Welcome to the second module examining the causes of honey bee declines, on
pesticides. Make sure to take the take the previous quizzes while the information
is still fresh in your minds!
By the end of this module, you will have an
understanding of how neonicotinoid
insecticides affect honey bees,  understand
the tradeoff between pest control and
pollinator health, and have a detailed
understanding of an integrated Pest and
Pollinator Management framework and how
to apply this in a home garden.
In the previous lecture, I discussed the role
pathogens and parasites of honey bees play in declines of bees. This time, I
will discuss the impacts of pesticides and other agricultural practices, which
are often inextricably linked with regards to the impacts
they have on pollinator declines.
For as long as people have been growing food, they’ve
had issues with pest insects. Some of the oldest Chinese documents pertaining to
agriculture describe the use of arsenic to combat rice pests. As cities grew
and the demands for food became greater, so did the need for better insecticidal
agents. This figure gives a relative timeline of when many of the pesticides
still in use today first hit the markets. The chemistries of some products were
known for over 50 years before their insecticidal properties were recognized.
For example, DDT, a chlorinated hydrocarbon, was first synthesized in the
1870s, though the insecticidal properties weren’t recognized until 1939 when it
was used to fight typhus and malaria during World War II. It was the era just
after World War II when many new products were synthesized and marketed,
which also coincides with the Baby Boom and the large scale mechanization
of agriculture in the US and Europe. Notice the colors of the boxes –
each insecticide has what is described as a mode of action, or specific aspect
of the insect’s physiology that is targeted. Though chlorinated hydrocarbons
and pyrethroids are different classes of insecticides separate by about 20
years of research and development, they have the same mode of action, which is
to disrupt sodium channels in insects. The same is true for organophosphates
and carbamates, which are acetylcholinesterase inhibitors. This is
important, because it means that once an insect develops resistance to one of
these chemicals, it will have cross-resistance to others within the same
class. In spite of documented cases of increasing resistance of harmful insect
pests, it was over 30 years before a new class of insecticides was developed:
the neonicotinoids. Plant incorporated pesticides followed soon after, but given
the recent narrative surrounding the effects of neonicotinoids on honey bees
specifically, we’ll focus on this group as a case study.
When it comes to naming
pesticides, it can get a bit confusing. Every pesticide has three names: the
chemical name, the common name for that chemical, and the trade name. Your guess
is as good as mine for pronouncing those chemical names. When you hear the term
“neonicotinoid,” it refers to a class of seven different pesticides, whose common
names are listed in the middle (imidacloprid, thiamethoxam,
clothianidin, acetamiprid, thiacloprid, dinotefuran, and nitenpyram), and the
trade name through which they are most often identified. But when you purchase a
pesticide, either at a garden supply store or to apply on a farm,
you’re probably searching for products based on their trade name,
which is how they are marketed to the general public. Another example is the
weed killer glyphosate, which is marketed under the trade name Round Up. Currently,
there are over 500 neonicotinoid containing products that are registered
for use in 150 crops, ornamentals, landscape, and veterinary medicine
applications in the United States, though they’re not all currently registered for use in Hawaii.
The neonicotinoid insecticides, or neonics
for short, activate the nicotinergic acetylcholinesterase receptors in the
insects’ nervous system. Don’t stress too much about the big words. Basically once
once exposed, the insect’s nervous systems fires continuously causing tremors, paralysis,
and eventually death. Sometimes you may see a bee or wasp flying in a fast
circle near the ground. This disruption to orientation could be indicative of
exposure to a neonic. These insecticides were developed to be
systemic, meaning the insecticide doesn’t sit on the outside of the plant leaves
but rather is taken up and circulated inside the plant. This makes them
particularly effective against historically difficult to control pests,
such as piercing and sucking insects like aphids as well as some leaf chewing
insects. However, being systemic, they reach parts
of the plant other than the leaves, and can actually concentrate in the pollen
just consumed by beneficial insects.
