972-9062

Volume: 49;
Issue: 3;
Start page: 175;
Date: 2012;
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Keywords: Anopheles stephensi | diel activity | India | indoor resting | pre- and post-biting rests | Rajasthan | sprayed surfaces

Background & objectives: In the present study, an attempt was made to find reasons of ineffectiveness of indoorresidual spray to interrupt malaria transmission by investigating the behaviour of two variants of Anophelesstepnesi, viz. type form and mysorensis in rural areas of Rajasthan, India.Methods: Both low malarious (DDT spray from 1958 to 1976) and high malarious (DDT spray from 1958 to April2006) villages were selected for the study in Arid zone district Jodhpur, Rajasthan during March–April 2006.Resting behaviour of the species during all its movement rhythms covering 24 h period related to: (i) swarming/mating; (ii) pre- and post-biting rest; (iii) after feed resting between hoping movements; (iv) night and day timeresting and; (v) diel activity movements in response to temperature changes, were carried out.Results: The results showed that household objects like cupboards, furnitures, hanging clothes, goods stacked onloft, stored clothes, cobwebs and floor were the dominant resting sites both in sprayed and unsprayed villages.About 95 and 97% of An. stephensi preferred to rest on household objects of unsprayed and sprayed villagesrespectively. There was no significant difference in resting behaviour of the species in both groups of villages(p >0.05). The pre-biting resting time was recorded as 5 to 15 min whereas post-biting resting time lasted for 15 to25 min. After biting outdoor (in courtyard – open to sky) species starts entering the rooms at around 2330 hrs. Itwas observed that during III quarter (0100 to 0400 hrs) maximum species entered into the room were 56% inunsprayed and 62% in sprayed villages. Statistically there was no significant difference in the entry of mosquitoes(p >0.05) in both the groups of villages.Conclusion: Before DDT era, An. stephensi was found resting at all heights of the walls inside the human dwellings.Present study revealed that An. stephensi is trying to avoid sprayable surfaces and tend to rest on unsprayablesurfaces during all its movement rhythms starting from swarming, pre-/post-biting and during hopping movementsin the courtyard and thereafter household objects inside the room as final day time resting. It was concluded thatchanged behaviour of resting of An. stephensi on unsprayable objects in sprayed rooms largely accounted for failureof malaria control. Control of An. stephensi, thus requires an integrated vector control strategy based upon interesectoral, environmental, larviciding with chemical/biolarvicide and use of larvivorous fish wherever feasible. Sucha control strategy offers cost-effective and sustainable option than indoor residual spray

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