Metabolic response of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) to essential oil of Ajwain and thymol

The effects of Carum copticum essential oil (CC EO) and thymol were assayed against fourth instar of Ephestia kuehniella Zeller by determining insecticidal activities and enzymatic responses. Concentrations of 5.42 and 6.81?μl/ml were obtained as LC₅₀ values for CC EO and thymol, respectively. The activities of esterases, aminotransferases, aldolase, and lactate dehydrogenase significantly decreased in the treated larvae by CC EO and thymol. Significant increases in glutathione S-transferases, γ-glutamyl transferase, and phosphatases were observed after treatment. Results revealed that CC EO and thymol significantly influenced the enzymatic activities of E. kuehniella leading to disruption of survival and metabolic responses.     

Antimalarial efficacy of dynamic compound of plumbagin chemical constituent from Plumbago zeylanica Linn (Plumbaginaceae) against the malarial vector Anopheles stephensi Liston (Diptera: Culicidae)

In the present investigation, the effective root compound of plumbagin of Plumbago zeylanica (Plumbaginaceae) was evaluated for chemical constituent and antimalarial effect against the fourth instar larvae of Anopheles stephensi Liston (Diptera). In the chromatographic analyses of root compound with Rf value of 0.788 and NMR analyses also revealed that the effective compound contain naphthoquinone plumbagin were identified as the major chemical constituent. Larval mortality was observed after 3 h of exposure period. The plumbagin compound showed remarkable larvicidal activity against A. stephensi (LC₅₀ 32.65 and LC₉₀72.27 ppm). Histopathological effects of compound was observed in the treated larvae. Based on the results, the plumbagin compound of P. zeylanica can be considered as a new source of natural larvicide for the control of malarial vector.     

Effect of azadirachtin on acetylcholinesterase (AChE) activity and histology of the brown planthopper Nilaparvata lugens (Stål)

The effect of azadirachtin (AZA), a tetranortriterpene from neem, on the mortality, acetylcholinesterase (AChE) activity, and the development of the ovaries of female brown planthopper (BPH), Nilaparvata lugens (Stål) was tested in laboratory experiments. The lethal concentrations were determined and applied topically to the adult female BPH (LC₅₀=0.47 ppm and LC₉₀=0.96 ppm). The treated insects exhibited toxic symptoms with a dose-dependent mortality. The LC₅₀ concentrations were tested against AChE activity of the BPH. The results indicate that AZA significantly inhibits the activity of AChE only at the high dose (P<.0001) compared with control. Adult females that were exposed to AZA showed a significant reduction in weight (23%, 40%, and 64% for 0.1, 0.25, and 0.5 ppm, respectively). Fecundity was also significantly reduced in AZA treatments compared to the control. Histological study of ovary sections revealed abnormalities in follicular epithelial cells due to AZA treatment.     

Toxicity and physiological effects of neem pesticides applied to rice on the Nilaparvata lugens Stål, the brown planthopper

The effects of two different neem products (Parker Oil™ and Neema^®) on mortality, food consumption and survival of the brown planthopper, Nilaparvata lugens Stål (BPH) (Homoptera: Delphacidae) were investigated. The LC₅₀ (3.45 ml/L for nymph and 4.42 ml/L for adult in Parker Oil™ treatment; 4.18 ml/L for nymph and 5.63 ml/L for adult in Neema^® treatment) and LC₉₀ (8.72 ml/L for nymph and 11.1 ml/L for adult in Parker Oil™ treatment; 9.84 ml/L for nymph and 13.07 ml/L for adult in Neema^® treatment) were identified by probit analysis. The LC₉₀ (equal to recommended dose) was applied in the rice field. The effective concentration of both Parker Oil™ and Neema^® took more than 48 h to kill 80% of the N. lugens. Fourth instar nymph and adult female N. lugens were caged on rice plants and exposed to a series (both LC₅₀ and LC₉₀) of neem concentrations. Nymph and adult female N. lugens that were chronically exposed to neem pesticides showed immediate mortality after application in laboratory experiment. The quantity of food ingested and assimilated by N. lugens on neem-treated rice plants was significantly less than on control rice plants. The results clearly indicate the neem-based pesticide (Parker Oil™ and Neema^®), containing low lethal concentration, can be used effectively to inhibit the growth and survival of N. lugens.     