The first majorly publicized die off of
non-target insects as a result of neonic exposure was of bumble bees in
Wilsonville Oregon. In June of 2013, ironically during national pollinator
week, over 50,000 bumble bees were found dead in a Target parking lot after
foraging on linden trees that had been treated with dinotefuran, which had been
applied to 55 trees to control aphids whose
honey dew had been dripping on to cars. This caused a quick public backlash, and
this incident started a broader national discussion on the safety of neonics to
pollinators in general. This die off occurred because the product had been
applied during bloom, and after a review period, and to exercise an abundance of
caution, the Oregon Department of Agriculture banned the use of products
containing dinotefuran, imidacloprid, thiamethoxam, and clothianidin
on linden trees in 2015. This may seem like a victory for the bees, but keep in mind,
the pests are still attacking the linden trees, and applicators now have to
use older products that may not be as effective on those pests.
Since that recorded event, a lot of research money has been spent worldwide to determine
the full extent of impacts to pollinators, particularly bees. I
too jumped on that band wagon. To date, over 1,100 scientific
studies have been published evaluating the effects of neonics
on bees. My own research in South Dakota, an agricultural landscape dominated by
prophylactically treated corn, found that conservation strips intended to boost
pollinator habitat that has been planted near corn fields actually took
up the pesticide from the adjacent farmland. In this case, I was measuring
the concentration of clothianidin in bee bread, or field collected pollen
that had been stored by the honey bees, nectar from the conservation strip
plants, and from honey inside the hive. I found that flowers near organic corn
had significantly less clothianidin in their pollen than flowers planted near
conventionally treated corn fields, though the pesticide was present
regardless of whether a farm used it or not, indicating widespread landscape
contamination. While the amount of clothianidin I recovered in nectar
was really low, shown by the dotted line on the right graph, it was much higher in
the honey. This is actually what we would expect given the dehydration that
occurs when converting nectar to honey. But this is concerning however because it
indicates that even after nectar is converted to honey, clothianidin
does not break down inside the hive. While problematic get face value, keep in
mind that the dose makes the poison, and these pesticide concentrations are
too low to have any affects on humans. Even for the bees, with the
concentrations I found, a single honey bee would have to consume 530
microliters of honey, or 17 stomachs full
in one sitting in order to experience a
a lethal toxic effect. Or they would have to consume the equivalent of 10 pollen
balls in one sitting to experience a toxic effect. So, though neonicotinoids
were detected in pollen and honey, the concentrations were not high enough to
kill the bees outright. However, I did find a significant negative effect of
these concentrations on honey bee physiology, indicating a strong
likelihood of sublethal effects. This implies that prophylactic treatments,
or using a pesticide whether you need it or not, can have significant sublethal
impacts on honey bees, which could then make them more susceptible to secondary
stressors, like pathogens or poor nutrition.
As a follow up to this study, I
wanted to see how periods of starvation resulting from low pollen inputs while
honey bees were developing as larvae would ultimately affect adult
susceptibility to clothianidin exposure. For this, I established an
apiary where half of the colonies had pollen traps restricting the flow of
pollen, and the other half were supplemented with
that pollen in addition to what they were already collecting. I maintained
these pollen deprived and supplemented treatments for a week until a cohort of
larvae reached pupation. I emerged those as adults in the lab, and then exposed them
to clothianidin at field realistic exposures that I determined from my
previous study. What I found was that when adult honey bees were reared in
pollen deprived conditions, they experienced greater mortality as a
result of exposure to sublethal concentrations of clothianidin, or
concentrations of 10 and 40 ppb. In contrast, when their colony
had access to an excess of pollen, these same sublethal concentrations had no
effect on adult bee mortality. This highlights the importance of
nutrition in mitigating the effects of other stressors in the environment
that honey bees may be exposed to, such as pesticides. It also demonstrates that the
full impacts of neonicotinoids will be dependent on factors other than the
pesticide itself, and that alternative steps can be taken to mitigate these
effects before needing to ban a pesticide outright.
Much of what we know now regarding neonic impacts
to bees was information generated well after
these pesticides were registered. But still, if they are so harmful to
beneficial insects like pollinators, why bother with them at all? It’s always a
balance, because there are benefits to these insecticides. When they were first
introduced, they replaced a number of even more toxic compounds to which pests
had developed resistance. The nature of how they work by being systemic, often
coating seeds before they’re planted, means they are really easy to use.
