Influence of the physicochemical and microstructural properties on the insecticidal efficacy of diatomaceous earth on the poultry pest Alphitobius diaperinus

Abstract

Different diatomaceous earth (DE) samples were studied to evaluate the influence of physicochemical and microstructural characteristics on insecticidal activity against Alphitobius diaperinus. The insecticidal efficacy study showed that DE4 was more effective for larvae and adults (98% and 88% mortality, respectively), contrasting with DE1, which presented similar results to the control (49% and 6% mortality for larvae and adults, respectively). DE2 and DE3, in turn, exhibited promising insecticidal results. X-ray diffraction analyses showed a predominantly crystalline profile for DE1, while an amorphous profile was found for DE4. Laser diffraction analysis and scanning electron microscopy showed that DE1 had a larger average particle size (∼45 μm) than DE2, DE3, and DE4 (∼28, 26, and 25 μm, respectively). In addition, DE1 showed poor powder adherence to the adult insects and reduced adsorption/absorption capacity compared with the other samples (p < 0.05). The calcined treatment promoted significant microstructural changes in DE samples. An increase in the crystallinity of the samples is perceived, accompanied by an increase in particle size and a reduction in their adsorption/absorption capacity. These changes significantly impact the insecticidal activity of DE samples against adult insects, resulting in mortality rates of around ∼10–20%. In summary, the results showed that increasing the degree of crystallinity of DE samples negatively affects their insecticidal activity against A. diaperinus and seems to be the DE characteristic that most influences insecticidal activity.