Effects of the topical application of an insect growth regulator (fenoxycarb) on some physiological parameters in the fifth instar larvae of the silkworm Bombyx mori

Abstract

The effects of topical applications of the commercial insecticide Insegar ( 25% fenoxycarb) on the fifth instar larvae of Bombyx mori fed on an artificial diet were investigated. Clear dose-response relationships were established with respect to frass production as well as to the percentage of dauer larvae, whereas less evident was the correlation to the growth rate and the percentage of pupation. The Insegar concentration, giving 50% of dauer larvae, was 60 pg per larva, but effects on the parameters tested were evident also with concentrations as low as 100 fg per larva. Apparently, this insect growth regulator (IGR) causes a reduced intake of food as well as a reduction in growth rate. The absorption of amino acids carried out by the K +-dependent symporter in the anterior-middle and the posterior regions of the midgut was evaluated in vitro from leucine uptake into brush border membrane vesicles obtained from control and treated larvae. IGR in a dose of 10 fg per larva causes a significant, albeit small, increase of amino acid intake in both midgut regions. At higher doses, no effect of Insegar on leucine uptake is evident in the posterior midgut, whereas a significant decrease of the uptake in the anterior-middle region is apparent at the dose of 10 μg per larva.