Since crops take up the pesticide when they’re still young, it confers
protection against early season pests, which can often be the most damaging
for seedling crops. As I mentioned before, they are effective against insect pests
that are otherwise difficult to control, and are really effective when they’re
necessary. They’re also less toxic to mammals in
comparison to older products. Unfortunately, their use is now largely
prophylactic, particularly in parts of the country where row crops like corn
and soybeans are grown. This leads to large amounts of pesticide in the
environment that isn’t always necessary. And that is costly to farmers. This means
they’re widespread in the landscape and thus can be taken up by nontarget
vegetation. They are toxic against beneficial insects, and newer evidence
suggests they may not be as safe as first thought. Further, their track record
for increasing yields is a bit spotty. In a Center for Food Safety study, an
analysis of all published studies found a negative economic return when neonics
were applied to wheat, no positive benefit to yield in corn, dry beans, and
canola, and a limited effect on yield with inconsistent protection in soybeans.
This certainly raises questions about whether they are even necessary if yield
or profits don’t benefit from their use.
Even with demonstrated positives and negatives of this particular class of
insecticides, I want to point out that the neonicotinoids have become a bit of a
scape goat for what are really larger issues with regards to unnecessary or
prophylactic use of pesticides in agricultural areas of all pesticide
types, as well as in home gardens. These replaced even more ecologically harmful
chemicals when they were first introduced in the 1990s, and there are
circumstances in which their use is warranted, but it is when they are used
prophylactically that substantial environmental problems are likely to
arise. Never the less, environmental groups have been successful
in pushing to ban this group of insecticides because of the harm they
cause pollinators. In response to declining honey bee populations in Europe,
the European Union banned neonics in flowering crops in 2013, and recently
expanded that ban for use on all field crops. This has been controversial,
because growers of certain crops, like sugar beets, now have no sustainable
alternatives for pest control. Similar bills have been introduced in the United
States, but have not had the support to move forward in the legislature at the
national level. However, just this year in Hawaii,
senate bill 445 was introduced, which would ban the use of neonicotinoids
in the state without a permit from the
Hawaii Department of Agriculture,
effective in June of 2020. Keep in mind that it’s always a balancing act – there
will always be pests, and pesticides will be needed to combat those in some
circumstances. Even with negative impacts to pollinators, farmers will balance the
economics of controlling their pest issues with maintaining healthy
pollinator populations. Fortunately, there are integrated strategies anyone can
adopt to minimize chemical use and nontarget impacts to beneficial organisms.
Integrated pest management, or IPM, is defined as using a combination of
conventional and ecologically-based pest control strategies, based on science, to
minimize environmental impacts while maximizing crop yields. This definition
is agriculture centric, but IPM can be applied to a number of circumstances, for
example controlling pests in your home. There are four major categories of pest
control strategies that fall under this pest control paradigm: biological,
cultural, physical, and chemical control.
A typical IPM approach would look
something like this. Let’s pretend you’re growing vegetables in your back yard. The
The first step in your IPM approach is going to be pest prevention – you won’t have
issues with pests if you employ strategies from the onset that reduce
the likelihood of pest populations building up. Along with prevention is
monitoring. You should never treat for a pest unless you have confirmed that it
is present. Doing so contributes to ongoing issues with prophylactic
pesticide treatments. If in your monitoring you notice something, such as
a new insect or pathogen in your garden, identify it. Continue to monitor it to
see if it reaches economically damaging levels. If this happens,
identification is critical for choosing a least toxic intervention for that pest.
Evaluate after a treatment to determine whether the pest was reduced below
economic thresholds. If so, great! Go back to preventative measures to minimize the
likelihood of that pest becoming an issue again. If, on the other hand, least
toxic interventions prove unsuccessful, it is ok to choose a chemical control
method. Just like farming, home gardening is a lot of work, and you shouldn’t be
afraid to use all the tools available to control pests and not waste the effort
you have put in. But by using them in the context of an IPM framework, you will
hopefully be minimizing chemical inputs and lessening nontarget effects to
beneficial insects in the environment.
But what about bees and other pollinators?
How do they fit in to this paradigm? Well, the IPM paradigm that is
already largely understood by growers and home gardeners can be used to
facilitate the adoption of pollinator protection practices through an
integrated pest and pollinator management framework, or IPPM. This is
defined as the integration of alternative pollinators into
crop production systems and integrating the welfare of all pollinators into an IPM
protection program. By only slightly tweaking the practices we use for
biological, culture, physical, and chemical control, we can easily adapt
best management practices to also benefit pollinators. Let’s break down
what the control methods actually are, and how pollinator conservation can
be integrated into each one.
