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ABSTRACT
Toxicity of the two biorational insecticides, spinosad and buprofezin and a mixture of the two was tested against the fourth instar larvae of the cotton leafworm, Spodoptera littoralis (Boisduval). The results showed that spinosad was more effective on the fourth instar larvae than buprofezin. The LC50 values for spinosad and buprofezin were 70.7 and 278.2 ppm, respectively. When spinosad was mixed with buprofezin, the percent of mortality increased; it was 85 %, compared with 63.3% in spinosad and 43.3% in buprofezin treatment. This means that the biorational insecticides spinosad and buprofezin can be used in a combination and cause good results with the cotton leafworm. This result suggested that the mixture of spinosad and buprofezin was more active than spinosad or buprofezin alone in all concentrations used. The larval duration, pupal period and adult longevity were not affected by all tested treatments. The number of eggs laid per female and percent of hatchability were affected in buprofezin and spinosad buprofezin in combination treatments compared with that in control. These results suggest that the combination of lethal effects of spinosad and buprofezin might affect pest population dynamics significantly by decreasing its survival and reproduction and by delaying its development.
Key words: Spodoptera littoralis, buprofezin, spinosad, combination, biological aspects.
INTRODUCTION
Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) is one of the most destructive pests of several crops such as cotton, Gossypium hirsutum L., peanut, Arachis hypogaea L., soybean, Glycine max L. and vegetables in Africa, Asia and Europe (El-Aswad et al., 2003). In addition to its direct damage reducing photosynthetic area, its larval presence, feeding marks and excrement residues reduce marketability of vegetables and ornamentals (Pluschkell et al., 1998). Over the past 25 years, the intensive use of broad-spectrum insecticides against S. littoralis has led the development of resistance to many registered pesticides for its control (Aydin and Gurkan, 2006).
Spinosad is a bioinsecticide based on the fermentation product of the soil bacterium Saccharopolyspora spinosa (Sparks et al., 1998). This compound has two unique modes of action, acting primarily on the insect nervous system at the nicotinic acetylcholine receptor, and exhibiting activity at the GABA receptor (Watson, 2001). It has a low toxicity for mammals with an LD50 of 3783 - 5000 mg/kg for rats (Tomlin,...