Impact of Diatomaceous Earth Modifications for Controlling the Granary Weevil, Sitophilus granarius (Linnaeus) (Coleoptera: Curculionidae)

During different exposure intervals (one, two, four, seven, and fourteen days), the efficacy of different concentrations of original Diatomaceous Earth (DE) and DEs-modifications against the granary weevil, Sitophilus granarius (Linnaeus) adults, were evaluated. The efficacy of DEs was evaluated by recording adult mortality and other parameters including effect on the progeny, grain weight loss, and DE-coherence on wheat kernels. The modified DEs showed higher efficacy than the original-DE. The most effective DE–modification was Al-DE followed by Ca-DE and Na-DE. At 14 days interval, the highest adult mortality reached 98% for Al-DE and Ca-DE modifications in comparison to the control untreated (10%) that indicates highly significant difference between them and control. At 1.5% concentration, Al-DE treatment almost suppressed the progeny (5.0±2.0) in comparison with the untreated treatment (83.333±4.041). The least weight loss was recorded for Al-DE treatment (7.0%) followed by Ca-DE (10.0%), Na-DE (13.0%) and the original-DE (25.0%) compared with the control (38%). Ultrastructural investigations of the antennae, mouth parts and posterior end of control and treated adults were performed using scanning electron microscope. DEs particles damaged sensory organs and parts of the integument throughout the body. Clear destruction among different types of the club segment sensilla was recorded. Moreover, integument cracking and cutting of the mouth parts and the genitalia were recorded. Both Al-DE and Ca-DE treatments strongly cohered very well to the wheat kernels with (1.493±0.002 and 1.492±0.002) at 1.5% concentration, respectively. The DEs coherence on wheat kernels matched directly to the insecticidal efficacy of the DE modifications against S. granarius adults.