Biological control is using natural enemies, such as
predators, parasites, and parasitoids, to reduce pest populations. For the home
gardener, this means providing habitat for beneficial insects and other groups,
like birds and lizards, to help control pest insect populations. Classical
biocontrol is when natural enemies of an exotic origin are introduced permanently
to control a pest of the same exotic origin. This is a lengthy research
process that requires years of development and permits, so while there
are examples of success with this approach in Hawaii, you as a private
citizen won’t be able to do this on your own.
Augmentative biocontrol is when you mass rear and release natural enemies that are
already present within a region. Home gardeners could do this by encouraging
lady bugs in a certain area of their garden, then transplanting these voracious
predators to another area where pests are present. Conservation biocontrol
is when you actively enhance habitat for natural enemies, and is the strategy that
will have the greatest positive effect on pollinators. Many predators, like wasps
and lady bugs, also require carbohydrate and plant protein sources to survive,
which they obtain from flowers. By incorporating insectary plants in to the
landscape, you encourage not only the beneficial groups, but support healthy
local pollinator populations as well.
Cultural control refers to techniques and strategies that
can be applied by you that disrupt pest life cycles or remove extra habitat
where they may thrive or reproduce. For the most part, these are beneficial
practices for pollinators. The first of these is reducing or disrupting pest
habitat. This includes sanitation, or removing debris that pests may thrive in,
though this can also compromise soil health by removing substrate for
microbes, or exposing bare ground that could contribute to Phytophthora
infections. Tilling helps to kill any pests that may live in the soil, though
it also contribute to worse weed issues, and in areas where ground nesting
bees are present, it also destroys their nests. Cover crops may also disrupt pest
habitat when incorporating flowering plants that may be deterrent to the
pests. Pests may be diverted away from gardens
by trap cropping with same or similar host species
that are preferential to what you are growing, or strip harvesting, which is a good stewardship
practice that reduces the disruption of all pests from your garden or field to
your neighbors in the event you harvest first. Adjusting planting schedules
interfere with life cycles of pests as well and can be achieved by adjusting
plant spacing to increase or decrease space between plants, depending on how
the pest insect locates its host; planting dissimilar crops next to each
other; crop rotations which prevents the buildup of soil pathogens in the same
area, and adjusting crop planting times. This is especially helpful for early
season pests – if you can plant a little later, then your plants could possibly
develop after the dispersive stage of the pest is over.
Finally, reducing yield reductions can be achieved by planting genetically
resistant or pest tolerant varieties that minimize chemical inputs, keeping
plants healthy so their immune systems can also help fight off
pests, and harvesting early when possible.
Finally, physical control measures act to physically block the pest from reaching
the crop, which can be achieved using screen houses or floating row covers,
good old fashioned hand picking of larger pests like caterpillars, and
products like tangle foot which prevents crawling pests from
climbing into orchard trees. This is particularly helpful against ants, which will tend
other insect pests for honey dew and fight off biocontrol agents. Sometimes
you’ll see palm trees with metal around the trunks – this is to prevent rats from
nesting in the canopies, and follows the same principle. Keep in mind that when
you block the pest, you’re also blocking the pollinator,
so row covers may be best deployed at night to keep out moths such that
pollinators have access during the day, or only using them on self compatible
plants that don’t require pollination.
Going back to our diagram of the IPPM approach, the control measures I spoke of
would mostly fit under the preventative stage of IPPM. Monitoring and
identification are relatively self explanatory, and many of you
volunteer in your county call centers and at public events where you assist
with just that! So let’s discuss pollinator friendly options
for controlling pests once they have been identified.
Least toxic interventions
mostly include low toxicity organic options, some of which are described here.
However, it is always important to follow the label directions to make sure these
products are applied correctly. Some are only effective against certain life
stages, and must come in to direct contact with the pest to be effective as they
have no residual efficacy. Keep in mind that none of these are pest-specific,
meaning they will kill any insects they come in to
contact with, including pollinators, so apply with caution, and avoid spraying
flowering parts of the plants visited by pollinators. Also make sure they are safe
to use on your particular plant as the smothering capabilities may kill plants
when they're applied incorrectly.
After using a least-toxic intervention,
evaluate to see how effective it was. Are the pests reduced or gone? Does the plant
look healthier? Are any pest insect populations below economic thresholds?
