Biodiversity Protects Plant-Pollinator Phenological Synchrony from Climate Change

by Lia Metzger

Biodiversity has been linked to the protection and sustenance of ecosystems against the loss of individual species. Studies have found that climate change, a contributor to the loss of species, has caused significant changes in phenology, mostly in species active in the spring. The biodiversity insurance hypothesis has never been expanded to include phenological synchrony as a possible buffer against the loss of individual species due to climate change. Bartomeus et al. (2013) investigated the phenological changes of wild bee species and of commercial apple crops over 46 years to find if bees and apples had phenological synchrony and if this was related to the richness of pollinator species. Using a contemporary data set, the authors picked pollinators that most frequently visited apple and tested for their phenological complimentarity. Bee and apple data were compared over time to find phenological mismatch and the rate of phenological change for different species with respect to apple bloom. Phenological synchrony was then tested against wild bee biodiversity. Phenological synchrony was found to increase with increasing biodiversity of the bee species and stabilize over time even though the rate of phenological shifting differed between species. Continue reading

Cholinergic Pesticides Cause Negative Neuronal Effects in Honeybees

by Lia Metzger

Recently, pesticides that target cholinergic neurotransmission have been found to aid in the decline of insect pollinators. In particular, neonicotinoids (nicotinic receptor agonists) and organophosphate miticides (acetylcholinesterase inhibitors) are commonly used and thus, frequently come in contact with honey bees. Palmer et al. (2013) investigated how these pesticides affect the neurophysiology of honey bees by using recordings from mushroom body Kenyon cells. Instead of studying the learning and behavior of honey bees that are exposed to neonicotinoids and organophosphate miticides, the authors used whole-cell recordings from Kenyon cells in honey bee brains, and assessed the native connectivity and nAChR expression in KCs. They found that the two neonicotinoids, imidacloprid and clothianidin, and coumaphos oxon decreased the KC excitability by inhibiting action-potential firing and reduced KC responsiveness to ACh. When the honey bee brains were exposed to both neonicotinoids and miticides as is common in large crops, the combined exposure added to the effects on KC excitability and nAChR-mediated responses. The honey bees are usually exposed to much higher concentrations of cholinergic pesticides, which indicates that the negative effects on the neurophysiological responses of the mushroom body cells would be heightened in reality. Continue reading

Native Bee Species Disappearing, but Pollination Still OK So Far

by Lia Metzger

Over the past decade, bee populations have been decreasing significantly in North America. While many studies have investigated why there has been a decrease, few have researched the long-term change in species richness, in interaction between pollinators and plants, or in function of pollinators. Burkle et al. (2013) studied the loss of species of plant-pollinators, focusing on bees, and forbs, their interactions, and the function of bees over 120 years. Using data collected by Charles Robertson from 1888 to 1891 and data collected in 2009 and 2010 from natural habitats near Carlinville, Illinois, USA, the authors quantified and analyzed the changes in the network structure, bee diversity, and phenologies of bees and forbs. Additionally, data from 1971 to 1972 in Carlinville were used to investigate the changes in bee diversity, quality of pollination, and bee visitation rates to Claytonica virginica. Over 120 years, a substantial number of species interactions and bee species were lost and bee phenologies shifted significantly. The authors found that richness of bee species and the rate of visitation to C. virginica declined dramatically in the last 40 years and that there was a loss of redundancy in bee species. Continue reading

Mass-flowering Crops Positively Affect Wild Bee Brood Numbers


by Lia Metzger

The expansion of mass-flowering crops has been linked to the loss of biodiversity of farmlands because they escape into natural and semi-natural habitats. However, these mass-flowering crops have a higher density of flowers than non-crop species, and thus produce more food resources with more access to nectar and pollen, so they may enhance the abundance of wild foraging bees. Holzschuh et al. (2013) investigated how oilseed rape, a mass-flowering crop, affects the abundance of the solitary and polylectic Red Mason Bee Osmia bicornis, a generalist bee species that nests in both natural and semi-natural habitats. Using data from 67 sites in Germany, they compared the abundance of Osmia bicornic in grasslands adjacent to oilseed rape fields and isolated from oilseed rape fields and vice versa. Artificial nests were assessed for Continue reading

Honeybees Exposed to Acetylcholinesterase Inhibitors Exhibit Impaired Motor Function

