Effect of nonviruliferous wheat curl mites on yield of winter wheat

The effect of nonviruliferous wheat curl mites (Aceria tosichella Keifer) o n yield of the hard red winter wheat cultivar 'Ike' was evaluated in field plots. Plots artificially infested with wheat curl mites reared in the gree nhouse averaged 8,821 +/- 3,814 mites per spike compared with 1,166 +/- 644 per spike in the naturally infested controls. The yield of the infested pl ots (3,707 +/- 401 kg/ha) was significantly less (17%) than the naturally i nfested control plots (4,481 +/- 349 kg/ha). Assuming a linear effect, whic h may or may not be valid, it is estimated that a 1% loss in grain yield ma y result from 450 wheat curl mites per spike. Test weights and 1,000 kernel weights were also significantly lower for the infested plots than for the naturally infested controls. There were no significant differences among tr eatments for numbers of kernels per spike or for any other variables associ ated with the May 1, 8, and 15 dates of infestation. These results indicate that wheat curl mites cause yield losses to wheat aside from that caused b y the viruses they vector. The limited information available on natural inf estations of wheat spikes indicates that yield losses due to wheat curl mit es may range from less than 1% to 15%.