Bee cells can mask the effects of pesticides

The indiscriminate use of pesticides on crops and the disposal of toxicants – such as trace metals in low concentrations – in the soil and air, in addition to rivers and lakes, are pointed out as some of the factors responsible for the decline in populations and the disappearance of species of bees.

The real effects of these chemical substances on insects, however, are still not very well understood, since studies carried out in recent years in Brazil and other countries to diagnose whether the exposure of bees to varying concentrations of certain types of pesticides altered the rate of mortality and survival, in addition to the animal’s behavior and internal organs – such as the brain –, no significant changes were identified.

“Sometimes, just because there are no changes in the mortality rate and behavior, as well as in specific internal organs that can be impacted by a certain pesticide, does not mean that the product is not causing effects on bees”said Fábio Camargo Abdalla, professor at the Department of Biology at the Federal University of São Carlos (UFSCar).

The researcher and student Caio Eduardo da Costa Domingues, master’s student in the Postgraduate Program in Biotechnology and Environmental Monitoring at UFSCar de Sorocaba with Fapesp, identified that bees of the genus Bombus –popularly known as mamangavas or mamamgabas– have an integrated cellular system capable of “compensate” the effects of pesticides and, by combating them, “mask” its real impacts up to a certain concentration and exposure time.

The discovery, the result of “Action of cadmium and original Roundup® on internal organs of Bombus morio and Bombus atratus (Hymenoptera: Bombini)”supported by Fapesp, was reported in an article in the magazine PloS One.

“The effects of bee exposure to a particular xenobiotic [substâncias químicas sintéticas que não atuam naturalmente no ambiente, como agrotóxicos e metais-traço] can be compensated by this integrated cellular system, which we call hepatonephrocytic.”said Abdalla.

According to the researcher, the hepatonephrocytic system that they identified through microscopy in bumble bees is composed of cells that make up the insect’s so-called fat body – which have a homologous function to that of the liver in humans –, as well as pericardial cells and immune system cells. (hemocytes) of the animal.

This set of cells and tissues is located and arranged, not by chance, in layers in a contractile (myogenic) region around the dorsal vessel (the “heart”) of bees – a tube with a blind bottom that extends through the abdomen and opens at the beginning of the insect’s head – and works, in a coordinated way, as a filter for the blood (hemolymph) of bees.

When bees are exposed to xenobiotics, fat body cells are the first to be activated and represent the first barrier against chemical aggression.

If the fat body cells are unable to stop the “attack” of the chemical substance and are hit or destroyed, the pericardial cells are summoned.

The immune cellular response, however, occurs throughout the process of “fight”revealed through morphology and blood cell counts throughout the period of exposure to pesticides and trace metals.

The toxic substances neutralized by the pericardial cells are released back into the hemolymph and can be filtered by the Malpighian tubule – the insect’s excretory organ.

The bees’ immune cells, in turn, participate throughout the process, explained Abdalla.

“This association of cells, together with the Malpighian tubule, functions in bees in a similar way to the kidneys and liver of humans and represents the front line for insects to compensate for the harmful effects caused by exposure to chemical substances”he stated.

Possible biomarker

In order to evaluate the limit of compensation for the effects of toxicants by the hepatonephrocytic system of bees, researchers carried out experiments in which they exposed bumble bees (Bombus morio) doses of cadmium considered safe for class 1 and 2 waters by Conama (National Environmental Council), in addition to sublethal doses of thiamethoxan – the most used pesticide in Brazil – and glyphosate for variable periods.

The results of analyzes of the insects’ cellular response – carried out by counting cells from the hepatonephrocytic system in the hemolymph – revealed that exposure for 2 days to one part per billion (ppb) of cadmium, diluted in 2 milliliters (ml) of water , caused the death of fat body cells and intense activity of pericardial cells, leading the system to collapse and the destruction of the animals’ dorsal vessel.

“We are observing that this also exists with different species of bees, not only Bombus morio, but also Bombus atratus, Apis mellifera and Xylocopa suspecta, which shares the same niche with Bombus, with the difference that it is a solitary bee, and not social”he explained.

“Therefore, this hepatonephrocytic system can be used as a morphological biomarker to analyze the level of environmental stress in bees”he indicated.

According to the researcher, the simple activation of the cells that make up this system by bees when exposed to a certain type of xenobiotic is already an indicator of the harmful effect of the chemical substance, since the insect would be metabolically diverting energy that could be used for other purposes. functions, such as collection activity, to make this entire physiological system work.

“This could harm a colony if this effect of energy diversion is extrapolated to all species of field bees exposed in the field”said Abdalla.

The hepatonephrocytic system can also predict, with great accuracy, which insect organs may be affected by a given toxicant by evaluating which types of cells are being most damaged in the system, since they have several functions associated with other organs, pointed out the researcher.

In addition to detoxification and filtration, the cells of the hepatonephrocytic system are involved with ovarian development, formation and maintenance of the cuticle that covers the bees’ body (cuticulogenesis), with hormones regulating glands in the insects’ brain, he explained.

“This system could be used as a checkpoint. When studying the effect of a certain neonitocinoid insecticide – which is extremely harmful to the cells of the bee nervous system – on the insect using classical methods, morphological changes may not be noticed in the brain or in the animal’s mortality and survival rate. But you can check if this detoxification and filtration system is being activated”pointed.

The researchers intend in the future to analyze, using gas chromatography and mass spectrometry techniques, the fat body and pericardial cells that make up the hepatonephrocytic system of bees to study the dynamics of xenobiotic metabolism by insects.

Like what is seen in the human liver, agrochemicals, for example, are “broken” by the bees’ metabolic system into smaller molecules, called second metabolites.

In certain cases, these second metabolites are much more potent and harmful to the insect’s organism than the original agrochemical molecule, said Adballa.

“This exists with thiamethoxan, which is an agrochemical intensely studied in our laboratory and, when ingested, its toxicant potential can increase by up to 300 times”he stated.

With information from the agency.