Multiple Agrochemicals in Honeybees

29 Pages·2013·0.32 MB·English

by  Brad Hyland

Effects
 of
 Exposure
 to
 Multiple
 Agrochemicals
 in

Honeybees
 (Apis
 mellifera)

Tommaso
 Ignesti

Page
 1
 of
 29
Abstract

  The
  Honeybee
  (Apis
  mellifera)
  is
  one
  of
  the
  most
  economically
  and

environmentally
 valuable
 pollinators
 today.
 Beekeepers
 have
 often
 been
 threatened

by
 periodic
 high
 colony
 losses,
 but
 the
 ability
 to
 attribute
 them
 to
 specific
 practices

or
 pathogens
 and
 parasites
 has
 allowed
 for
 the
 mitigation
 of
 such
 losses
 fairly

efficiently
 and
 quickly.
 However,
 this
 has
 not
 been
 the
 case
 with
 the
 more
 recent

losses
 that
 have
 decimated
 North
 American
 and
 European
 apiaries
 since
 2006.
 The

phenomenon
  has
  been
  named
  Colony
  Collapse
  Disorder
  and
  it
  differs
  from

previously
  described
  losses
  in
  that
  it
  is
  characterized
  by
  the
  unexplained

disappearance
 of
 large
 numbers
 of
 individuals
 from
 seemingly
 healthy
 hives.
 In
 this

study
 it
 was
 hypothesized
 that
 an
 increased
 mortality
 is
 expected
 as
 the
 number
 of

agrochemicals
 to
 which
 individuals
 are
 exposed
 increases.
 Data
 on
 colony
 losses

and
  pesticide
  use
  was
  gathered
  for
  49
  Californian
  counties,
  and
  a
  correlation

analysis
 performed.
 A
 significance
 of
 0.086
 suggested
 that
 a
 moderate
 relationship

could
 be
 demonstrated,
 meaning
 that
 the
 threat
 posed
 by
 pesticides
 to
 honeybees
 is

expected
 to
 rise
 as
 the
 variety
 of
 these
 pesticides
 is
 increased,
 possibly
 due
 to

synergism.
  In
  light
  of
  such
  results,
  further
  investigation
  of
  the
  problem
  is

recommended,
 and
 the
 development
 of
 a
 better
 understanding
 of
 the
 impacts
 of

sublethal
 doses
 of
 pesticides
 on
 honeybees,
 as
 well
 as
 of
 the
 ways
 these
 interact
 to

possibly
 increase
 their
 toxicity
 to
 beneficial
 species
 is
 necessary.

Introduction

Perhaps
 one
 of
 the
 properties
 of
 honeybees
 that
 have
 given
 them
 worldwide

fame
 is
 their
 ability
 to
 produce
 honey,
 a
 widely
 enjoyed
 sweetener
 used
 by
 human

beings
 since
 the
 time
 of
 the
 Ancient
 Egyptian
 Civilizations.

 Honey
 production
 is
 only

one
 of
 the
 services
 provided
 by
 bees,
 and
 this
 currently
 amounts
 to
 an
 estimated

value
 of
 $1.25
 billion
 worldwide
 (vanEngelsdorp,
 2009).
 Although
 this
 is
 not
 at
 all

insignificant,
 the
 most
 essential
 role
 of
 honeybees
 is
 that
 of
 pollinators
 of
 a
 great

variety
 of
 plants.
 Not
 only
 are
 these
 insects
 required
 for
 the
 reproduction,
 and
 thus

survival
 of
 a
 number
 of
 species
 in
 the
 wild,
 they
 also
 play
 a
 fundamental
 role
 in

modern
 agriculture.
 “Fifty
 two
 of
 the
 115
 leading
 global
 food
 commodities
 depend

on
 honeybee
 pollination,”
 a
 few
 of
 which
 would
 experience
 a
 90%
 or
 greater
 yield

reduction
 in
 their
 absence
 (Klein
 et
 al.,
 2007
 as
 found
 in
 vanEngelsdorp,
 2009).
 It
 is

consequently
  estimated
  that
  the
  annual
  value
  of
  agricultural
  bee
  pollination

Page
 2
 of
 29
worldwide
  approximates
  $212
  billion
  (9.5%
  of
  total
  agricultural
  value),
  $15-­‐20

billion
 of
 which
 is
 in
 the
 United
 States
 alone
 (vanEngelsdorp
 et
 al.,
 2009).

