Impacts of the insecticide thiamethoxam on the native stingless bee Plebeia catamarcensis (Hymenoptera, Apidae, Meliponini).

Agricultural production and the indiscriminate use of insecticides such as thiamethoxam have put at risk the biodiversity and ecosystem services provided by bees, including native stingless species. Since most of the native species do not present economic importance, they may suffer "silent extinction", due to lack of monitoring of their colonies. Therefore, this study aimed to determine the lethal and sublethal concentrations of the insecticide thiamethoxam, with evaluation of its sublethal effects on mobility, in the stingless bee Plebeia catamarcensis (Holmberg, 1903). Foraging bees were collected and exposed to thiamethoxam to determine lethal (LC50) and sublethal concentrations. The 24 h LC50 was 0.408 ng a.i./µL, a value demonstrating that this species may be as sensitive as other stingless bees already studied. Sublethal concentrations influenced the locomotion abilities of the bees, making them hyperactive when exposed to LC50/10 and lethargic when exposed to LC50/100. The effects of sublethal concentrations on individuals may have collective consequences, especially in colonies with few individuals, as is the case of P. catamarcensis. The findings reinforce the hypothesis that thiamethoxam may contribute to the decline of native stingless bees, which can be significantly impacted when chronically exposed to agricultural production systems that use this insecticide, consequently affecting the ecosystem services provided by these bees.

Effects of chronic exposure to sublethal doses of neonicotinoids in the social wasp Polybia paulista: Survival, mobility, and histopathology.

Several studies have investigated the consequences of exposure to neonicotinoids in honeybees. Given the lack of studies concerning the consequences of exposure of social wasps to neonicotinoids, as well as the ecological importance of these insects, the objective of this study was to test the hypothesis that chronic exposure to sublethal concentrations of thiamethoxam decreases survival and mobility by causing damage to the brain and midgut of the social wasp Polybia paulista. The wasps were exposed to different concentrations of thiamethoxam, in order to obtain the mean lethal concentration (LC50), which was used as a reference for calculation of two sublethal concentrations (LC50/100 and LC50/10) employed in subsequent experiments. To calculate survival, groups of exposed (EW) and unexposed (UW) wasps were monitored until death, allowing calculation of the average lethal time. The EW and UW groups were evaluated after 12, 24, 48, and 72 h of exposure, considering their mobility and histopathological parameters of the midgut and brain. A lesion index based on semiquantitative analyses was used for comparison of histopathological damage. The results demonstrated that exposure to the LC50/10 led to a significantly shorter survival time of the P. paulista workers, compared to unexposed wasps. In addition, both sublethal concentrations decreased mobility and caused damage to the intestine (loss of brush border, presence of spherocrystals, loss of cytoplasmic material, and pyknosis) and the brain (loss of cell contact and pyknosis), regardless of the exposure time. The findings showed that, like bees, social wasps are nontarget insects susceptible to the detrimental consequences of neonicotinoid use, with exposure leading to impaired survival, locomotion, and physiology.

Lethal and Sublethal Dose of Thiamethoxam and Its Effects on the Behavior of a Non-target Social Wasp.

In the last few years, with the increase in agricultural productivity, there has also been an increase in the use of insecticides to combat insects considered pests. However, these chemical compounds end up affecting nontarget insects that also interact with the crops. Studies have shown that social bees are among the insects that are suffering most from the effects of these compounds, resulting in negative ecological and economic impacts, considering that these insects provide pollination services in ecosystems. At the same time, social wasps also interact with plants, including cultivated ones, and perform ecological services similar to those of social bees, so it can be hypothesized that insecticides are also affecting social wasp colonies. Therefore, the purpose of this study was to evaluate contamination and sublethal effects of neonicotinoids on the mobility of the social wasp Protopolybia exigua (Saussure). In the first step, oral exposure experiments were performed to determine lethal and sublethal concentrations. In a second step, the wasps were exposed to sublethal concentrations, in order to evaluate the effects on their mobility. The results demonstrated that this species is more susceptible to exposure to neonicotinoids, compared to several bee species that have so far been studied, but lower than others. Exposure to sublethal concentrations can significantly reduce wasp mobility, which can have short-term consequences both for worker wasps and for the maintenance of their colonies.

Magnetic nanoparticles in the body parts of Polistes versicolor and Polybia paulista wasps are biomineralized: evidence from magnetization measurements and ferromagnetic resonance spectroscopy.

The detection of the geomagnetic field by animals to use as a cue in homing and migration is known as magnetoreception. The ferromagnetic hypothesis explains magnetoreception assuming that magnetic nanoparticles in cellular structures are used as magnetic field transducers. Considering magnetoreception in social insects, the most studied has been the honeybee Apis mellifera and only in two wasp species (Vespa orientalis and Polybia paulista) have been shown a magnetosensitive behavior. In the present report the body parts (abdomen, head and antennae) of Polistes versicolor and Polybia paulista wasps were studied aiming to find biomineralized magnetic nanoparticles, using magnetometry measurements and ferromagnetic resonance spectroscopy. The magnetometry measurements show the presence of magnetic nanoparticles in all body parts, being characterized as mixtures of superparamagnetic, single domain and pseudo-single domain nanoparticles. From the ferromagnetic resonance spectra were obtained the asymmetry ratio A and the effective g factor geff, and those parameters are consistent with the presence of biomineralized magnetic nanoparticles in both wasps. In the case of Polybia paulista, the magnetic nanoparticles can be associated with some sort of magnetosensor once this wasp is magnetosensitive. For Polistes versicolor, the results indicate that this wasp can be magnetosensitive as Polybia paulista once their magnetic nanoparticles are biomineralized in the body. Behavioral studies with Polistes versicolor wasps deserve to be performed.

