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RELIABILITY OF DEGREE-DAY INDICES FOR PREDICTING SPRING EMERGENCE OF THE SPOTTED TENTIFORM LEAFMINER, PHYLLONORYCTER BLANCARDELLA (LEPIDOPTERA: GRACILLARIIDAE), IN ONTARIO

Published online by Cambridge University Press:  31 May 2012

R. M. Trimble
R. M. Trimble
Affiliation:
Research Station, Agriculture Canada, Vineland Station, Ontario L0R 2E0
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Abstract

The validity of using 40 ± 12 degree-days (DD) above 6.7 °C summed from 1 April for predicting first spring emergence of the spotted tentiform leafminer, Phyllonorycter blancardella (Fabr.), was tested. In Ontario's major apple growing areas from 1978 to 1981, the observed day of first emergence occurred 12–45 days before the predicted day. Reasons for this inaccuracy are discussed.

An alternative method, summing DDs from 1 March above a base temperature of 5.5 °C, was also tested using three methods of computation. The number of DDs accumulated to the day of first emergence and to the day of 50% cumulative emergence varied greatly between years at one location and between locations during one year. This variation is likely due to a variable relationship between air temperature and temperature in the leafminer's habitat. It is suggested that a more accurate predictive index could be developed through an understanding of the relationship between habitat temperature and weather factors such as air temperature, insolation, and snow cover.

Résumé

On a vérifié le bien-fondé d'utiliser 40 ± 12 degrés-jours (DD) au delà de 6.7 °C (additionnés à partir du 1er avril) pour prédire la première apparition printanière de la mineuse du pommier, Phyllonorycter blancardella (Fabr.). Dans les principales régions productrices de l'Ontario de 1978 à 1981, la date de la première émergence survient 12 à 45 jours avant la date prévue. L'auteur examine les raisons de cet écart.

On a également vérifié une autre méthode qui consiste à additionner les DD au delà d'une température seuil de 5.5 °C à compter du 1er mars, au moyen de trois techniques de calcul. Le nombre de DD accumulés à la date de première sortie et à celle de 50% d'émergence cumulative varie considérablement d'une année à l'autre à un endroit et d'un endroit à l'autre au cours d'une même année. Cette variation est probablement due à la variabilité du rapport entre la température de l'air et celle de l'habitat de la mineuse. Il semblerait possible d'établir un indice prévisionnel plus précis par une meilleure compréhension de la relation qui existe entre la température de l'habitat et certains facteurs météorologiques comme la température de l'air, l'insolation et la couverture de neige.

Type
Articles
Information
The Canadian Entomologist , Volume 115 , Issue 4 , April 1983 , pp. 393 - 398
Copyright
Copyright © Entomological Society of Canada 1983

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