Kinetics of diatomaceous earth (Fossil-Shield®) uptake by Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Fossil-Shield (R) is an industrial diatomaceous earth (DE) which is recommended for grain and surface applications. Callosobruchus maculatus (F.), the cowpea weevil, picks up the DE particles as it moves through the dust-treated grains. Mn+2 ion was used as a tracer element to detect the amount of DE accumulation on the bodies of male and female insects over 4 days at dosages of 500 mg/kg, 1000 mg/kg and 2000 mg/kg. The amount of Mn+2 in the accumulated DE was analysed by inductively coupled plasma spectrometry (ICP). Before the Mn+2 was used as a tracer, the natural Mn+2 content of the insects' bodies was evaluated. The kinetics of DE uptake were analysed using three different types of kinetics models. The kinetics of Fossil-Shield (R) uptake by a cowpea weevil can be determined more precisely by using the two-compartment model than by using the one-or three-compartment models. Therefore, it can be concluded that DE uptake occurs as a two-site reaction. First, pick-up and loss happens quite rapidly. Second, picked-up DE particles are incorporated into the cuticle lipid layer. It is also significant that Fossil-Shield (R) is effectively adherent to mung bean kernels to about 90% (wt/wt).