Just because pest insects are present on a plant does not mean you need to treat
them. It is only when populations get great enough that they overwhelm the
plants immune system. So as long as you’ve knocked them below that threshold
with your preliminary treatment, you don’t need to pursue another treatment
and can go back to preventative practices and monitoring.
However, sometimes pests do not respond to
other methods, or their populations increase too rapidly for a
least-toxic method to be effective. In these cases, it is ok to use a chemical control.
Just be sure to read the label to make sure that the product is
approved for use on the plant and against that specific pest.
Quick pop quiz – both organic and conventional pesticides
can be a part of a responsible IPPM framework. But are organic pesticides
safer for beneficial insects?
Not necessarily. Broad spectrum insecticides do not distinguish between insect groups,
regardless of whether they are organic or conventional. Organic just means that
the pesticide is derived from a natural source, while conventional are
synthesized in the lab. However, the exact same chemical could be in products
labeled as organic and conventional. For example, pyrethrum is an organic
insecticide that is derived from chrysanthemum flowers. The conventional
alternative, pyrethroids, are the same chemical, just synthesized in a lab.
The table on the right lists organic pesticides and their
relative toxicity to honey bees, and was compiled by the Xerces Society. The
The products highlighted in yellow are found at home improvement stores on Oahu in
pest control isles. What I want to point out here is that though they are organic,
almost all are considered highly toxic to bees. I just want to emphasize that
for garden pesticides, it is how you are using a product, not necessarily what
you’re using, that determines how toxic it will be to bees
and other beneficial insects in your garden.
So, always read the label! The reason being the product
may require dilutions. Application timing could reduce nontarget effects,
such as spraying outside of bloom times or spraying in the early morning
or evening when bees aren’t flying. Captain Jacks Deadbug pictured here is a
certified organic pesticide. But notice how under environmental hazards it
states that the product is toxic to bees and aquatic invertebrates. The product
producers recommend spraying outside of bloom times
and early or late in the day, and when it isn’t raining.
Bayer’s 3-in-1 product, which is conventional,
is also toxic to honey bees, but only if they’re exposed to a direct
application. Dried residues are not toxic, so applying
during non-foraging periods will minimize any effects. Not all chemicals
may be safe on edible plants, so if using in a home vegetable garden, double check
this. Improper applications could also damage plants, as I mentioned with
insecticidal soaps. Finally, adhere to application intervals. If a product
didn’t work the first time, there is either a delay between application and
and death, the product isn’t appropriate for the pest, or the pest is resistant and
you need to chose something else.
In response to declining honey bees in the
US, the Environmental Protection Agency did develop a label to be put on certain
pesticides that are particularly toxic to honey bees as an additional caution to
applicators and farmers. Their guidelines mirror what we’ve already discussed,
and include spraying when pollinators are not active and outside of bloom times,
choosing targeted vs. broad spectrum insecticides whenever possible, only
spraying areas that have the pests and avoid spraying refuges where bees and
other beneficial insects may be foraging, and moving colonies before an area-wide spray.
This IPM discussion has been very centric on farmers and gardeners who may
be applying pesticides to bee forage plants. However, pesticides are inside the
hive as well, and there are steps beekeepers can take to minimize this. In
a landmark study from 2010, a team of researchers found very high levels of
fungicides and miticides in beeswax from colonies across North America. Over
87 pesticides or their metabolites were detected in beeswax, with some samples
having as many as 39 different chemicals present, though on average there were
eight pesticides per wax sample. Unsurprisingly, almost all samples tested positive for
miticides, but it was a surprise at how many samples were positive for
agricultural fungicides. But, it should be noted that these chemicals were in the
wax, and we still do not know the effects that pesticides in the wax have on
developing brood, though the effect is likely minimal. But this does provide a
justification for cycling out old frames and foundation from colonies, as well as
employing some of the organic mite control options that are available in
Hawaii, and discussed in the previous video. Non-chemical alternatives should
also be considered, such as drone brood removal. For small hive beetles, using
paper towels to aid the bees in trapping adults is very successful
in apiaries across the state.
This concludes module 8. Don’t forget to take the quiz
while the information is still fresh in your mind. Stay tuned for the next video
on nutrition as a cause for pollinator declines.