Is the social wasp Polybia paulista a silent victim of neonicotinoid contamination?

Neonicotinoids are among the chemicals most widely used against insects considered agricultural pests, although they may also affect nontarget species, as has been reported for social bees. Social wasps are recognized as efficient predators of larvae of other insects, including pest species, so they may have contact with insecticides, at least indirectly. However, to date, there have been no studies investigating the consequences for social wasps of the use of neonicotinoids. Therefore, the aim of this study was to obtain the topical and oral acute lethal mean doses of the neonicotinoid thiamethoxam, as well as to evaluate the effects of sublethal contamination, for the social wasp Polybia paulista. Foraging wasps were exposed orally and topically, with monitoring of their mortality after 24 and 48 h, in order to calculate the LD50 values. Other wasps were then exposed with sublethal doses, in order to evaluate the effects of contamination on their mobility. The results indicated that P. paulista workers are as sensitive to thiamethoxam contamination as several nontarget species studied previously. Exposure to a sublethal dose (LD10) negatively affected their mobility. It could be concluded that social wasp colonies may be as much affected by exposure to neonicotinoids as social bees. Further toxicological studies should be conducted, evaluating other parameters and different species, in order to understand the extent of the problems faced by these insects due to the use of neonicotinoids.

A 3D model to illustrate the nest architecture of Acromyrmex balzani (Hymenoptera; Formicidae)

ABSTRACT For eusocial insects, the nest is a place where the main social interactions occur. The nest architecture ensures protection from predators and the environment, as well as suitable conditions for brood rearing, food storage, and in some cases the cultivation of fungus farms. Variations in nest architecture can occur, according to the environmental conditions. In order to elucidate the internal organization of nests, most studies use 2D schemes and photographs to illustrate the nest architecture models. However, 3D models can provide a different and more realistic view of the nest architecture. The aim of this study was to describe the nest architecture and colony size of the grass-cutting ant Acromyrmex balzani (Emery), using 3D models to illustrate these features. The structures of eight colonies were measured and the data were used to create a 3D model of each nest. Externally, the nests had one or more piles of loose soil and waste, with a single straw turret over the entrance. Underground, the nests had from 2 to 6 chambers, at a maximum depth of 122 cm. It could be concluded that the observed nest architecture of Acromyrmex balzani followed, at least in part, the pattern already reported in the literature. However, this is the first report of connection between two chambers made by two shafts, as well as the presence of the turret at the nest entrance/exit, regardless of the season of the year. These differences evidence that the nest structures may vary, depending on intrinsic or local environmental conditions.

The complex nest architecture of the Ponerinae ant Odontomachus chelifer.

In social insects, nests are very important structures built to provide a protected microhabitat for immature development and food storage and are the places where most interactions between all members of a colony occur. Considering that nest architecture is an important behavioural trait that can clarify essential points of the social level of the species, here we describe the architectural model of the Ponerinae ant Odontomachus chelifer. Five subterranean nests were excavated; one of them filled with liquid cement for extraction of casts of chambers, shafts and tunnels. All nests were found in a woodland area, with Dystrophic Red Latosol soil, associated with roots of large trees and, differently from the pattern currently described for this subfamily, presented a complex structure with multiple entrances and more than one vertical shaft connected by tunnels to relatively horizontal chambers. The number of chambers varied from 24 to 77, with mean volume ranging from 200.09 cm3 to 363.79 cm3, and maximum depth of 134 cm. Worker population varied between 304 and 864 individuals with on average 8.28 cm2 of area per worker. All nests had at least one Hall, which is a relatively larger chamber serving as a distribution centre of the nest, and to our knowledge, there is no record of Ponerinae species building similar structure. All nests had chambers "paved" with pieces of decaying plant material and on the floor of some of them, we found a fungus whose identification and function are being investigated. Thus, our findings provide evidence to suggest that nests of O. chelifer can be considered complex, due to the great number and organization of chambers, shafts and connections, compared to those currently described for Ponerinae species.

Variation of cuticular chemical compounds in three species of Mischocyttarus (Hymenoptera: Vespidae) eusocial wasps

Abstract The social wasps have a remarkable system of organization in which chemical communication mediate different behavioral interactions. Among the compounds involved in this process, cuticular hydrocarbons are considered the main signals for nestmate recognition, caste differentiation, and fertility communication. The aims of this study were to describe the cuticular chemical compounds of the species Mischocyttarus consimilis, Mischocyttarus bertonii, and Mischocyttarus latior, and to test whether these chemical compounds could be used to evaluate differences and similarities between Mischocyttarus species, using gas chromatography coupled to mass spectrometry (GC-MS). Workers from these three species presented a variety of hydrocarbons ranging from C17 to C37, and among the compounds identified, the most representative were branched alkanes, linear alkanes and alkenes. The results revealed quantitative and qualitative differences among the hydrocarbon profiles, as confirmed by discriminant analysis. This study supports the hypothesis that cuticular chemical profiles can be used as parameters to identify interspecific and intercolony differences in Mischocyttarus, highlighting the importance of these compounds for differentiation of species and populations.