Dengue fever is one of the most rapidly spreading arthropod-borne diseases. Diurnal vectorial properties of Aedes albopictus contribute to the dispersion of the dengue viruses. Frequent and injudicious use of synthetic insecticides led to the evolution of resistant phenotypes in Ae. albopictus which necessitates the search for an alternative of current control strategies. Developing a long-lasting and environmentally safe tactic based on knowledge of ecology and population dynamics of Ae. albopictus is critical. Therefore, with a view towards biological control and ecology, the effect of entomopathogenic fungi (EPF) Beauveria bassiana on filial and first filial generations of Ae. albopictus were studied. Investigations showed 87.5% adulticidal activity leading to altered fecundity and adult longevity in a filial generation. The lethal (LC50) and sublethal (LC20) concentrations of B. bassiana were applied to filial generation (F0) to study demographic parameters in the first filial generation (F1). Results showed reduced net reproductive rates (Ro) intrinsic rate of increase (r), and mean generation time (T) compared to uninfected controls. Prolonged larval and pupal duration were observed followed by reduced longevity of male and female adults. Fecundity in the first filial generation was significantly changed with the lethal and sublethal concentrations of B. bassiana. Thus, it is concluded that B. bassiana has the potential to play a vital role in integrated mosquito management strategies.
In the current study, to combat insecticide resistance, we explored larvicidal, ovicidal, synergistic, and repellent activities of Sophora alopecuroides extract and its dominant constituents against Aedes albopictus. The results of the toxicity bioassays demonstrated that the extract of S. alopecuroides exerted significant larvicidal activity (16.66-86.66%) against the third-instar larvae of Ae. albopictus at different concentrations (5-50 ug/mL) and low hatchability of eggs (2.32-75%) at 5-50 ug/mL. The constituents of S. alopecuroides showed a synergistic effect when applied as a mixture (LC 30 + LC 30 ) against larvae, while no synergistic effect was observed against the eggs of Ae. albopictus. S. alopecuroides extract provided 93.11% repellency in the first 90 min and gradually decreased to 53.14% after 240 min, while the positive control DEET (N,N-diethyl-3-methylbenzamide) showed 94.18% in the first 90 min and 55.33% after 240 min. All of the results exhibited a concentration-dependent effect. To the best of our knowledge, this is the first time that a study has identified a highly effective extract of S. alopecuroides, which could be used as an alternative agent to control larvae and eggs and to repel adults of Ae. albopictus.
Entomopathogenic fungi are naturally existing microbes, that can serve as a key regulator of insect pests in integrated pest management strategies. Besides having no hazardous effects on the environment, these entomopathogens are alternatives to synthetic insecticides that can control notorious insect-like Plutella xylostella, a destructive pest of cruciferous crops. Three different species of entomopathogenic fungi were evaluated before the selection (high larval mortality and least LC50) of Metarhizum anisopliae. The study was designed to investigate the mortality, development, and immune responses of P. xylostella when challenged with M. anisopliae, a naturally existing soil-borne entomopathogenic fungus. M. anisopliae resulted in high pest mortality by killing 93% of larvae. However, no statistically significant effect on hemocyte concentration was observed. The activity of enzymes (Phenoloxidase and Superoxide dismutase) and immune genes (Defensin, Spaetzle, Cecropin, Lysozyme, and Hemolin) did vary at different time points (24, 48, 72 and 96 h) after exposure to M. anisopliae. Disturbance in the biological cycles of P. xylostella was also detected, significantly shorter adult life span (8.11:6.87, M:F) and reduced fecundity (101 eggs/female) were observed along with disturbed larval and pupal duration. Results suggest that M. anisopliae can efficiently hinder the P. xylostella defense and developmental system, resulting in mortality and disturbed demography.
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