Nesting dynamic and sex allocation of the oil-collecting bee Centris (Heterocentris) analis (Fabricius, 1804) (Apidae: Centridini)

Sensitivity of the Neotropical Solitary Bee Centris analis F. (Hymenoptera, Apidae) to the Reference Insecticide Dimethoate for Pesticide Risk Assessment

Currently, only Apis mellifera is used in environmental regulation to evaluate the hazard of pesticides to pollinators. The low representativeness of pollinators and bee diversity in this approach may result in insufficient protection for the wild species. This scenario is intensified in tropical environments, where little is known about the effects of pesticides on solitary bees. We aimed to calculate the medium lethal dose (LD50) and medium lethal concentration (LC50) of the insecticide dimethoate in the Neotropical solitary bee Centris analis, a cavity-nesting, oil-collecting bee distributed from Brazil to Mexico. Males and females of C. analis were exposed orally to dimethoate for 48 h under laboratory conditions. Lethality was assessed every 24 h until 144 h after the beginning of the test. After the LD50 calculation, we compared the value with available LD50 values in the literature of other bee species using the species sensitivity distribution curve. In 48 h of exposure, males showed an LD50 value 1.33 times lower than females (32.78 and 43.84 ng active ingredient/bee, respectively). Centris analis was more sensitive to dimethoate than the model species A. mellifera and the solitary bee from temperate zones, Osmia lignaria. However, on a body weight basis, C. analis and A. mellifera had similar LD50 values. Ours is the first study that calculated an LD50 for a Neotropical solitary bee. Besides, the results are of crucial importance for a better understanding of the effects of pesticides on the tropical bee fauna and will help to improve the risk assessment of pesticides to bees under tropical conditions, giving attention to wild species, which are commonly neglected. Environ Toxicol Chem 2023;42:2758-2767. © 2023 SETAC.

Sublethal behavioral impacts of resource limitation and insecticide exposure reinforce negative fitness outcomes for a solitary bee

Contemporary landscapes present numerous challenges for bees and other beneficial insects that play critical functional roles in natural ecosystems and agriculture. Pesticides and the loss of food resources from flowering plants are two stressors known to act together to impair bee fitness. The impact of these stressors on key behaviors like foraging and nesting can limit pollination services and population persistence, making it critical to understand these sublethal effects. We investigated the effects of insecticide exposure and floral resource limitation on the foraging and nesting behavior of the solitary blue orchard bee, Osmia lignaria. Bees in field cages foraged on wildflowers at high or low densities, some treated with the common insecticide, imidacloprid, in a fully crossed design. Both stressors influenced behavior, but they had differential impacts. Bees with limited food resources made fewer, but longer foraging trips and misidentified their nests more often. Insecticide exposure reduced bee foraging activity. Additionally, insecticides interacted with bee age to influence antagonistic behavior among neighboring females, such that insecticide-exposed bees were less antagonistic with age. Our findings point towards mechanisms underlying effects on populations and ecosystem function and reinforce the importance of studying multiple drivers to understand the consequences of anthropogenic change.

Management of Centris analis (Hymenoptera: Apidae): Investigating the Ideal Dimensions of Trap Nests for Use in Crop Pollination

Centris analis (Fabricius, 1804) is a solitary, cavity-nesting bee that is often recorded in studies through the use of trap nests. This species is considered to be a good candidate as a manageable pollinator for some orchards. However, further studies are still needed to optimize its rational rearing. This study sought to analyze female preference for different lengths and diameters of trap nests, as well as the effects of nest dimensions on the number of constructed cells, mortality rates, parasitism rates, and sex ratio. We used compact trap nests comprised of tubes with internal diameters ranging from 0.6 to 0.8 cm, and lengths ranging from 8 to 12 cm. The results showed that females preferred the narrowest (0.6 and 0.7 cm) and two of the longest cavities (10 and 12 cm). The greatest number of cells built was observed in the most used lengths. The lengths that were tested did not affect the mortality or parasitism rates or the sex ratio. Based on our findings concerning the dimensions examined, we recommend using the narrowest and longest cavities. The combined analyses of the tested parameters (diameter and length) demonstrated new data that can help improve the rearing and maintenance techniques applied to C. analis populations.