The fungicide azoxystrobin causes histopathological and cytotoxic changes in the midgut of the honey bee Apis mellifera (Hymenoptera: Apidae).

Apis mellifera is an important bee pollinating native and crop plants but its recent population decline has been linked to the use of pesticides, including fungicides that have been commonly classified as safe for bees. However, many pesticides, in addition to direct mortality cause sublethal effects, including damage to target selective honey bee organs. The midgut is the organ responsible for the digestion and absorption of nutrients and the detoxification of ingested substances, such as pesticides. This study evaluated the histopathological and cytotoxic changes in the midgut of A. mellifera workers caused by the pesticide azoxystrobin. The limit-test was performed, and a 100 µg a.i./bee dose was administered orally and midgut analyzed with light and transmission electron microscopies after 24 h and 48 h of pesticide exposure. The midgut of the control bees has a single layer of digestive cells, with spherical nuclei, nests of regenerative cells, and the lumen coated with the peritrophic matrix. The bees fed on azoxystrobin showed morphological changes, including intense cytoplasm vacuolization and cell fragments released into the gut lumen. The protein detection test showed greater staining intensity in the nests of regenerative cells after 24 h of exposure to azoxystrobin. The occurrence of damage to the midgut in A. mellifera exposed to azoxystrobin indicates that although this fungicide has been classified as low toxicity for bees, it has sublethal effects in the midgut, and effects in other organs should be investigated.

Behavioral and ultrastructural effects of novaluron on Aedes aegypti larvae.

Chitin synthesis inhibitors (CSI) are supposed to inhibit formation of chitin microfibrils in newly synthesized cuticle during molting process. Conversely, there has been comparatively few data on morphological effects of CSI on non-target insect organs. In this work, the effects of the CSI novaluron on behavior and midgut of A. aegypti were evaluated. Toxicity bioassays revealed that novaluron is toxic to A. aegypti larva with LC50 = 18.57 mg L-1 when exposed in aqueous solution for 24 h. Novaluron treated larvae were less active and spent more time resting compared to the control group. Histopathology showed that midguts of novaluron-treated larvae had cytoplasm vacuolization and damaged brush border. Cytotoxic effects in midguts of treated larvae induced necrosis, autophagy and damage to mitochondria. Despite being chitin synthesis inhibitor, novaluron did not induce alterations in the integument of A. aegypti larvae. Fluorescence microscopy revealed that the number of digestive cells were higher in novaluron-treated larvae than in control, in response to digestive cell apoptosis. The present study highlights the importance of novaluron against A. aegypti larvae by causing injuries to non-target organs, altering behaviors, inducing cell death and inhibiting cell proliferation.

Spiromesifen induces histopathological and cytotoxic changes in the midgut of the honeybee Apis mellifera (Hymenoptera: Apidae).

The honeybee Apis mellifera is an important pollinator that, similarly to other bees, undergoes colony losses due to several problems, including the use of pesticides in the agriculture. In addition to direct mortality, pesticides cause side-effects in some non-target organs, such as the midgut, which is the main organ for digestion and absorption. Spiromesifen is a pesticide used to control mites and whiteflies, which can be ingested by bees feeding on contaminated floral resources. This study evaluated the histopathological and cytological effects of the ingestion of spiromesifen on the midgut of A. mellifera workers. The bees were exposed per os to the field recommended dose of spiromesifen, and the midgut was analyzed after 24h and 48h of exposure to the pesticide. The midgut has a single layer of digestive cells, with spherical nucleus, nests of regenerative cells and layers of peritrophic matrix in the lumen. Bees treated with spiromesifen presented histological and cytological changes in the midgut, including disorganization of the epithelial architecture, release of cell fragments to the lumen, accumulation of mitochondria in the apical cytoplasm, alteration of the basal labyrinth, changes in the rough endoplasmic reticulum and cell degeneration. The occurrence of damage in the digestive cells of the A. mellifera midgut indicates that spiromesifen does not cause mortality in honeybees, but its side-effects can damage the midgut, which may affect the longevity and behavior of this pollinator.

Cytotoxic effects on the midgut, hypopharyngeal, glands and brain of Apis mellifera honey bee workers exposed to chronic concentrations of lambda-cyhalothrin.

The honeybee, Apis mellifera is economically important for its products (honey, wax, and propolis) and for its role in pollination. This insect is threated due to high population losses in both agriculture and beekeeping. Within causes involved in the loss of honeybees is the increased pesticide use on agriculture. Although current testing for the regularization of insecticide use considers its acute toxic effects on pollinators, little is known about the effects of chronic exposure to sublethal concentrations that may persist in the environment. This study investigated the effect of chronic exposure to sublethal concentrations of lambda-cyhalothrin on the midgut, hypopharyngeal glands, and brain of A. mellifera. Honey bees were fed for eight days with LC50/100 insecticide. Subsequently, the midgut, hypopharyngeal glands, and brain were analyzed in light and transmission electron microscopies. The midgut was not affected after exposure, except in the posterior region with cell fragments in the lumen and changes in the mitochondria. The hypopharyngeal glands were severely affected by the insecticide with changes in the rough endoplasmic reticulum and cell death. The brain has extensive gaps in the neuropil as well as in the cellular bodies, especially in the corpora pedunculata. These resembled cellular alterations similar to those seen in death processes. The results of this study indicate that lambda-cyhalothrin is toxic to bees at sublethal concentrations and ingested chronically, causing damage to the midgut, hypopharyngeal glands, and brain, and may affect physiological and behavioral aspects of these insects.