Sublethal Effects of the Insect Growth Regulator Novaluron on the Midgut Integrity and Survival of Adult Honey Bee Apis mellifera Workers.

Abstract

The insect growth regulator novaluron is a benzoylurea compound that disrupts the polymerization of chitin filaments. It is commonly used to control agricultural pests, particularly during their immature stages, and is generally considered nontoxic to adult insects. However, there is a lack of studies addressing the potential side effects of this insecticide on nontarget organisms, such as pollinating bees. In honey bees, the midgut is the primary organ responsible for digestion and nutrient absorption, where ingested food is surrounded by the peritrophic matrix, a structure composed of chitin microfibrils, glycosaminoglycans, and glycoproteins synthesized by digestive cells along the midgut. This study investigated whether chronic oral exposure to novaluron affects adult workers of the honey bee Apis mellifera. Specifically, we assessed the effects of the insecticide on the composition and permeability of the peritrophic matrix, the histopathology of the midgut, and worker mortality. Bees exposed chronically to a sublethal concentration of novaluron for 10 days showed reduced chitin levels in the peritrophic matrix, which appeared disorganized and diffuse, along with increased permeability of this barrier. Furthermore, exposed bees exhibited histopathological alterations in the midgut epithelium and elevated mortality rates. These findings indicate that, in the context of chronic oral exposure, commercial formulation of the insecticide novaluron, although classified as an insect growth regulator, is toxic to adult A. mellifera workers at the tissue level.