Fungicides on Blue Orchard Bees

The Ongoing Search for Fungicide Effects on Blue Orchard Bees

Male and female blue orchard bees.

Blue orchard bees were trained in a plastic cage with
a feeder modified from a syringe. Odors were applied
to a filter paper collar which was attached with hot glue.
The cage had a mesh lid that facilitated air flow
(not shown)

An individual bee entered the testing arena from a glass
vial attached to the side. The bee had 10 min to choose
between two water-filled feeders that were inserted
through opposite sides of the arena, equally distant
from the entrance. One feeder was scented with
geraniol, and the other was scented with PAA.

Blue orchard bees (Osmia lignaria), like other mason bees, nest in pre-existing cavities (e.g., hollow berry canes or holes left behind by wood boring beetles). Unlike honey bees and bumble bees, blue orchard bees are solitary, meaning that they do not live in a hive, and each female creates her own nests and lays eggs. They are one of about 900 species of bees that are native to Utah, most of which are solitary (Cane and Kervin, 2011).

Concern over declining populations of honey bees and other pollinators has led to increased use of blue orchard bees as a managed pollinator of tree fruits. As use of blue orchard bees has increased, so have reports that blue orchard bee nesting slows down, pauses, or ceases altogether following fungicide treatments. Derek Artz, a researcher at the USDA-ARS Bee Biology and Systematics Laboratory in Logan, Utah, recently observed the disruption of nesting behavior after fungicide sprays in field cages in California and soon will publish his findings. Previous research found only one of the five fungicides tested, captan, was lethal to blue orchard bees (Ladurner et al., 2005). However, despite lack of evidence for fungicides resulting in bee fatalities, the possibility remains that fungicides may cause other physiological and behavioral effects in blue orchard bees.

As part of an ongoing collaboration with Dr. Theresa Pitts-Singer (USDA-ARS), my lab has been determining if fungicides affect the ability of blue orchard bees (Osmia lignaria) to learn olfactory cues encountered during foraging. Olfactory cues are important for bee navigation, nest selection, foraging, and a variety of other bee activities. If fungicides disrupt blue orchard bees’ ability to learn or remember olfactory cues that they encounter during normal activities, bees may become confused and disoriented, possibly hindering their ability to create and find a nest, or find food. If the bees are not successful in these activities, they are also not going to be successfully pollinating the crops that we depend on for food.

The simple experiment is testing the fungicides Rally, Rubigan, Procure, and Pristine by training bees to associate a particular odor with a sugar reward. We assume that they will have learned to choose the odor that was always associated with sugar. If a fungicide affects blue orchard bee learning, it is expected that fungicide-fed bees will not choose the sugar-associated odor as often as bees that were never given that fungicide.

Proportion of trained female and male fungicide-fed and control blue orchard bees that, when given a choice between two water-filled scented feeders , chose the odor that was previously associated with sugar. An odor pair designation of ‘gp’ indicates that geraniol was associated with the sugar-filled feeder and PAA was associated with the water-filled feeder. An odor pair designation of ‘pg’ indicates that PAA was associated with the sugar-filled feeder and geraniol was associated with the water-filled feeder. No fungicide-fed group was significantly different from its corresponding control group.

Proportion of trained female and male fungicide-fed and control blue orchard bees that, when given a choice between two water-filled scented feeders , chose the odor that was previously associated with sugar. An odor pair designation of ‘gp’ indicates that geraniol was associated with the sugar-filled feeder and PAA was associated with the water-filled feeder. An odor pair designation of ‘pg’ indicates that PAA was associated with the sugar-filled feeder and geraniol was associated with the water-filled feeder. No fungicide-fed group was significantly different from its corresponding control group.

Upon emerging from their cocoons, bees are fed sugar water laced with a known amount of one of the fungicides for a full day. The feeder containing the sugar water is scented with either geraniol or phenylacetaldehyde (PAA), both of which are components of common floral aromas. On day two, they are fed water that contains fungicide, but not sugar, from a feeder scented with the odor that they didn’t experience on day one. The swapping of the scented sugar-fungicide feeder and scented water-fungicide feeder occurs over two more days, for a total of four days of exposure to the odors and the fungicide. On the fifth day, each bee is placed in a testing arena and allowed to choose between the sugar-associated odor and the water-associated odor. Their choices are then compared to the choices of a set of bees that went through the exact same procedure, but were never fed a fungicide.

In spring of 2011, a total of 380 fungicide-fed blue orchard bees and 449 bees not fed fungicides, both males and females, were tested in this manner. Although a small proportion of fungicide-fed bees did seem less likely to choose between the two scents than bees that were not fed fungicides, thus far there has not been significant evidence that fungicide ingestion affects bees’ ability to learn the odors. This is important to growers and others who wish to combat powdery mildew and other fungal diseases without decreasing pollinator efficiency and vitality.

This research is ongoing. Additional bees will be tested for learning effects in spring of 2012, and the effects of fungicides on bee memory will also be tested. Because fungicides are usually used with adjuvants such as stickers or spreaders, and because the effects of adjuvants on bees have not been rigorously tested, an experiment testing the synergistic effect of fungicide/adjuvant mixtures on blue orchard bee learning and memory is also being initiated in spring 2012.

-Cory Stanley, USU CAPS Coordinator

References:

Cane, J. H., and L. Kervin. 2011. Gardening for native bees in Utah and beyond. Utah State University Extension and Utah Plant Pest Diagnostic Laboratory, Pub. ENT-133-09.

Ladurner, E., J. Bosch, W. P. Kemp, and S. Maini. 2005. Assessing delayed and acute toxicity of five formulated fungicides to Osmia lignaria Say and Apis mellifera. Apidologie. 36:449-460.