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.

Although pyrethroids are increasingly being used to control a number of agricultural insect pests, especially the cotton leafworm, Spodoptera littoralis (Boisd.), pyrethroid resistance is a major obstacle limiting effective control. With the aim of maintaining the effectiveness of pyrethroids in managing pests, a study was undertaken to evaluated the effectiveness of oxidase and esterase inhibitors for synergizing pyrethroids in S. littoralis larvae. Compared with the insecticide-susceptible strain (L-SS) of S. littoralis, the resistance ratio (RR) in the field population (F-RS) was 271.43–fold to cypermethrin. The use of profenofos as an esterase inhibitor significantly increased larval susceptibility to cypermethrin in the F-RS strain, with a synergy ratio (SR) of up to 192.57–fold. Significant inhibition of esterase by profenofos in the F-RS strain was found in vivo. Also, piperonyl butoxide (PB) as an oxidase inhibitor had slight effect of cypermethrin toxicity, so its addition is not a solution for pyrethroid resistance. Thus, modifying the toxicity of cypermethrin by mixing it with organophosphorus compounds (OPs) increased its toxicity and decreased the population of S. littoralis, which is a successful strategy for managing pyrethroid resistance.