Honeybee
 Ecology

The
 genus
 Apis
 includes
 a
 total
 of
 10
 species
 found
 throughout
 the
 world
 in
 a

variety
 of
 climatic
 regions
 (Le
 Conte,
 2008).
 This
 study
 focuses
 on
 Apis
 mellifera,
 the

European
 honeybee,
 whose
 importance
 is
 not
 only
 limited
 to
 honey
 production,
 but

extends
 especially
 to
 its
 role
 as
 natural
 pollinator
 of
 both
 human
 raised
 crops
 and
 a

variety
 of
 wild
 plant
 species.
 The
 domestication
 of
 the
 European
 honeybee
 traces

back
 to
 the
 Ancient
 Egyptians
 for
 whom
 honey
 was
 the
 only
 sweetener
 available,

and
  was
  subsequently
  transferred
  to
  Greek
  and
  Roman
  civilizations,
  until
  it

eventually
 spread
 throughout
 the
 world
 (Ransome,
 1937).
 This
 domestication,
 as

Crane
 (1975)
 has
 pointed
 out,
 can
 be
 compared
 in
 magnitude
 to
 that
 of
 the
 dog,
 as

both
 accompanied
 man
 since
 the
 first
 major
 migrations
 (Crane,
 1975).
 On
 the
 other

hand,
 the
 remaining
 nine
 species
 of
 the
 Apis
 genus
 have
 for
 the
 most
 part
 remained

in
 Asia,
 where
 the
 genus
 is
 thought
 to
 have
 originated
 (Le
 Conte,
 2008).
 What

differentiated
 A.
 mellifera
 from
 other
 species
 of
 the
 Apis
 genus
 was
 the
 evolution
 of
 a

total
 of
 22
 subspecies
 that
 stemmed
 from
 various
 waves
 of
 colonization
 to
 parts
 of

Europe,
 Africa,
 the
 Middle
 East,
 and
 Russia.
 Unlike
 the
 Asian
 species,
 the
 western

honeybees
 were
 thus
 often
 subject
 to
 cold
 winters
 and
 had
 to
 develop
 strategies
 to

survive
 colder
 periods.
 This
 was
 done
 by
 the
 accumulation
 and
 storage
 of
 sufficient

amounts
 of
 food
 to
 sustain
 the
 colony
 when
 flowers
 were
 not
 blooming,
 and
 thus
 a

greater
 amount
 of
 work
 was
 required
 throughout
 the
 year,
 and
 the
 supplemental

source
 of
 nutrition
 had
 to
 be
 stored
 in
 the
 form
 of
 honey.

Colony
 Structure

Honeybees
 organize
 in
 colonies,
 each
 including
 one
 queen,
 20
 to
 80
 thousand

females,
 and
 a
 few
 hundred
 males,
 or
 drones.
 Males
 only
 live
 for
 a
 few
 weeks
 in
 the

summer,
  their
  only
  role
  being
  mating
  with
  the
  queen
  in
  a
  phenomenon
  called

swarming.
 In
 swarming
 the
 queen
 leaves
 the
 hive
 with
 half
 the
 colony,
 mates,
 and

relocates
 to
 a
 new
 hive,
 while
 a
 new
 queen
 will
 emerge
 in
 the
 previous
 one,
 swarm,

and
 return
 to
 the
 same
 hive
 where
 she
 will
 start
 laying
 eggs.
 The
 queen
 usually

stores
 enough
 sperm
 within
 her
 abdomen
 to
 last
 for
 about
 2
 years
 of
 constant
 egg

Page
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laying,
 after
 which
 swarming
 and
 relocation
 will
 take
 place.
 The
 queen
 has
 the

ability
 to
 either
 fertilize
 an
 egg
 before
 laying
 it,
 thus
 producing
 a
 female
 worker
 bee,

or
 lay
 an
 unfertilized
 egg,
 which
 will
 result
 in
 a
 drone.
 Each
 egg
 is
 laid
 in
 a
 cell

within
 the
 hive,
 although
 new
 queens
 might
 accidentally
 lay
 more
 than
 one
 per
 cell,

and
 the
 larva
 will
 feed
 on
 food
 provided
 by
 adult
 workers,
 grow,
 and
 undergo

pupation
 within
 the
 cell.
 The
 cell
 is
 capped
 by
 an
 adult
 worker
 and
 will
 be
 uncapped

by
 the
 emerging
 young
 bee.
 This
 developmental
 process
 will
 take,
 on
 average,
 two

to
 three
 weeks
 (https://agdev.anr.udel.edu/maarec/honey-­‐bee-­‐biology/the-­‐colony-­‐
and-­‐its-­‐organization/).

