Using Phenology Models in Insect Management Decision-making

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.

Phenology, DDs, & Insect Management

Why use phenology models?

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

The underlying biological idea

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?

Applying the general idea without measuring temps or doing calculations

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?)

Natural indicators for insect phenology

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.

Upper threshold cutoff methods for degree-day calculations vary … a topic for more advanced discussions.

So we know how to estimate lower and upper thresholds and count degree-days. When do you start? And what do the totals tell you? 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.

Codling moth

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.

Black cutworm

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 …

First Generation European Corn Borer

Accumulated Degree-Days

First occurrence Days to first occurrence

General activity

0 First spring moth - -

212 Larval hatch (1st instar)

16.3 Pinhole leaf feeding

318 2nd instar 6.6 Shot-hole feeding

435 3rd instar 6.5 Mid-rib & stalk boring

567 4th instar 6.6 Stalk boring

792 5th instar 10.2 Stalk boring

1,002 Pupa 7.6 Changing to adult

Second Generation European Corn Borer

Accumulated Degree-Days

First occurrence Days to first occurrence

General activity

0 First spring moth - -

1,404 Larval hatch (1st instar)

8.2 Pollen & leaf axil feeding

1,510 2nd instar 4.1 Leaf axil feeding

1,627 3rd instar 4.3 Sheath, collar, & midrib feeding

1,759 4th instar 5.1 Stalk boring

1,984 5th instar 10.2 Stalk boring

Western bean cutworm

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

WBCW scouting & monitoring 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%

Corn earworm

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Corn Earworm Pheromone Trap Captures, 2007

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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

Degree-day accumulations, base 50 F, January 1 – June 6, 2007 (left), and projected through June 13 (center) and June 20 (right).

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.◦ Consult the University of Illinois web site titled

Degree-Day Calculator.