Photosensitivity and a precise combination of size-dependent lambda-cyhalothrin microcapsules synergistically generate better insecticidal efficacy

In this study, lambda-cyhalothrin (LC) loaded polyurea microcapsules (MCs) with different particle sizes were fabricated. All of the MCs showed varying degrees of physical collapse, which was more obvious among those with smaller particle sizes. MCs with particle sizes of 1.38 μm (MC-S), 5.13 μm (MC-M) and 10.05 μm (MC-L) had shell thicknesses of 39.6, 50.3 and 150.1 nm, respectively. MCs with smaller particles tended to have significantly faster release profiles, and the MC-S group had much higher bioactivity against Agrotis ipsilon and better foliar affinity on the peanut leaves (indicated by rainfastness) than MC-M and MC-L. All of the MCs exhibited light-enhanced release profiles and had much slower degradation compared with the emulsifiable concentrate (EC) group, among which MC-L had the slowest degradation. To generate MCs with both favorable quick efficacy and long-lasting efficacy, binary mixtures of MC-S, MC-M and MC-L were produced by mixing them in pairs at ratios of 2:1, 1:1 and 1:2. The mixture of MC-S:MC-L at 1:2 showed the best comprehensive efficacy in the peanut foliar spray scenario among the nine tested combinations, and its effective duration was three times longer than that of EC. Overall, the precise combination of MCs with different particle sizes can regulate the efficacy of pesticide control and serve as a strategy for the better utilization of pesticides.