Synergistic insecticidal effects of zinc-loaded zeolite nanoparticles combined with essential oils against Callosobruchus maculatus

Callosobruchus maculatus (F.) is a serious pest that causes post-harvest losses, which is a threat to global food security, therefore there is need to develop sustainable pest management strategies. This study investigates the synergistic insecticidal effects of zinc-loaded zeolite nanoparticles in combination with essential oils from Rosmarinus officinalis (L.) and Pimpinella anisum (L.) against C. maculatus adults and their progeny. Zeolite-A and zeolite-X were synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), and found to be highly crystalline and successfully zinc functionalized. The chemical profiles of the essential oils were elucidated by gas chromatography-mass spectrometry (GC-MS). The results showed that zeolites alone had moderate insecticidal activity against the tested insect. Zeolites loaded with zinc enhanced insecticidal activity on C. maculatus. Combining zeolites with essential oils further increases insecticidal activity, with LC₅₀ values ranging from 161 to 306 mg/kg. Zeolite nanoparticles and P. anisum essential oil formulation was the most effective in killing C. maculatus adults and progeny. Co-toxicity factor analysis indicated that there were synergistic effects between the essential oils and zeolites, especially between P. anisum and Zn-zeolite-A. Morphological examination of treated C. maculatus adults via SEM revealed cuticle abrasions, desiccation areas, and damage to sensilla, indicating a physical mode of action for the zeolites. This study suggests that zeolite nanoparticles and essential oil combinations can be used as eco-friendly insecticides for the management of C. maculatus in stored cowpea seeds.