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

TL;DR

This study shows that the insecticide novaluron, though considered safe for adult insects, harms honey bees by damaging their gut and reducing survival.

Contribution

The study reveals novaluron's sublethal toxicity to honey bees, challenging its classification as safe for adult insects.

Findings

Chronic exposure to novaluron reduced chitin levels and disrupted the peritrophic matrix in honey bee midguts.

Exposed bees showed increased gut permeability, histopathological changes, and higher mortality rates.

The findings suggest novaluron is toxic to adult honey bees despite being an insect growth regulator.

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.

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