Stress from parasites, pathogens, and pesticides have been contributing to the global decline of populations of honeybees and many pollinators for the past two decades. Specifically, the use of pesticides that affect neuromuscular functioning and kill parasitic mites have caused the accumulation of acaricides, or mite pesticides, in the wax combs of bees’ hives. To investigate the possibility of this accumulation contributing to the decline of bee populations, Williamson et al. (2013) studied the effects of prolonged exposure to pesticides that inhibit acetylcholinesterase (AChE) on the physiology and behavior of bees. Adult worker bees were fed sub-lethal concentrations of four AChE inhibitors in sucrose solutions and then were observed for walking, stopped, grooming, and upside down behavior. After the behavioral study, the bees were dissected to confirm that the four compounds they assayed or their metabolites were responsible for the change in behavior by testing for transcript expression levels of two honeybee AChE inhibitors and through biochemical assays. All AChE inhibitors caused increased grooming behavior, but coumaphos in particular caused more grooming and symptoms of sickness as the concentration increased. The authors found that the effects of pesticides that inhibit AChE on the motor functioning of bees could reduce their survival and contribute to the decline of bee colonies. —Lia Metzger

                  Williamson, S.M., Moffat, C., Gomerall, M.A., Saranzewa, N., Connolly, C.N., Wright, G.A., 2013. Exposure to acetylcholinesterase inhibitors alters the physiology and motor function of honeybees. Frontiers in physiology 4.

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Mortality of Bees Exposed to Neonicotinoid Clouds around Corn Drilling Machines

Several studies have linked the spring sowing of maize seed to the lethal poisoning of bees and have found that worker bees coming in contact with the exhaust from the drilling machines became contaminated with insecticides and rapidly died. In previous studies with still caged bees and free bees, the correlation between the particles from the drilling machines and the poisoning of bees was not clear. To specify how close the bees have to be to be poisoned, Girolami et al. incorporated the distance from the drilling machines, the type of drilling machine, and the number of times the bees had to pass by the machines before they were killed.  The authors also ran the drilling machines with 200 g of Talc added to the seed containing hoppers during three trials in order to capture the extent of the exhaust cloud. After being exposed to high humidity, bees that were moved alongside the machines were lethally poisoned. No significant difference in bee mortalities was found between modified and unmodified corn drillers. The exhaust cloud extended approximately 20 feet around the drilling machine. —Lia Metzger

                  Girolami, V., Marzaro, M., Vivan, L. Mazzon, L., Giorio, C., Marton, D., Tapparo, A., 2013. Aerial powdering of bees inside mobile cages and the extent of neonicotinoid cloud surrounding corn drillers. Journal of Applied Entomology 137, 35-44.

                  In order to mimic the movement of foraging bees, ten cages, each containing one bee, were attached to a four meter aluminum bar, held 2.5 meters high, and walked by the side of the drilling machine. In some trials, the bees were held at 2, 4, and 6 meters from the still drilling machine, and then placed in either lab humidity or high humidity to test for the lethality of the neonicotinoid cloud. In addition, the bees were walked 1—5 meters or 5—9 meters from the right side of the mobile drilling machine and parallel to its movement for 30 seconds. Then the caged bees made a U-turn around the drilling machine and were walked along the left side, reflecting the movement of bees making a round-trip around the sowing field. To test for the exposure to insecticides in the exhaust, the bees underwent chemical analysis and were only exposed on one side of the drilling machine in the same way. This allowed for the authors to differentiate the levels of contaminants on each side of the drilling machines and the lethality of the exhaust at varying distances from the machines.
                  The authors found bees that had been exposed at 2, 4, and 6 meters by passing by the drilling machine rapidly died from clothianidin if they were placed in high humidity afterward. Mapping the deaths of the bees between 2 to 12 meters on the right side and up to 8 meters on the left side of the drilling machine, the extent of the neonicotinoid cloud was measured as approximately 10 meters on each side and 2 meters high. Possible change in the shape of the cloud was considered, but the proposed elliptical shape formed by wind and movement would not reduce the extent of the cloud. Even though the modified drilling machines direct their exhaust at the ground instead of at a 45° anglethere was no significant difference between the mortality of bees passing by modified or unmodified drilling machines. Machines sowing seeds that were coated in fungicide did not cause significant poisoning to the bees, but the coatings clothianidin, imidacloprid, and thiamethoxam all caused more than 50 % of the bees that passed by to die. Furthermore, the chemical analysis revealed that all of the bees contained very large quantities of insecticide, with the highest levels of insecticide in bees passing by at 1 meter and decreasing in insecticide levels at greater distances.

