Insect development relies on the accumulation of heat
throughout the season to progress through their life stages, allowing their
development to be tracked with the use of degree day models specific to the
insect. By tracking the degree days, the timing of key activities such as adult
flight and egg hatch can be predicted, facilitating scouting and pest
management activities. To calculate degree days for a particular insect, there
are two pieces of information that need to be known: the base temperature (the minimum
temperature required for the development of that insect), and the biofix date
(the date on which degree day calculations for that insect will begin). The
equation used to calculate degree days for insect development is:
GDD = ((Tmax +
Tmin)/2) – Tbase
In the equation, Tmax and Tmin refer to the maximum and
minimum temperatures on a single day. Using this equation, the growing degree
days can be calculated anywhere that has daily temperature information
available, making it possible to tailor the model to a particular geographic
area. Being able to customize data is important in Nova Scotia where we have a
number of microclimates with sometimes significantly different weather often
caused by the geography and proximity to the Atlantic Ocean or the Bay of
Fundy. Environment Canada lists all of the weather
stations available in Nova Scotia both past and present, and can provide
the temperature data needed to calculate degree days. Choose the closest
weather station logging hourly data for the current year. It is important to
note that while degree day modeling can be a useful tool, development models
from other geographic areas are not necessarily validated for use in Nova
Scotia. Degree day modelling should be used in conjunction with, not as a
replacement for, regular scouting.
European corn borer (ECB) is a pest of a number of crops in
Nova Scotia. There are two types of ECB, with significantly different
development schedules. The univoltine type completes one life cycle in a
growing season while the bivoltine type can have two lifecycles in a growing
season, though in cool summers the second generation of the bivoltine corn
borer may not be able to complete its development.
 |
| European corn borer larva in a corn stalk. Photo: https://extension.entm.purdue.edu/fieldcropsipm/insects/euro-cornborer.php |
Both univoltine and bivoltine types of European corn borer
use a base of 10°C and
a start date of April 1st for degree day development models. As of June 21st,
239* degree days had been accumulated in Kentville and 190 in Debert. According
to the model, at 231 degree days, about 5% of pupae are emerged for univoltine
types, with egg laying starting to occur around 425 degree days. For bivoltine
types, about 50% of 1st generation adults are emerged by 281 degree days, with a second generation
starting their flight around 792 degree days.
For more information on European corn borer in Nova Scotia,
check out Perennia’s new
fact sheet!
*These numbers were generated with CIPRA software, AAFC,
Saint-Jean-sur-Richelieu, Quebec.