The
 totality
 of
 the
 work
 needed
 for
 the
 proper
 functioning
 and
 survival
 of
 the

colony,
 with
 the
 exception
 of
 mating
 and
 egg
 production,
 is
 carried
 out
 by
 worker

bees,
 which
 are
 sterile
 females.
 Their
 tasks
 depend
 on
 both
 age
 and
 the
 time
 of
 year.

For
 the
 first
 few
 days
 after
 emerging,
 bees
 stand
 still
 within
 the
 hive
 and
 are
 fed
 by

others.
 A
 special
 kind
 of
 glands
 will
 activate
 after
 a
 few
 days
 which
 is
 used
 to

produce
 brood
 food,
 and
 the
 young
 workers
 will
 use
 these
 to
 feed
 developing
 larvae.

Once
  these
  glands
  stop
  functioning
  properly,
  wax-­‐producing
  glands
  will
  have

developed,
 and
 they
 begin
 their
 tasks
 of
 hive
 building
 and
 maintenance,
 together

with
 taking
 the
 first
 journeys
 outside
 the
 hive
 during
 which
 individuals
 learn
 the

location
  of
  the
  hive
  and
  get
  accustomed
  to
  the
  surroundings.
  Before
  becoming

foragers,
 workers
 within
 the
 hive
 will
 also
 aid
 in
 the
 collection
 and
 storage
 of
 pollen

and
 nectar
 from
 incoming
 foragers,
 and
 in
 the
 production
 of
 honey.
 Finally,
 about

three
 weeks
 after
 emerging
 from
 their
 original
 cell,
 the
 workers
 will
 be
 ready
 do

serve
 as
 foragers,
 leaving
 the
 hive
 during
 the
 day
 for
 food
 and
 water
 collection

unceasingly,
  until
  they
  die
  within
  the
  next
  three
  weeks
  (http://www.biology-­‐
resources.com/bee-­‐01.html).

During
 the
 coldest
 months
 of
 the
 year
 the
 colony
 will
 stop
 its
 usual
 activities.

At
 this
 time
 a
 sufficient
 amount
 of
 food
 will
 be
 stored
 and
 the
 drones
 will
 be
 forced

out
 of
 the
 colony
 as
 to
 reduce
 the
 amount
 of
 food
 that
 will
 be
 consumed
 during
 the

winter.
 As
 temperatures
 drop,
 cracks
 within
 the
 hive
 are
 sealed,
 and
 the
 entrance

tightened
 as
 to
 minimize
 the
 amount
 of
 in-­‐coming
 cold
 air.
 As
 the
 temperature

within
 the
 hive
 should
 not
 drop
 below
 32°C,
 adult
 workers
 form
 a
 tight
 cluster

Page
 4
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around
 brood
 cells
 and
 the
 queen,
 regulating
 the
 temperature
 using
 their
 body
 heat.

The
 cluster
 will
 be
 tighter
 or
 looser
 according
 to
 outside
 temperature,
 and
 will
 move

during
 warmer
 moments
 as
 to
 always
 be
 within
 reach
 of
 honey
 supplies.
 In
 this

period
 the
 older
 bees
 progressively
 die,
 and
 by
 late
 winter
 the
 hive
 will
 almost

entirely
 consist
 of
 young
 individuals.
 As
 days
 become
 longer,
 and
 temperature
 rise,

the
 queen
 begins
 laying
 eggs
 anew,
 and
 the
 population
 is
 normally
 restored
 within

the
  following
  months.
  (Information
  from
  Mid-­‐Atlantic
  Apiculture,
  British

Beekeepers’
 Association,
 Biology
 Teaching
 and
 Learning
 Resources
 websites)

The
 colony
 structure
 of
 honeybees
 is
 worth
 mentioning
 not
 only
 because
 of
 its

fascinating
 complexity,
 but
 because
 it
 will
 also
 help
 in
 understanding
 how
 certain

factors
 that
 will
 be
 discussed
 later
 might
 be
 contributing
 in
 the
 Colony
 Collapse

Disorder
 phenomenon
 that
 will
 be
 investigated
 in
 this
 thesis.

