Earlier studies on different geographical strains of An.
stephensi and Ae. Aegypti have reported varied levels of
susceptibility to various insecticides commonly used in
mosquito vector control [26, 38–43]. Unlike conventional
insecticides which are based on a single active ingredient,
plant derived insecticides comprise botanical blends of chemical
compounds which act concertedly on both behavioral
and physiological processes. Thus, there is very little chance
of pests developing resistance to such substances. Identifying
bioinsecticides that are efficient, as well as being suitable and
adaptive to ecological conditions, is imperative for continued
effective vector control management [21]. In order to develop
cost effective pesticides from the plant leaves used in the
present study, it will be necessary to carry out further studies
to determine the active compounds in these plants, their
larvicidal efficacies, their individual and synergistic modes
of action, the feasibility of large scale use, and stability of
these active compounds under field conditions. Most studies
using biological extracts have been tested against a single
strain of a species. This is probably because one would not
expect to observe large variations in the susceptibility of one
strain to another. Unlike the varied resistance status observed
in the case of synthetic insecticides, the biological extracts
used in this study have not been used by municipal bodies
as insecticides. Therefore, the observed variation in response
between different strains does not appear to have been caused
by such a selection event, but rather by the intervention of
biological and genetic factors, resulting in the change in the
susceptibility to different plant extracts.