Using Phenology Models in Insect Management Decision-making

1. Using Phenology Models in Insect Management Decision-making Rick Weinzierl, University of Illinois

2. Phenology, DDs, & Insect Management 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.

3. 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

4. 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?

5. 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?)

6. 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.

7. 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).

8. Rearing Temperature

9. 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)

10. Midnight

11. Example: Daily maximum temp is greater than the lower developmental threshold and daily minimum is less than the lower developmental threshold.

12. Example: Daily maximum and minimum temps are greater than the lower developmental threshold.

13. Example: Daily maximum temp is exceeds the upper developmental threshold and daily minimum is greater than the lower developmental threshold.

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

15. 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.

16. Linking degree-day accumulations to insect development in the field … based on extensive laboratory and field research.

17. 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)

20. Black cutworm

21. Black cutworm

22. Alfalfa weevil

23. From The Bulletin (The Illinois Pest Management and Crop Development Bulletin), April 4, 2008, “Preparations for Early-Season Insect Activity” … 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.

24. From a later issue of The Bulletin in 2008 … 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

30. 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

31. 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

32. Corn earworm

33. Frontal Boundary L DROP ZONE H Insect Pump CEW Source Region

36. Soybean aphid 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.

37. Twospotted spider mite

38. Insect Degree-Day Calculator http://www.sws.uiuc.edu/warm/pestdata/sqlchoose1.asp?plc=

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

41. 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.