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Diapause is the major mechanism in temperate production areas that allows Helicoverpa armigera pupae to survive the winter months when food plants are scarce and temperatures are too low for normal development.  This mechanism contributes to the carry-over of resistance genes from one season to the next, and is the primary driver for the pupae busting requirement in both conventional and Bt transgenic cotton which aims to reduce survival of diapausing pupae under crops.  Information about when diapause is induced is useful for identifying ‘high risk’ fields i.e. those fields likely to have diapausing pupae and which are essential targets for pupae busting.  Knowing the timing of spring emergence from diapause identifies the latest opportunity for pupae busting operations and provides an alert of potential moth activity.

Decreasing daylength and temperature in late summer/autumn trigger the diapause response. The proportion of pupae entering diapause increases from low levels in early March to high levels (almost 100%) by late April.  Increasing temperatures in late winter/spring trigger the termination of diapause and result in the subsequent emergence of moths (September to November).

The Helicoverpa Diapause Induction and Emergence Tool uses day length and temperature data to predict the level of diapause induction and the emergence of moths from overwintering pupae.

Information about diapause induction can help identify those high risk fields which are essential targets for pupae busting.  By knowing when moths are likely to emerge can help identify the latest opportunity to pupae bust.
 

Helicoverpa armigera
 
 

Helicoverpa armigera

Diapause
 
The induction of diapause in Helicoverpa armigera is in response to decreasing daylength and lower temperatures.  An algorithm has been developed from studies on the Darling Downs (Murray) to predict the level of diapause induction.

Diapause % = 1.426+98.7/((1+EXP(25.37*D-310.4))*(1+EXP(0.5722*T-12.53)))

where
D = daylength (hours).
T average temperature for the preceding 5 days and is normally derived from daily maximum and minimum temperatures.

Diapause Analysis
To help understand the impact of warmer or cooler seasons, we have developed an in-depth analysis of predictions generated for each year of the historical climate records.  This analysis is based on sorting each year in a historical dataset by calculating the Day of the Year (DOY) from 1st March (or other selected start date) to when diapause reaches 99% (or other selected threshold).  By sorting the years from lowest to highest DOY we are then able to calculate the years that are in the 1st and 9th deciles.

What are deciles?  Deciles are commonly used to rank historical climate data.  The first group or 1st decile contains the lowest 10% of records and the 9th decile (highest) contains the highest 10% of records.  To calculate deciles, we sort the data in ascending order and then split the data into 10 equal groups.  Because the number of records is often not divisible by 10, we use a formula that steps through the records.

For Diapause induction, the years in the 1st decile reach 99% diapause earlier due to lower temperatures and the years in the 9th decile will be hotter and take longer to reach 99% diapause.

Getting Started
After selecting Diapause Analysis from the main menu, select a Silo (weather) station by clicking on the ‘Change Silo Station’ button.  Then check/ change the report options including start date and year to be displayed.   Other report / analysis options can also be modified under the advanced options drop down.  These include diapause threshold % to reach and which deciles to include in the analysis.

To generate the analysis, click on the ‘Calculate’ button.

Diapause Chart
The chart will graph the diapause % over time for:
  1. The year selected to display
  2. The Long Term Average
  3. The Lowest Decile
  4. The Highest Decile

Diapause Induction Summary
This table will appear directly under the chart and shows the date when diapause reached 99% (or other specified %) for the location selected.  Dates are included for the Long Term Average, the selected year, the Coldest (Lowest) Decile/s and the Hottest (Highest) Decile/s.

Diapause Details
This table contains the information that is plotted in the chart.  Each row represents a day starting on a default of the 1st March (or other selected start date) and finishing on the 30th June.  Information for each day includes the % diapause for; the year that you have selected to view; the lowest decile; the highest decile; and the long term average.   Other information includes the accumulative average temperature for the low and high deciles and the long term average, and the number of years included in the low and high deciles and the long term average.

