Rick Weinzierl, University of Illinois

Know: Insect growth and development are temperature-dependent. The developmental threshold for a phenology model

represents the temperature below which insect development is negligible.

Insect development models calculate developmental units --"degree-days" -- that can be used to measure and predict insect development.

Know how to calculate the number of degree-days that accumulate in a day if given the maximum and minimum temperatures and a specific insect's developmental threshold.

A biofix is an observable event (often the capture of insects in a pheromone trap) that signals when to start counting degree days.

Phenology models are designed to predict or understand insect development to time sampling or control efforts as efficiently as possible.

Insect monitoring and insect management practices are necessary in crop production, horticulture, forestry, etc.

Monitoring and management are expensive◦ Costs of field scouting efforts◦ Costs of insecticide application

Timing monitoring and management activities accurately makes them efficient and effective

Seasonality in growth and activity of insects is related to poikilothermy ... cold-blooded animals' developmental rates are temperature-dependent.

If we want to predict the timing of insect occurrence, it makes sense to base predictions on “physiological time” -- developmental time indicated somehow by heat accumulations, not calendar days.

Modelling and predictions also depend on life cycles of specific insects◦ What stage overwinters?◦ What triggers immigration?

Annual white grubs damage turf in August and September

Elm bark beetle adults emerge in the spring Eastern tent caterpillars hatch from eggs in

May First generation corn borer infests corn in

June

(These generalizations usually hold true here, in central to southern IL, but what about unusual years or other locations?)

Perennial plants respond to the same weather / temperatures that regulate insect development, so their bloom and growth stages may be used as predictors of insect development◦ The first flight of codling moths begins around bloom

to petal fall in apples◦ Using Degree-Days and Plant Phenology to Predict

Pest Activity. Daniel A. Herms. http://www.entomology.umn.edu/cues/Web/049DegreeDays.pdf

Helpful indicators but not precise or applicable to all needs

So maybe we should

understand and measure

what drives insect

development … heat.

Phenology Models (Degree-Day Models)

If insects are reared at a range of

temperatures (say 100 insects at

each of 6 to 10 temperatures – or

more for the data set in the graphs

to the right), development is faster

at higher temperatures (up to a

point). The graphs at the right

illustrate this for the time required

for eggs of a fruit fly to hatch at

different temperatures (top) and

the insect’s RATE of development

(bottom).

Rearing Temperature

We can determine the number of degree days (DD) above the threshold required for development through the stage(s) studied. ◦ Total DD = d (T - ThL)

where d = days to develop at rearing temperature T; and ThL = lower developmental threshold.

At a rearing temperature of 25C, the number of days required for development in the previous example was 20

Total DD = 20 (25-10) = 300 (that is, 300 Celsius degree-days above a 10C threshold)

Midnight

Example: Daily maximum temp

is greater than the lower

developmental threshold and

daily minimum is less than the

lower developmental threshold.

Example: Daily maximum and

minimum temps are greater than

the lower developmental

threshold.

Example: Daily maximum temp is

exceeds the upper developmental

threshold and daily minimum is

greater than the lower

developmental threshold.

When to start …◦ A calendar date considered to correspond to the

end of dormancy◦ An observable biological event called a biofix …

often the first capture of moths in a pheromone trap.

Codling moth development:

First hatch of first generation larvae ~220 DD50 after biofix

50 percent of first generation moths emerged ~240 DD50 after biofix

50 percent of first generation eggs hatched ~500 DD50 after biofix

99 percent of first generation eggs hatched ~920 DD50 after biofix

First moths of second generation emerge ~900 DD50 after biofix

First hatch of second generation larvae ~1100 DD50 after biofix

50 percent of second generation moths emerged ~1340 DD50 after biofix

(Table based on Orchard Pest Management by Beers et al., published by Good Fruit Grower, Yakima, WA.)

Linking degree-day accumulations to insect development in the field …

based on extensive laboratory and field research.

Hang traps in the upper third of the tree canopy by early bloom

Begin counting degree-days (base 50 F) when traps begin to consistently catch moths (the biofix)

Egg hatch begins approximately 220-240 DD (base 50 F) after first sustained catch (biofix)

Generation time is approximately 1100 DD (base 50F)

Orchard

Location

Weather

Station

CM

Biofix

Date

DD50

June 6,

2007

DD50

projected

June 13,

2007

DD50

Projected

June 20,

2007

Comments (based on DD accumulations and

predictions and the model cited above for

codling moth development):

Murphysboro Carbondale 18 April 904 1052 1218 Currently: Nearly all first-generation eggs have

hatched, and second-generation moth flight is just

beginning. By June 20, ~ 30 percent of second-

generation moths will have emerged, and second-

generation hatch will be at about 4 percent.

Belleville Belleville 23 April 844 985 1145 Currently: 97 percent of first-generation eggs have

hatched, and second-generation moth flight will

begin in 1-2 days. By June 20, ~ 20 percent of

second-generation moths will have emerged, and

second-generation hatch will be at about 2 percent.

Edwardsville Belleville 29 April 753 894 1054 Currently: 92 percent of first-generation eggs have

hatched, and second-generation moth flight will

begin in 4-5 days. By June 20, ~ 10 percent of

second-generation moths will have emerged, and

second-generation hatch will begin by around June

21-22.

Brussels Brownstown 27 April 733 881 1052 Almost the same as Edwardsville.

Urbana Champaign 30 April 702 840 1003 Currently: First-generation flight is just ending,

and 87 percent of first-generation eggs have

hatched. Second-generation moth flight is

predicted to begin about June 14. By June 20, ~ 5

percent of second-generation moths will have

emerged, and second-generation hatch is predicted

to begin around June 25.

