LOS AFIDOS SITOBION AVENAE (FAB.) Y METOPOLOPHIUM DIRHODUM (WALK.), SU INFLUENCIA EN EL RENDIMIENTO, UBICACION EN LA PLANTA Y SUS ENEMIGOS NATURALES

Abstract

A study to determine the relations between the infestation density of S. avenae and the reduction in the wheat yield, the course of the infestation of different aphid species, the locations of the aphids on the plant and its natural enemies, took place in the Provinces of Nuble, Bio-Bio and Valdivia.
Farmers' wheat stands were used to establish random blocks design with four replications.
The damage of S. avenae and M. dirhodum affected significantly the wheat yield in all the trials performed. The number of grains per spike was the most affected yield component up to the grain formation stage, damage in later growth stages affected principally the weight of 1.000 grains. The attacks of S. avenae reduced the hectolitre weight in all the trials.
S. avenae lingered on the plant until more advanced vegetatigrowth stages than M. dirhodum.
M. dirhodum located itself in the intermediate leaves of the cereal likewise B. padi, but this later species was also obssrved on the spike. S. avenae located itself on the superior leaves and on the spike. Schizaphis was found on the leaves only.
The action of three entomophagous fungii was determined, E. aphidis, E. planchoniana and E. thaxteriana. The action of the fungii was greater on the foliage than on the spike.
The depredators were the coccinellidae A. bipunctata, A. deficiens, E. connexa and the sirphidae A. hortensis and A. pulchra.
The sirphidae showed more than fifty per cent parasitism by the ichneumonidae D. lactaorius, the pteromalidae P. eurygasterand Pachyneuron sp. and brachonidae of Aphaereta genus. Some aphids parasited by insects were observed on the spike, although the parasited aphids species was not determined.