Abstract:

Following preliminary screening of 13 ethanolic plant extracts, belonging to 10 different families, a total of 11 extracts were subjected to detailed toxicity evaluation against the larval stage of the housefly, Musca domestica L. The larvicidal LC50 values were < 100 ppm for Piper nigrum (50.1 ppm), Azadirachta indica (76.9 ppm), Conyza aegyptiaca (77.0 ppm) and Cichorium intybus (96.8 ppm); representing the highest potent extracts among the bioassayed candidates. Punica granatum extract exhibited the lowest toxicity (213.9 ppm). In comparison, commercial insecticides showed superior larvicidal toxicity; accounting to the following LC50 values: 0.029, 0.03, 0.61 and 0.64 ppm for deltamethrin, methomyl, chlorpyrifos and flufenoxuron, respectively. Combining botanical extracts with insecticides, at equitoxic dosages (e.g., LC₂₅ values), induced potentiating effects for a 44 bioassayed mixtures against the housefly larvae. Moreover, mixing the insecticides at LC₀ (a concentration level causing no observed mortality) with the LC₅₀ of each of the plant extracts have resulted in 44 paired combinations. Mostly, the "synergistic factor; S.F." ranged between 1.6 - 1.9; giving rise to high synergistic effects. Specifically, the synergistic effect was much pronounced for mixtures of the insecticide deltamethrin with different botanical extracts. Most of the tested toxicants induced different forms of developmental effects after exposure of 3rd larval instars to sublethal concentrations (LC₂₅ ppm). Larvae treated with A. indica, Citrus aurantifolia, Eucalyptus globulus (leaves or fruits), P. granatum, Salix safsaf, Sonchus oleraceus, Zea mays, as well as the insecticides chlorpyrifos, deltamethrin and methomyl failed to develop into adult stages. Morphologically, there were different forms of pupal and adult abnormalities, where the treatments of P. granatum and S. oleraceus caused abnormal pupal size in addition to pupal-adult intermediate. In the resulted Musca domestica adults, the effects were seen as one-winged insects, small size, compressed body and abdomen elongation. Such deformations were attributed to treatments of C. intybus, C. aegyptiaca, Piper nigrum and the IGR flufenoxuron. The overall results of the present investigation reveal the broad-spectrum toxic properties of the tested plant extracts against Musca domestica larvae; which may encourage further research on housefly control in tropics using indigenous plants.