Effect of Calocoris norvegicus (Hemiptera: Miridae) on Pistachio Yields

Abstract

Exposure of pistachio ( Pistacia vera L.) nut clusters to adult Calocoris norvegicus (Gmelin) during different periods of pistachio nut development showed that the period of susceptibility occurred between nut set and shell hardening, or between early April and early June. Correlation of pistachio nut development with degree-days accumulated after 75% bloom in 1987 predicted shell hardening to occur within 2 d of observed shell hardening in 1988. Abortion rates of pistachio nuts exposed to C. norvegicus for 1 wk were not significantly higher than unexposed nut clusters. However, rates of epicarp lesion in the exposed clusters were significantly higher, which would lead to nut abortion and potential yield looses within a few weeks after exposure to C. norvegicus . The effect of C. norvegicus on yields of pistachios in the Sacramento valley was determined by creating four levels of epicarp lesion damage. Among the different levels of damage, epicarp lesion ranged from 4 to 48%. The number of nuts remaining on the clusters was significantly reduced in the highest damage level. Regression of percentage epicarp lesion with pistachio yields at harvest indicated that 31% of the variation in yield was explained by epicarp lesion due to C. norvegicus . The timing of insecticide treatments before the adult phase of C. norvegicus was shown to be an important means of protecting pistachios from extensive early season damage.