Lower pollen nutritional quality delays nest building and egg laying in Bombus terrestris audax micro-colonies leading to reduced biomass gain

Extreme heat exposure of host plants indirectly reduces solitary bee fecundity and survival

Extreme heat poses a major threat to plants and pollinators, yet the indirect consequences of heat stress are not well understood, particularly for native solitary bees. To determine how brief exposure of extreme heat to flowering plants affects bee behaviour, fecundity, development and survival we conducted a no-choice field cage experiment in which Osmia lignaria were provided blueberry (Vaccinium corymbosum), phacelia (Phacelia tanacetifolia) and white clover (Trifolium repens) that had been previously exposed to either extreme heat (37.5°C) or normal temperatures (25°C) for 4 h during early bloom. Despite a similar number of open flowers and floral visitation frequency between the two treatments, female bees provided with heat-stressed plants laid approximately 70% fewer eggs than females provided with non-stressed plants. Their progeny received similar quantities of pollen provisions between the two treatments, yet larvae consuming pollen from heat-stressed plants had significantly lower survival as larvae and adults. We also observed trends for delayed emergence and reduced adult longevity when larvae consumed heat-stressed pollen. This study is the first to document how short, field-realistic bursts of extreme heat exposure to flowering host plants can indirectly affect bee pollinators and their offspring, with important implications for crop pollination and native bee populations.

Colony performance of three native bumblebee species from South China and association with their gut microbiome

Bumblebees play an important ecological economic role as pollinators in nature and agriculture. For reasons of biosecurity, many countries promote the cultivation of native bumblebee species for crop pollination instead of importing "alien" species. In South China, a few bumblebee species are considered useful in this way, particularly, Bombus atripes, Bombus bicoloratus and Bombus breviceps. However, whether they are suitable for artificial rearing and forming healthy colonies for pollination, remains unknown. In this project, queens from the 3 native species of Guizhou Province were collected and colonies were started under standardized conditions. The colonies were scored based on 19 parameters, including the stage of colony development, number and weight of offspring, and diet consumed. The data revealed that B. breviceps had the best performance, produced more workers and consumed the smallest diet. Next, we performed 16S rDNA sequencing of the bacterial communities found in the guts of offspring workers, and then a correlation analysis between colony performance and gut bacteria was conducted. Here, B. breviceps showed the highest diversity in gut bacterial composition, dominated by the bacteria Gilliamella, Snodgrassella, Enterobacter, and Lactobacillus Firm5. The higher the abundance of Snodgrassella, the better the performance of the colony in the foundation stage, and later Lactobacillus Firm5, Apibacter and Bifidobacterium were beneficial during the stages of rapid growth and colony decline. Although we do not understand all of the interactions yet, these correlations explain why B. breviceps demonstrated better colony performance. Our data provide valuable information for breeding local Bombus species and will contribute to developing strong colonies for crop pollination.

Comparison of Morphological Characteristics of Antennae and Antennal Sensilla among Four Species of Bumblebees (Hymenoptera: Apidae)

Bumblebees, as pollinators, play an important role in maintaining natural and agricultural ecosystems. Antennae with sensilla of bumblebees as social insects have essential effects in foraging, nest searching, courting, and mating, and are different in species and sexes. Previous studies on the morphology of antennae and sensilla in bumblebees have been limited to a few species and a single caste. To better understand how bumblebees detect and receive the chemical signal from nectariferous plants and foraging behavior, the morphology of antennae with sensilla, including the antennal length, and type, distribution, and number of antennal sensilla in four species, Bombus atripes, Bombus breviceps, Bombus flavescens, and Bombus terrestris was compared by scanning electron microscopy (SEM) herein. The total antennal length of queens are the longest and workers are the shortest in three castes, and in four species the longest of the total antennal length among three castes all are in B. flavescens, which is significantly longer than other species (p < 0.05) and the length of the scape in queens and workers are both longer than males, significantly different in queens (p < 0.05), and not significantly different in workers (p > 0.05), and the length of flagellums in females are not always shorter than males, of which the length of flagellms in queens of B. flavescens are significantly longer than males (p < 0.05), and the length of pedicel and all flagellomeres varies among species and castes. A total of 13 major types of sensilla in total were observed, including trichodea sensilla (TS A-E), placodea sensilla (PS A-B), basiconica sensilla (BaS), coeloconica sensilla (COS A-B), chaetic sensilla (CS A-B), and Böhm sensilla (BS), of which chaetic sensilla B (CS B), only observed in females of B. atripes, was firstly reported in Apidae. Moreover, the number of all sensilla was the most in males, the least was in workers, the number of sensilla varies within castes and species. Furthermore, the morphological characteristics of antennae and the potential functions of sensilla are discussed.

