_____________Mun. Ent. Zool. Vol. 9, No. 1, January 2014__________ 429 TOXICITY AND BIOCHEMICAL IMPACTS OF SPINOSAD ON THE PINK CORN STEM BORER SESAMIA CRETICA LED. (LEPIDOPTERA: NOCTUIDAE) M. A. M. Osman*, Y. Y. Mosleh* and M. F. Mahmoud* * Plant Protection Department, Faculty of Agriculture, Suez Canal University 41522, Ismailia, EGYPT. E-mails: naeim70@hotmail.com, mfaragm@hotmail.com [Osman, M. A. M., Mosleh, Y. Y. & Mahmoud, M. F. 2014. Toxicity and biochemical impacts of spinosad on the Pink Corn Stem Borer Sesamia cretica Led. (Lepidoptera: Noctuidae). Munis Entomology & Zoology, 9 (1): 429-439] ABSTRACT: The toxicity of Spinosad to different larval instars of the pink corn stem borer, Sesamia cretica Led. (Lepidoptera: Noctuidae), was evaluated under laboratory and field conditions. The impact of Spinosad on the protein content and glycogen level of larvae was also taken into consideration. Data indicated that Spinosad had toxic activity against the tested larval instar and the mortality was in the order of first instar > second instar > third instar > fourth instar > fifth instar with respective LC50 values of 0.008, 0.016, 0.028, 0.044 and 0.159 ml/l after 7 days of treatment. Also, the field experiment showed high efficiency of Spinosad at the highest three concentrations down to 25% FR (0.125 m/l) against S. cretica larvae, which resulted in significant reduction in the number of plants containing either perforated stem or dead hearted case, number of larvae, tunnels and excavated areas inside infested plants. Regarding the biochemical parameters, results proved that the protein content and glycogen level in the treated larvae was significantly lower than that of the control at all concentrations of exposure. The highest rate of decreasing in total protein content was -54.5% for 2 nd instar larvae exposed to 50% FR (0.25ml/l). Also, the decrease in glycogen level in the treated larvae was concentration-dependent and reached -55.8% to 2 nd instar larvae exposure to 50% FR (0.25 ml/l.). KEY WORDS: Spinosad, Sesamia cretica, toxicity, biochemical impacts, protein contents, glycogen level. Maize Zea mays L., also called corn, is the third most important cereal crops in the world agricultural economy after wheat and rice. Maize occupies a crucial place since it used for human and livestock's consumption and as a source of industrial raw material for the production of oil, alcohol and starch. In Egypt, the cultivated area in 2012 stood approximately 750,000 hectares with a total grain yield of 7 M.T. (FAO, 2012). However, this crop is subjected to sever attack by several insect pests causing considerable damage estimated about 25% annually (Setamou et al., 2000). Stem borers are one of the major limiting factors to maize production in the world (Tende et al., 2005). In Egypt, maize is infested by three stem borer species: the pink borer Sesamia cretica Led. (Lepidoptera: Noctuidae), the striped stem borer Chilo agamemnon Blesz. and European corn borer Ostrinia nubilalis Hbn. (Lepidoptera: Pyralidae) (Moyal et al., 2002). The pink borer, Sesamia cretica Led. (Lepidoptera: Noctuidae), is a key pest damaging corn mainly in the eastern Mediterranean countries, and is also spread in Africa and Asia (Onukogu, 1984; Moyal et al., 2002). In Egypt, attacks by S. cretica are usually high especially on early maize crops, sown between late March and mid-May, in which the borer may cause severe damage (Semeada, 1988). Stem borers affect maize yields by reducing the photosynthetic area of the leaves. Also, crop losses due to death of the growing point, early leaf senescence, reduced translocation, lodging and direct damage to ears. Secondary losses have been documented due to infections by bacterial and fungal pathogens via entry points created by the stem borers within the plant tissues (Ndiritu, 1999). The