The efficacies of different plant extracts against 4th stage larvae of
A. aegypti were recorded (Table 1). The results revealed 100% mortality of larva in 1000 ppm and 500 ppm concentrations in all extracts of all three plants after 12 and 24 hours of exposure. The petroleum ether extract of
P. hydropiper caused 5% and 12% mortality at concentration 15.6 ppm, chloroform extract showed 4% and 15% mortality at 31.3 ppm and methanolic extract showed 11% and 24% mortality at concentration 31.3 ppm after 12 and 24 hours of exposure. Similarly, the petroleum ether extract of
L. salicifolia caused 34% and 6% mortality at concentration 125 ppm and 62.5 ppm, chloroform extract showed 11% and 5% mortality at 125 ppm and 62.5 ppm and methanolic extract showed 16% and 10% mortality at 125 ppm and 62.6 ppm after 12 and 24 hours of treatment. Likewise, the results of
C. indicum showed that petroleum ether extract caused 21% and 9% mortality at 62.50 ppm and 31.25 ppm, chloroform extract caused 27% and 9% mortality at 62.50 ppm and 31.25 ppm and methanolic extract of
C. indicum showed 21% and 4% mortality at 62.50 ppm and 31.25 ppm after 12 and 24 hours of treatment respectively. The highest (12%) mortality of petroleum ether extract of
P. hydropiper was recorded at the lowest concentration of 15.6 ppm and it has been increased upto 100% at concentration 125 ppm after 24 hours of treatment. However, chloroform and methanolic extracts of
P. hydropiper were found to be the most effective compared to its respective extract of
C. indicum and
L. salicifolia. The commercial and synthetic plant based insecticide Deltamethrin was compared as positive control where 100% mortality was found in even in the lowest concentration same as experimental concentration. Acetone was used as negative control and zero mortality was recorded in negative control. Extracts from more than 429 plants have been evaluated earlier as insecticide against mosquito. Essential oils extracted from neem
(Batra et al., 1998) and
T. patula (
Dharmagadda et al., 2005) was effective on the larvae of
A. aegypti,
A. stephensi and
C. quinquefasciatus.
Amusan et al. (2005) studied the larvicidal efficacy of ethanolic extracts and the petroleum ether extract of
C. sinensis on
A. aegypti. The insecticidal properties of
Z. nitidum stem bark was reported earlier (
Bhattacharya and Zaman 2009;
Gogoi and Bora, 2012) and also found excellent result in a study by
Devi and Bora (2017) against
A. aegypti. Sonowal and Rahman (2010) reported the larvicidal activity of leaf extracts of
P. hydropiper against
C. quinquefasciatus. The larvicidal potential of many plants like
Pongamia pinnata, Azadirachta indica, Croton tiglium, Cascabela thevetia, Ricinus communis, Datura stramonium, Jatropha curcas, Pedilanthus tithymaloides, Phyllanthus amarus, Euphorbia hirta, Euphorbia tirucalli, Stichopus horrens and
Lantana camara were already studied against
A. aegypti (Rahuman et al., 2008; Borah et al., 2012;
Rajasekaran and Duraikannan, 2012;
Hari and Mathew, 2018;
Sharawi, 2024).
Noosidum (2014) mixed two essential oils extracted from
L. cubeba and
L. salicifolia and the result showed potential repellent activity against
A. aegypti.
Patil (2014) studied insecticidal properties of organic solvent extracts of
C. inerme leaves against larval stages of
A. aegypti and
C. quinquefasciatus where hexane extract was reported as effective one. Extract of
Zingiber officinale showed excellent results in controlling different stages of
A. albopictus (
Nasir et al., 2017).