Colony
 Collapse
 Disorder

Colony
 losses
 have
 not
 been
 an
 uncommon
 phenomenon
 throughout
 history,

and
 a
 number
 of
 instances
 have
 been
 documented
 starting
 in
 1896.
 At
 the
 same

time,
 large
 increases
 in
 bee
 populations
 have
 been
 experienced
 elsewhere
 which

often
 were
 more
 substantial
 than
 decreases.
 Fluctuations
 have
 thus
 been
 affecting

different
 continents
 in
 different
 ways,
 and
 even
 within
 each
 continent
 there
 has

been
 high
 variation
 from
 one
 region
 to
 the
 next.
 In
 the
 past
 50
 years
 for
 instance,

the
 global
 bee
 stock
 has
 increased
 by
 an
 estimated
 45%
 (Aizen
 and
 Harder,
 2009).

Although
 this
 may
 be
 considered
 a
 positive
 fact,
 managed
 honeybee
 populations
 in

North
  America
  and
  Europe
  have
  declined
  by
  49.5%
  and
  26.5%
  respectively

(vanEngelsdorp,
 2009).
 At
 the
 same
 time
 the
 demand
 for
 pollinators
 for
 agricultural

needs
 has
 seen
 a
 300%
 increase
 or
 greater
 (Aizen
 and
 Harder,
 2009).
 Even
 more

alarming
 is
 the
 impact
 of
 a
 fairly
 new
 condition,
 named
 Colony
 Collapse
 Disorder,

which
 since
 2006
 has
 caused
 substantial
 losses
 in
 North
 American
 apiaries,
 mostly

in
 those
 found
 within
 the
 United
 States.

Colony
 Collapse
 Disorder
 (CCD)
 has
 been
 the
 object
 of
 detailed
 investigation

and
 although
 a
 definite
 cause
 has
 not
 yet
 been
 isolated,
 those
 characters
 that
 seem

to
 be
 common
 of
 all
 hives
 affected
 by
 the
 condition
 have
 been
 well
 described.
 These

are:
 (1)
 “Rapid
 losses
 of
 adult
 worker
 bees
 from
 affected
 colonies
 as
 evidenced
 by

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 5
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weak
  or
  dead
  colonies
  with
  excess
  brood
  populations
  relative
  to
  adult
  bee

populations,”
 (2)
 “Noticeable
 lack
 of
 dead
 worker
 bees
 both
 within
 and
 surrounding

the
 affected
 hive,”
 (3)
 and
 “Delayed
 invasion
 of
 hive
 pests
 and
 kleptoparasitism

from
  neighboring
  honey
  bee
  colonies.”
  (vanEngelsdorp,
  2009)
  Kleptoparasitism

refers
 to
 the
 practice
 of
 stealing
 previously
 gathered
 or
 prepared
 food
 from
 another

organism.
 Thus,
 in
 affected
 hives
 a
 small
 cluster
 of
 adult
 bees
 and
 the
 queen
 are

present,
 and
 honey
 and
 pollen
 are
 not
 missing
 (Johnson,
 2010).
 While
 the
 condition

might
 not
 seem
 particularly
 alarming,
 the
 colony
 structure
 is
 modified
 to
 such
 an

extent
 that
 makes
 it
 impossible
 for
 the
 remaining
 individuals
 to
 both
 fight
 diseases

and
 pest
 invasions,
 and
 to
 carry
 out
 those
 activities
 required
 for
 their
 survival,

including
 food
 collection
 and
 storage,
 rearing
 larvae,
 and
 survive
 unexpected
 drops

in
 temperature.

