# Larvicidal effects of selected medicinal plant extracts against Anopheles arabiensis, Anopheles stephensi, and Aedes aegypti

## TL;DR

This study tests plant extracts as eco-friendly alternatives to chemical insecticides for killing mosquito larvae.

## Contribution

The study evaluates the larvicidal potential of four traditional plant extracts against three mosquito species.

## Key findings

- n-hexane extracts of Ocimum lamiifolium and Amaranthus hybridus showed high larvicidal activity against mosquito larvae.
- Lepidium sativum and Premna schimperi n-hexane extracts exhibited 100% larvicidal activity against Anopheles arabiensis.
- The plant extracts are effective and could serve as bioinsecticides.

## Abstract

The emergence of resistance to synthetic (chemical) insecticides along with their harmful effects on human health, non-target organisms and the environment necessitates the development of new complementary bioinsecticides that are effective, environmentally friendly, biodegradable and target-specific. This study was undertaken to evaluate larvicidal activities of 80% methanol and n-hexane extracts of four plants that are traditionally used by communities against mosquitoes.

The dried plant parts of Ocimum lamiifolium, Amaranthus hybridus, Premna schimperi, and Lepidium sativum were extracted with 80% methanol and n-hexane solvents. Bioinsecticidal activities of these extracts were evaluated under laboratory condition in the range of 62.5–2000 ppm against late 3rd to early 4th instar larvae of An. arabiensis, An. stephensi and Ae. aegypti mosquitoes. Larval mortality was observed after 24 h of exposure. The mortality data were subjected to probit analysis to determine LC50 and LC90 values.

In the concentration ranges of 62.5–2000 ppm, the LC50 and LC90 values of the most potent n-hexane extracts tested plants; Ocimum lamiifolium against An. arabiensis, An. stephensi and Ae. aegypti with a general ranges 666.07 to 1278.22, and 1920.82 to 2139.91, and Amaranthus hybridus against An. stephensi and Ae. aegypti 412 to 1426.03 and 736.150 to 1222.62, Lepidium sativum and Premna schimperi against An. arabiensis exhibited 100% larvicidal activity with LC50 and LC90 values ranges 713.25 to 1278.22, and 636.76 to 988.90, respectively. All the n-hexane extracts showed larvicidal activities.

The n-hexane crude extracts of the tested plants have the potential to be used as bioinsecticides against larvae of An. arabiensis, An. stephensi and Ae. aegypti. Therefore, it is necessary to undertake studies that focus on bioassay-guided isolation, purification and structural elucidation of active compound (s) from the most active n-hexane fractions of the tested plants to develop a product that may complement the current existing vector control tools.