Carmona retusa (Wild Tea) Leaves as an Efficient Larvicide for Aedes Aegypti

Abstract

INTRODUCTION

Dengue mosquitoes, specifically females, have caused the most serious outbreaks of dengue in the Philippines. This crucial fact prompted the search for plant extracts with promising larvicidal activity against 3rd and 4th instars Aedes aegypti larvae. Besides, it will be helpful to utilize native flora for identifying useful compounds that might prove effective against Aedes aegypti larvae and it is always better to opt for plant-based solutions for reducing the cases. The study made use of two leaf extracts: Plectranthus amboinicus (Cuban oregano) and Carmona retusa (wild tea).

METHODS

Theleaf crude extracts were applied in concentrations of 15,000, 30,000, 45,000, and 60,000 ppm on set-ups containing 20 Aedes aegypti larvae for each plastic cup. There were three replicates for the wild tea extract and five replicates for the Cuban oregano extract. The mortality of the larvae was recorded within 24 and 48 hours after the extracts' application. The lethal concentrations (LC) at 50% and 90% larval mortalities were identified using linear regression probit analysis. After determining the LC50 and LC90 values of the leaf extracts, the wild tea extract was chosen to be formulated in pellet form.

RESULTS

The tests revealed that the wild tea extract has a stronger larvicidal activity than the Cuban oregano. The LC50 and LC90 of the wild tea extract were estimated at 23,675 and 54,954 ppm respectively. The LC50 and LC90 of Cuban oregano extract were estimated at 35,312 and 65,250 ppm respectively. This means that the wild tea leaves contain more active or potent bioactive compounds than the Cuban oregano, making the extract require fewer amounts in concentration to induce 50% and 90% mortality in the larval population. Hence, only the wild tea leaves were formulated into pellets. The pelletized wild tea leaves extract was tested for its larvicidal activity on similar set-ups in concentrations of 20,000, 40,000, 60,000, 80,000, 100,000, 300,000, and 600,000 ppm. The wild tea leaves pellets, at its appropriate doses, showed 100% mortality even at its lowest concentration against Aedes aegypti larvae after the 48 hour-exposure.

DISCUSSIONS

Through this study, the community will discover ways of benefitting from making an environmentally safe and cheap wild tea larvicidal pellets since it showed 100% larval mortality rate. The ability of pellets in preventing the Aedes aegypti larvae from developing into adult stage will help reduce the number of dengue fever cases as its prevalence continue to arise each year.