ECONOMIC INJURY FOR THE GREEN APHID Schizaphis graminum (RONDANI) (HOMOPTERA: APHIDIDAE) ON IRRIGATED WHEAT IN GUANAJUATO, MEXICO

Abstract

In the State of Guanajuato, México, the presence of various species of aphids on wheat (Triticum aestivum L.) has forced the growers to apply insecticides two or three times per cycle for their control; however, there is not a sound basis to tell if these treatments are necessary, and if so when the applications are more useful. This research was conducted to determine the right time and the aphid population density at which control measures should be taken. Two experiments were established; the first in the 1990-1991 cycle, and the second in the 1991-1992 cycle. Treatments were applied to protect the crop from 10 to 100 % of the time during the first cycle and from 0 to 100 % during the second cycle. Chemical products were applied every 9 to 11 days during the period of insect attack. Insect population of Schizaphis graminum the prevailing species, and yield data were taken. The lowest yields were obtained with 10 % of protection in both cycles, and this treatment presented the highest insect population. A 25.6 % yield loss resulted in the first cycle and 20.9 % in the second cycle, with the 10 % protection treatment. Populations of 30.7, 31.9, 32.9 and 38.8 aphids per plant caused damage of economic importance. No differences in grain yield were found between 40 and 100 % protection periods.