Toxicity and behavioral effect of 3beta,24,25-trihydroxycycloartane and beddomei lactone on the rice leaffolder Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae)

Treatment of Dysoxylum pure triterpenes 3beta,24,25-trihydroxycycloartane and beddomei lactone to the rice leaffolder (RLF), Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae), resulted in prolonged larval duration and reduced larval weight. In leaf cut choice assay and topical application experiments, beddomei lactone and 3beta,24,25-trihydroxycycloartaneto showed strong antifeedant and growth inhibitor activity against fourth instar larvae of C. medinalis. Also average leaf consumption was decreased (89%) by the treatment of the two terpinoids when compared with controls. Number of eggs laid by the female (fecundity) was decreased and oviposition deterrence index was increased due to the treatment. This result further shows that the pure triterpenes of Dysoxylum act as both an antifeedant and chronic toxin to the rice leaffolder larvae.     

Larvicidal efficacy of Adhatoda vasica (L.) Nees against the bancroftian filariasis vector Culex quinquefasciatus Say and dengue vector Aedes aegypti L. in in vitro condition

The larvicidal activities of methanolic fractions from Adhatoda vasica leaf extracts were investigated against the bancroftian filariasis vector Culex quinquefasciatus and dengue vector Aedes aegypti. The results indicated that the mortality rates was high at 100, 150, 200 and 250 ppm of methanol extract of fractions III with R _f value 0.67 and methanol extract of fraction V with R _f value 0.64 of A. vasica against all the larval instars of C. quinquefasciatus and A. aegypti. The result of log probit analysis (at 95% confidence level) revealed that lethal concentration, LC₅₀ and LC₉₀ values were 106.13 and 180.6 ppm for fraction III, 110.6 and 170 ppm for fraction V of C. quinquefasciatus. And, the LC₅₀ and LC₉₀ values were 157.5 and 215.5 ppm for fraction III of A. aegypti and 120 and 243.5 ppm for the fraction V of A. aegypti, respectively. All the tested fractions proved to have strong larvicidal activity (doses from 100 to 250 ppm) against C. quinquefasciatus and A. aegypti. In general, second instar was more susceptible than the later instar. The results achieved suggest that, in addition to their ethnopharmacology value, A. vasica may also serve as a natural larvicidal agent.     

Biological activity of selected Lamiaceae and Zingiberaceae plant essential oils against the dengue vector Aedes aegypti L. (Diptera: Culicidae)

The larvicidal activity of hydrodistillate extracts from Mentha piperita L. Ocimum basilicum L. Curcuma longa L. and Zingiber officinale L. were investigated against the dengue vector Aedes aegypti L. (Diptera: Culicidae).The results indicated that the mortality rates at 80, 100, 200 and 400 ppm of M. piperita, Z. officinale, C. longa and O. basilicum concentrations were highest amongst all concentrations of the crude extracts tested against all the larval instars and pupae of A. aegypti. Result of log probit analysis (at 95% confidence level) revealed that lethal concentration LC₅₀ and LC₉₀ values were 47.54 and 86.54 ppm for M. piperita, 40.5 and 85.53 ppm for Z. officinale, 115.6 and 193.3 ppm for C. longa and 148.5 and 325.7 ppm for O. basilicum, respectively. All of the tested oils proved to have strong larvicidal activity (doses from 5 to 350 ppm) against A. aegypti fourth instars, with the most potent oil being M. piperita extract, followed by Z. officinale, C. longa and O. basilicum. In general, early instars were more susceptible than the late instars and pupae. The results achieved suggest that, in addition to their medicinal activities, Lamiaceae and Zingiberaceae plant extracts may also serve as a natural larvicidal agent.     

Combined effect of biopesticides on the digestive enzymatic profiles of Cnaphalocrocis medinalis (Guenée) (the rice leaffolder) (Insecta: Lepidoptera: Pyralidae)

Plant extracts, especially botanical insecticides, are currently studied more and more because of the possibility of their use in plant protection. Many of the natural plant compounds and organic compounds used in the control of insect pests are known to affect digestive enzymes. When fed a diet of rice leaves treated with botanical insecticides and bacterial toxins in bioassays, activities of the digestive enzymes protease, amylase, and lipase in the rice leaffolder larvae are affected. Digestive enzyme activities were affected by botanical insecticides and bacterial toxins individually and in combination. When combined, the effect was more severe at low concentration. There were statistically significant differences (P < or = 0.05) in enzyme activities in combined and individual treatments. The combination of Btk and botanical insecticides caused a two-fold decrease in enzyme activity even at reduced concentration. Clear dose-response relationships were established with respect to enzyme activity. A synergistic effect of botanical insecticides and bacterial toxins was found when combined in low doses. These effects are most pronounced in early instars.