Higher Essential Amino Acid and Crude Protein Contents in Pollen Accelerate the Oviposition and Colony Foundation of Bombus breviceps (Hymenoptera: Apidae)

Pollen is an important source of nutrition for bumblebees to survive, reproduce, and raise their offspring. To explore the nutritional requirements for the egg laying and hatching of queenright Bombus breviceps colonies, camellia pollen, oilseed rape pollen, apricot pollen, and mixtures of two or three types of pollen in equal proportions were used to feed the queens in this study. The results showed that the camellia pollen with a higher essential amino acid content was superior to the pollen with a lower essential amino acid content in the initial egg-laying time (p < 0.05), egg number (p < 0.05), larval ejection (p < 0.01), time of first worker emergence (p < 0.05), and the average weight of workers in the first batch (p < 0.01). It took less time for colonies under the camellia pollen and camellia-oilseed rape-apricot pollen mix treatments, both with a higher crude protein content, to reach ten workers in the colony (p < 0.01). On the contrary, the queens fed apricot pollen never laid an egg, and larvae fed oilseed rape pollen were all ejected-both pollens with a lower essential amino acid content. The results emphasize that the diet should be rationally allocated to meet the nutritional needs of local bumblebees at various stages when guiding them to lay eggs, hatch, and develop a colony.

Supplementation in vitamin B3 counteracts the negative effects of tryptophan deficiencies in bumble bees

Increasing evidence highlights the importance of diet content in nine essential amino acids for bee physiological and behavioural performance. However, the 10th essential amino acid, tryptophan, has been overlooked as its experimental measurement requires a specific hydrolysis. Tryptophan is the precursor of serotonin and vitamin B3, which together modulate cognitive and metabolic functions in most animals. Here, we investigated how tryptophan deficiencies influence the behaviour and survival of bumble bees (Bombus terrestris). Tryptophan-deficient diets led to a moderate increase in food intake, aggressiveness and mortality compared with the control diet. Vitamin B3 supplementation in tryptophan-deficient diets tended to buffer these effects by significantly improving survival and reducing aggressiveness. Considering that the pollens of major crops and common plants, such as corn and dandelion, are deficient in tryptophan, these effects could have a strong impact on bumble bee populations and their pollination service. Our results suggest planting tryptophan and B3 rich species next to tryptophan-deficient crops could support wild bee populations.

Food preferences in a generalist pollen feeder: A nutritional strategy mainly driven by plant carbohydrates

Introduction

Animal nutritional strategies have been extensively studied in vertebrates, where generalism at the individual scale is the rule. In insect herbivores, the determinants of the nutritional strategy of individual-scale generalists remain poorly studied, and the focus has been placed mainly on the influence of plant defense. Moreover, the integration of a physiological dimension in such studies remains rare. Here, we investigated the determinants of the nutritional strategy of pre-diapausing pollen beetles, Brassicogethes aeneus, with a focus on the influence of macronutrients. Before their diapause, pollen beetles are known to feed from plants belonging to many different families. This raises three questions: (i) Is the generalism of pollen beetles a populational consequence of individuals specialized on different plant families? (ii) Do individuals feed at random on flowers available or do they have a particular nutritional strategy? and (iii) In case of non-random feeding choices, do pollen macronutrients explain this nutritional strategy?

Methods

To answer these questions, we used a series of laboratory experiments including feeding choice tests on flowers and artificial substrates, quantification of pollen nutrient content, quantification of the insect energetic budget, and performance experiments.

Results

We show that pollen beetles are generalist at the individual scale, and that clear and stable food preferences are established over a few hours in a multi-choice context. Pollen beetles prefer to feed on flowers with a carbohydrate-rich pollen, and this preference is adaptive since performance correlates positively with the plant carbohydrate content. This better performance may be explained by the fact that individuals feeding on carbohydrate-rich resources accumulate more glycogen and total energetic reserves.

Discussion

This study represents one of the few evidences of generalism at the individual scale in an herbivorous insect. It provides a better understanding of the nutritional strategy of a non-bee pollen feeder and shows the importance of carbohydrates in this strategy. It highlights the need to combine assessments of the plant macronutrient content and insect energetic budget in an adaptive framework to better understand the nutritional strategies of herbivores.

Sublethal doses of imidacloprid and pyraclostrobin impair fat body of solitary bee Tetrapedia diversipes (Klug, 1810)

Solitary bees present greater species diversity than social bees. However, they are less studied than managed bees, mainly regarding the harmful effects of pesticides present in agroecosystems commonly visited by them. This study aimed to evaluate the effect of residual doses of imidacloprid and pyraclostrobin, alone and in combination, on the fat body (a multifunctional organ) of the neotropical solitary bee Tetrapedia diversipes by means of morphological and histochemical evaluation of oenocytes and trophocytes. Males and females of newly-emerged adults were submitted to bioassays of acute topical exposure. Experimental groups were essayed: control (CTR), solvent control (ACT), imidacloprid (IMI, 0.0028 ng/μL), pyraclostrobin (PYR, 2.7 ng/μL) and imidacloprid + pyraclostrobin (I + P). The data demonstrated that the residual doses applied in T. diversipes adults are sublethal at 96 h. Both oenocytes and trophocytes cells responded to topical exposure to the pesticides, showing morphological changes. In the IMI group, the bee oenocytes showed the greatest proportion of vacuolization and altered nuclei. The pyraclostrobin exposure increased the intensity of PAS-positive labeling (glycogen) in trophocytes. This increase was also observed in the I + P group. Changes in energy reserve (glycogen) of trophocytes indicate a possible mobilization impairment of this neutral polysaccharide to the hemolymph, which can compromise the fitness of exposed individuals. Also, changes in oenocytes can compromise the detoxification function performed by the fat body. This is the first study to show sublethal effects in neotropical solitary bees and highlight the importance of studies with native bees.