Impact of sunlight exposure on the residual efficacy of biolarvicides Bacillus thuringiensis israelensis and Bacillus sphaericus against the main malaria vector, Anopheles gambiae

Abstract

Background Biotic and abiotic factors have been reported to affect the larvicidal efficacy of Bacillus thuringiensis israelensis ( Bti ) and Bacillus sphaericus ( Bs ), although the extent to which they are affected has been poorly documented. This paper studies the effect of sunlight exposure on the efficacy of a new larvicide formulation based on both Bti and Bs , herein after referred to as BTBSWAX, applied against two different larval stages. Methods The emergence of inhibition exhibited by BTBSWAX at three different dosages (1 g/m 2 , 1.5 g/m 2 , and 2 g/m 2 ) was monitored under semi-field conditions using a total of 32 containers comprising 16 that were covered and 16 that were uncovered. Two experiments were conducted using first- and second-instar larvae of Anopheles gambiae , respectively. Results BTBSWAX at 2 g/m 2 in covered containers exhibited high emergence inhibition (> 80%) when larvae were exposed from 1st instar on day-6 post-treatment, whereas the emergence inhibition was only 28% in uncovered containers. For larvae exposed from 1st instar on day-12 post-treatment, the emergence inhibition was moderate (70%) in covered containers but was low (< 20%) in uncovered containers. For larvae exposed from 2nd instar on day-10 post-treatment, the emergence inhibition was moderate (31%) in covered containers but was very low (< 10%) in uncovered containers. Moreover, the residual efficacy of BTBSWAX was markedly affected by environmental stresses, including sunlight exposure (Hazard ratio (HR) = 0.12, p < 0.001 and HR = 0.63, p = 0.033 for BTBSWAX at 2 g/m 2 against 1st and 2nd instar larvae, respectively). Conclusion These findings emphasize the impact of environmental variables (e.g., sunlight exposure) on the residual efficacy of Bti and Bs biolarvicides in the field. They hence highlight the need to take these factors into account for larvicide formulation development processes. Moreover, studies of the ecology of Anopheles larvae in targeted areas are also crucial for the integration of larval control strategies into malaria transmission plans devised by national malaria control programmes of endemic countries. Electronic supplementary material The online version of this article (10.1186/s12936-019-2687-0) contains supplementary material, which is available to authorized users.

Bacterial larvicides used for malaria vector control in sub-Saharan Africa: review of their effectiveness and operational feasibility

“…s . )1–2 g/m 2 –< 10– > 80 (10 days)[73] Note : Proportional of tested Anopheles: a Anopheles population accounted for 40% b Anopheles population accounted for 87% c Anopheles population accounted for 89% d Anopheles population accounted for 85% e Larval reductions: based on late instars except study [66] in which reductions were based on all larval instars Abbreviations : CRSN, Centre de Recherche en Sante de Nouna; ITU, international toxic units; CREC, Centre de Recherche Entomologique de Cotonou; WDG, water-dispersible granules; GR, granules; FC, flowable concentrate; Bti , Bacillus thuringiensis var . israelensis ; Bs , Bacillus sphaericus ; MRC, Medical Research Council; KCCR, Kumasi Centre for Collaborative Research; ICIPE, International Centre of Insect Physiology and Ecology; DP, Department of Pikine…”

Yeast-encapsulated essential oils: a new perspective as an environmentally friendly larvicide

“…aegypti exhibit well documented resistance to these compounds [42]. Similarly, the bioinsecticides Bacillus thuringiensis israelensis (Bti) and Bacillus sphaericus (Bs) are effective against different species of mosquito larvae under laboratory and environmental settings [42], but their stability is reduced under sunlight and heat exposure [43,44]. Thus, development of new insecticides effective in tropical climate where mosquito-transmitting diseases are important public health problems, is an urgent need.…”

Characterization of CwlC, an autolysin, and its role in mother cell lysis of Bacillus thuringiensis subsp. israelensis

“…1996; Zogo et al . 2019). Various measures have been taken to achieve protection from solar inactivation including encapsulation (Dunkel and Shasha 1989; Ramirez‐Lepe et al .…”