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EVALUATION OF INFRARED THERMOMETRY AS A NON-DESTRUCTIVE METHOD TO DETECT FEEDING ON CORN ROOTS BY THE WESTERN CORN ROOTWORM (COLEOPTERA: CHRYSOMELIDAE)

Published online by Cambridge University Press:  31 May 2012

A.W. Schaafsma
Affiliation:
Ridgetown College of Agricultural Technology, Ridgetown, Ontario, Canada N0P 2C0
G.H. Whitfield
Affiliation:
Agriculture Canada Research Station, Delhi, Ontario, Canada N4B 2W9
T.J. Gillespie
Affiliation:
Department of Land Resource Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1
C.R. Ellis
Affiliation:
Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1

Abstract

Infrared thermometry was investigated as a diagnostic tool to detect root injury in corn caused by feeding of the western corn rootworm, Diabrotica virgifera virgifera LeConte. Plots were infested with 50–1000 eggs per plant, and the study was conducted over 2 years. Differences (P < 0.05) in canopy temperatures were detected in severely infested plots in 6 out of 13 days and 7 out of 11 days on which measurements were made during the period of feeding by rootworm larvae in 1989 and 1990, respectively. Temperature differences between the air and leaves from infested plants were never greater than 3.5 °C and usually occurred within ± 1 °C. Feeding by rootworm larvae at infestation levels of less than 200 eggs per plant could not be detected with infrared thermometry. Above densities of 200 eggs per plant, increases in canopy temperatures corresponded with increases in the level of infestation with rootworm eggs, and with reduced plant height, and lower grain yield. Losses in grain yield due to rootworm infestation were manifested through smaller cobs and fewer seeds per cob. Kernel weight was not affected by rootworm feeding. Crop maturity was delayed at infestation levels of 1000 eggs per plant.Elevated canopy temperatures induced by rootworm feeding were detected through infrared thermometry in commercial corn fields, however differences (P < 0.05) in canopy temperatures were noted only after 10 July. Although these data show that elevated canopy temperatures induced by rootworm feeding can be detected with infrared thermometry, some inconsistency in results was observed. Various reasons for why the technique was not more reliable are discussed.

Résumé

L’efficacité de la thermométrie à l’infra-rouge comme outil diagnostique des dommages causés aux racines du maïs par la chrysomèle Diabrotica virgifera virgifera LeConte a été évaluée. Des grilles-échantillons ont été infestées à raison de 50–1000 oeufs par plant et l’étude a duré 2 ans. Des différences (P < 0,05) de température ont été décelées dans le feuillage dans les carrés-échantillons très infestés durant 6 des 13 jours de mesure en 1989 et durant 7 des 11 jours de mesure en 1990, au cours de la période d’alimentation des larves de la chrysomèle. Les différences de température entre l’air et les feuilles des plants infestés ne dépassaient jamais 3,5 °C et se situaient généralement autour de ± 1 °C. La thermométrie à l’infra-rouge ne permettait pas d’enregistrer l’alimentation des larves de la chrysomèle aux taux d’infestation inférieurs à 200 oeufs par plant. Au-dessus de ce taux d’infestation, les augmentations de température de la couverture de feuilles correspondaient aux augmentations du taux d’infestation et étaient reliées à une réduction de la hauteur des plants et à une diminution de la production de grains. La réduction de la production de grains causée par l’infestation des chrysomèles se manifestait par une réduction de la taille des épis et aussi par la réduction du nombre de grains par épi. En revanche, la masse de chaque grain n’était pas affectée. La maturation de la récolte était retardée aux taux d’infestation supérieurs à 1000 oeufs par plant.Des augmentations de température du feuillage attribuables à l’alimentation des chrysomèles ont été détectées par thermométrie à l’infra-rouge dans des champs de maïs commerciaux, mais ces différences de température (P < 0,05) n’ont été enregistrées qu’après le 10 juillet. Bien que les résultats démontrent que la thermométrie à l’infra-rouge permet de déceler les augmentations de température du feuillage causées par l’alimentation des chrysomèles, les données ne reflètent pas toujours la même tendance. Les raisons susceptibles d’expliquer l’efficacité relative de la méthode sont ’ examinées.

[Traduit par la rédaction]

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1993

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