How long is long enough? Decreasing on plant extract lethal effects, over time, affectingAedes aegyptilarval mortality

Abstract

26The mosquito Aedes aegypti has overcome all kinds of human being mosquito control attempts 27 over the last century. Strategies for vector population control resorts to the use of synthetic 28 insecticides, which can lead to problems of intoxication in humans and environmental 29 contamination. We evaluated the effects of Bacillus thuringiensis var. israelensis (Bti), Ilex 30 paraguariensis (mate-herb) and Ilex theezans (caúna-herb) extracts against A. aegypti larvae 31 mortality. The bioassays were conducted under controlled laboratory conditions of temperature 32 (27±3°C) and photoperiod (12h). Hydroalcoholic I. theezans leaves extract displayed better 33 residual effect compared to I. paraguariensis fruit aqueous extract. Variation in larval mortality 34 was also observed in the exposure periods (low after a few weeks). Low mortality after a few 35 weeks may mean increased the food for mosquito in a oppose effect over time. The residual effect 36 of Bti was observed during the 56 days of the study duration (100% of mortality). The strongest 37 residual effect of I. theezans was probably due to the presence of chemical on its leaves, such 38 coumarins, hemolytic saponins and cyanogenic glucosides, absent in I. paraguariensis. On the 39 other hand, alternative methods to vector control present risks in a long term scale by reversal of 40 larvicide effect into food resource. Our results contributed to the prospection of natural insecticides 41 and open the possibility for subsequent studies of the use of plant extracts in field situations in a 42 short time scale.43 44 Keywords: Dengue, vector control, inseticide, entomology, yerba mate. 3 3 45 Introduction 46 Over the last century the mosquito Aedes aegypti Linnaeus, 1762 has overcome all 47 mosquito control attempts by human being. Aedes females are well known by their capacity of 48 naturally and/or under laboratory conditions replicate and transmit over 100 kinds of viruses [1]. 49 As an example, in Brazil dengue, chikungunya, zika and most recently mayaro [1] viruses are a 50 real threat to public health [2]. It became necessary the A. aegypti population control in order to 51 reduce viruses' transmission and consequently the epidemic status. Although several chemical and 52 natural products have being extensively used on attempts to reduce adults and immature mosquito 53 population [3,4], appropriated mosquito population reduction is not close to come true. Especially 54 because the gene resistance selectivity due to chemicals and natural products application misuse 55[5]. Accordingly, the most effective disease prevention method still remains targeting the mosquito 56 population by elimination of mosquito breeding places [6]. 57A very promising field for mosquito population reduction is focusing the mosquito control 58 strategies on the immature aquatic stages, when the insect is more vulnerable [7,8]. For this 59 purpose, the use of synthetic insecticides is well known as being quite effective causing mosquito 60 larvae mortality [9][10][11][12][13]....