One
 of
 the
 main
 reasons
 CCD
 has
 become
 an
 alarming
 issue
 not
 only
 for

beekeepers,
  but
  for
  scientists
  and
  politicians
  also,
  is
  that
  it
  differs
  in
  some

significant
 ways
 from
 previous
 incidences
 of
 colony
 losses,
 and
 while
 remaining
 for

the
 most
 part
 unknown,
 its
 causes
 seem
 to
 have
 coincided
 with
 the
 significant

changes
 caused
 by
 an
 expanding
 global
 economy.
 The
 major
 difference
 between

past
 colony
 losses
 and
 CCD
 is
 that
 for
 the
 former
 clear
 causes
 had
 been
 evident
 and

clearly
 detected
 through
 scientific
 inquiry.
 These
 included
 increasing
 number
 of

pests,
 parasites,
 diseases,
 habitat
 losses,
 reduction
 in
 pollen
 and
 nectar
 availability,

and
 exposure
 to
 toxic
 pesticides
 (Johnson,
 2010).

In
 contrast,
 a
 correlation
 between
 any
 of
 these
 factors
 and
 current
 losses
 has

not
  yet
  been
  found
  for
  CCD
  even
  though
  substantial
  studies
  have
  been
  done.

Furthermore,
  the
  disorder
  has
  coincided
  with
  the
  radical
  agricultural
  changes

driven
 by
 the
 fast
 increase
 in
 human
 population
 and
 the
 development
 of
 a
 global

economy.
 This
 led
 to
 a
 significant
 modification
 of
 the
 habitat
 honeybees
 are
 exposed

to
 both
 because
 of
 the
 increasing
 ease
 with
 which
 non-­‐native
 species
 are
 carried

from
  place
  to
  place,
  and
  because
  of
  the
  implementation
  of
  poorly
  understood

agricultural
 practices
 focused
 on
 increasing
 productivity,
 including
 the
 introduction

of
 genetically
 engineered
 crops
 and
 an
 expanding
 arsenal
 of
 agrochemicals
 (Johnson

et
 al.,
 2010).

Page
 6
 of
 29
Because
  no
  single
  cause
  has
  been
  isolated
  in
  studies
  on
  CCD
  to
  date,

scientists
 were
 led
 to
 believe
 that
 a
 number
 of
 factors
 are
 acting
 simultaneously
 and

contributing
 in
 the
 losses.
 These
 include
 both
 pathogenic
 factors
 such
 as
 diseases

and
 pests,
 as
 well
 as
 non-­‐disease
 factors
 such
 as
 pesticide
 exposure,
 genetically

modified
 organisms,
 and
 climate
 change.

The
 Threats
 and
 Their
 Origins

It
 should
 be
 clear
 that
 the
 environment
 to
 which
 bees
 are
 exposed
 has
 a

substantial
  impact
  on
  their
  ability
  to
  perform
  well.
  In
  addition,
  the
  effects
  of

environmental
 changes
 on
 honeybee
 populations
 become
 threatening
 relatively
 fast,

despite
 beekeepers’
 attempts
 to
 moderate
 them.
 This
 can
 largely
 be
 explained
 by

the
 colony
 being
 an
 organism
 onto
 itself
 which
 relies
 on
 the
 delicate
 interaction
 of
 a

multitude
 of
 individual
 parts
 governed
 by
 a
 variety
 of
 behaviors.
 These
 behaviors

are
 not
 merely
 the
 individual’s
 reactions
 to
 its
 environment
 as
 driven
 by
 its
 own

needs.
 Rather,
 individuals
 understand
 themselves
 as
 necessary
 components
 of
 a

colony,
 understand
 the
 needs
 of
 the
 colony
 as
 their
 own,
 and
 their
 behaviors
 are

governed
 by
 the
 colony’s
 needs.
 As
 a
 result,
 a
 colony
 can
 survive
 only
 because,
 and

as
 long
 as
 these
 behaviors
 are
 not
 radically
 modified.
 Behavioral
 modifications
 can

either
 be
 due
 to
 the
 physical
 unsuitability
 of
 the
 individual,
 as
 when
 a
 failure
 to

perform
 foraging
 activities
 is
 determined
 by
 the
 malfunctioning
 of
 the
 wings
 and

therefore
 an
 inability
 to
 fly,
 or
 to
 cognitive
 impairment,
 as
 when
 an
 individual
 fails

