Influence of the Physicochemical and Microstructural Properties on the Insecticidal Efficacy of Diatomaceous Earth on the Poultry Pest <i>Alphitobius diaperinus</i>

Different diatomaceous earth (DE) samples were studied to evaluate the influence of physicochemical and microstructural characteristics on insecticidal activity against <i>Alphitobius diaperinus</i>. 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 (<i>p</i> < 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 <i>A. diaperinus</i> and seems to be the DE characteristic that most influences insecticidal activity.