Probit analyses of all extracts were carried out in order to determine the respective LC
50 and LC
90 values after 12 and 24 hours of treatment (Table 2, 3, 4). The LC
50 and LC
90 in
P. hydropiper for petroleum ether extract were recorded as 39.55 ppm and 77.25 ppm whereas for chloroform extract 56.29 ppm and 118.23 ppm and for methanolic extract, it was 52.77 ppm and 106.71 ppm respectively after 24 hours of treatment. The efficacy of plant extracts were categorized into high (LC
50<50), moderate (LC
50< 500) and low (LC
50>500)
(Cheng et al., 2003). The lowest LC
50 was calculated as 39.55 ppm in
A. aegypti (LC
50<50). Hence, the insecticidal efficacy of petroleum ether extract of
P. hydropiper can be noted as the highest during the study. The efficacy was higher than that of
Azadirachta indica which is an effective insecticide against mosquito. Previously, the larvicidal efficacy of essential oil of leaves of
P. hydropiper against
C. quinquefasciatus and
A. aegypti were reported (
Maheswaran and Igcinumuthu, 2013;). A study conducted by
Duraipandiyan (2006) revealed the potentiality of compound confertifolin with bactericide and fungicidal properties isolated from
P. hydropiper. The efficacy of petroleum ether extracts of
C. occidentalis and
O. basilicum were reported by
Kumar et al. (2014) and
Maurya et al. (2009).
In present study, emergence inhibition assay was conducted by the most effective extract of our larval bioassay (petroleum ether extract of
P. hydropiper). A total of 47% of emergence inhibition (Table 5) was recorded and EI
50 in
A. aegypti was recorded as 41.07 ppm (Table 6). The mean duration of immature stages in
A. aegypti were significantly increased after treatment of petroleum ether extract of
P. hydropiper for 24 hours. The developments of pupal and adult stages were also influenced by the treatment of petroleum ether extract of
P. hydropiper for 24 hours. The study recorded the mortality of 4th instar larvae as 5.0±0.95, pupae as 13±0.50 and adult as 30±0.50 in
A. aegypti after treatment of EI
50 dose for 24 hours. The mean time duration for developmental period was 6.0±0.50 days. The mean developmental period of the immature stages of untreated larvae (untreated EI
50) was recorded as 5.0± 0.50 days (Table 7). The results of petroleum ether extract of
P. hydropiper were also found significant in reducing adult life span. The adult life span of
A. aegypti was recorded as 24.0±0.95 days in post EI
50 treatment for 24 hours (Table 8). The growth index has decreased in treated group of
A. aegypti (GI-8.87) in compared to untreated group (GI-10.6). Increased malformations have been recorded in pupal and adults by the presence of larval-pupal and pupal-adult intermediates and formation of unmelanised larvae and pupae. Plant extract induced changes in growth period and longevity of insects have been reported by many workers (
Kraiss and Cullen, 2008;
Ibanez et al., 2012; Granados et al., 2014; Devi and Bora, 2017;
Masih and Ahmed, 2019). The normal growth and development of insects are interrupted various ways by the chemical compounds present in different plant extracts
(Bede et al., 1999; Divekar et al., 2022). The mode of action can be the inhibition of chitin synthesis or interference with hormonal system during molting. Numerous bioactive compounds in plant extracts can affect the endocrine regulation of molting and metamorphosis and thereby act as IGRs
(Kabir et al., 2013). The larval bioassay tests of
A. aegypti was carried out using 16 IGRs which resulted that the juvenile hormone (EI
50= 0.010-0.229 ppb; EI
95 = 0.066-1.118 ppb) and chitin synthesis hormone (EI
50 = 0.240-2.412 ppb; EI
95 = 0.444-4.040 ppb) showed higher inhibition in adult
A. aegypti emergence, blood feeding rate and fertility
(Fansiri et al., 2022). In another experiment, exposure to phenolic extracts of
Z. jujuba leaves significantly prolonged the larval duration and reduced the adult lifespan of
A. aegypti (
Devi and Bora, 2017). The ovicidal, larvicidal, adulticidal, repellent and the decrease in fecundity and fertility of
A. aegypti, A. stephensi and
C. quinquefasciatus were also reported by the effect of leaf extracts of
Lippia alba and
Piper longum (Mahanta et al., 2019; Dey et al., 2020). Similarly, the extracts of
Ipomoea cairica reduced the fecundity and hatching rates of
A. aegypti and
A. albopictus (Zuharah et al., 2016).