Speer Peoria 07 May 561 693 849 Currently: First-generation flight is 94% complete,

and 66 percent of first-generation eggs have

hatched. By June 20, first-generation egg hatch

will be 97 percent complete, and second-generation

flight will be about to begin.

Harvard Freeport 10 May 419 538 685 Currently: First-generation flight is 80% complete,

and 35 percent of first-generation eggs have

hatched. By June 20, first-generation flight will be

99% complete, first-generation egg hatch will be 85

percent complete.

Yield Loss Factor

Average Adequate Moisture Inadequate Moisture

Number of Leaves Number of Leaves

Instar 1 2 3 4 5 1 2 3 4 5

3 2.4 1.8 0.8 0.7 0.7 1.6 1.2 0.4 0.4 0.2

5 1.2 1.4 0.6 0.3 0.3 0.8 0.9 0.3 0.2 0.2

6 0.7 0.2 0.1 0.1 0.1 0.5 0.2 0.1 0.0 0.0

___ Yield Loss Factor x ___ % Cutting x ___ Expected Yield (bu/A) = ___ bu/A Loss

___ bu/A Loss x $ ___ Price/bu = $___ Loss/A

$___ Loss/A x ___% Control = $___ Preventable Loss

(95% control with adequate moisture, 80% control with inadequate moisture)

$___ Preventable loss/A - $___ Cost of control/A = $___ Gain (+) or Loss (-) from Treatment

Black cutworm

Alfalfa weevil

Most experts suggest that scouting for alfalfa weevils should commence

when about 150 to 200 degree-days above a threshold of 48°F have

accumulated from January 1. A quick check of the "Daily Pest Degree-

Day Accumulations" on April 2 revealed that as of April 1, 196, 165, and

171 degree-days for alfalfa weevil development had accumulated at

Dixon Springs, Rend Lake, and Belleville, respectively. So the time for

scouting for alfalfa weevils is now for southern Illinois alfalfa fields. Our

fact sheet on the Web provides the necessary information to enable

accurate decision-making related to alfalfa weevil management.

From The Bulletin (The Illinois Pest Management and Crop

Development Bulletin), April 4, 2008, “Preparations for Early-Season

Insect Activity” …

Alfalfa Weevil Larvae Should Be Evident in the

Southern Half of Illinois

As of April 22, 200 degree-days (base 50°F) had accumulated from January

1 as far north as Adams County, southern Tazewell County, and southern

Champaign County, suggesting that alfalfa weevil larvae may be active in

alfalfa fields in the southern half of Illinois. As of the same date, 300 degree-

days had accumulated along a line from St. Louis, Missouri, to White County.

Symptoms of leaf-feeding injury caused by small alfalfa weevil larvae should

be evident in several southern Illinois counties. Don't forget to scout alfalfa

fields, even though most concern will be directed to planting corn and

soybeans. -- Kevin Steffey

From a later issue of The Bulletin in 2008 …

Native to North America Pest of the western corn

belt 1970’s – occasional pest

in Iowa 2000 – 1st economic

damage in Iowa 2004 – 1st

documentation in Illinois & Missouri

Detected in Indiana in 2006

Michigan in 2007

Use black light or pheromone traps to detect moth flights◦ Flights generally begin in

early to mid July Begin scouting when moths

are first noticed◦ Continue scouting until after

moth flights peak◦ Egg laying declines after peak

moth flight◦ Continue to monitor for 7 –

10 days after peak Can also use degree-days to

predict moth emergence◦ Begin May 1, base 50°F

Spray programs aimed at earworm or ECB are effective; this insect Is not controlled by all Bt corn hybrids

Accumulated

Degree-days

% Moth

Emergence

1319 25%

1422 50%

1536 75%

CEW

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Corn Earworm Pheromone Trap Captures, 2007

Collinsville

Urbana

Burlington

St.Charles

Population growth is affected by offspring production, survivorship, and maturation.

The optimal temperature for soybean aphid maturation is 80°F. At 68°F, soybean

aphid populations can double in less than 2 days. At 77°F, populations can double in

1.5 days. At 86°F, populations double in 2 days. This result may seem counter-intuitive

because offspring production and survivorship are reduced at this temperature.

However, at 86F, offspring mature rapidly (within 5 days). This slight advantage in the

timing of reproduction compensates for the lower number of offspring that are

produced in total. It is also important to note that at 95F, populations are no longer

increasing. In fact, they are decreasing over time.

Soybean aphid

Twospotted spider mite

http://www.sws.uiuc.edu/warm/pestdata/sqlchoose1.asp?plc=

Insect Degree-Day Calculator

http://www.specmeters.com/home_usa.html

Specialty suppliers:◦ Great Lakes IPM (lures, traps, mating disruption

products), 989-268-5693; http://www.greatlakesipm.com/

◦ Spectrum Technologies (environmental monitoring equipment and phenology programs); 12360 South Industrial Dr. East - Plainfield, Illinois 60585(800) 248-8873 / (815) 436-4440 Fax: (815) 436-4460; http://www.specmeters.com/home_usa.html

References: ◦ Consult the University of California's web site titled

Degree-Days and Phenology Models(http://www.ipm.ucdavis.edu/WEATHER/ddconcepts.html)

◦ Consult the University of Illinois web site titled Degree-Day Calculator(http://www.sws.uiuc.edu/warm/pestdata/sqlchoose1.asp?plc=)