Swelling and release kinetics of larvicide-containing chitosan/cashew gum beads

A new pesticide formulation (bead) based on chitosan (CH) and cashew gum (CG) containing dichlorvos [2,2-dichlorovinyldimethyl phosphate (DDVP)] was prepared and investigated as a larvicide for Acdes aegypti control. Beads were characterized with respect to their size, shape, larvicide loading, swelling, and in vitro and in vivo release kinetics. CH and CH/CG beads were loaded with DDVP from 5.15 to 71.4%. In the first hour, the in vitro release was similar for CH and CH/CG beads, faster release being observed after 5 h for CH/CG beads; at equilibrium (30 h), CH beads released up to 55% of the larvicide, and CH/CG beads reached 66%. The data were fitted to a mathematical model, being in good agreement with the literature. In vivo release showed that CH/CG beads reached a plateau after 30 h, resulting in a highest mortality of approximately 60%, whereas CH beads killed only 42% of the larvae by 30 h and seemed not to have released their whole larvicide content even after 72 h. The DDVP lethal dose for 50% mortality was found to be 0.01 +/- 0.002 ppm; the persistence studies revealed that after 168 h, 42.5% larval mortality was obtained by CH beads, and only approximately half of that was obtained by CH/CG beads. DDVP-loaded beads were effective up to 336 h. It could be concluded that beads containing DDVP at an average concentration of 7.2 ppm could provide good larval control up to 7 days. (c) 2006 Wiley Periodicals, Inc.