Comparison of the Sensitivity of Tetragonisca angustula (Apidae-Meliponini) and Apis mellifera (Apidae-Apini) to Three Insecticides (Malathion, Imidacloprid, and Fipronil) Used in Costa Rica.

The decline of insect pollinators is a significant concern within the current biodiversity crisis. The paradox between the benefits that these animals represent to humans and the evidence of human activities driving their extinction calls for the urgent protection of bees. To address the role of chemical pollution in this scenario, we assessed the acute toxicity as well as four biomarker responses (cholinesterase [ChE], glutathione S-transferase, catalase, and lipid peroxidation [LPO]) elicited by dietary 24-h exposure to three insecticides (malathion, imidacloprid, and fipronil) on the stingless neotropical bee Tetragonisca angustula and the honeybee Apis mellifera. Malathion was the most toxic substance to both species, with 48-h median lethal doses (LD50s) of 0.25 ng/bee to A. mellifera and 0.02 ng/bee to T. angustula. Fipronil was also highly toxic and presented a similar toxicity to both species, with 48-h LD50s of 0.5 ng/bee (A. mellifera) and 0.4 ng/bee (T. angustula). Imidacloprid had the lowest acute toxicity with a 48-h LD50 of 29 ng/bee for A. mellifera, whereas T. angustula tolerated exposure higher than 35 ng/bee. Apparent biomarker responses were observed in bees of both species that survived exposure to higher concentrations of malathion (ChE inhibition) and fipronil (increased LPO). Our results suggest that specific sensitivity to insecticides varies greatly among compounds and pollinator species, but the use of different representative species can facilitate the prioritization of substances regarding their risk to pollinators. Further research is necessary to better characterize the risk that pesticides represent in neotropical agricultural landscapes. Environ Toxicol Chem 2023;42:1022-1031. © 2023 SETAC.

An unusual recruitment strategy in a mass-recruiting stingless bee, Partamona orizabaensis.

Foragers of several stingless bee species deposit attractive scent marks on solid substrates to precisely recruit nestmates to food. Interestingly, Partamona workers quickly recruit large numbers of nest mates to resources, likely even without the deposition of attractive scent marks. However, systematic studies of the recruitment system of these bees are lacking. We now studied the recruitment behavior of P. orizabaensis. Our findings show that foragers of this species can recruit large numbers of nestmates to food sources at a particular location. The precise nestmate recruitment does not rely on attractive scent marks deposited on substrates. We never observed any scent marking behavior and feeders baited with labial or mandibular gland extracts were not attractive for the bees. Chemical analyses showed that the foragers' labial gland secretions exclusively contain long chain hydrocarbons, which render their role in recruitment communication unlikely. Whether mandibular gland secretions, which contain esters and alcohols that are known as attractive pheromones in other bee species, are used to guide recruits toward food during flight, remains elusive. We conclude that Partamona's quick recruitment system that does not rely on conspicuous scent marks has evolved as a strategy against competition with sympatrically occurring and more aggressive bee species.

Stingless bees (Scaptotrigona pectoralis) learn foreign trail pheromones and use them to find food.

Foragers of several species of stingless bees (Hymenoptera, Apidae and Meliponini) deposit pheromone marks in the vegetation to guide nestmates to new food sources. These pheromones are produced in the labial glands and are nest and species specific. Thus, an important question is how recruited foragers recognize their nestmates' pheromone in the field. We tested whether naïve workers learn a specific trail pheromone composition while being recruited by nestmates inside the hive in the species Scaptotrigona pectoralis. We installed artificial scent trails branching off from trails deposited by recruiting foragers and registered whether newly recruited bees follow these trails. The artificial trails were baited with trail pheromones of workers collected from foreign S. pectoralis colonies. When the same foreign trail pheromone was presented inside the experimental hives while recruitment took place a significant higher number of bees followed the artificial trails than in experiments without intranidal presentation. Our results demonstrate that recruits of S. pectoralis can learn the composition of specific trail pheromone bouquets inside the nest and subsequently follow this pheromone in the field. We, therefore, suggest that trail pheromone recognition in S. pectoralis is based on a flexible learning process rather than being a genetically fixed behaviour.

The trail pheromone of a stingless bee, Trigona corvina (Hymenoptera, Apidae, Meliponini), varies between populations.

Stingless bees, like honeybees, live in highly organized, perennial colonies. Their eusocial way of life, which includes division of labor, implies that only a fraction of the workers leave the nest to forage for food. To ensure a sufficient food supply for all colony members, stingless bees have evolved different mechanisms to recruit workers to foraging or even to communicate the location of particular food sites. In some species, foragers deposit pheromone marks between food sources and their nest, which are used by recruited workers to locate the food. To date, pheromone compounds have only been described for 3 species. We have identified the trail pheromone of a further species by means of chemical and electrophysiological analyses and with bioassays testing natural gland extracts and synthetic compounds. The pheromone is a blend of wax type and terpene esters. The relative proportions of the single components showed significant differences in the pheromones of foragers form 3 different colonies. This is the first report on a trail pheromone comprised of esters of 2 different biogenetic origins proving variability of the system. Pheromone specificity may serve to avoid confusions between the trails deposited by foragers of different nests and, thus, to decrease competition at food sources.

