a microspore fungal parasite; Nosema is known to be a major disease by beekeepers,
where infected colonies fail to thrive shortly after overwintering [59].
To further knowledge of fungicide exposure effects upon other pollinators
besides honey bees, a controlled experiment was conducted upon a native bumblebee species. Colonies were exposed over a month to flowers treated with fieldrelevant levels of a fungicide and then quantitatively assessed by number and
biomass of the three bee growth stages (larvae, pupae, adult). Exposed bumblebee
colonies were found to produce fewer adult workers bees and lower bee biomass,
including smaller and lighter queens, than control colonies. The number of worker
bumblebees was reduced from an average 43 bees in control cages to a mere 12 in
fungicide-treated cages.
While these effects were sublethal, reduced individual and colony health has
direct bearing on ability to resist variable environmental conditions and
stressors [60].
Fungicides have been typically believed to be safe for bees, but sublethal effects
observed in recent studies should be taken into consideration for future agricultural
control efforts, otherwise the long-term result may be trading fungicide advantages
for pollinator decline that can still lead to reduced crop production.
4.2.4 Herbicides
Herbicides are pesticides that target plants perceived to be weeds, or those plants that
compete against crops or preferred ornamentals in the same land space.
The herbicide market is projected to be worth nearly US$30 billion by 2019, with
glyphosate occupying the largest market segment [61]. Glyphosate is a broadspectrum herbicide used for weed control, which some may remember as the original
retail product Roundup. As of 2007, glyphosate was the most common herbicide
used in the US agriculture market and the second-most used herbicide in the home
garden market [62].
An experiment to study sublethal effects of this herbicide upon honey bees was
conducted using field-realistic doses of glyphosate, exposing the bees chronically or
acutely to the herbicide. In the groups chronically exposed to concentrations within
the range of recommended doses, a reduced sensitivity to sucrose and reduced
learning performance were found. Acute glyphosate exposure decreased learning
and short-term memory retention when compared against control groups. These
results implied that glyphosate at common concentrations found in standard spraying
can reduce sensitivity to nectar reward and impair associative learning in honey bees.
However, no effect on foraging-related behavior was found, which implies that
successful forager bees could become a source of constant inflow of nectar with
glyphosate traces that could then be distributed and stored in the colony, causing
long-term negative consequences on colony performance [63].
Another sublethal experiment revealed that honey bees that had been fed with a
glyphosate solution of a common concentration took a longer time to return home
and took more indirect flight paths than control bees or bees treated with lower
1 Understanding, Conservation, and Protection of Precious Natural Resources: Bees
23
where infected colonies fail to thrive shortly after overwintering [59].
To further knowledge of fungicide exposure effects upon other pollinators
besides honey bees, a controlled experiment was conducted upon a native bumblebee species. Colonies were exposed over a month to flowers treated with fieldrelevant levels of a fungicide and then quantitatively assessed by number and
biomass of the three bee growth stages (larvae, pupae, adult). Exposed bumblebee
colonies were found to produce fewer adult workers bees and lower bee biomass,
including smaller and lighter queens, than control colonies. The number of worker
bumblebees was reduced from an average 43 bees in control cages to a mere 12 in
fungicide-treated cages.
While these effects were sublethal, reduced individual and colony health has
direct bearing on ability to resist variable environmental conditions and
stressors [60].
Fungicides have been typically believed to be safe for bees, but sublethal effects
observed in recent studies should be taken into consideration for future agricultural
control efforts, otherwise the long-term result may be trading fungicide advantages
for pollinator decline that can still lead to reduced crop production.
4.2.4 Herbicides
Herbicides are pesticides that target plants perceived to be weeds, or those plants that
compete against crops or preferred ornamentals in the same land space.
The herbicide market is projected to be worth nearly US$30 billion by 2019, with
glyphosate occupying the largest market segment [61]. Glyphosate is a broadspectrum herbicide used for weed control, which some may remember as the original
retail product Roundup. As of 2007, glyphosate was the most common herbicide
used in the US agriculture market and the second-most used herbicide in the home
garden market [62].
An experiment to study sublethal effects of this herbicide upon honey bees was
conducted using field-realistic doses of glyphosate, exposing the bees chronically or
acutely to the herbicide. In the groups chronically exposed to concentrations within
the range of recommended doses, a reduced sensitivity to sucrose and reduced
learning performance were found. Acute glyphosate exposure decreased learning
and short-term memory retention when compared against control groups. These
results implied that glyphosate at common concentrations found in standard spraying
can reduce sensitivity to nectar reward and impair associative learning in honey bees.
However, no effect on foraging-related behavior was found, which implies that
successful forager bees could become a source of constant inflow of nectar with
glyphosate traces that could then be distributed and stored in the colony, causing
long-term negative consequences on colony performance [63].
Another sublethal experiment revealed that honey bees that had been fed with a
glyphosate solution of a common concentration took a longer time to return home
and took more indirect flight paths than control bees or bees treated with lower
1 Understanding, Conservation, and Protection of Precious Natural Resources: Bees
23