The fumigation toxicity of Melaleuca alternifolia (Maid. & Betche) Cheel. (Myrtales: Myrtaceae) essential oil and its major fractions was studied under laboratory conditions against adults of Sitophilus oryzae L. (Coleoptera: Curculionidae) to protect wheat grains ( Triticum aestivum L.) (Poales: Poaceae) from this global pest that destroys the host plant during storage. By analyzing M. alternifolia essential oil (EO) using GC/MS terpinen-4-ol and γ-terpinene were detected as major components. In the fumigation toxicity, M. alternifolia EO showed the highest toxicity (LC50 = 0.31 μl · l–1 air), followed by terpinen-4-ol (LC ₅₀ = 23.65 μl · l–1 air) and γ-terpinene was the least toxic (LC ₅₀ = 43.55 μl · l–1 air). When tested for their insecticidal activities against S. oryzae in stored wheat, no progeny emerged after 3 months of treatment with M. alternifolia EO at 10 mg · g–1 or with terpinen-4-ol and γ-terpinene for 2 months. However, none of these compounds could protect wheat grain from damage throughout the entire study period (4 months). Interestingly, all tested compounds at the highest application rate did not show any phytotoxic effects after 4 months of storage.