to
 return
 to
 the
 hive
 due
 to
 memory
 loss,
 or
 when
 an
 individual
 fails
 to
 recognize
 its

role
 within
 the
 colony.
 Both
 physical
 suitability
 and
 cognitive
 functions
 are
 in
 turn

largely
 influenced
 by
 both
 biotic
 and
 abiotic
 factors
 present
 within
 the
 colony’s

environment,
 and
 the
 threat
 they
 pose
 to
 the
 species
 will
 be
 related
 to
 the
 degree
 by

which
 they
 deviate
 from
 the
 norm.
 At
 the
 same
 time,
 this
 deviation
 is
 strongly

determined
 by
 climatic
 conditions
 and
 weather
 patterns.
 It
 can
 thus
 be
 concluded

that
 colonies
 are
 threatened
 mostly
 by
 changes
 in
 climatic
 and
 weather
 events,

followed
 by
 changes
 among
 single
 environmental
 (biotic
 or
 abiotic)
 factors
 to
 which

bees
 are
 exposed
 to.
 This
 notion
 will
 aid
 in
 the
 understanding
 of
 the
 following

discussion.

Parasites
 and
 Pathogens

Page
 7
 of
 29
Parasites
 and
 pathogen
 are
 among
 the
 biotic
 factors
 mentioned
 previously,

and
 they
 can
 impact
 behavior
 by
 impairing
 individuals
 either
 physically,
 cognitively,

or
 both.

One
 of
 the
 main
 parasites
 that
 have
 contributed
 to
 colony
 losses
 over
 the

past
  30
  years
  is
  the
  mite
  Varroa
  destructor.
  Varroa
  destructor
  is
  a
  known

ectoparasite
 (a
 parasite
 that
 only
 remains
 on
 the
 skin
 of
 the
 host,
 not
 attacking
 it

internally)
  of
  the
  Eastern
  honeybee
  (Apis
  cerana)
  and
  was
  first
  discovered
  in

European
 honeybees
 in
 the
 first
 half
 of
 the
 last
 century
 (Rosenkranz,
 2009).
 Since

then
 it
 has
 spread
 worldwide,
 and
 has
 been
 one
 of
 the
 major
 threats
 to
 beekeepers

because
 of
 its
 ability
 to
 transfer
 a
 variety
 of
 viruses
 to
 their
 host,
 and
 because
 of

their
 use
 of
 substantial
 amounts
 of
 hemolymph
 from
 both
 adult
 bees
 and
 broods,

thus
 greatly
 weakening
 the
 host
 since
 its
 early
 life
 stages.
 The
 mites
 attach
 to
 adult

bees
 and
 feed
 on
 their
 hemolymph,
 reproducing
 by
 entering
 the
 capped
 brood
 cells

within
 the
 hive
 where
 they
 can
 lay
 eggs
 and
 have
 enough
 food
 from
 the
 brood’s

hemolymph
 to
 sustain
 their
 offspring
 (Rosenkranz,
 2009).
 This
 loss
 of
 hemolymph

since
 early
 developmental
 stages
 results
 in
 significant
 weight
 loss
 for
 the
 hatching

bees
 and
 drones,
 and
 consequently
 a
 reduced
 flight
 performance
 is
 experienced

(Duay
 et
 al.,
 2002).
 Parasitism
 has
 also
 been
 related
 to
 reduced
 life
 span
 (Amdam
 et

al.,
  2004),
  reduced
  learning
  capability,
  increased
  absence
  from
  the
  colony,
  and

reduced
 ability
 to
 return
 to
 the
 colony
 (Kralj
 et
 al.,
 2007).
 Finally
 a
 decreased
 chance

of
 mating
 is
 experienced
 by
 parasitized
 drones
 (Duay
 et
 al.,
 2002).
 In
 addition
 to
 the

transfer
 of
 several
 viruses
 to
 their
 host,
 and
 the
 damage
 caused
 at
 both
 an
 individual

and
 the
 colony
 level,
 the
 threat
 is
 increased
 by
 several
 other
 factors;
 (1)
 being
 a
 new

parasite
 to
 European
 honeybees
 “a
 balanced
 host-­‐parasite
 relationship
 is
 lacking

and
 beekeepers
 do
 not
 have
 long-­‐term
 experience
 in
 dealing
 with
 this
 pest,”
 (2)
 “it

has
 spread
 almost
 worldwide
 within
 a
 short
 time
 period
 and
 it
 may
 now
 be
 difficult

to
  find
  a
  Varroa
  free
  honeybee
  colony
  anywhere,
  other
  than
  in
  Australia,”
  (3)

