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Stem Pests:(some Homoptera)
Before we move on to stem pests, there are still some basic entomological topics to discuss.
In particular, the digestive system. Why?
In order to better understand your favorite aphid and other homopterans
Remember Aphid Feeding
Mo
uth
ForegutMidgutHindgut
Ma
lpig
hia
ntu
bu
lesRe
cta
la
rea
Generalized insect digestivesystem
Foregut
Midgut
Hindgut
Malpighian
tubule
Midgut
Filter chamberof aphids andother homopterans
Honey dew
Honeydew from aphids
Now we can move on to the stempests, starting with the balsamwoolly adelgid1
1 Really belong to the family Phylloxeridae
0.5mm
The Balsam Woolly Adelgid1,Adelges piceae.
1 Phylloxerid
GallsGalls
1905 in a small coastal town in Maine, a Quarantine Inspector.
These European fir trees have only femaleAdelges piceae -- I’ll let them pass.
“Males? We don’t need males; we’reparthenogenic.”
Unfettered population growth by the BWA began and in a few decades; they killed fir trees in the Canadian Maritime Provinces and today are into the Appalachian Mtns. destroying Fraser fir across thousands of acres.
Dead Fraser-fir
BWA
Adelgid
The BalsamWoolly Adelgid
Comes West in1950
The BWA infest and kill: No. 1 subalpine fir, No. 2 grand fir, No.3 silver fir & noble fir, and No. 4 Shasta-red fir is barely attacked.
(1) The BWA overwinter as a diapausing1st instar, the winter form.
(2) In early spring, the 1st instar swells andbegins to produce honey dew as the treesap starts flowing.
(3) The immature female molts several timesand becomes an adult in ± 3 weeks.
(4) Each female then lays ± 100 eggs.
BWA layingeggs
Life Cycle of the BWA
(5) Eggs hatch in about a week and eachmotile nymph crawl rapidly around thenew foliage, twigs and branches.
BWA crawlers
(6) These motile nymphs then thread theirstylets through the bark and tap a vascularbundle -- they are stuck for life, a life of sucking sap, the summer form.
(7) This summer generation, then aestivatesfor 1 - 2 months.
(8) In July they “wake up” and quicklymolt to adults. These summer-generationadults lay ± 50 eggs apiece.
(9) Dependingon the climate,elevation, site,aspect etc., theremaybe 2 - 3generations/yr.
Egg
Adult
Motile nymph
Nymph stuckin the phloem
One mm
The BWA in action!
Bark surface
As BWA feed they inject a toxin intothe actively growing tissues, whichcauses hyperactive growth & galls
A fewBWA
MillionsBWA
The BWA Disaster
Subalpinefir nearthe town ofConcrete
More BWA Damage
In order to understand why its so difficult to control the BWA, let’sdiscuss the Mortality Quotient.
The Mq asks: “how many individuals of an insect population must be killed to prevent the population from increasing.”
Mq depends on: (1) fecunditynumber of eggs a female will lay, & (2) sex ratio.
Mq = (F)(SR) - 1 (F)(SR)
Mq = Mortality Quotient
F = Average No. Eggs
SR = No. Females No. Females + Males
The iris bulb fly:
Fecundity = 150
Out of 1000 puparia you collected, 500are males.
There is one generation/yrof the gladiola bulb fly.
Mq = (150)(0.5) - 1 ( 150)(0.5)
150 X 0.986 = 148
So: 150 - 148 = 2 (a male and a female) 150 eggs
= 0.986 (75) - 1 (75)
Mq = (100)(1) - 1
(100)(1)= 0.99/generation
i.e., 100 eggs - 99 killed = 1 female!
BWA
Management of BWA in the urban environment:
• Avoid planting subalpine fir
• Maintain a high vigor in plantings of other Abies spp.
• Consider applied control of BWA-infested firs if they have special intrinsic value, e.g. a historical fir planting within the Japanese Garden.
• Consider applied control when the aesthetic value of a commercial Abies spp. planting is threatened, e.g. the Christmas tree industry.
With valuable trees, you may have to treat -- about bud-break time.
Apply insecticideat time of budburst,you should see tinycrawlers.7
The balsam twig aphid, Mindarus abietinus
Eggs
Stem mothers
Twistingnew growth
BTA on the stem
The balsam twig aphid can severely damage true firs:
In nurseries, the terminal needles twist and become deformed.
In urban plantings, BTA suck on twigs and foliage producing great amounts of honey dew and sooty mold -- firs become unsightly.
April - May: stem mothers sucking on stem next to new buds or on new foliage – needles twist.
May - Mid June:vivipary in action:2 or more generationsof wingless females.
Mom?
Mom?
Mom?
Mom? Mom?
Mom?
Mom?
Mom?
Mom?
Mom?
June: a winged generationflies off to an alternatehost.
July - August:both males and femalesare produced and theyfly back to true firs
MaleFemale
Unknown host?
True fir: primaryhost
Late summer:males & femalesoccur
August - September: egg laying and the winter is spent in the egg stage. Early next spring eggs hatch and stem mothers start inserting their stylets at the bases of buds.
Mating Aphids
The bowlegged aphid, Cinara curvipes; occurs in California Oregon, Washington, Colorado and Utah -- on firs, Engelmann spruce,and deodar cedar.
The Cinara spp. aphids have a typical conifer-aphid life cycle and they feed on trunks, stems, and roots. These aphids often are herded by ants, typicallyFormica spp. (e.g. western thatching ants) and Camponotus spp., the carpenter ants.
Ants tending Cinara aphidsand Cinara curvipes onbark of white pine.
What to do?
Aphids:
Pest description and crop damage: Soft-bodied insects that suck sap on stems, branches, leaves etc.
Biological control: Aphids have many natural enemies.
Cultural control: A strong spray of water often effectively removes these suckers.
Chemical control: It’s important to cover foliage thoroughlyas well as stem and branches with:
o azadirachtino insecticidal soapo acephateo horticultural oils as dormant sprayso imidacloprid