A field experiment to test the effect of containers brushing and scrubbing on Aedes aegypti eggs and non-target accompanying dipterans

Abstract

Aedes aegypti populations survive long periods of drought and winter temperatures in the egg stage, which remain attached to the walls of the containers until favourable conditions occur. Cleaning of water storage containers may not eliminate all immatures and cleaning techniques commonly used may lack the specificity needed to effectively remove Ae. aegypti eggs. More extended ovicidal procedures such as ?the untadita? and its modifications requires concentrated chemicals (chlorine bleach and/or detergent), which not always are accepted or available in the entire community. In addition, there is a constant need to search for environmentally friendly control methods of Ae. aegypti, including the preservation of the accompanying fauna in the aquatic habitat. In this work, we compare the efficiency of two non-chemical methods, brushing and scrubbing, to remove Ae. aegypti eggs and the collateral effects on non-target dipterans that lay eggs on container walls. A field experiment was carry on during March 2022 on pre-existent and standardized flower vases (conic, plastic, black, 300cc) from Benavídez cemetery, Buenos Aires, Argentina. On three groups of 70 vases each, the following treatments were randomly applied: BR) brushing with toilet brush, SC) scrubbing with an all-purpose microfiber cloth and CT) control without intervention. In all the treatments, the water contained in the vase was previously emptied to eliminate pre-existing immatures and, after the application of the treatment, the vase was filled with tap water up to the top to promote the hatching of the remaining eggs. In two consecutive samplings carried out every 5 days, the content of each vase was checked to record and extract all Ae. aegypti immatures and non-target dipterans. The proportion of infested vases (vases with immatures/vases with water) was compared among treatments with Chi2 and Tukey tests. The proportion of infested vases of Ae. aegypti was significantly lower in scrubbing than in brushing and control vases (SC: 3/126, BR: 16/129, CT: 26/128; X2(2)=19,99, p<0,0001; SC<CT, p<0,001; SC<BR, p<0,01). On the other hand, the proportion of infested vases with non-target Diptera was lower in both ovicidal treatments than in the control, both for the Psychodidae Clogmia albipunctata (SC: 0/126, BR: 0/129, CT: 5/128; X2(2)=7,07, p<0,029; SC<CT>BR, p<0,05) and the Ceratopogonidae Dasyhelea necrophila (SC: 0/126, BR: 3/129, CT: 15/128; X2(2)=21,92; p<0,0001; SC<CT, p<0,001; BR<CT, p<0,01). Scrubbing was the most efficient ovicidal method and reduced markedly the infestation levels of Ae. aegypti without the need of using chemical. Unfortunely, both ovicidal methods also had a strong impact on non-target insects with similar oviposition strategy than the dengue vector. In a wide-ranging control campaign there could be a drastic decrease in non-target urban insects.