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