Influence of Tea Harvesting Season on the Insecticidal Activity of Bacillus thuringiensis serovar kurstaki Formulation against Smaller Tea Tortrix, Adoxophyes honmai (Lepidoptera: Tortricidae), and Its Relationship to Catechins Contained in Tea Leaves.

Abstract

We evaluated the effects of tannic acid and four major catechins present in tea on the insecticidal activity of Bacillus thuringiensis serovar kurstaki formulation against Adoxophyes honmai Yasuda (Lepidoptera: Tortricidae) using the oral administration method. We also evaluated the insecticidal activity of B. thuringiensis against A. honmai using the leaf dipping method with tea leaves plucked in different tea seasons in 2010 and 2011: in May(hereafter referred to as 1st tea), June to July (hereafter referred to as 2nd tea), August to mid-September (hereafter referred to as 3rd tea), and late September to October (hereafter referred to as 4th tea). The catechin content was measured at the time of each harvest in 2011. Tannic acid and catechins decreased the B. thuringiensis activity in a dose responsedependent manner. The insecticidal activity was decreased by the late tea season and was found to be lowest in the 4th tea. The content of the catechins in the four seasons was in the following order: 2nd tea > 3rd tea > 4th tea > 1st tea. Though these results suggest no direct relationship between the content of catechins and insecticidal activity on tea leaves, other factors might be involved to influence the effects of B. thuringiensis.