Additional details
Threshold Details
The term ‘Threshold’ used here refers to the percentage of diapause selected for the calculations.  In sorting the cooler and warmer seasons we have estimated the day of the year (DOY) when 99% diapause is reached for a particular location for each year in the historical climate records.  At the same time the average temperature and cumulative average temperature is calculated for the period from the 1st March to 99 % diapause.

Years that did not reach the threshold In some warmer cotton growing locations, not all years in the historical climate records will experience temperatures cool enough to allow Helicoverpa armigera to reach 90-99% diapause.  In this case, these years will be displayed in a separate table titled – ‘Years that did not reach the threshold’.

Display Year Details This table contains details about the selected year, which by default will be the current year unless specified.  This table contains all of the information used in the diapause calculation.  Eg. min, max, average and accumulative average temperatures, day length, 5 day average temp and average diapause %.


Moth Emergence
 
The Moth Emergence tool, predicts the emergence of Helicoverpa armigera moths from overwintering pupae.

The Threshold temperature influences the break of diapause.
The literature (Cunningham et al. 1981) states 18º C, as the threshold temperature for Moth Emergence.

The Emergence % is calculated from the day after, the threshold temperature is first exceeded.

Note

The lines presented on the Diapause or Emergence graphs, will not appear smooth due to daily fluctuations in temperatures.


Emergence Analysis
This analysis is based on sorting each year in a historical dataset by calculating the Day of the Year (DOY) from the 1st July (or other selected start date) to when emergence reaches 5% (or other selected threshold between 1-10%).  By sorting the years from lowest to highest DOY we are then able to calculate the years that are in the 1st and 9th deciles.   However when referring to emergence using deciles, the years in the 1st decile (or bottom 10%) reach 5% emergence earlier due to warmer temperatures and the years in the 9th decile (or top 10%) will be cooler and take longer to reach 5% emergence.   This is the opposite to diapause induction.

Getting Started
After selecting Emergence Analysis from the main menu, select a Silo (weather) station by clicking on the ‘Change Silo Station’ button.  Then check/ change the report options including start date, temperature threshold and year to be displayed.   Other report / analysis options can also be modified under the advanced options drop down.  These include emergence threshold to reach and which deciles to include in the analysis.

To generate the analysis, click on the ‘Calculate’ button.

Emergence Chart
The chart will graph the accumulated emergence % over time for;
  1. The year selected to display– Black line
  2. The Long Term Average (Yellow)
  3. The Coldest (Lowest) Decile (Purple)
  4. The Hottest (Highest) Decile (Blue)

The chart will start plotting emergence % from the first incidence of emergence after July 1 (or nominated start date), even if only one year in the historical dataset has produced an emergence % for that day.  This is why the lowest decile (10% warmer years) and long term average will normally have the same % until all years in the lower decile have all reached the emergence threshold.

Emergence Summary
This table will appear directly under the chart and shows the date when Emergence reached 5% (or other specified %) for the location selected.  Dates are included for the Long Term Average, the selected year, the Coldest (Highest) Decile/s and the Hottest (Lowest) Decile/s.

Emergence Details
This table contains the information that is plotted in the chart.  Each row represents a day starting on a default of the 1st March (or other selected start date) and finishing on the 30th June.  Information for each day includes the % diapause for; the year that you have selected to view; the lowest decile; the highest decile; and the long term average.   Other information includes the accumulative average temperature for the low and high deciles and the long term average, and the number of years included in the low and high deciles and the long term average.

Additional details
Threshold Details
The term ‘Threshold’ used here refers to the percentage of emergence selected for the calculations.  In sorting the cooler and warmer seasons we have estimated the day of the year (DOY) when 5% emergence is reached for a particular location for each year in the historical climate records.  This table presents the date and DOY for every year in the climate data file when the emergence % reaches 5% or greater.
Display Year Details
This table contains details about the selected year, which by default will be the current year unless specified.  This table contains all of the information used in the emergence calculation.  Eg. min, max, and average temperatures, calculated day length, emergence % and cumulative emergence.

 
Predicting Autumn diapause induction in Helicoverpa using long term average temperatures
Has Your Pupae Busting Been Effective?

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