Final results

The goal of our project was to assess whether entomopathogenic roundworms (ERs) would be effective in killing A. aegypti larvae in the environments more often visited by female mosquitoes to lay their eggs. These are floor drains, water reservoirs (often used in households not served by city water) and pot saucers (Figure below).

 

Household environments favored by female mosquitoes for oviposition. Clockwise from top lef: floor drains, water reservoirs and pot saucers (midsize shown).

In floor drains, we started applying 100 ERs per mosquito larva. The killing rate reached up to 74% (Table 1), but we remained dissatisfied. Building on previous results by Cardoso et al. (2015, 2016), we increased the ER dosage. Killing rates improved to a max of 82%, which is an excelent rate for a biological control agent.

 

Table 1: Killing rates (%) of mosquito larvae by ERs, using different dosages, in four kinds of floor drains. In each table cell, different letters indicate statistical significancy according to Tukey test at 5%.

In pot saucers, the efficacy of ERs was comparatively lower, regardless of the dosage used (Table 2). Apparently, the irregular surface of pot saucers made it difficult for ERs and mosquito larvae to encounter. Healthy officials could apply ERs in pot saucers to reduce the emergence of adult mosquitoes, but the strategy used today remains the best - applying sand in the pot saucers to avoid standing water.

 

Killing rates (%) of mosquito larvae by ERs, using different dosages, in three sizes of pot saucers. In each table cell, different letters indicate statistical significancy according to Tukey test at 5%

In water reservoirs, the efficacy of ERs was poor (Table 3). Most likely, ERs sinked to the bottom of the reservoirs and most mosquito larvae managed to remain in the water column. This made the encounter ER-larvae a rare event. We conclude that ERs are not an appropriate biological control agent for water reservoirs and pools.

 

Killing rates (%) of mosquito larvae by ERs in water reservoirs. In each table cell, different letters indicate statistical significancy according to Tukey test at 5%

These results will be appropriately discussed in a manuscript to be submitted to a journal focused on biological control of pests and vectors. Once the manuscript is accepted and published, will share it with all of you.

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