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The effects of powdered herbs (lavender Lavandula officinalis L., peppermint Mentha piperita L. and basil Ocimium basilicum L.) added to the food substances of three insect species: the rice weevil Sitophilus oryzae (L.), lesser grain borer Rhyzopertha dominica (F.), and the saw-toothed grain beetle Oryzaephilus surinamensis (L.) on the life span and development of the three insect species as well as habitat conditions, sex structure, and the survivability of males and females were considered. The experiments were conducted in the laboratory at a temperature of 28°C and relative humidity (RH) 60 ±5%. In all the studied populations, high female mortality was found (♂/♀ < 1). The studied populations were: the rice weevil and the lesser grain borer cultured in wheat grain with herb additions, and the saw-toothed grain beetle cultured in semolina with herb additions. Among the herbs used, peppermint caused a significant effect in the form of increased mortality rates among females of S. oryzae and O. surinamensis. Lavender and basil had a similar impact among R. dominica females. The herbs applied in the experiments intensified the mortality of females and, consequently, led to the disappearance of entire populations.
Bioassays were conducted to assess the effects of two silicon dioxide nanoparticles of Aerosil® and Nanosav against adults of Rhyzopertha dominica F. and Tribolium confusum Jacquelin du Val. Silica nanoparticles were applied at the rates of 50, 100, 200 and 300 mg · kg–1 on wheat and peeled barley. The mortality was counted after 1, 2, 3, and 7 days of exposure. Another experiment was carried out to evaluate the effect of food source on the survival of beetles after exposure to silica nanoparticles. Adults were exposed to silica nanoparticles at the rate of 0.2 mg · cm–2 for 1 and 2 days on filter paper inside plastic Petri dishes, respectively. After exposure, the initial mortality was counted and live individuals of both species were held for a week in empty glass vials or vials containing wheat and wheat flour, respectively. Silica nanoparticles have high toxicity on R. dominica and T. confusum adults. Rhyzopertha dominica was more susceptible than T. confusum. However, the mortality of both species increased with increasing concentrations and time exposed to each concentration. At low concentrations, Aerosil® was more effective than Nanosav. Silica nanoparticles were more effective in wheat grains than barley. Results indicated that the initial mortality was so high that the impact of food source on delay mortality was unclear in most cases. Silica nanoparticles were efficient against tested species and can be used effectively in a stored grain integrated pest management program.
Plant secondary metabolites play an important role in plant-insect interactions and therefore such compounds may have insecticidal activity against insects. The chemical composition of the essential oil from leaves and flowers of Lavandula stoechas grown in Kashan, Iran, was studied by gas chromatography mass spectrometry (GC-MS). 1,8-Cineole (7.02%), γ-Cadinene (5.33%), T-Cadinol (5.07%), p-Mentha-1-en-8-ol (5.02%) and Caryophyllene (5.01%) were found to be the major constituents of the oil. In fumigant toxicity tests with the essential oil against adults of Tribolium castaneum Herbst, Lasioderma serricorne F. and Rhyzopertha dominica F. at 27±1°C and 60±5% RH, it was observed that L. serricorne (LC50 = 3.835 μl/l) were significantly more susceptible than R. dominica (LC50 = 5.66 μl/l) and T. castaneum (LC50 = 39.685 μl/l) 24 h after treatment. In all cases, considerable differences in mortality of insects to essential oil vapor were observed with different concentrations and times. Mortality increased as the doses of essential oils and exposure period increased and after 72 h fumigations, greatest percentages of mortality were obtained. The findings indicate the strong insecticidal activity of L. stoechas oil and it may be used in grain storage against insects L. serricorne, R. dominica and T. castaneum.
Concerns about food quality and environmental protection have led to the search for effective and safe insect control measures. This study was carried out to evaluate the efficacy of some insecticides (malathion, alpha-cypermethrin, lambda-cyhalothrin) and clove oil, alone and in combinations, to protect wheat grain against Rhyzopertha dominica. Adult mortality, progeny emergence and weight loss of treated grain were examined. The results revealed that the tested insecticides and clove oil alone showed high efficiency to R. dominica with respect to mortality, progeny of the adults and weight loss of wheat grain. The mixing of lambda-cyhalothrin and clove oil with the most effective insecticide (alphacypermethrin) enhanced its efficacy to R. dominica. It was more efficient against R. dominica than when used alone with respect to mortality and progeny of the adults. However, mixing alpha-cypermethrin with malathion reduced the efficacy of alpha-cypermethrin against R. dominica with respect to mortality and progeny of the adults. Combinations of alpha-cypermethrin and clove oil reduced wheat grain loss more than using them alone. Mixing lambda-cyhalothrin and clove oil with low concentrations of alpha-cypermethrin improved its efficacy against R. dominica and therefore may reduce environmental pollution, lower risks to human health, and delay insect resistance development.
The populations of Rhyzopertha dominica, a dangerous pest in stored grains were investigated. This laboratory study assumed the hypothesis that the introduction of powdered leaves of Salvia officinalis L. and Artemisia absinthium L. containing feeding inhibitors into grain may delay the development and therefore reduce population size of R. dominica. These herbs were powdered and added at 0.5 g of herb per 40 g wheat. The research was conducted in optimum conditions of temperature and humidity (28ºC and relative humidity 60%). The insects used in the experiment were initially obtained from mature individuals of uniform age and were bred in glass containers with base area 28 cm² covered with gauze. The experiments were continued for 310 days and the herb supplements were renewed each month. The results of the study show that the introduction of chemical substances contained in the powdered leaves of S. officinalis and A. absinthium into an optimal substrate (wheat) infested with R. dominica decreases its population size. These substances have properties that inhibit the feeding of this insect species.
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