“without
 periodic
 treatment,
 most
 of
 the
 honey
 bee
 colonies
 in
 temperate
 climates

would
 collapse
 within
 a
 2-­‐3
 year
 period,”
 (4)
 “regular
 treatments
 increase
 the
 cost

for
 beekeeping
 and
 the
 risk
 of
 chemical
 residues
 in
 bee
 products”
 (Rosenkranz,

2009).

Page
 8
 of
 29
Another
 pathogen
 that
 has
 been
 related
 to
 reduced
 lifespan,
 reduced
 colony

performance,
 and
 increased
 winter
 mortality
 (Fries
 et
 al.,
 1984)
 is
 the
 microsporidia

of
 the
 genus
 Nosema.
 One
 species
 of
 Nosema,
 N.
 apis
 has
 been
 a
 known
 pathogen
 of

the
 European
 honeybee
 for
 a
 long
 time,
 and
 thus
 has
 not
 been
 the
 object
 of
 intensive

studies
  regarding
  recent
  colony
  collapse.
  On
  the
  other
  hand,
  the
  fairly
  new

introduced
 N.
 ceranae
 from
 Asia,
 has
 posed
 a
 much
 greater
 hazard
 to
 beekeepers

since
 1995
 (vanEngelsdorp,
 2009).
 Not
 only
 have
 beekeepers
 been
 unable
 to
 treat

this
 new
 pest
 properly
 due
 to
 their
 inexperience
 with
 it,
 N.
 ceranae
 also
 seems
 to
 be

more
  virulent
  than
  its
  predecessor
  (vanEngelsdorp,
  2009).
  This
  species
  is

transmitted
  through
  the
  ingestion
  of
  spores
  to
  which
  bees
  are
  exposed
  in
  the

environment
 or
 within
 the
 hive,
 as
 housecleaning
 bees
 remove
 infected
 feces
 and

other
  unwanted
  residues
  (vanEngelsdorp,
  2009).
  While
  Nosema
  infestation
  has

been
 correlated
 with
 heavy
 losses
 in
 some
 European
 countries
 such
 as
 Spain,
 a

recent
  study
  conducted
  in
  the
  United
  States
  found
  that
  only
  about
  half
  of
  the

sampled
 colonies
 were
 infected
 with
 Nosema
 ceranae,
 and
 there
 wasn’t
 a
 significant

difference
 between
 populations
 with
 CCD
 and
 control
 populations
 (vanEngelsdorp,

2009).
 Subsequently,
 hives
 that
 have
 been
 affected
 by
 Colony
 Collapse
 Disorder

typically
 do
 not
 have
 populations
 of
 Varroa
 and
 Nosema
 that
 are
 known
 to
 cause

economic
 injury
 or
 population
 decline
 (vanEngelsdorp,
 2009).

  In
 addition
 to
 the
 negative
 effects
 related
 to
 the
 presence
 and
 activity
 of

these
  pests
  within
  hives
  and
  individuals,
  the
  risk
  of
  virus
  transmission
  is
  also

significantly
 increased
 when
 infestation
 occurs.
 Of
 the
 18
 viruses
 that
 have
 so
 far

been
 discovered
 to
 affect
 honeybees
 (Chen
 and
 Siede,
 2007),
 five
 have
 been
 shown

to
 be
 vectored
 by
 Varroa
 mites.
 These
 include
 the
 Kashmir
 bee
 virus,
 Sacbrood

virus,
 Acute
 bee
 paralysis
 virus,
 Israeli
 acute
 paralysis
 virus,
 and
 Deformed
 wing

virus
 (Boecking
 and
 Genersch,
 2008),
 all
 of
 which
 had
 been
 a
 minor
 problem
 for

honeybee
 health
 before
 the
 introduction
 of
 Varroa
 mites
 (Allen
 et
 al.,
 1986).
 Even

though
  none
  of
  these
  viruses
  have
  been
  described
  as
  a
  major
  cause
  of
  Colony

Collapse
 Disorder,
 their
 presence
 decreases
 the
 colony
 strength
 and
 speeds
 the

collapse
 process,
 especially
 in
 later
 stages
 and
 over
 winter
 months.

