Larvicidal, ovicidal and pupicidal activities of Gliricidia sepium (Jacq.) (Leguminosae) against the malarial vector, Anopheles stephensi Liston (Culicidae: Diptera)

Evaluation of five medicinal plants for the management of Sitophilus oryzae in stored rice and identification of insecticidal compound

Sitophilus oryzae is a kind of stored grain pest. This is controlled by using natural pesticides, which are more reliable, cost-effective, biodegradable, and eco-friendly than synthetic pesticides. Several plants show different insecticidal activities against various pests on their different parts (leaves, seeds, etc.). In this study, methanolic extracts of Lantana camara (leaves), Carica papaya (seeds), Ricinus communis (leaves), Calotropis gigantea (flowers), and Gliciridia sepium (leaves) were used to identify the best insecticidal activity against the rice weevil by doing mortality tests for one week with four replications under laboratory conditions. Gliciridia sepium leaves showed the highest insecticidal activity (100 ± 0) after seven days, and its extract was fractionated by using column chromatography and yielded 12 fractions. A contact bioassay of each fraction was performed, and fraction-11 showed the highest insecticidal activity against Sitophilus oryzae with a 100 % mortality after four days. Fraction-11 was analyzed by using GC-MS and FT-IR. Results revealed that the major constituent identified in fraction-11 was 4-C-methyl-myo-inositol. Therefore, 4-C-methyl-myo-inositol acts as a natural insecticide against rice weevils.

Entomofaunal survey and larvicidal activity of greener silver nanoparticles: A perspective for novel eco-friendly mosquito control

The entomofaunal survey and its toxicity of Blumea mollis (Asteraceae) leaf aqueous extract-mediated (Bm-LAE) silver nanoparticles (AgNPs) were assessed against selected human vector mosquitoes (HVMs). A total of 1800 individuals of 29 species belongs to 7 genera were identified. Month-wise and Genus-wise abundance of HVMs larval diversity were calculated and one-way ANOVA statistically analyzed the average physico-chemical characteristics. The relationship between physicochemical characteristics and HVMs larvae in KWS was interpreted. The total larval density and container index were 23530.18 and 1961.85 examined against 10 different containers. Various spectroscopic and microscopic investigation characterized Bm-AgNPs. The Bm- AgNPs tested against HVMs larvae, the predominant LC50/LC90 values of 18.17/39.56, 23.45/42.49 and 21.82/40.43 μg/mL were observed on An. subpictus Cx. vishnui and Ae. vittatus, respectively. The findings of this investigation, improperly maintained drainages, containers and unused things in study sites, are engaged to HVMs development. This will be essential for designing and implementing HVMs control. The larval toxic potentiality of Bm- AgNPs had a prompt, inexpensive and compelling synthesis of multi-disperse action against HVMs.

Larvicidal and histopathological efficacy of inhabitant pathogenic bacterial strains to reduce the dengue vector competence

BACKGROUND

Aedes aegypti is a primary vector of dengue virus, and the causative agent of dengue is emerging globally as one of the most important arboviral diseases currently threatening human populations. Therefore, vector control is presently the primary intervention method of population reduction, in which natural A. aegypti populations would be reduced with inhabitant bacterial strains that are unable to transmit dengue virus.

RESULT

Based on the pathogenicity of strains, only four isolates effectively show larvicidal activity. The 16S rRNA gene sequences and the phylogeny depicted that the potential isolates were Bacillus firmus (MK791255), Bacillus paramycoides (MK788268), Bacillus siamensis (MK788212), and Bacillus licheniformis (MK791256). After 24 and 48 hours exposure, the B. licheniformis strain (cell mass of 2.2 × 10⁷ CFU mL^-1 ) showed potent larvicidal activity with LC₅₀ of 16.22 μg mL^-1 and 9.57 μg mL^-1 and the B. paramycoides (cell mass of 3.1 × 10⁷ CFU mL^-1 ) strain inhibits the larval and pupal development with LC₅₀ of 42.62 μg mL^-1 and 26.97 μg mL^-1 . Intermittent stages and causes of abscess in the gut and siphon regions were observed through histopathological studies. These two bacterial strains extend larval duration up to 15-16 days as well as reduce development.

CONCLUSION

These studies demonstrate the challenge for dengue vector in reducing developmental and reproduction competence. © 2020 Society of Chemical Industry.

Toxicity of Boswellia dalzielii (Burseraceae) Leaf Fractions Against Immature Stages of Anopheles gambiae (Giles) and Culex quinquefasciatus (Say) (Diptera: Culicidae)

Mosquitoes are vectors of several human pathogens, and great attention has recently been placed on insecticides from plant-derived products, in search for mosquito control agents. This study, thus, investigated the potency of Boswellia dalzielii methanol leaf extract and its four fractions as mosquito ovicide, larvicide, and pupicide against Anopheles gambiae and Culex quinquefasciatus. The plant products were tested at the following concentrations: 125, 250, 500, 1000, and 2000 ppm on eggs and 312.5, 625, 1250, and 2500 ppm on the larvae and pupae of the mosquitoes. For results, hatchability of A. gambiae eggs was reduced to 5% with n-hexane fraction at 2000 ppm. Among the plant products tested, n-hexane fraction was most toxic against A. gambiae (LC50 = 385.9 ppm) and C. quinquefasciatus (LC50 = 3394.9 ppm). The n-hexane fraction of B. dalzielii might be used as a mosquitocidal agent in the breeding sites of A. gambiae and C. quinquefasciatus.