                  The poisonous exhaust can account for the mass deaths of bees in sowing season from corn drillers that are used during this time. Although there were differences in levels of poisons in the bees, the majority of the bees that passed by the drilling machines in the way that bees normally forage were killed. The authors showed that, even with modified drillers or insecticides not affecting the bees directly, the airborne contaminants are extremely lethal to bees.

Wild Insect Pollinators Enhance Crop Production Irrespective of Honeybees

Recently, the abundance and variety of wild insect pollinators have significantly decreased globally. This poses a threat to the ability of crops to produce enough food for the rapidly growing human population. With fewer wild insect pollinators, crops that rely on animals to spread their pollen will be limited in their ability to reproduce and thus will likely produce a smaller crop yield. European honeybees are often used to assist the pollination of crops, but the research of Garibaldi et al. (2013) suggests that this strategy may not be the most effective for food production. Garibaldi et al. investigated the amount of pollen the wild insect pollinators and the honeybees deposited on flowers and the mean fruit set of crops around the world to determine if wild insect pollinators and honeybees enhance pollination of flowers and increase the fruit set of crops. The results imply that, while both wild insect pollinators and honeybees increase pollination of crops, the wild insect pollinators pollinate crops more effectively than honeybees and honeybees are not a substitute for wild insect pollinators, but a supplement. In lieu of this, the intentional management of a combination of wild insect pollinators and honeybees may improve global crop yields. —Lia Metzger
                  Garibaldi, L.A., Steffan-Dewenter, I. Winfree, R., Aizen, M.A., Bommarco, R., Cunningham, S.A., Kremen, C., Carvalheiro, L.G., Harder, L.D., Afik, O., 2013. Wild pollinators enhance fruit set of crops regardless of honey bee abundance. Science 339, 1608-1611.

                  Garibaldi et al. studied the pollination and fruit sets of 600 fields in 41 crop systems in 19 countries in all regions of the world except Antarctica. The authors studied pollinator-dependent crops of annual and perennial nuts, seeds, and fruit crops to account for a wide variety of crop types. Crops varied in management practices, landscape styles, abiotic and biotic factors, and native and non-native ranges. Many factors could affect the trends for pollinators, so Garibaldi et al. standardized the crop systems from which they collected data. Each of the crop systems consisted of the same species but from at least three spatially separated fields with similar management. This reduced the possibility of random factors significantly affecting the results.
                  The authors created strict criteria to consistently count the visitations by an assemblage of wild insects to crop flowers in the sampled fields.  Pollen deposition was calculated as the number of pollen grains per stigma and fruit set was determined by the percentage of flowers setting mature fruits or seeds. In order to analyze whether the wild insect pollinators and the honeybees enhanced the crop yield, the pollen deposition for each insect species was compared with the resulting mean fruit set of each field. The variation in space and time of pollen deposition and fruit set was accounted for as the coefficient of variation (CV). Descriptive and explanatory graphs with CV for each species of crop and assemblage of wild insect pollinators and honeybees were included.
                  The study found that crops with more visits from wild insects and honeybees had more pollen on their flowers than crops with fewer visits. Honeybees were responsible for more pollination than wild insects by 74%. This did not match the prediction that crops pollinated by honeybees would have higher mean fruit sets. On the contrary, for all crop systems visited by wild insects, fruit set increased significantly, whereas fruit set only increased in 14% of the crop systems with only honeybee visitation. Disparate visitation and unequal abundance were shown not to be factors that could have affected this trend.
                  Increased pollinator visitation, however, did not result in as significant an increase in fruit set as the pollen disposition on flowers. The authors considered pollen excess, seed abortion, and filtering of pollen as possible reasons for the visitations not always resulting in pollination. The results suggest that wild insects were more efficient pollinators than honey bees because the difference in pollen disposition and fruit sets was much wider for honeybees than for wild insects. In addition, fruit sets increased in crop systems with visitation by wild insects, whether honeybees visited frequently or not. In crops with both wild insects and honeybees, the fruit sets increased more than crops without honeybees. These results suggest that honeybees supplement the pollination of crops by wild insects but cannot replace it.

                  The increase in fruit sets with more visitations by wild insect assemblages and honeybees suggests that the integration of managed pollinators with wild pollinators could produce better crop yields. The authors found that wild insects more effectively pollinate crops while honeybees pollinate more with less results. Since there was no negative correlation between the two pollinators when they visited the same crops, integrating the pollinators would likely produce more crop yields. The consideration of wild insects as part of the management of crops could encourage diversity of animal pollinators and increase food production globally.