Page
 9
 of
 29
One
 of
 the
 viruses
 impacting
 honeybees
 mostly
 at
 the
 individual
 level
 is
 the

Deformed
 Wing
 Virus
 (DWV),
 an
 RNA
 virus
 that
 mainly
 affects
 bees
 on
 the
 pupal

stage,
 but
 does
 not
 usually
 result
 in
 colony
 failure
 (Martin,
 2001).

 The
 virus
 is

vectored
 by
 Varroa
 mites,
 which
 transfer
 it
 to
 their
 host
 while
 feeding
 on
 them,
 and

it
 is
 now
 one
 of
 the
 most
 widespread
 viruses
 in
 colonies
 parasitized
 by
 these
 mites

(Martin,
 2001).
 As
 demonstrated
 by
 Martin
 et
 al.
 (2001),
 the
 virus
 is
 especially

damaging
 to
 bees
 encountering
 it
 in
 the
 pupal
 stage,
 resulting
 in
 higher
 pupae

mortality
 (20%
 of
 infected
 individuals),
 and
 reduced
 longevity
 of
 emerging
 adults,

while
 individuals
 becoming
 infected
 as
 adults
 are
 not
 affected
 in
 any
 significant
 way

other
  than
  becoming
  potential
  vectors
  until
  they
  die
  (Martin,
  Ball
  &
  Carreck,

unpublished
 data).
 Under
 field
 conditions,
 many
 of
 the
 pupae
 that
 have
 become

infected
 will
 survive,
 thus
 leaving
 the
 colony
 in
 a
 seemingly
 healthy
 status
 by
 the

end
  of
  the
  fall,
  with
  a
  sufficient
  number
  of
  emerging
  adults
  to
  withstand

overwintering.
 But
 being
 infected
 by
 the
 virus,
 the
 majority
 of
 these
 adults
 die

prematurely,
 thus
 leading
 to
 an
 imbalance
 in
 age
 structure
 and
 inability
 to
 perform

the
 activities
 necessary
 for
 the
 survival
 of
 the
 colony
 (such
 as
 maintaining
 a
 suitable

temperature)
 (Martin,
 2001).
 Thus,
 the
 negative
 effects
 of
 the
 virus
 on
 the
 colony

are
  amplified
  when
  Varroa
  mites
  are
  present,
  as
  the
  parasite
  feeds
  on
  pupae

hemolymph
 and
 reproduces
 within
 the
 brood
 cell,
 resulting
 in
 higher
 infection
 rates.

This
 overwintering
 collapse
 of
 seemingly
 healthy
 colonies,
 together
 with
 evidence

indicating
  DWV
  presence
  in
  a
  large
  number
  of
  CCD
  colonies,
  lead
  to
  the

investigation
 of
 a
 possible
 correlation
 between
 the
 two
 phenomena.
 However,
 such

correlation
 has
 not
 been
 established
 (Cox-­‐Foster
 et
 al.,
 2007).

  Another
  virus
  associated
  with
  Varroa
  presence
  and
  potentially
  a
  factor

playing
 a
 role
 in
 Colony
 Collapse
 Disorder
 is
 the
 Israeli
 Acute
 Paralysis
 Virus
 (IAPV).

This
 virus
 is
 part
 of
 a
 larger
 complex
 of
 similarly
 acting
 viruses
 including
 the
 Acute

Bee
 Paralysis
 Virus,
 and
 Kashmir
 Bee
 Virus.
 The
 viruses
 persist
 within
 the
 colony

usually
  without
  presenting
  apparent
  signs
  of
  infection
  at
  either
  the
  colony
  or

individual
 level,
 but
 are
 highly
 virulent
 in
 both
 larvae
 and
 adults,
 causing
 paralysis,

trembling,
 and
 inability
 to
 fly
 soon
 followed
 by
 death
 (de
 Miranda,
 2009).
 IAPV
 has

been
 the
 subject
 of
 recent
 investigation
 both
 because
 it
 is
 known
 to
 be
 vectored
 by

Page
 10
 of
 29