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THE EFFECT OF LIGHT ON THE RESISTANCE OF HARD RED SPRING WHEATS TO THE WHEAT STEM SAWFLY, CEPHUS CINCTUS (HYMENOPTERA: CEPHIDAE)

Published online by Cambridge University Press:  31 May 2012

N. D. Holmes
N. D. Holmes
Affiliation:
Research Station, Agriculture Canada, Lethbridge, Alberta T1J 4B1
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Abstract

Sawfly-resistant bread wheats varied widely among years in resistance to the wheat stem sawfly, Cephus cinctus Nort. Experimental evidence showed that the major factor involved was a reduction in the intensity of sunlight. A reduction in the intensity of sunlight by up to 50%, which was produced by shading the growing plants with cotton sheeting, caused minor decreases in sawfly resistance. More intensive shading with solid-sided cages and with combined light filters of red and yellow caused the plants to become hollow-stemmed and very susceptible to sawfly damage.

Annual variations in sawfly resistance in plants grown in the field from 1949 to 1978 were significantly related to variations in the number of days with measurable precipitation, to the amounts of precipitation, and to the hours of bright sunshine in the period between 25 May and 5 July. These weather variables were significantly interrelated and were important primarily because they indicated the amounts of light received by the plants. A sufficient reduction in the amount of light (particularly during mid-June) significantly reduced sawfly resistance.

Résumé

La résistance à la cèphe du blé, Cephus cinctus Nort., de variétés de blé tendre résistantes à cet insecte varie grandement d'une année à l'autre. Des expériences ont démontré que la réduction de l'intensité d'ensoleillement constituait le principal facteur responsable. Une réduction de l'intensité lumineuse allant jusqu'à 50%, produite en ombrageant les plants en croissance avec des linges de coton, a entraîné de légères diminutions de la résistance à la cèphe. Une ambiance plus ombragée, réalisée à l'aide de cages à parois solides et de combinaisons de filtres de couleurs rouge et jaune, a provoqué l'évidement des tiges et rendu les plants très sensibles aux dégâts par la cèphe.

Il y a une corrélation significative entre les variations annuelles de la résistance à la cèphe des plants cultivés en plein champ entre 1949 et 1978 et les variations du nombre de jours de précipitations mesurables, le volume des précipitations et les heures de plein ensoleillement durant la période allant du 25 mai au 5 juillet. Il y avait une corrélation significative entre ces variables météorologiques, dont l'importance était surtout due au fait qu'elles indiquaient les quantités de lumière qui atteignaient les plantes. Une réduction suffisante de l'intensité lumineuse (en particulier vers la mi-juin) entraîne une diminution importante de la résistance à la cèphe.

Type
Articles
Information
The Canadian Entomologist , Volume 116 , Issue 5 , May 1984 , pp. 677 - 684
Copyright
Copyright © Entomological Society of Canada 1984

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References

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