Workers make the queens in melipona bees: identification of geraniol as a caste determining compound from labial glands of nurse bees.

Reproductive division of labor in advanced eusocial honey bees and stingless bees is based on the ability of totipotent female larvae to develop into either workers or queens. In nearly all species, caste is determined by larval nutrition. However, the mechanism that triggers queen development in Melipona bees is still unresolved. Several hypotheses have been proposed, ranging from the proximate (a genetic determination of caste development) to the ultimate (a model in which larvae have complete control over their own caste fate). Here, we showed that the addition of geraniol, the main compound in labial gland secretions of nurse workers, to the larval food significantly increases the number of larvae that develop into queens. Interestingly, the proportion of queens in treated brood exactly matched the value (25%) predicted by the two-locus, two-allele model of genetic queen determination, in which only females that are heterozygous at both loci are capable of developing into queens. We conclude that labial gland secretions, added to the food of some cells by nurse bees, trigger queen development, provided that the larvae are genetically predisposed towards this developmental pathway. In Melipona beecheii, geraniol acts as a primer pheromone representing the first caste determination substance identified to date.

Recruits of the stingless bee Scaptotrigona pectoralis learn food odors from the nest atmosphere.

The ability to learn food odors inside the nest and to associate them with food sources in the field is of essential importance for the recruitment of nestmates in social bees. We investigated odor learning by workers within the hive and the influence of these odors on their food choice in the field in the stingless bee Scaptotrigona pectoralis. During the experiments, recruited bees had to choose between two feeders, one with an odor that was present inside the nest during the recruitment process, and one with an unknown odor. In all experiments with different odor combinations (linalool/phenylacetaldehyde, geraniol/eugenol) a significant majority of bees visited the feeder with the odor they had experienced in their nest (chi (2)-tests; p < 0.05). By contrast, the bees showed no preference for one of two feeders when they were either baited with the same odor (linalool) or contained no odor. Our results clearly show that naïve workers of S. pectoralis can learn the odor of a food source during the recruitment process from the nest atmosphere and that their subsequent food search in the field is influenced by the learned odor.

Preparación de aatalizadores de hierro y cobalto soportados en aerogeles de carbono / Preparation f irron and cobalt catalysts supported on carbon aerogels / Preparaão de cattalizadores de ferro e cobalto suportados em aerogeles de carbono

Se prepararon catalizadores de hierro y cobalto, soportados en aerogeles de carbono (AGC), por los métodos de humedad incipiente, intercambio catiónico y adición de una sal del metal a la mezcla precursora de los aerogeles. La caracterización de los catalizadores se realizó por adsorción de N2 a 77 K, descomposición con temperatura programada (DTP) y difracción de rayos X (DRX). Se encontró que los catalizadores preparados por humedad incipiente e intercambio catiónico tienen una textura microporosa, mientras que los preparados por adición de la sal del metal a la mezcla inicial son mesoporosos. Los resultados de DTP muestran que la química superficial del aerogel está influida por el método de preparación y la naturaleza química del metal, y los análisis de DRX pusieron en evidencia que la matriz carbonosa de los aerogeles tiene un carácter reductor capaz de carburizar o reducir el metal incorporado.

Iron and cobalt catalysts supported on carbon aerogels (CA) were prepared by incipient wetness, cationic interchange and the addition of a metal salt to the precursory mixture of the aerogels. The catalysts were characterized by adsorption of N2 at 77 K, temperature programmed descomposition analysis (TPD), and X-ray diffraction (XRD). The results show that the catalysts prepared by incipient wetness and cationic interchange have a microporous texture, whereas the prepared by addition of a metal salt to the initial mixture are mesoporous. TPD results show that the surface chemistry of the aerogels is influenced by the preparation method and the chemical nature of the metal. XRD analyses reveal that the reducing character of the aerogels carbonaceous matrix is able to carburize and/or to reduce the built-in metal.

Foram preparados catalisadores de ferro e cobalto suportados nos aerogeles de carbono (AGC) pelos métodos de umidade incipiente, intercâmbio catiônico e adição de um sal do metal à mistura precursora dos aerogeles. Os catalisadores foram caracterizados por adsorção do N2 em 77 K, desorção a temperatura programada (DTP), e difração de raios X (DRX). Os resultados mostram que os catalisadores preparados por umidade incipiente e intercâmbio catiônico têm uma textura mi-croporosa, enquanto que os preparados pela adição de um sal de metal à mistura inicial são mesoporosos. Os resultados de DTP mostram que a química de superfície dos aerogeles está influenciada pelo método da impregnação e pela natureza química do metal. As análises de DRX revelam que a matriz carbonosa dos aerogeles tem um caráter reductor capaz de carburar e/ou reduzir o metal incorporado.