Insecticidal activity of Jatropha curcas extracts against housefly, Musca domestica

The hexane and ether extracts of leaves, bark and roots of Jatropha curcas were screened for their toxicity against different developmental stages of housefly. The larvicidal, pupicidal and adulticidal activities were analysed at various concentrations (0.78-7.86 mg/cm(2)) of hexane and ether extracts. The lethal concentration values (LC50) of hexane extract of J. curcas leaves were 3.0 and 0.27 mg/cm(2) for adult and larval stages of housefly, respectively, after 48 h. Similarly, the ether extract of leaf showed the LC50 of 2.20 and 4.53 mg/cm(2) for adult and larval stages of housefly. Least toxicity was observed with hexane root extract of J. curcas with LC50 values of 14.18 and 14.26 mg/cm(2) for adult and larvae of housefly, respectively, after 48 h. The variation in LC50 against housefly pupae was found to be 8.88-13.10 mg/cm(2) at various J. curcas extract concentrations. The GC-MS analysis of J. curcas leaf extract revealed the presence of trans-phytol (60.81 %), squalene (28.58 %), phytol (2.52 %) and nonadecanone (1.06 %) as major components that could be attributed for insecticidal activity of J. curcas extracts.

Mosquito larvicidal and pupaecidal potential of prodigiosin from Serratia marcescens and understanding its mechanism of action

Mosquitoes spread lethal diseases like malaria and dengue fever to humans. Considering mosquito vector control as one of the best alternatives to reduce new infections, here we have analyzed the effect of purified pigment prodigiosin extracted from Serratia marcescens (NMCC 75) against larval and pupal stages of Aedes aegypti and Anopheles stephensi mosquitoes. Mosquito larvicidal activities of purified prodigiosin revealed LC50 values of 14 ± 1.2, 15.6 ± 1.48, 18 ± 1.3, 21 ± 0.87 µg/ml against early IInd, IIIrd, IVth instar and pupal stages of Ae. aegypti, respectively. LC50 values for An. stephensi were found to be 19.7 ± 1.12, 24.7 ± 1.47, 26.6 ± 1.67, 32.2 ± 1.79 µg/ml against early IInd, IIIrd, IVth instar and pupae of An. stephensi, respectively. Further investigations toward understanding modes of action revealed variations in the activities of esterases, acetylcholine esterases, phosphatases, proteases and total proteins in the fourth instar larvae of Ae. aegypti indicating intrinsic difference in biochemical features due to prodigiosin treatment. Although there was no inhibition of enzymes like catalase and oxidase but may have profound inhibitory effect on carbonic anhydrase or H(+)-V-ATPase which is indicated by change in the pH of midgut and caeca of mosquito larvae. This reduced pH may be possibly due to the proton pump inhibitory activity of prodigiosin. Pure prodigiosin can prove to be an important molecule for mosquito control at larval and pupal stages of Ae. aegypti and An. stephensi. This is the first report on the mosquito pupaecidal activity of prodigiosin and its possible mechanism of action.

Ovicidal activity of Atalantia monophylla (L) Correa against Spodoptera litura Fab. (Lepidoptera: Noctuidae)

OBJECTIVE

To evaluate the efficacy of Atalantia monophylla (A. monophylla) leaf in different solvent crude extracts and fractions against eggs of Spodoptera litura (S. litura).

METHODS

Hexane, ethyl acetate and chloroform solvent extracts of A. monophylla leaf and 12 fractions from hexane extract were screened at 5.0%, 2.5%, 1.0% and 0.5% for crude extracts and 1 000, 500, 250 and 125 mg/kg for fractions against the eggs of S. litura for the ovicidal activity. LC50 and LC90 were calculated using probit analysis.

RESULTS

Hexane crude extract showed maximum ovicidal activity of 61.94% at 5.0% concentration with a correlation value of r (2)=0.81, and least LC50 value of 3.06%. Hexane extract was fractionated using silica gel column chromatography and 12 fractions were obtained. Fraction 9 was active which showed maximum ovicidal activity of 75.61% at 1 000 mg/kg with the LC50 value of 318.65 mg/kg and LC90 value of 1 473.31 mg/kg. In linear regression analysis, significant and high correlation (r (2)=0.81%) was seen between concentration and ovicidal activity of hexane crude extracts and its active fraction.

CONCLUSIONS

As per our knowledge, this is the first report for ovicidal activity of A. monophylla against S. litura, A. monophylla could be used for the management of S. litura and other insect pests.