Acute and oral exposure to imidacloprid does not affect the number of circulating hemocytes in the stingless bee Melipona quadrifasciata post immune challenge.

In the present work, the effects of the neonicotinoid imidacloprid formulation on the total hemocyte counts (THC) and differential hemocyte counts (DHC) were investigated in foraging workers of the stingless bee Melipona quadrifasciata under (or not) the challenge with the bacteria Escherichia coli. The THC was not altered with the insecticide exposure and/or bacterial infection. However, the DHC of the bees changed with the imidacloprid exposure and/or bacterial infection. The number of prohemocytes (stem cells) increased in bees exposed to imidacloprid, but it did not change after the bacterial infection. The number of plasmatocytes (phagocytic cells) increased in imidacloprid-exposed and uninfected bees and decreased in infected bees regardless of the exposure to imidacloprid. On the other hand, there was a reduction of granulocytes, the most active immune cells, after imidacloprid exposure and an increase of granulocytes after the infection. Previous studies have shown that the neonicotinoids exposure can impair the immune system of bees. Our findings showed that the relative number of granulocytes declined with imidacloprid exposure, but the overall capacity of hemocyte responses in terms of total numbers after bacterial infection persisted even after the insecticide exposure.

Variations in circulating hemocytes are affected by age and caste in the stingless bee Melipona quadrifasciata.

The insect immune system faces various challenges; particularly in social bees, caste system and age polyethism expose individuals to numerous environmental and working conditions. However, little is known about how cellular defenses in social bees may be organized to respond to a variety of immune challenges. Here, we describe the morphological features and the total and differential counts of hemocytes in different female classes (newly emerged workers, nurses, foragers, and virgin queens) of the eusocial stingless bee Melipona quadrifasciata. Granulocytes and prohemocytes were, respectively, the most and the least abundant cells among all classes of females. Furthermore, there were more prohemocytes in virgin queens than in foragers. The total number of hemocytes was smaller in foragers, whereas the largest number was observed in nurse workers. This reduced amount of hemocytes in foragers might allow energy savings to perform colony activities such as foraging and defense. Foragers also had the biggest hemocytes (either prohemocytes, granulocytes, or plasmatocytes) in comparison to the other classes of females, which might have arisen as a compensation for the reduction in number of these cells during aging. These results suggest that profiles of hemocytes of M. quadrifasciata vary according to the caste and age of this eusocial bee.

The Antennal Sensilla of Species of the Palpalis Group (Diptera: Glossinidae).

Infection of tsetse fly with trypanosome parasites could be influenced by its ability to locate vertebrate host(s) in the wild. Generally, the antennae of insects are known to bear chemo-sensory organs (sensilla), which are used for host search among other functions. In order to exploit the potentials of tsetse-search behavior, knowledge of sensilla types on the antennae is desirable. In line with this, the dorsal and ventral surfaces of the antennae of Glossina palpalis and Glossina tachinoides (Westwood) were examined under the scanning electron microscope. Results showed that trichoid and chaetica (subtypes I and II) sensilla are present only on the scape and pedicel, while basiconica (subtypes I and II) and sensory pits are seen on the flagella. Microtrichia are present on all the segments of the antennae with Ca II being most abundant. Specifically, in females of G. tachinoides, there is a near-even distribution of Ca I and Ca II on the pedicel while more number of sensory pits was seen on females than males in both species. This study hypothesizes that host-search efficiency could be influenced by the number of olfactory-sensilla types on the antennae, in which case, females present greater potentials.

The antennal sensilla of Melipona quadrifasciata (Hymenoptera: Apidae: Meliponini): a study of different sexes and castes.

The sensilla of insects are integumental units that play a role as sensory structures and are crucial for the perception of stimuli and for communication. In this study, we compared the antennal sensilla of females (workers and queens), males (haploid (n) and diploid (2n)), and queen-like males (QLMs, resulting from 2n males after juvenile hormone (JH) treatment) in the stingless bee Melipona quadrifasciata. Images of the dorsal antenna surfaces were acquired using a scanning electron microscope. As reported for other hymenopterans, this species exhibits a heterogeneous sensillar distribution along the antennae. Thirteen different types of sensilla were found in the antennae of M. quadrifasciata: trichodea (subtypes I to VI), chaetica (subtypes I and II), placodea, basiconica, ampullacea, coeloconica, and coelocapitula. Sensilla trichodea I were the most abundant, followed by sensilla placodea, which might function in olfactory perception. Sensilla basiconica, sensilla chaetica I, sensilla coeloconica, and sensilla ampullacea were found exclusively in females. In terms of the composition and size of the sensilla, the antennae of QLMs most closely resemble those of the 2n male, although QLMs exhibit a queen phenotype. This study represents the first comparative analysis of the antennal sensilla of M. quadrifasciata. The differences found in the type and amount of sensilla between the castes and sexes are discussed based on the presumed sensillary functions.