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ECONOMIC IMPORTANCE OF INSECTS ON REGROWTHS OF ESTABLISHED ALFALFA FIELDS IN ONTARIO

Published online by Cambridge University Press:  31 May 2012

S. M. Smith  and
C. R. Ellis
S. M. Smith
Affiliation:
Department of Environmental Biology, University of Guelph, Guelph, Ontario N1G 2W1
C. R. Ellis
Affiliation:
Department of Environmental Biology, University of Guelph, Guelph, Ontario N1G 2W1
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Abstract

Damage caused by Empoasca fabae (Harris) and Philaenus spumarius (L.), caged on second and third alfalfa harvests, was additive. Numbers of E. fabae were linearly correlated negatively with plant height, leaf area, and percentage protein, and positively with percentage chlorosis. Perceptible stunting and yellowing occurred with mean infestations per stem of 0.09 E. fabae and 0.6 P. spumarius nymphs. P. spumarius adults reduced plant height only at infestations of 0.3/stem, while 0.6 nymph/stem also reduced dry weight. E. fabae reduced protein at 0.11/stem and dry weight and leaf area at higher populations of 0.17/stem. None of these parameters was affected on subsequent regrowths. Lygus lineolaris (P. de B.) could not be maintained on pre-bloom alfalfa and was not considered a pest. Adelphocoris lineolatus (Goeze) reduced protein at levels of 0.01 bug/stem and dry weight at 0.06 bug/stem but results were confounded by high mortality. Field populations of all these species were reduced by the second cutting but redeveloped on the regrowth. Although applications of dimethoate (200 g AI/ha) and dimethoate (200 g AI/ha) plus endosulphan (280 g AI/ha) were effective in reducing populations of E. fabae, Acyrthosiphon pisum (Harris), A. lineolatus, and Hypera postica (Gyllenhal), insecticides were cost-effective on only one field. This field had 1.9 E. fabae/sweep and a 3% loss in protein resulted. Plant height, density, dry weight, protein content, and overwintering survival were not significantly affected at harvest in other fields. With the exception of E. fabae, the sum of the maximum field populations, each expressed as a fraction of its threshold, did not reach 50% of an economic threshold.

Résumé

Les dommages dus à Empoasca fabae (Harris), et Philaenus spumarius (L.) maintenus en cage sur de la luzerne de deuxième et de troisième coupe, étaient additifs. Les nombres de E. fabae étaient linéairement corrélés (1) avec la hauteur des plants, la surface foliaire et le pourcentage de protéine, de façon négative, et (2) avec le pourcentage de chlorose, de façon positive. Du fannage visible et du jaunissement se sont manifestés à une densité larvaire moyenne par tige de 0.09 pour E. fabae ou de 0.6 pour P. spumarius. Les adultes de P. spumarius n'ont réduit la hauteur des plants qu'à un niveau d'infestation de 0.3/tige, alors que 0.6 larve/tige ont également réduit le poids sec. E. fabae a réduit les protéines à une densité de 0.11/tige, et le poids sec ainsi que la surface foliaire à une densité de 0.17/tige. Aucun de ces paramètres ne fut affecté lors des repousses subséquentes. Lygus lineolaris (P. de B.) n'a pu être maintenue sur la luzerne pré-floraison et n'a pas été considérée comme nuisible. Adelphocoris lineolatus (Goeze), a réduit les protéines à la densité de 0.01 individus/tige et le poids sec à 0.06/tige, cependant les résultats étaient affectés par la mortalité élevée. Les populations de terrain de ces espèces ont diminué à la deuxième coupe mais ont remonté avec la repousse. Quoique des applications de dimethoate (200 g IA/ha), ou de dimethoate (200 g IA/ha) avec endosulphan (280 g IA/ha) se sont avérées efficaces pour réduire les populations de E. fabae, Acyrthosiphon pisum (Harris), A. lineolatus, et Hypera postica (Gyllenhal), les insecticides ont été rentables dans un champ seulement. Ce champ avait 1.9 E. fabae/coup de filet, causant 3% de perte en protéine. La hauteur des plants, la densité, le poids sec, la teneur en protéine et la survie hivernale n'ont pas été affectés significativement à la récolte dans les autres champs. A l'exception de E. fabae, la somme des maxima des populations de terrain, chacune exprimée en rapport avec son seuil, n'a pas atteint 50% du seuil économique.

Type
Articles
Information
The Canadian Entomologist , Volume 115 , Issue 7 , July 1983 , pp. 859 - 868
Copyright
Copyright © Entomological Society of Canada 1983

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